8. Capacitor Discharge Bonder (2026)
Whilst designing a replacement IR energy emission element for a FTIR chemistry analyser, [Repairs: FT IR Source], I needed a bonder to weld its Kanthal A-1 [T18a] resistance wire to a solderable lead wire.
EBay is flooded with cheap Chinese capacitor discharge bonders, but they are far less powerful than sellers would have you believe and those that appear to work, do so more out of creating a spark than a bond: typically their energy is in the order of 100s of mJ.
NOTE: issues highlighted in red or fuschcia still need resolving.
AI
I brainstormed the initial design with DeepSeek AI, similar to Iron Man and JARVIS [G28] but minus the fancy virtual 3D. Having never owned an electric welder, I could not guess the physical and electrical parameters and had to start from scratch, and from first principles.
In 2026 towards the end of the design I noticed Google AI had become much more capable, and I used it to fine-tune DeepSeek's initial advice, particularly the low resistance mechanical path to the capacitor discharge star points.
I have included their advice below in different italicised shades of blue, see above. For more information on Deepseek, see [HOME: PC Builds Win 10 fixes & AI].
Initial assessment
I told DeepSeek I wanted to avoid high voltages and it provided an initial design assessment:
Ideal Circuit Parameters:
Voltage: 20V - 50V (Lower voltage promotes current flow over arcing).
Capacitance: 5,000µF - 20,000µF (Large capacitance for a longer pulse).
Current Limiting Resistor: Very low, just to control the peak, e.g., 10mΩ - 50mΩ.
Electrodes: Use a flat electrode on the Kanthal side and a pointed electrode on the TCW.
The flat electrode will protect the Kanthal from vaporising.
Step-by-Step Experimental Procedure: Start low at 1 Joule.
Example: With a 10,000µF cap, V = √(2 x 1 / 0.01) ≈ 14V.
Implementation
As this bonder is only required for the IR element, I'm not interested in making a full project of it that would ideally be PIC based. Instead and to save time, lab instruments provide all voltages:
Amrel PPS-1202 0-18V, 4A, 1mV rms ripple, programmable linear PSU with isolated outputs,
Manson EP-613 12V, 0.5A, 5mV rms ripple, linear PSU with isolated outputs (fixed output),
The Amrel PPS-1202 PSU charges the capacitors,
The Manson EP-613 PSU powers the drive electronics,
Required energy
I got DeepSeek to do the hard work:
Mathematically determine using existing datasets and established theory, the minimum weld energy density in Joules to bond a 0.3mm Kanthal wire to a 0.6mm tinned copper wire (TCW).
DeepSeek:
A complete model must include the energy to raise the temperature of both the TCW volume and the Kanthal volume to the bonding temperature.
Let's define the bonding temperature as the point where the TCW is molten (~1085°C) and the Kanthal is sufficiently hot for the molten copper-tin alloy to wet it and form a intermetallic bond.
We will use 1100°C as the target interface temperature.
Define the Two Volumes to be Heated:
Volume of a cylinder = π × r² × l
Where:
r is the radius of the TCW.
l is the length of the TCW cylinder being heated.
TCW Volume (V_tcw):
For 0.6mm diameter TCW and a 0.3mm bond width (the Kanthal diameter):
TCW radius r = 0.6/2 = 0.3mm
TCW length l = 0.3mm
V_tcw = π x (0.3 mm)² x 0.3mm ≈ 0.0848mm³
Kanthal Volume (V_kan):
Diameter = 0.3mm
l = 0.3mm (symmetrical)
V_kan = π x 0.15mm)² x 0.3mm ≈ 0.0212mm³
Calculate mass of TCW and Kanthal:
m = V × ρ
Where:
m is the mass of the wire volume (in grams).
V is the volume of the wire segment being heated (in mm³).
ρ is the density of the material (in g/mm³).
Mass for the TCW:
ρcu = 8.96×10−3g/mm³
mtcw = Vtcw × ρcu
Mass (m_tcw) = V_tcw x ρ_cu = 0.0848 mm³ x 8.96e-3 g/mm³ ≈ 7.60e-4g
Mass for the Kanthal:
ρkan = 7.1×10−3 g/mm³
mkan = Vkan × ρkan
Mass (m_kan) = V_kan x ρ_kan = 0.0212mm³ x 7.1e-3 g/mm³ ≈ 1.51e-4g
Calculate Energy to Heat TCW to 1100°C:
The total energy equation used was the sum of the sensible heat and latent heat required to raise the material to the bonding temperature and melt it:
Qtotal = (m × c × ΔT) + (m × L)
Where:
Qtotal is the total energy required (in Joules).
m is the mass of the material (in grams).
c is the specific heat capacity of the material (in J/g·°C).
Tinitial is my lab temperature which is usually 27°C (I like it warm).
ΔT is the temperature change, Tfinal − Tinitial (in °C).
L is the latent heat of fusion (in J/g). This term is only applied to the TCW, as it is the material that melts.
This was calculated separately for the TCW and Kanthal volumes, then summed:
Qtotal = Qtcw + Qkan
Calculate Energy to Heat TCW to 1100°C:
ΔT = Tfinal − Tinitial = 1100°C - 27°C = 1073°C
Q_heat_tcw = m_tcw x c_cu x ΔT = (7.60e-4g) x (0.385 J/g·°C) x (1073°C) ≈ 0.314J
Q_melt_tcw = m_tcw x h_cu = (7.60e-4g) x (205J/g) ≈ 0.156J
Q_total_tcw = 0.316 J + 0.156 J = 0.472J
Calculate Energy to Heat Kanthal to 1100°C:
ΔT = Tfinal − Tinitial = 1100°C - 27°C = 1073°C
Q_heat_kan = m_kan x c_kan x ΔT = (1.51e-4 g) x (0.46 J/g·°C) x (1073°C) ≈ 0.074J
Kanthal does not melt, so no latent heat is added.
Calculate Total Theoretical Minimum Energy:
Q_total = Q_total_tcw + Q_heat_kan
Q_total = 0.314J + 0.074J = 0.544J
Conclusion:
The mathematically determined minimum energy require to heat the combined volumes of both wires to a bonding temperature of ~1100°C when starting from 27°C ambient, is approximately 0.54J.
In other words, the minimum required energy is 0.54J.
We also need to know the maximum energy because we don't want to destroy it.
The optimum energy for a good bond is between the two.
Maximum permitted energy
The upper limit is defined by the point of catastrophic failure: vaporizing the wires.
Let's calculate the energy required to vaporize the bonding volume.
1Energy to Vaporize the TCW Volume (0.0848mm³):
Mass (m_tcw) = 7.60e-4g (as before)
Energy to Heat from 27°C to Boiling Point (2562°C):
ΔT = 2562°C - 27°C = 2535°C
Q_heat_to_boil = m_tcw x c_cu x ΔT = (7.60e-4g) x (0.385 J/g·°C) x (2535°C) ≈ 0.742J
Latent Heat of Vaporization (L_v,Cu):
4790 J/gQ_vaporize = m_tcw x L_v,Cu = (7.60e-4g) x (4790J/g) ≈ 3.64J
Total to Vaporize TCW: 0.742J + 3.64J = ~4.38J
Energy to Heat Kanthal to its Boiling Point (~3000°C)
Mass (m_kan): 1.51e-4g (as before)
ΔT = 3000°C - 27°C = 2973°C
Q_heat_kanthal = m_kan x c_kan x ΔT = (1.51e-4g) x (0.46J/g·°C) x (2973°C) ≈ 0.207J
Conclusion: The Maximum Energy
The total energy to begin vaporizing the materials is dominated by the TCW.
Q_max_theoretical ≈ 4.38J + 0.21J ≈ 4.6J
Safe Operating Range:
Theoretical Minimum: ~ 0.54JT
Theoretical Maximum (Vaporization): ~ 4.6J
This gives a theoretical range of ~ 0.54 to < 4.6J
'Sweet spot'
I asked DeepSeek where it thought the sweet spot for a bond might be within the range 0.54 to 4.6J:
Based on the calculated minimum (0.54J) and maximum (4.6J) energies, the sweet spot for a reliable bond will likely be in the range of 1.5J to 2.5J.
Reasoning:
Margin over Minimum (0.54J):
The theoretical minimum has no safety factor. It assumes perfect, lossless heat transfer. In reality, significant energy is lost to conduction into the cold ends of the wires, radiation, and heating the electrodes. A practical energy needs to be 2 to 3 times the minimum to ensure the bond volume actually reaches the required temperature.
This suggests an operating point above ~1.1 - 1.6J.
Safety Margin from Maximum (4.6J):
The maximum energy is a catastrophic failure point (vaporisation). A good design operates far from this cliff. A sweet spot should have a comfortable buffer, at least 40-50% below the maximum, to account for variations in hand placement, surface oxidation, and capacitor voltage tolerance.
This suggests operating below ~2.3 - 2.8J.
The overlap of these two derived ranges—'well above the minimum' and 'safely below the maximum' points directly to a sweet spot of 1.5J to 2.5J.
Required capacitance
The next step was to determine the required capacitance to bond the wires. I asked DeepSeek to calculate the capacitance for 1.5J and 2.5J at several low voltages:
C = 2E / V²
1.5J 5V 120,000µF 2.5J 5V 3200,000µF
1.5J 10V 30,000µF 2.5J 10V 50,000µF
1.5J 15V 13,300µF 2.5J 15V 22,200µF
1.5J 20V 7,500µF 2.5J 20V 12,500µF
A low ESR capacitor is essential to produce the required high peak pulse current and I would be wiring several capacitors in parallel to drop that. The best choice on eBay seemed to be Panasonic EEUFC1E222 2,200µF 25v 105C 12.5m x 35mm with ESR 22mΩ.
I then asked it to calculate for 12V: 27,777µF
27,777µ / 2,200µF = 12.6 capacitors.
The capacitors were on offer in packs of 4, so I bought 4 packs, total 35,200µF; ESR 22mΩ/16 = 1.4mΩ.
Energy at 12V: E = 0.5 x 0.0352 x (12)² = 2.53J.
To get exactly 2.5J from 35,200µF, charge it to 11.92V.
For 1.5J, charge to 9.23V.
I set the maximum voltage at 12V.
Destruction voltage
I asked DeepSeek to calculate the 35,200µF capacitor voltage at 4.6J:
E=0.5 x CV²
_______
V = / E
√ 0.5 x C
Where:
E = Energy in Joules (4.6J)
C = Capacitance in Farads (0.0352F)
V = Voltage in Volts
_____________
V = / 4.6 = 16.17V
√ 0.5 x 0.0352F
Conclusion:
To store 4.6J of energy in 35,200µF you would need to charge it to ~16.2V.
The maximum voltage of 12V gives a 26% margin of safety.
Capacitor bank safety discharge
Initially I designed this in but it isn't necessary, as simply initiating another weld pulse into the anvil will discharge any residual voltage.
Capacitor bank charging current
Based on the calculation below, the Amrel current limit will be set to 1A.
Capacitor bank energy formula: t = (C × V) / I
C = 35,200µF
V = 12V (maximum)
I = 1A
t = (0.0352 × 12) / 1 = 0.4224 seconds
Capacitor bank wiring
The best way to wire a capacitor bank is to ensure wires from every capacitor are of equal length in order to minimise inductance and resistance. Star points are required but the + star point takes priority over the 0V starpoint. Deepseek puts it succinctly:
For a capacitor discharge welder, the capacitor bank positive lead star-pointed to a short cable to the tungsten electrode is significantly more critical than the ground lead star point.
Explanation:
The weld energy is delivered in a high-current pulse. The dominant parasitic element in this path is inductance (L), not resistance. Inductance opposes the instantaneous rise of current (di/dt). The voltage drop across an inductance is V = L × di/dt.
Summary:
Positive Lead (Priority): This must be the absolute shortest, most direct path possible from the capacitor bank positive terminal to the tungsten electrode. This minimises loop inductance, ensuring the fastest possible current rise time into the weld joint .
Ground Star Point (Secondary): Implement a star ground for the control and return paths (TC4422 ground, PPS-1202 negative, Manson negative) at the capacitor bank negative terminal. This isolates the sensitive gate drive from high-frequency noise created by the main discharge loop.
The capacitors are arranged as 4 columns of 4 rows: +||- +||- +||- +||-, rotated 45° so the leads align with gaps between adjacent capacitors.
Star Points
There is one 0V star point origin, which is the centralised point of the combined capacitor bank - terminals; all 0V signals are referenced to this point. The capacitor high current discharge path is 2x 6mm² copper braid. The same is true of the + terminals which have their own Vcap star point and high current discharge path braid.
The capacitor - is the capacitor bank - star point and central 0V star point reference.
The capacitor + is the capacitor bank + star point.
Implementation
bonding is best for kanthal + TCW but crimping is best for caps
hex crimper is best and takes 0.08mm² to 16mm²
ALWAYS CLEAN ALL WIRES WITH IPA BEFORE CRIMPING
use 0.75mm² ferrule for prototype element
use 2 x 2.5mm² ferrule (total 32) in series for cap -ve 0.8mm to TCW 1mm WITH 0.5mm GAP BETWEEN to stop crushing. secure with Kaptan
use 10mm² for 4x1mm cap -ve & 1x 6mm2 braid. = 4 braids for 16 caps x2 sides (8 ferrules)
no more than 50mm each of 4x braid to mosfet source (+12µs)
25mm = 7µs
run braids close to each other.
+ve also 4 x braid. 4 separate is better than 1 big.
The ideal implementation for the mechanical arrangement is an axial capacitor bank with + and - leads on opposite ends however the trend nowadays is radial and I have yet to find an axial capacitor matching the low ESR and high ripple current of the Panasonic EEUFC1E222, nor would it be an eBay bargain.
All leads from every capacitor to a star point must be the same gauge and length. The 4x4 block of capacitors is further divided down to four 2x2 corner blocks, .
The +ve lead length is more critical than the -ve, so the -ve capacitor lead is bent over the can and additional TCW crumped to it to extend it beyond the can bottom. The capacitor lead is 0.8mm (~21 SWG), the additional TCW is 19 SWG (1.016mm dia). Google AI determined a 2.5mm² crimp ferrule is the best fit, with two in series to lower inductance and a 0.5mm gap between them to remove the likelihood of the crushed crimps impinging.
One side of double-sided Kapton tape wrapped around the can secures the -ve lead to it, the other side secures it to the adjacent capacitors.
At the can end the emerging 4 -ve equal length TCW leads terminate in a star point, extending outward just long enough for a 10mm² crimp ferrule to join them to 6mm² braid. This is repeated for all four of the 2x2 corner blocks.
The TCW is arranged to appear from the 4 spacing gaps around one capacitor, the most efficient in terms of lead length and mechanical routing to the brass clamping block at the base, being a cap each end at the bottom (v), and two caps in the middle in the cap layer above (^) with the arrangement swapped for the other cap terminal:
-ve ends: v^^v
+ve ends: ^vv^
From this 4 x 6mm² braids emerge, leading to a brass clamping block that combines them with the sources of 3 MOSFETs. The braids are insulated and kept close together to reduce pickup.
Since their leads would snap if crimped and solder is a less effective, the final connection between the 4 braids and the MOSFETs is a compression block. Google AI recommended copper blocks with bare braid ends but mechanically is it more practical to use the braid ring crimp M8 bolts to close the clamp, and locate the 3 MOSFET source pins between them.
Google AI:
Here is the step-by-step assembly for the 1600A Solderless Power Clamp. This design maximizes surface contact while protecting the brittle MOSFET leads from the mechanical "kick" of the discharge.
Preparation of Components
Copper Plates: Cut 2 pieces of 20mm x 3mm Tinned Copper Bar, approx. 50mm long. Drill two holes for M5 bolts at the ends, leaving enough space in the middle for the 4 MOSFET leads and 4 braids.
Copper Shims: Cut 2 pieces of 1mm Soft Copper Shim to match the 'contact zone' (the area between the bolts).
MOSFETs: Position the 4 IRLB3813s in two pairs. Invert one pair so all 4 Source leads point toward the centre of the clamp.
Braids: Flatten the ends of your 4 x 6mm² braids. If using 10mm² ferrules, hammer them flat to ensure a wide, even contact patch.
Cleaning: Use a Scotch-Brite pad to buff the MOSFET leads, copper plates, and shims until they are bright and shiny.
Clean everything with IPA.
Apply a tiny smear of conductive contact grease if you have it.
The Assembly 'Sandwich' (Bottom to Top)
Build the stack in this exact order to ensure every interface is clamped:
Base Plate: 3mm Tinned Copper Bar.
MOSFET Layer: Lay the 4 Source leads side-by-side, flat against the base plate.
Lower Shim: Lay the first 1mm Copper Shim over the MOSFET leads.
Braid Layer: Lay the 4 flattened 6mm² braids (or ferrules) over the lower shim. Fan them out so each braid sits roughly over one MOSFET lead.
Upper Shim: Lay the second 1mm Copper Shim over the braids.
Pressure Plate: 3mm Tinned Copper Bar.
The Bolting Procedure
Insert Bolts: Pass two M5 Grade 8.8 (or A4 Stainless) bolts through the holes.
Add Nord-Locks: Place one M5 Nord-Lock pair under the head of the bolt and another pair under the nut. Critical: Ensure the 'cams' (wedge sides) of the Nord-Lock pairs are facing each other.
Initial Snug: Tighten both nuts by hand until the sandwich is held together and aligned.
Final Torque: Use your torque wrench to tighten both bolts to 5 Nm. Do this in stages (e.g. 2Nm on both, then 5Nm on both) to ensure even pressure across all 4 MOSFET leads.
Technical Checklist
Lead Stress: Ensure the MOSFET bodies are secured (e.g. zip-tied or bolted to the chassis) so the heavy braids don't pull on the leads.
Clearance: Check that no part of the 'Source' clamp is accidentally touching the 'Drain' clamp or the aluminium box.
Bias Ground: Connect the TC4422 0V (GND) return wires directly to one of the M5 bolts on this clamp to ensure the gate drive sees the true Source potential.
This 'Cold Weld' assembly is superior to soldering and will provide the lowest possible resistance for your 176µs rise time and easily handle the 1600A peak without micro-arcing.
Google AI: 1mm TCW has roughly 1µH of inductance per millimetre
The hybrid axial capacitor assembly is further secured within 4-sides of single-sided copper clad pcb, with the copper on the outside soldered to electrically join every section. The copper is connected to the box Earth, providing both an open-ended Faraday shield and secure mechanical support.
Power supplies
Thin 0V wires are separately routed from the capacitor - to the places where the incoming Amrel 0-12V and Manson fixed +12V supplies appear on the pcbs. From those points, twisted pairs of the separate 0V & 0-12V and 0V & +12V signals are carried to their respective electronics. The thinner the wire from the capacitor -, the higher the inductance and the less noise is carried to the pcbs; the psu wires are only as thick as they need to be to carry their required currents:
Wire CSA Amps Resistance Vdrop over
gauge @30°C /km /150mm 0.15m @ 1A
30AWG ~0.05mm² 0.14A ~335Ω ~55.0mΩ ~55mV
28AWG ~0.08mm² 1.0A ~216Ω ~32.4mΩ ~32.4mV
24AWG ~0.21mm² 3.5A ~88Ω ~13.2mΩ ~13.2mV
22AWG 0.33mm² 5.0A ~53Ω ~8.0mΩ ~8.0mV
Depending upon my supplies: 24AWG for the Amrel, 28AWG for the Manson and 30AWG for the sense.
However 24AWG is a convenient gauge for all.
Google AI:
If you have a clip-on ferrite core, snap it over the 12V leads near where they enter the TC4422 board. This will block high-frequency noise from traveling back into the Manson.
Amrel sense wires
Sense wires are not used because they could act as aerials when the weld takes place. Due to the potential for damage by the electromagnetic weld pulse, the Amrel PSU has to be physically unplugged from the welder once the capacitor bank is charged. If sense wires were present they would float.
PSU supply indicators
Green LED (3.2Vf) & 2kΩ 1/4W resistor across the 12V supply from the Manson EF-613.
Green LED (3.2Vf) & 1kΩ 1/4W resistor across the 5V regulator powered by the Amrel PPS-1202.
Mosfet switch
A low side mosfet switch source connects via another 6AWG lead to the star-pointed 0V that is also the negative terminal of the capacitor bank. The NMOSFET drain leads to the negative electrode 'anvil'. A positive voltage pulse on its gate turns the mosfet on and when the positive electrode (the capacitor bank +) is placed on the wires to be welded, current flows through the weld joint and returns through the mosfet drain to the capacitor negative terminal.
ESD protection
However this configuration means the drain of the mosfet is exposed to the world, and it could be damaged by static electricity. In addition, a capacitive discharge welder acts like a large fast inductive pulse generator and induces noise spikes on power rails. To counter this and potential ESD, I placed a P6KE15CA Transient Voltage Suppressor (TVS) close to the mosfets and across the drain to 0V.
I also placed one across the capacitor bank and a fuse on its supply inlet in case the charging PSU develops a fault (don't want the capacitor bank to blow).
The P6KE15CA is a Bi-directional TVS: it clamps both positive and negative voltage spikes equally, and its 15V standoff breakdown range is 14.3V - 15.8V (capacitor voltage will be 12V max), clamp 27.2V maximum (the mosfet is rated at 30V max). It has a peak pulse power dissipation of 600W for a 10/1000µs transient waveform with a 10A peak, defined by two parameters:
t₁ (10µs): pulse rise time, measured from 10% to 90% of the peak current (I_PP).
t₂ (1ms): pulse duration, from 50% on the rising edge to 50% on the falling edge.
Essentialy this is the equivalent of a long, high-energy surge of the type you might expect with a capacitive welder. The energy from a fast ESD spike is less, but still needs to be clamped.
Normal Operation: The TVS diode is invisible. It has a very high impedance at voltages below ~14.3V.
ESD/Overvoltage Event: If a voltage spike tries to push Vgs beyond ±16V, the TVS diode instantly 'clamps' the voltage, shunting the destructive current away from fragile semiconductors.
Placement: Solder it as physically close as possible between the MOSFET source and 0V.
Google AI:
Because you are dealing with (fast current changes), the inductance of the TVS leads matters.
Bolt or clamp the TVS leads directly across the Drain and Source copper blocks of your MOSFET sandwich.
Short Leads: Keep the TVS legs as short as possible. Even 10mm of wire adds enough inductance to let a "spike" bypass the TVS and hit the MOSFET silicon first.
Mosfet selection
DeepSeek recommended using a fast 30V 240A (1050Apk) IRLB3813 NMOSFET: RDSon 1.6 mΩ max @ 10V Vgs. Its high switching current, low RDSon and relatively low 650pF typ reverse transfer capacitance, Crss, were key reasons for its selection: low Crrs allows for very fast switching with a high-current driver. For improved reliability I wired two in parallel with separate drivers.
