4. 20Vac 60Hz PSU (2016)
I bought a Chugai Boyeki YC-22 0.5" NTSC 330 line 5 Lux AWB 10,000th sec electronic shutter 24V 60Hz colour CCD camera + lens for the LHC project, primarily to view the laser hitting the target as it should assist in determining the quality of ablation which is in turn related to fractionation and the quality of LIBS spectra release.
An alternative use is for laser beam profiling, for which I had a different camera in mind, but to keep all options open I bought a couple of cheaper cameras with larger sensors to experiment with before risking the main camera. The large 0.5" sensor also means a larger beam can be accommodated although of course it must first be heavily attenuated - this process being part of my reason to have more than one camera to experiment with.
The YC-22 NTSC output is synchronised to its 24Vac 60Hz supply. This would be all well and fine if I was in the USA which has a 110Vac 60Hz mains supply, but I am in the UK with 230Vac 50Hz.
I already had a cheap Chinese USB 4-channel Digital Video Recorder/ video capture dongle that came with the very useful MultiViewer software which accepts both UK PAL and USA NTSC video formats so that side of the interface was catered for, but I needed a 60Hz 24Vac power supply.
Left top:
4-channel USB Video Capture dongle
Right:
Multiviewer
4-channel DVR running on a PC
Left bottom:
PAL or NTSC video standards are catered for
My first idea was to buy a small inverter and eventually I found what I thought was a more than adequate 75W 12Vdc to 110Vac 60Hz inverter from eBay China, intended to run off a car cigar lighter, for a mere $13. When it arrived, I discovered why:
Before hooking it up to the camera I first checked the frequency and voltage.
The appalling waveform to the right was the same regardless of load, although the output voltage started at 129Vac off load.
I have heard horror stories of equipment blowing up when connected to the outputs of 'inverters' like these.
Now you know why!
After a little more thought I came up with an idea for a novel low cost power supply: it occurred to me I could feed the output of a cheap eBay China DIY ICL8038 sine wave frequency generator ($3) into a similarly cheap eBay China DIY stereo TDA2030 power amp ($6) rigged for bridge drive. I deliberately chose a kit based on the TDA2030 because it is capable of running off ±22V (44V total), that I considered sufficient to generate a 24Vac supply. It even included a bridge rectifier and smoothing capacitors so all I had to provide was a heatsink and transformer.
In my parts box I found a diecast aluminium box (albeit with no lid) and a 40mm CPU heatsink/fan combo. The fan just cools the outside of the metal box behind the TDA2030s so the only holes needed are for its power lead and two spring loaded PC motherboard mounting clips.
The YC-22 datasheet says it consumes 3.5W. At 24V that amounts to 3.5/24 = 146mA. To even the loads up I ran the 8038 from -16V (its output ac-coupled to the amp input), the fan from a 7808 regulator off the +16V to reduce wear, noise and current and the power amps from ±16V. Max requirement around 7 watts. For simplicity I used a 3.5mm stereo socket / jack to carry power to the camera.
Above left the 8038 DIY kit and to the right, the TDA2030 stereo power amp kit.
Once I had built the PSU, it turned out the YC-22 would happily start up at 14Vac and I could run the dc supplies down to +14V 270mA,-14V 210m4V. The closest match was a transformer with ±12V secondaries and the cheapest was a potted safety type for around $10. Since the fan is external, I mounted the transformer in a corner of the box at the opposite of the power amp so the box would double up as a heatsink for the transformer too.
Left:
The heatsink mounted on the power amp end of the metal box
Right:
The finished interior of the 20Vac 60Hz PSU
Below left:
A DIY finger guard on the fan
The waveform isn't quite a perfect sinewave, but it's a heck of a lot better than the abysmal attempt that came out of the Chinese inverter. The highest voltage I could get out without distortion was 20Vac, and this co-incided with the minimum current consumption from the YC-22, so I left it set at this voltage.
Below, a bit of fun with the YC-22 camera:
