Capacitors in series - would it work?

[arcpaws]

Hi,

Someone gave me a couple of big electrolytic capacitors (something like 200,000 microfarad). They could be great on my MIG welder excepy they are only rated for 20 volts (35 volts "max surge", apparently). The open circuit voltage of the welder on full power is something like 30-35 volts.

So, could I wire two capacitors in series or would that be just silly? Also, do MIG welders require special caps (due to high currents)?

 

[rtbcomp]

Putting 2 identical capacitors in series will halve the capacitance and double the working voltage, however with the ones you've got you'll be a bit close to the limit anyway.

I don't think you need anything special for a MIG welder, after all the welding current doesn't go through the cap as it is in parallel with the rectifier, you just need a lot of capacitance.

No doubt Shenion will be along soon to elaborate!

 

[R Kraft]

The voltage doubles and the capacitance halves, when they are in series.
The ESR of the capacitance set would be higher than a single capacitor,but any capacitance would be better than none.
The OC voltage would go to 50V or so,you would need a bleed resistor and maybe a couple of small resistors across the capacitors to balance the voltage.
Do you have space in your welder for 2 of the things ?
Robert

 

[shedhobbit]

Hmm
Special caps ?
The output caps/inductor form a two pole low pass filter (techno babble) that try to produce a steady dc for your weld. The caps used should be designed to support high (ripple) currents i.e. have big stud/screw connections and the afore mention low ESR (equivalent series resistance - can explain if rquired).
Commonly available caps with the required values needed are usualy designed for low (<10 amps) currents and have solder tags fitted. Check it out and have fun.
Hope this helps.
Terry

 

[shenion]

They should go before the inductor/reactor. It will raise the minimum current and below about 60A, it will be more sensitive to torch/work length.

Will make the arc more stable and the "buzz" of short-arc will be easier to hear as there will be less 100/120hz buzz.

 

[arcpaws]

Cool!

Well, I have a reasonable idea what ESR and low pass filters are, so that's helpful. The caps I have don't have much written on them, but they do have big meaty screw terminals so I guess they can handle some current. I'll have to check the OC voltage to be sure. I'd hate them to blow up.