Google AI later recommended increasing this to four, as peak current could reach 1600A and it said the 1050A figure is the silicon failure point; 400A each is a good safety margin.
Thermal dissipation
Absolute Maximum Continuous Current (Id) of 240A per MOSFET from the IRLB3813 datasheet, giving a worst-case combined pulse current of 480A.
Conduction Loss (P_cond):
Formula: Pcond = I² × Rds(on) × D
I_pulse: 480A
R_{ds(on)} (total for 2x MOSFETs): 0.0008Ω
Duty Cycle (D): 0.001 (10ms pulse every 10s) [10ms worst case; in reality <1ms should suffice]
Calculation: Pcond=(480)² × 0.0008 × 0.001
Pcond=230,400 × 0.0008 × 0.001=0.184W (per MOSFET)
Switching Loss (P_sw)
Formula: Esw ≈ 1² × Vds × Id × (tr+tf)
V_ds: 12V
I_d: 480A
t_r + t_f: 200ns (estimated total switching time)
Calculation:
Esw = 0.5 × 1² × 480 × (200×10−9)
Esw = 0.000576J (Joules per switching cycle)
Power: Psw = Esw × Switching Frequency
Psw = 0.0000576 W
Total Power Dissipation (P_total):
Formula: Ptotal = Pcond + Psw
Calculation:
Ptotal = 0.184 + 0.0000576
Ptotal ≈ 0.1846W (per MOSFET)
Heatsink Requirement Analysis:
Junction-to-Ambient Thermal Resistance (RθJA): 62°C/W
Temperature Rise: ΔT = Ptotal × RθJA = 0.1846W × 62 ≈ 11.4 °C
Conclusion:
A heatsink is completely unnecessary. The MOSFETs will run only slightly above ambient temperature, with a worst-case temperature rise of ~11°C.
Self-discharge protection
The Amrel PPS-1202 PSU charges the capacitors at 1A. This PSU has isolated outputs and sense inputs. I added a forward conducting diode between the PSU + and the capacitor bank + feeding back to PSU sense+. Similarly a reverse biased diode with its cathode to the PSU - and its anode to capacitor - which goes to the star pointed 0V on the NMOSFET sources and back to PSU sense- the diodes protect the PSU from damage when it is turned off and there is still charge on the capacitors; it also stops the capacitors from discharging through it. I asked DeepSeek to recommend suitable diodes, suggesting 6A.
Recommendation: FR607 6A fast recovery rectifier
Datasheet (Diodes Incorporated FR607):
Average Forward Current (I_F): 6A (at Tc=75°C).
Peak Forward Surge Current (I_FSM): 150A (8.3ms).
Repetitive Peak Reverse Voltage (V_RRM): 1kV.
Reverse Leakage Current (I_R): < 10µA at 25°C.
Package: R-6.
The R-6 is a huge 9mm dia package but it's difficult to find a smaller one at 6A, even at low voltages; Schottky diodes are unsuitable due to their high reverse leakage current.
Vcap fuse
The second channel of this PSU has a fault that drives its output to 29V [Repairs: 10 Power supplies]. To counter the channel I'm using developing the same fault, I added a P6KE15CA, 15V transzorb across the capacitor bank and a 4A polyswitch fuse where the supply comes in: MF-R400 30Vmax Ihold 4.00A Imax 40A. In the event of it triggering, its (+5V supply) green PSU LED will extinguish.
Gate driver
The NMOSFETs are each separately driven by a Microchip (formerly Telcom) TC4422 9Apk fast MOSFET driver. DeepSeek recommended the drivers be decoupled with ceramic X7R 100nF and 10µF:
The TC4422s are powered from the Manson EP-613 12V supply. There is a MF-R050 30Vmax Ihold 0.50A Imax 40A polyswitch where the supply enters and a 1.5KE15CA TVS across the +12V physically close to the TC4422s. In the event of it triggering, the green +12V PSU LED will extinguish.
After the fuse thw 12V supply has 2x 10µF MLCs in parallel for low ESR fast current pulse decoupling.
The TC4422 datasheet recommends decoupling with 1.0µF for each 1000pF of load capacitance.
IRLB3813 input capacitance = 8420pF. Required Bulk Capacitance = (8420pF / 1000pF) x 1.0µF = 8.42µF x2.
Gate Driver ICs: 2 x TC4422, 9A peak, fast low side MOSFET drivers.
Local Decoupling: 2x 10µF + 100nF MLCs 50V (for high current switching) between driver Vdd and GND.
Gate Resistors: 2.2Ω to 4.7Ω, non-inductive (carbon composition or metal film) per MOSFET gate.
Datasheet advice:
Layout: star point for gate drive connections. Keep driver IC and capacitors 1-2cm near MOSFET gates.
Pulse width
I was going to use an external variable pulse generator but the pulse width is only necessary to ensure the MOSFETs are on long enough to discharge the capacitor bank, so I replaced it with a one-shot.
Discharge time constant: τ = R × C
For the 4.7Ω discharge resistor, τ = 165ms but for the weld itself, the resistance is the extremely low resistance of the MOSFETs, cables, and workpiece:
Assume total loop resistance (R_loop) ~5mΩ
τ_weld = 5mΩ × 35,200µF = 176µs
DeepSeek general information:
The minimum usable pulse width is approximately 0.2ms (200µs) for capacitor discharge welding of fine materials, though practical equipment often starts around 0.45-0.65ms depending on the application.
I chose 2ms as this satisfies both my needs and DeepSeek's advice.
Since +12V is the only constant supply, a CMOS HEF4538 dual retriggerable one-shot produces this pulse. The first one-shot Q- is wired to its positive input to force it to a *non-retriggerable one-shot. The negative input to both one-shots is from a small push switch to 0V in parallel with 1µF and with a 10kΩ pullup to +12V. The second one-shot Q- drives a white LED giving a visual indication of the weld taking place; *as it's only an LED, switch chatter extending Q2 is actually an advantage.
ADD A TRIMPOT TO EACH 1-SHOT
Component Values:
One-shot #1 (pulse): R = 20kΩ, C = 100nF time = 2ms on Q+ to TC4422.
One-shot #2 (LED): R = 10kΩ, C = 1µF time = 10ms for HE WE LED on Q- to LED cathode.
HEF4538 Iout ±3.6mA max; I'll drive the LED at 2mA.
HE WE LED 3.2Vf means 12V-3.2V/2mA = 4.4 kΩ so I'll limit its current with 5.1 kΩ to +12V.
Power up reset to clear both one-shots CLR- pin: 10kΩ to +12V & 100nF to 0V.
100nF decoupling across supply pins.
This chip is located as far away from the electrodes as possible to minimise inductive triggering, which is why there is a second pcb near the power input terminals called 'timing pcb'. Its 2ms pulse is routed to the TC4422s via miniature screened audio coax with its shield originating at the HEF4538 0V which originates at the Manson 0V star point ADD TO SCHEMATIC REV 5]; the TC4422 can accommodate large ground bounce, so is not affected. Although the TC4422 has good noise immunity, a 100pF X7R MLC filter has been added to each TC4422 input at the end of its coax.
Gate resistor
The TC4422 is capable of a 9A peak output current. The gate resistor sits between its output and the NMOSFET gate input.
Minimum Resistor for 9A with Vdd set to 12V [Manson EP-613 PSU]:
Rg = 12V = 1.33Ω
9A
Target Range (2.2Ω to 4.7Ω):
With 2.2Ω, the initial peak current is I = 12V/2.2Ω ≈ 5.45A
This is well within the driver's capability but provides strong control.
With 4.7Ω, the initial current is I = 12V/4.7Ω ≈ 2.55A
This is ideal for damping and still provides very fast switching.
The 2.2Ω to 4.7Ω range is the ideal starting point, ensuring robust performance and stability.
Resistor wattage
I asked Deepseek to calculate the maximum wattage of 2.2Ω and 4.7Ω gate resistors:
Peak Instantaneous Power (W_peak)
This is the power the instant the TC4422 switches on, when the full supply voltage is dropped across the resistor.
V_drive = 12V (from Manson PSU)
Formula: Ppeak = Vdrive²
R
Peak Instantaneous Power:
For 2.2Ω, P = 12²/2.2 = 144²/2.2 ≈ 65.5 W
for 4.7Ω, P = 12²/4.7 = 144²/4.7 ≈ 30.6 W
Average Power (W_avg) per Pulse:
This is the total energy dissipated in the resistor during one gate charge/discharge cycle, divided by the pulse width. The energy dissipated in the resistor is approximately half of the total gate energy.
Q_g (Gate Charge) = 110nC
V_drive = 12V
Energy in Gate (E_gate):
Egate ≈ 0.5 × Qg × Vdrive = 0.5 × 110×10⁻⁹ × 12 ≈ 0.66 μJ
Energy in Resistor (E_res):
Eres ≈ Egate ≈ 0.66 μJ (It shares roughly half the energy).
Pulse Width (t_pulse) (Assume a conservative 1ms):
Formula: Pavg = Eres/tpulse
Pavg = 0.66×10⁻⁶/1×10⁻³ = 0.66×10⁻³W = 0.66 mW
Conclusion:
The average power is negligible (~0.66mW) for both resistors.
The critical specification is the peak instantaneous power and the pulse handling capability.
2.2Ω Resistor: Must handle ~66W pulses.
4.7Ω Resistor: Must handle ~31W pulses.
A wirewound resistor is not suitable because it will:
Slow down the switching speed by resisting the rapid current change (dI/dt).
Cause ringing and voltage overshoot on the gate signal, which can stress or damage the gate oxide.
You must use non-inductive, pulse-rated resistors (e.g., metal oxide film or carbon composition) rated for these high peak pulses, even though the average power is tiny; a standard 1/4W carbon film resistor would be destroyed. Requirement: Must withstand a ~65W peak pulse for ~100ns.
I asked Deepseek to recommend a suitable resistor.
It suggested non-inductive Vishay PR02 2W metal film:
Analysis:
The resistor is subjected to a high-power pulse when switching the MOSFET gate. Suitability is determined not by its continuous power rating, but by its ability to absorb the pulse's energy without damage.
Calculate Pulse Energy:
Peak Power, Ppeak: 65W
Pulse Duration, tpulse: 100ns
Pulse Energy, Epulse: Ppeak × tpulse = 65 × 1×10⁻⁷ = 6.5 μJ
Compare to Resistor Thermal Capacity:
A 2W metal film resistor has a larger mass. Let's estimate 0.5 grams (5 x 10⁻⁴ kg) and a specific heat capacity similar to ceramic/glass/plastic (~800J/kg·°C).
The energy required to raise its temperature by just 1°C is:
E = m × c × ΔT = (5 x 10⁻⁴ kg) × (800J/kg·°C) × (1°C) = 0.4J
Conclusion:
The pulse energy is 6.5µJ/400mJ = 0.00001625 (or 0.001625%) of the energy needed for a 1°C rise.
This means the 6.5µJ pulse is over 61,500 times maller than the energy needed to raise the resistor's temperature by a single degree Celsius. Therefore, the Vishay PR02 0.5W resistor is perfectly suitable and will not be damaged or degraded by the 65W, 100ns gate drive pulse.
The component's thermal mass renders the brief power spike harmless.
I couldn't find reasonably priced 2.2Ω and 4.7Ω PR02s but I did find 50x 10R 5% PR02s on eBay for £4.60.
Deepseek approved of my idea to parallel them by soldering them on top of each, minimising inductance.
The large number is also beneficial in finding matching resistors out of the 5% tolerance although when I came to measure them, I found most were close to spot-on.
Deepseek now recommended starting with 5Ω:
5.0Ω (2x 10Ω in parallel): Slower, more damped, most stable.
3.3Ω (3x 10Ω in parallel): A balanced middle ground.
2.0Ω (5x 10Ω in parallel): Fastest switching, highest current, highest risk of ringing.
Start with the 5Ω configuration.
Use an oscilloscope to check the gate waveform for ringing and overshoot.
If the waveform is clean and stable, try 3.3Ω to see if you can achieve faster switching without introducing instability. Only proceed to 2.0Ω if the 3.3Ω waveform remains clean.
New text box
Electrodes
I asked DeepSeek to recommend suitable electrodes:
Look for blue 2% Lanthanated Tungsten Electrodes, often used for TIG welding, diameter 1mm: the small mass will provide a good point for focusing current and has low thermal inertia so will heat to emission temperature faster and cool faster after the discharge, which is beneficial for pulsed operation. These usually come with flat tips and you will need to grind a pointed tip on it.
Why Lanthanated Tungsten:
It has excellent high-temperature stability, good arc characteristics, and is non-radioactive (unlike the popular but radioactive Thoriated Tungsten).
Negative electrode:
A large, flat-faced electrode. This acts as the anvil. It provides a stable, supportive backing for the
workpiece.
Initially DeepSeek was happy using the aluminium box as the negative anvil, but as the design progressed, later sessions questioned this:
Aluminium (235 W/m·K): Original baseline (1.5J-2.5J).
Copper (400 W/m·K): Sinks heat fastest, requiring the largest energy increase (~+0.5J est.).
Brass (115 W/m·K): Will sink heat slower than Aluminium.
The aluminium box presents a high and variable contact resistance. This is not the bulk resistance of the aluminium, but the high and non-reproducible surface contact resistance of the aluminium oxide layer at the microscopic points of contact with the Kanthal wire. This could lead to inconsistent weld energy delivery.
Copper does not have this issue but has a thermal conductivity 60% higher than aluminium that would likely increase the energy requirement by 0.5J, Shifting the target operational 'sweet spot' from 1.5J - 2.5J, to approximately 2J - 3J (10.7V - 13.1V), with little room for experimentation above this: if the 12V limit is now raised to 14V, that leaves only 13.6% below the 16.2V point of vaporisation.
Copper thermal conductivity is 40% greater than aluminium.
Brass thermal conductivity is 51% less than aluminium.
Brass is a better compromise as it requires less energy than aluminium and retains the safety margin.
A 3mm thick 50mm x 100mm brass sheet is secured to, but insulated from, the aluminium box.
EMI minimisation
The brass is electrically insulated from the box because a) we need a defined return path and b) we don't want EMI radiated through the box to the components inside it. The brass is bolted (M3) to the mosfet drain heatsink tabs, creating a short, low impedance path.
The entire weld current return path—MOSFET sources, capacitor negative, and anvil is contained within a very small area on the lid, minimizing parasitic inductance and ensuring a sharp, powerful pulse is delivered to the workpiece.
The return path through the brass from the electrode to the MOSFET drains is very short however the brass is relatively large in order to dissipate the heat from the weld that would melt a smaller area.
Positive electrode
1.6mm Lanthanated Tungsten; grind a small, flat tip on it ~0.5mm to 1.0mm diameter.
This small flat tip concentrates the current onto a precise spot on the wires, but the flat surface applies pressure without cutting into them.
For TIG welding electrodes, the color code for Lanthanated Tungsten is not universally standardized, but the most common conventions are:
Gold: Typically denotes 1.5% Lanthanated (EWLa-1.5)
Blue: Typically denotes 2.0% Lanthanated (EWLa-2.0)
For this micro-welding application, the Blue (2.0% Lanthanated) is the better choice.
