fechter wrote:...
Is there any data on what the optimum starting voltage for the caps is?
Who knows what the REAL data is on those car audio caps. I haven't been able to find anything that I'd trust. There is so much exaggeration in their marketing and in their manufacturing specifications, that you really can't trust anything. Since they are making products intended for consumers rather electronics engineers, marketing hype substitutes for precise specifications.
Seems like you could use a higher voltage and a smaller capacitance to get the same energy. Too far toward either extreme will run into problems. I just wonder what the best range is......
I've been trying to remember what voltage I used on the one I built 15 years ago... I think it was somewhere between 24 & 30V. but I'm a LOT happier with how this new setup works. (Although the main functional difference may just be due to using copper instead of tungsten electrodes).
I
think that somewhere between 15 & 16 V is optimum for this kind of setup, but the way it is now at 14.2v (
the adjustment limit on the power supply I'm using now) gives consistent, solid and neat welds that I am VERY happy with.
Years ago, I worked in an aerospace repair facility for a while, and the commercially made industrial one they had there that I got to play with when no one was looking, was,
(if I remember correctly), adjustable between 30 & 40 V. I doubt that it was more than .3 or .5 Farad, (my estimate based on the size of the unit and the available caps at the time.) And I think that it was adjustable between about 100 watt/seconds and 225ws.
So, yeah, increasing voltage should allow you to use smaller caps; But I don't know what is optimum. There must be some kind of trade- off, and the type of materials you are trying to weld must be a significant factor in choosing voltage.
(you are making me work harder than I planned here
and math is not my best friend)either
So, if the formula I just found ( ws=F/2 X V²) for converting volts & farads into watt seconds is right and my failing memory isn't too far off:
:
.3 to .5 farad works out right , if you factor in losses due to resistance, inductance etc:
.3/2 X 30² = .15 X 900 = 135ws
.3/2 X 40² = .15 X 1600 = 240ws
Which means that the setup I have now should be (if the farad specs are not vastly over rated) putting out about 140- 150ws.
1.5/2 X 14.2² = 151.23ws
Looking more closely at the Sunstone Engineering CD
welder, it looks like they are using 16.5 V as a maximum in their units ...
http://sunstoneengineering.com/site/pages/spDatasheet
I wonder if they are using car audio caps too?
You might have led me to something important:
Since I haven't been able to spot weld to aluminum with my CD experiments yet, I'm wondering if it might be possible to make a cheap CD
welder for doing the aluminum cans of A123 cells by using just a couple of 220,000 mfd higher voltage capacitors charged at around 40 volts. Have to try that if I can find the caps without sending a fortune, and rewire the secondary of a microwave transformer for the power supply.
You could use one of those solid state relays on the input to the charger to kill the output when you discharge so the SCR can unlatch. With the right timing, you'd be able to zap a weld and recharge almost immediately depending on the current output of the charger.
Well, I thought about that, but the residual voltage in the power supply caps would just add to the timing problems if you cut the input, rather than the output. Of course If I just use a transformer and bridge rectifier rather than a regulated power supply, cutting the input would simplify things.
