I got my higher voltage welder
put together last night... twelve 36,000 uF 35V (45V surge) Mallory high quality
electronics capacitors. connected in parallel to give 432,000uF.... pretty close to half a farad.
Using a 30V - 3A bench power supply to charge them. Other than that, same basic setup as before.
Still have a lot of experimentation to do to figure out what will work best, but these are my initial findings:
1: The difference in the ESR between 'real' capacitors and even the better quality audio ones is very noticeable Some of the audio capacitors are really lousy, and since you can't trust the marketing hype or even the manufacturer's specifications on the car Caps, getting a good one is a gamble.
3: As expected, higher volts allows you to use much less capacitance;
3: 30 volts with all 12 caps is too 'hot' for battery tab welding. I burned through several nickel tabs and a couple of battery cases. Almost as bad as the M.O.T. AC spot welder
, although it doesn't heat up the battery internals as much. I'm going to try it with fewer capacitors in the near future, to see if lower capacitance at higher voltage will give better results.
4: At 20-22 volts this setup produces battery tab welds about equal to the original '1.5F' car cap at 14V. Not quite as good as the '5F' car cap at 14V.
5: At these higher voltages you have to use more pressure on the electrodes and keep it pretty equal. Light or uneven pressure causes arcs, sparks and burn throughs. Several times I ended up with about 1/32 - 1/16 th of an inch of my electrodes burned off and stuck to whatever I was trying to weld. Maybe thick tungsten electrodes would do better.... (Although the thinner ones I used on the welder I built back in the early 90s were not very satisfactory.)
OR I have seen some copper / graphite electrodes somewhere before... That might do if it doesn't introduce too much resistance.
6: Still can't weld to aluminum with any acceptable results.
7: There was a seven, but it slipped my mind
So far, I am happiest with the '5F' capacitor at 14V. and even the 1.5F at 12-14V is better than I have been able to do with this higher voltage setup.
I can see that using 'real' capacitors at higher volts has a lot of potential (literally and figuratively
) but it will take a more refined technique and/or more electronic controls to produce consistent, safe welds.
If I do decide to put much more 'serious' work into this particular effort, the 3A PS is going to have to be replaced with something with higher amperage. Either a rewound microwave oven transformer (if I can discover an 'ideal' single voltage) or spend the big bucks on a more powerfull bench supply..... or something.
However, as long as you can find a car audio capacitor with decent ESR you should be able to produce excellent welds with much less effort with the lower voltage stuff as described previously.