Reasoning:
The higher lanthanum oxide content (2.0% vs 1.5%) provides slightly better electron emissivity and arc stability at lower currents. This translates to a more consistent and reliable performance for the precise, low-energy pulses in a capacitor discharge welder, giving a more forgiving and stable electrode.
Whilst searching for a 1.6mm electrode I found a 1.0mm one which Deepseek agreed was a better choice:
For your stated purpose of a discharge electrode or a robust, high-temperature point (not TIG welding), the 1.0mm blue lanthanated tungsten is a superior choice to the 1.6mm.
Sharper Tip:
A 1.0mm rod can be ground to a much finer, sharper point than a 1.6mm rod. This creates a higher electric field density, which promotes easier and more reliable arc initiation or electron emission at lower voltages.
Keeping the 1mm tip flat makes it easier for the weld arm to press down upon the wires and hold them in their place; the weight of the arm on a pointed tip on the relatively soft TCW leads could damage them.
Faster Heating/Cooling:
The smaller mass has lower thermal inertia. It will heat to emission temperature faster and cool faster after the discharge, which is beneficial for pulsed operation.
Material Suitability:
Lanthanated tungsten (blue) is an excellent general-purpose choice. It holds a sharp point well, has good electron emissivity, and is more forgiving than pure tungsten.
Durability:
The 1.0mm tip will erode slightly faster than a 1.6mm tip under identical arcing conditions however it will still last for thousands of cycles.
Electrode wiring
The wiring from the capacitor bank + to the + electrode is 4x xxxmm 11mm wide 6mm² copper braid, ensuring minimal voltage drop and a sharp current pulse to the bond point. The braid ends are 8mm ring crimps bolted to the rod using a brass M8 x 10mm screw and three 1mm compressible copper washers.
The electrode arm pivots inside a Delrin block mounted on top of the brass plate. The - electrode (return) is a brass plate that the mosfet drains are bolted into, minimising return path R and L.
EMC
The welder generates a powerful, fast-changing magnetic field with every discharge. The earthed metal box prevents the weld field from inducing stray voltages and currents in the sensitive timing (HEF4538) and gate drive (TC4422) circuits, which could cause misfiring or erratic behaviour.
Connectors & controls
Power enters the lid through two 4-way circular connectors on the box at the opposite end to the arm.
PL1 4-way +12V connector + 2 signals for debug: timing pulse o/p
PL2 5-way Vcap DIN+- sense+-
All connections to the Amrel PPS1202 are via its rear panel.
PL3 Earth turret to Amrel supply.
LEDs indicating PSU state are also at this end.
The discharge push switch and its red LED are located to the left of the electrode arm.
The weld push switch and its white LED are located to the right of the electrode arm.
Pcb
There are two separate circuit sections:
At side by 4-way +12V connector - Timing circuitry [HEF4538 dual 1-shot, +5V LED]
Opposite end near electrodes - Welding circuitry [mosfets + drivers, start & discharge swts; LEDs]
The electronics are mounted inside the lid of a large earthed aluminium box: 210mm x 110mm x 80mm.
Construction
The box internal height is 59mm. The box lid internal height is 16mm.
The anvil is a 50mm x 100mm x 3mm thick brass sheet, the 50mm dimension being orientated box lengthways.
A 50mm x 100mm x 2mm thick fibreglass sheet below the brass isolates it from the aluminium box lid.
A 50mm x 100mm x 0.3mm fibreglass sheet above the brass acts as a weld template with slits cut into it for the Kanthal wire to be pressed against the anvil at the weld point whilst isolating the TCW.
Four Nylon screws from within the drilled aluminium box lid pass through each corner of the drilled 2mm fibreglass sheet and are retained by matching threads tapped in the brass sheet above it. The screws extend above the brass sheet, securing the 0.3mm fibreglass template sheet via washers and nuts.
The template is easily reversed to weld the other side of the IR source.
Alternative custom templates can be fitted to weld different components.
The electrode arm is a 12mm diameter x150mm long brass rod that rotates on a pivot at one end.
At the other end a central slit with a clamping bolt secures the 1mm tungsten electrode to the arm.
A copper braid 200mm x 11mm 6mm² is folded over and its M8 end rings are bolted into the pivot end of the 12m rod using a brass M8 hex screw with interspaced M8x1 brass compression washers. The M8 bolt tightening torque is 8Nm (5.9ftLb); the shear limit is 12Nm.
Lazy loop
The braid is insulated by loose M8 flat heat shrink as it passes through an 8mm slit in the box lid top. A 'lazy loop' at the bottom compensates for arm rotation.
The electrode arm rotates within two Delrin vertical supports 32mm deep x 11mm thick x 65mm tall.
The electrode arm pivots on an M5? M6?x60mm screw with 1 washer each side, secured by a Nyloc.
The electrode pushes down on the target weld leads when its brass arm is horizontal, securing them.
The pivot end of the 12mm electrode arm is held within a small block of Delrin, the lower section of which is drilled for the non-threaded portion of the M6 pivot bolt. The block pivots within the Delrin side supports providing low friction precision movement that could not be achieved if the rod itself was drilled.
[OPTION] A spring-loaded pin allows the arm to be secured upward for template and target placement.
The Delrin vertical supports are secured by ??mm thick Delrin spacers top? and bottom
2x M4?xTBDmm bolts each side of centre fix the Delrin sides to the Delrin spacers.
2x M5?xTBDmm countersunk screws in the aluminium box lid pass up into and secure the Delrin blocks.
Current monitoring
A [E3] Pearson 410 current monitor is a loose fit on the 12mm electrode rod and held in place by neoprene O-rings each side at the hinge end with sufficient space for the rod to be raised. The centre hole in the 410 is 0.5". The tungsten electrode is removed and the 410 and O-rings slid onto the rod.
With a 50Ω inline terminator into a 1MΩ oscilloscope channel, the 410 can support up to 5000A, producing and output of 50V (1A = 100mV). The anticipated maximum current is estimated at 1600A.
Spring
The weight of the arm and 410 should be sufficient to hold the TCW over the Kanthal but a spring may be added to compensate for electrode bounce that could cause arcing due to rapid heating and electromagnetic forces from the near instantaneous 1600A surge, particularly if the 410 is removed.
Pcb
There is one large pcb secured to the inside of the lid.
The pcb is hand-wired 0.1" square pad.
The pcb measures 182mm x 104mm with a 2.4" x 0.5" cutout at the end for the circular connectors
The pcb solder side faces the box lid.
The pcb is screwed to the inside lid via 2x brass bars 5/16" (7.94mm) x 3/16" (4.77mm) along the lid length each side.
There are two separate circuit sections:
At side by 4-way +12V connector PL2 - Timing circuitry [HEF4538 dual 1-shot, +5V LED]
Opposite end near electrodes - Welding circuitry [mosfets + drivers, start & discharge swts; LEDs]
Layout & wiring assembly
The 0V star point is located on the braid at the point where all capacitor leads meet it. All 0V connections to the electronics are derived from this point.
Exposed +12V supply wires are twisted with 0V from the starpoint.
OPTION: A Bulldog clip on the aly box lid end beyond the electrode is isolated from the box using 2mm thick fibreglass sheet. The lower jaw rests on the 0.3mm fibreglass sheet on the brass anvil. Where it meets defines where the 50mm x 100mm brass sheet starts. The bulldog clamps the loose TCW ends and in turn, the rest of the element prior to welding the Kanthal to the TCW.
The MOSFETs, TC4422s and discharge circuit are be mounted on the weld pcb at the weld tip end.
The HEF4538 pulse generator and supply fuses are at the opposite end of the box.
The MOSFETs are located each side of the weld point [OPTION: in parallel with and inward of the Bulldog jaws] with their pins facing towards this end of the underside of the lid. One MOSFET is upside down so both sources can be soldered together.
