Dodgy generator voltage regulator repair

The voltage from my generator drooped so much that a 3500 watt generator would no longer start a 1/4 hp motor. So I opened up the back of the generator and removed the voltage regulator so I could see the part number. Upon removal I see the ubiquitous bulged electrolytic capacitor. All the electronics are are potted into the reg case but the bad cap protrudes from the potting compound by about 5/8". Today I ordered a new reg but I am thinking that since the bad cap sticks up so far why not just remove the contents of the cap and peel the can out of the potting compound, thereby exposing the cap leads. Then just solder a new cap to the old leads or even directly to the circuit board if I can get to it. I think that I will end needing to solder a couple wires to the old leads and then solder the cap to the wires though. If this turns out to be the case will having the cap connected to wires that may end up being about 6 inches long be a problem? The cap in question is 220 MFD 250 volt. I will be replacing it with one that has a higher voltage rating. Eric

A lot of smps designs want the bypass electros as close to the secondary rectifier as possible. I don't suppose a good electro a few inches away will be as bad as one with high esr properly mounted, but it still might cause problems.

Unless it's an epoxy potting, you should be able to de-pot the board and get that cap in as it should.

snipped-for-privacy@whidbey.com wrote on 11/15/2017 1:56 PM:

No.

Electrolytic caps have fairly high ESR and inductance so that they will never notice the effect of 6 inches of wire.

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The Prickman keeps reposting the SAME bollocks he has been for decades.

Adding 6 inches of wire to an electro will massively increase its self inductance, by a factor of 10 at least.

The OP should add just enough wire to make connection to the PCB and twist the pair.

.... Phil

which might or might not be a problem. I have a computer somewhere that had all its on-board supply caps replaced with the new ones hanging on wires. Works flawlessly.

Do what you can do.

NT

Put the biggest cap you can solder into the hole and parallel the wires to the external cap.

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Prickman complete mor>

How is that relevant to the Prickman's bullshit claim ?

FOAD

.... Phil

yes

it's relevant to the OP's situation

thanks charmer.

NT

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Prickman complete mor>

Wot a tenth-wit.

.... Phil

If it's an epoxy potting compound (usually hard and black), you can soften it with commercial epoxy paint remover (methanol and methylene chloride). Or, you can use a hot air SMT desoldering thing:

Much depends on at what frequency the regulator is operating.

Plugging all that into: I get 378 nano-henrys inductance. At 1 MHz, that 0.421 ohms.

You didn't supply the original capacitor value, voltage, manufacturer, and type, so I can't calculate what the ESR should be. For 250 uF and

Therefore, adding 12 inches of #16 AWG wire to the filter increases its ESR by about 25%. That's not a huge amount and will probably work, but I would increase the voltage rating of the capacitor in order to get something with a lower ESR.

I don't suppose you could disclose the maker and model of the generator, possibly a guess as to the original capacitor specs, and perhaps a photo of the regulator?

I wonder what caused the capacitor to bulge? Mostly, I find that it's the ripple current, where a small amount of AC voltage ripple is impressed across a filter capacitor. This causes a high current to flow through the capacitor, which causes heating, which causes the electrolyte to boil, which eventually blows the lid off the capacitor.

So, what would cause AC to flow through the capacitor? Well, the generator will do that if the output from each of the presumably two phases is different. That could be caused by having a radically different load on each of the two phases. A two phase 3500 watt generator is really a dual 1750 watt generator, where each phase can only supply 1750 watts. If you try to load all 3500 watts across one phase, bad things will happen. Another possibility is a shorted turn on one winding. I have a few other guesses, but can offer much without a clue as to how its wired, which might be available once you disclose the maker and model number.

Thanks for your replies Jeff. I did describe the cap in my first post. It is a 220 MFD 250 volt cap.I did not name the generator though. It is a Champion model C46540. It has an RV type 120 volt receptacle that used to put out the full 29 or so amps. It also has another 120 volt receptacle that is wired in parallel to the RV receptacle and it is the type that allows either a 15 amp or a 30 amp plug to be used. It also used to put out the full rated amperage. I don't know if it does now. It also has a 240 volt receptacle that I have never used except once just to test it. In your previous post you mentioned using a heat gun to remove the pottying compound. I'll take a look at the links you posted. Thanks, Eric

Does the shattering damage other stuff? I could get some dry ice and freeze it really hard and then go after the potting with a punch. Eric

I don't know what the compound is. It is black and hard. I'll try to get the new cap as close as possible. Thanks, Eric

Your's and Rick's replies pretty much agree. I'll just get the new cap as close as possible and then not worry about it. Thanks, Eric

Typically, not. This is not liquid-nitrogen cold. The stuff usually cracks into fairly separate pieces, but not explosively.

Peter Wieck Melrose Park, PA

I apologise for not considering you the centre of the universe. Have a nice plonk. Again.

Every so often, Phil goes off his meds and starts to act out. Dealing with him at these times is much like nailing Jell-O or peeling raisins. Not very rewarding despite considerable effort.

I am not sure what drives him back onto his meds - I expect he mouths off t o one-too-many people face-to-face and gets his clock cleaned, or he is fou nd moldering in an ally somewhere. A stint in rehab, and he is fit, once ag ain to be in polite society until the next 'event'.

Either way, he has some good knowledge, with the failing that it is neither absolute, entirely accurate or complete. This is true of all of us - howev er, Phil takes that failing very personally, and deems himself exempt from the consequences.

Peter Wieck Melrose Park, PA

h him at these times is much like nailing Jell-O or peeling raisins. Not ve ry rewarding despite considerable effort.

to one-too-many people face-to-face and gets his clock cleaned, or he is f ound moldering in an ally somewhere. A stint in rehab, and he is fit, once again to be in polite society until the next 'event'.

er absolute, entirely accurate or complete. This is true of all of us - how ever, Phil takes that failing very personally, and deems himself exempt fro m the consequences.

I hope I never end up so intolerant or crazy.

NT