Question about capacitors - HV caps to power low voltage device??

Discussion in 'General Electronics Chat' started by RogueRose, Jan 15, 2016.

Oct 10, 2014
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I have to admit that I don't have a very good understanding of capacitors so if this is a really dumb question I appologize.

I know there are a lot of applications that require fairly large capacitor banks, like spot welders and such. From what I've seen, these are usually pretty low voltage caps compared to something like a microwave oven (MWO) cap (2-2.5Kv).

Is it possible to use a number of the HV caps in parallel and then run it through a transformer to supply what is needed for something like a spot welder? I know MWO caps may be an extreme example so let's use something else like 275v or 480v caps run in parallel then through a transformer.

The reason I ask is that I would like to build one of those welders as well as an induction heater and from what I understand they require a fair number of caps and it seems to be a fairly expensive portion of the project. I have collected a lot of higher voltage caps over the years so that is why I'm asking this.

Is any of this possible or am I way off on my thinking here.

2. Aleph(0) Member

Mar 14, 2015
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Not practically cuz dumping energy from caps will destroy or saturate transformer! If the transformer is built heavy enough to take it, it will still throttle discharge anyway and cost more than cap bank!

Sorry VPN dropped me again!

So I was going to say FYI energy stored in a electrostatic is Energy = (C*E^2)/2 Joules, Farads, Volts

Last edited: Jan 15, 2016
3. Aleph(0) Member

Mar 14, 2015
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RogueRose I am also saying stay away from microwave caps cuz they have built in resistor (so equivalently high ESR) all to keep dummies who touch terminals of charged capacitors in gene pool

4. alfacliff Well-Known Member

Dec 13, 2013
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how would capacitors in paralell with a transforrmer power anything? as the caps were discharging, the transformer would have an output, when they were discharged it owuld have none. dc into a transformer only causes output from transformer when it is connected and disconnected.

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5. Kermit2 AAC Fanatic!

Feb 5, 2010
3,854
968
Inductive heating was done commercially over 100 years ago. One I have read about recently used a 6k volt AC line to feed a capacitor bank which was split in two rails. Using large solenoid driven contact banks. The two rails were alternately either charging or discharging through the inductor at the business end.
They called it an "oscillatory discharge" induction furnace. Smaller versions of this device let labs perform vacuum melting of refractory materials like platinum and metals from the tungsten series. It also allowed iron alloys to be made without creating dross or introducing large amounts of carbon. Google books has several old texts that describe the process.
Hint: building one on a hobby budget is not really possible. It will be costly.

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6. GopherT AAC Fanatic!

Nov 23, 2012
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4,083
You are way off in your thinking. Storing enough energy to heat steel to a melting point, all while insuring you have low enough resistance on everything up to the metal sandwich, will take a desk-sized bank of capacitors and control system. Or, it will require a very, very thin piece of sheet metal. In which case, a staple may suffice.