The MOSFETs are bolted to the brass sheet using M3 brass screws and brass M3 hex spacers isolated from the aly box and through the pcb, where M3 copper compression washers and Nylocs secure them. Torque is 0.5Nm to 0.6Nm (0.4ftLb). Each MOSFET central drain pin is connected to its drain bolt via a ring crimp.
The MOSFET gate is the outermost pin and is wired to its PRO2 gate resistor that runs down the outside length of its MOSFET, where it meets its TC4422 driver output pin. The gate resistor is two 10Ω PRO2s in parallel, forming 5Ω. Others may be paralleled later to fine tune.
The pulse driving HEF4538 one-shot is on the timing pcb, the two connected by coax with its shield at the TC4422 end to avoid trigger pickup. The Q- feeds into its trigger gate to convert it to a non-retriggerable one-shot. Initially the TC4422s will be in turned-pin IC sockets.
The capacitor bank is arranged as a 4 x 4 block -+ -+ -+ -+ with - towards the electrode end.
The radial pins are rotated 45° to allow them to be wired axially, see capacitor implementation.
The capacitor - and + star points are ferrule crimped to separate copper braids 200mm x 11mm 6mm².
The braids are cut to length, with 4 braids each for + and -.
The + braid at the electrode rod end has M8 ring crimps & Copper compression washers, 8Nm.
The - braid mosfet source (anvil) end has Faston spade & socket crimps.
Coil build
Coil build
9 turns of Kanthal A-1 are wound around the 1.2mm diameter ceramic rod and pushed together.
A Bulldog clip on a heatproof stick holds the Kanthal in place on the former.
The lead ends to be welded are insulated by silicone glass fibre tubing.
A blowtorch will insulate the Kanthal windings (just outside of the blue flame: 30 secs).
IPA will be used to remove silicone oils deposited by siloxane vapour released during heating.
TCW lead attachment
OPTION1: The TCW leads are wound around the 1.2mm ceramic former at each end beyond the Kanthal winding, acting both as a support for the ceramic former as well as the electrical supply leads.
OPTION2: OD 1.2mm ceramic tube with ID 0.7mm ends will take the TCW in the same manner as the original.
The Kanthal is then bonded to the TCW about 2mm below the former, mimicing the original element.
Preparation on welder
The Kanthal wire leads on the ceramic former are bent outward 90° behind the TCW leads.
The assembly is laid on the fibreglass template: 1 Kanthal end passing through 0.25mm wide slits onto the brass anvil. The TCW is laid across the Kanthal.
The heavy brass welder arm's 1mm electrode is lowered onto the TCW where it crosses the Kanthal.
THE ELECTRODE MAY BE HEAVY ENOUGH TO DO AWAY WITH THE BULLDOG (ESP IF 410 is on it):
OPTION: The ends of the TCW leads (& thus the ceramic former) are clamped in place by the Bulldog clip.
Components
2x FR607 6A fast recovery rectifier, R-6 [Vcap +,-]
16x Panasonic EEUFC1E222 2,200µF 25V, ESR 22mΩ, 105°C
4x NMOSFET IRLB3813 30V 240A (1050Apk), TO-220 [1600A max/4 = 400Apk each]
7x P6KE15CA bi-directional 15V 600W Transzorb TVS, DO-201 [Vcap, TC4422s, Mosfets]
1x polyswitch MF-R230 30Vmax Ihold 2.30A Imax 40A for Vcap supply input
1x polyswitch MF-R050 30Vmax Ihold 0.50A Imax 40A for +12V supply input
2x TC4422 9A peak fast low side MOSFET driver, DIP-8
1x HEF4538 dual retriggerable one-shot [2ms pulse & weld pulse LED]
[OPTION] 1x LP2950ACZ-5 TO-92 5V 50mA regulator 200mV dropout [OPTION: debug logic]
2x turned pic IC sockets 16-pin [1x HEF4538, 1x spare: potential logic driver for debug]
1x square pad pcb 182mm x 104mm [2 isolated sections: timing, welder]
2x 100pF X7R MLC [HF decouple: TC4422 inputs to increase noise immunity]
1x 100nF X7R MLC [input: LP2950ACZ-5 LDO 5V regulator]
1x 100nF X7R MLC [HF decouple: HEF4538]
1x 100nF X7R MLC [timing: HEF4538 one-shot Q2 for 2ms to pulse white LED
3x 100nF X7R MLC [HF decouple: TLC4422 12V supplies and LP2950ACZ-5 output]
1x 1µF X7R MLC [delay: HEF4538 Q1, Q2 power-up reset]
1x 1µF X7R MLC [timing: HEF4538 one-shot Q1 for 2ms weld pulse]
1x 10µF X7R MLC [output: LP2950ACZ-5 LDO 5V regulator]
5x 10µF X7R MLC [LF decouple: TLC4422 12V supplies (2x10µF each) & OPTION: LP2950ACZ-5 input]
2x 10µF X7R MLC [in parallel where 12V enters the board]
1x 5mm 2mA green LED [Amrel PSU (Vcap -> +5V)]
1x 5mm 2mA yellow LED [Manson PSU (+12V)]
1x 5mm 2mA white LED [weld pulse indicator]
20x 10Ω 2W Vishay PR02 [non-inductive: for experimental gate drive [initially 5Ω each]
[OPTION] 1x 1k0Ω 1/4W resistor [5V green LED (3.0Vf)]
1x 2k2Ω 1/4W resistor [12V green LED (3.0Vf)]
1x 5k1Ω 1/4W resistor [12V white LED (3.2Vf)]
4x 10kΩ 1/4W resistor [pull down: mosfet gates]
1x 10kΩ 1/4W resistor [pull up: HEF4538 EN- to +12V]
1x 10kΩ 1/4W resistor [pull up: HEF4538 CLR- to +12V]
1x 20kΩ 1/4W resistor [HEF4538 one-shot Q2 for 2ms to pulse white LED from +12V]
ADD A TRIMPOT TO EACH 1-SHOT
1x low current push switch [to activate HEF4538 weld pulse one-shots]
[OPTION] 1x LP2950ACZ-5 LDO 5V regulator
2x Miniature screened audio coax for the TC4422 inputs from the HEF4538s (~150mm) & to DMM
copper braid 200mm x 11mm 6mm² with M8 end rings x2
tinned copper wire 19SWG (1mm) [capacitor lead extension]
blue 2% Lanthanated Tungsten Electrode 1mm dia x 150mm
1x circular connector with 4x4A contacts [Manson +12V + 2 I/O debug]
1x DIN 5-way connector [Amrel Vcap + Sense + Vap- Sense- Earth]
Aluminium enclosure 160mm x 220mm x 80mm
OPTION: [insulated] metal Bulldog clip to secure element lead wires for welding
OPTION: 50mm L x 100mm W x 2.0mm fibreglass sheet above & below Bulldog handle to secure it to lid top
OPTION: 8mm diameter PVC rod to secure Bulldog handle to secure it to lid top
50mm L x 100mm W x 2.0mm fibreglass sheet below brass sheet anvil
50mm L x 100mm W x 0.3mm fibreglass sheet above brass sheet [Kanthal weld aperture template]
Delrin offcut 65mm x 30mm x 20mm x4
Brass sheet 50mm square x 100mm wide x 3mm [negative electrode anvil]
Brass bar 5/16" 9.5mm x 3/16" 4.8mm x 205mm x2 to support pcb on lid underside
Brass rod 12mm diameter x 150mm [weld arm]
Brass M3x11 screws + copper M3x1 compression washers [MOSFET drains to anvil]
Brass M8x6 screw + copper M8x1 compression washers [braid connection point at rod hinge end]
Spring loaded release point M6x12 plunger 4mm to lock welding arm in upward position
1x M6 x 60mm hinge bolt / sleeve bolt
4x M5 x 20mm Nylon screws to isolate the brass sheet from the aluminium box
General screws + spacers + washers + Nylocs
Element parts:
Kanthal A-1
1x hollow ceramic tube ID 0.7 OD 1.2mm x 100mm for element [TCW in tube ends to support coil]
OR 1x ceramic rod 1.2mm x 100mm for element [TCW wrapped around rod ends to support coil]
1x ceramic rod ID3.3mm x2 in OD10mm x 250mm long TC spacer [to be cut to length: Est. 10mm]
Initial crimp based element:
0.75mm² x 8mm bare crimp [0.3mm Kanthal wrapped around 0.6mm TCW]
LIBS 7 P.31 schematic LIBS 7 P.33 basic layout
508j01 P1150091 REV-5 cct for bonder 24-02-26 508j03 P1150092 REV-1 bonder basic layout 22-02-26
508j02 P1140956 LIBS 7 P.20 TWC & PR02 combos
508j04 P1150246 lid underside layout timing & discharge pcbs 13-03-26
508j05 Pxxxxxxx electrode is now a 12mm diameter brass rod so Pearson 410 probe can be released over it xx-04-26
508j06 P1150245 lid top assy
electrode & layout 17-03-26
508j07 P1150244 lid underside assy cap block & connectors 18-03-26 CAPS NOW AXIAL
Placing the work
Method:
The pointed tungsten electrode contacts the larger lead TCW; the Kanthal is pressed against the flat brass anvil.
The weld forms at the interface of highest resistance and current density, which is the contact point between the two dissimilar wires. Placing the pointed electrode on the larger TCW and the flat electrode under the finer Kanthal is the correct method. Here's why:
Current Concentration:
The sharp point on the TCW forces the immense current to focus into a tiny area at the contact point with the Kanthal.
Controlled Heat Generation:
This creates an intense, localized hotspot precisely where you want the metals to fuse—at their junction.
Anvil Function:
The large, flat electrode under the Kanthal provides a stable, cooling backing that prevents the fragile Kanthal from being vaporized and contains the weld.
Sequence of events
The wires are placed and the electrode brought down on them.
The DMM and PSUs connectors will be mated.
If present The Pearson 410 BNC will be connected to an oscilloscope: 50Ω terminator, 1MΩ input.
The PSUs are powered and the capacitor voltage set on the Amrel at a charging current of 1A.
When the DMM indicates the capacitor is charged, the Amrel PSU connector is disconnected.
The weld button is pressed to make the weld and the White LED should flash.
The discharge button is pressed to manually discharge the capacitors, if there is any charge left the red LED will glow.
Calibration first
There will be quite a bit of experimentation first with just the wires alone to determine the best bond voltage.
Making the bond (weld)
Based on the wire's tiny cross-sectional area and the goal of a localized fusion weld without vaporization, the sweet spot is likely 1 - 2 Joules.
Reasoning:
Below 1J: Risk of a cold, brittle joint due to insufficient melting.
Above 2J: High risk of vaporizing the 0.3mm Kanthal wire at the weld point.
Test:
Start at 1J, inspect the weld (it should be a fused nugget, not a sintered powder), and increase energy in 0.2J increments until you get a strong bond.
Make the bond using a cross-wire configuration.
No Bond? Increase energy by 0.25J - 0.5J and repeat.
Weak Bond? Increase energy slightly.
Sputtering/Splash? Energy is too high. Decrease immediately
The TCW will require less energy to melt than Kanthal, so the Kanthal is the limiting factor.
Reasoning:
Melting Point:
Kanthal A-1 (FeCrAl): ~1500°C
Copper (Cu): 1083°C
Brass: 900°C to 940°C
Solder Tin (Sn): ~232°C
The tinned copper wire will soften and melt its surface coating at a much lower temperature than the Kanthal will even begin to soften. The brass anvil will remain well below its melting point because
the weld energy is highly concentrated at the wire interface and brass has excellent thermal conductivity (~115 W/m·K), spreading heat rapidly across the large anvil.
The Welding Process:
The goal is to raise the interface to a temperature where the metals fuse. The tinned copper, with its lower melting point, will become molten first. This molten alloy wets the surface of the hot Kanthal, forming a eutectic bond.
Why Kanthal is the Limiting Factor:
You must pump enough energy into the junction to get the Kanthal hot enough to be wetted by the molten copper/tin. If the Kanthal isn't hot enough, the molten solder will just bead up on it without bonding. The entire process is gated by the temperature of the higher-melting-point material.
So, the statement holds: the Kanthal's need to reach bonding temperature is the limiting factor, which is why we focus the current on it via the pointed electrode on the tinned copper side.
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Additional notes from Google AI:
The "Dry Run" Check: Before you wrap the final Chomerics "skin," use a multimeter to check the resistance between your Positive Star Point and the Negative Honeycomb. It should be infinite. If you see even a few megohms, a positive lead is likely touching a "valley" in the negative shells.
The First Charge: For the first test, charge the bank to only 1V or 2V through a 1k-ohm resistor. If the voltage stays steady when you remove the charger, your "axial" conversion is a success.
If the MOSFETs aren't "snapping" fast enough (you'll hear a "hiss" instead of a "crack" during the weld), you can parallel a third or fourth 10R to drop the gate resistance further,
To prevent your 1mm lanthanated tungsten from sticking to the 0.6mm TCW (Tinned Copper Wire), you need to manage the intermetallic bonding that happens when the tin on the wire melts and "wets" the tungsten surface.
Since you are using a flat tip, follow these steps to pre-condition it for your 50-bond run:
The "Polished Flat" Finish
The Problem: Micro-scratches from grinding act as "teeth" that molten tin can grab onto.
The Fix: After grinding the tip flat, polish the face using 600 to 1000 grit emery paper. A mirror-like finish reduces the surface area available for the tin to "key" into.
Controlled "Blueing" (Oxidation)
The Trick: Unlike most welding where you want a clean electrode, a very thin layer of tungsten oxide acts as a non-stick barrier against molten copper and tin.
The Method: Before your first real weld, heat the tip slightly with a torch until it turns a straw or deep blue colour. This microscopic oxide layer is conductive enough for the pulse but chemically "slippery" enough to prevent the tin from wetting the tungsten.
The "Carbon" Barrier (The Pencil Trick)
The Hack: Rub a graphite pencil (HB or 2B) across the flat face of the tungsten tip before the first few welds.
Why: Graphite is a natural release agent and a decent conductor. It prevents the molten tin from making a direct molecular bond with the tungsten. After 2–3 "hot" pulses, the graphite will bake into the surface pores, providing a long-lasting non-stick coating.
Periodic "Flick" Cleaning
Maintenance: Every 5–10 welds, check the tip for a "silvery" buildup of tin. Do not file it off. Instead, use a brass wire brush or a piece of Scotch-Brite while the tip is still warm. This removes the tin without scratching the underlying tungsten.
The "Pulse" Advantage
Because you are using a high-speed axial honeycomb bank and a TC4422 driver, your pulse is extremely "stiff." Sticking usually happens when the pulse is too long (the "cook" phase). Your 2ms (or shorter) timing is your best defense against sticking, as it doesn't give the tin enough time to "soak" into the tungsten.
⌠ ⌡ ∫ │ ─ √ φ θ Θ ∂ δ ζ ξ ς λ ψ ω τ µ Ω ∆ Δ ∑ ∏ π Ξ ○ ≠ ³ ² ±
10⁻¹ 10⁻² 10⁻³ 10⁻⁴ 10⁻⁵ 10⁻⁶ 10⁻⁷ 10⁻⁸ 10⁻⁹