Blown capacitor and still works?

Hoster987

Hoster987

Joined
Jan 4, 2021
Messages
131
Since we have not used (luckily) our portable generator for 3+ years - Stanley G8000S (8K watts), I wanted to change the oil. However, when I started the generator to warm up the oil, I saw a cloud of smoke from the control panel and definitely smelled like electrical components burning.

1. The capacitor was replaced before we put it away - due to a blown capacitor
2. Looks like the Home Depot repair guy put in a wrong one (didn't have time to do this replacement at the time)
3. Based on my research, the original is 450V 45uf and the replacement is CCB61 250V 40uf (see pic)
4. Hence the smoke due to an under-capacity capacitor??
5. I stopped the generator then restarted to take a video and no longer smoking
6. The control panel indicates around 240v and 61 hz (which seems to work but may not be generating??)

Can a capacitor "partially" work? I thought a capacitor can either work or not work....I am going to replace the capacitor but out of stock for now (as my generator seems to require a rectangular one vs. a half-moon shaped).

20250228_165806.webp
 
Jetronic said:
the generator would work, but the power is very dirty
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Thanks for your advice. Does the shape (rectangular vs. half moon) matter? Not sure the half moon will fit but seems like the half moon shaped one is more readily available vs. a rectangular one.
 
Marcozi said:
Generally, once a capacitor is burned it doesn't work at all. Try www.mouser.com to find the correct capacitor.
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That's what I thought. In the past, the panel would not even indicate any voltage / hz but this time, it seems to be producing "something" - in any case, I am going to replace the capacitor.
 
The difference between 40uf and 45uf is basically margin of error. Rectified mains voltage in the US reaches only 170ish volts. That capacitor is fine.
 
Typically, in conventional generator heads, the capacitor simply smooths out the excitation power. Without it, the output current looks a bit ugly on an O-scope.

There are more complex systems that actively manage voltage, in these there are nearly always capacitors that smooth out excitation power and others used as filters for accuracy, in the circuitry to manage voltage.

As I am sure you know, many of today's capacitors have a very limited lifespan due to poor quality. A 250V capacitor is too low for a 240V generator. I understand the point above, but the RMS voltage produced is 240, not 170. The 170 number is the 'peak' voltage of a 120V circuit. The 240V circuit has a peak voltage of 340 or more in generators.

EDIT: If one were to rectify 240VAC, using a simple bridge rectifier (4 diodes) the resulting voltage is 325VDC. This is what that capacitor must deal with.
 
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jayjr1105 said:
The difference between 40uf and 45uf is basically margin of error. Rectified mains voltage in the US reaches only 170ish volts. That capacitor is fine.
Click to expand...
Understood and thanks for the info. Just worried as I saw a cloud of smoke with intense electrical component(s) burning smell....
 
Hoster987 said:
Since we have not used (luckily) our portable generator for 3+ years - Stanley G8000S (8K watts), I wanted to change the oil. However, when I started the generator to warm up the oil, I saw a cloud of smoke from the control panel and definitely smelled like electrical components burning.

1. The capacitor was replaced before we put it away - due to a blown capacitor
2. Looks like the Home Depot repair guy put in a wrong one (didn't have time to do this replacement at the time)
3. Based on my research, the original is 450V 45uf and the replacement is CCB61 250V 40uf (see pic)
4. Hence the smoke due to an under-capacity capacitor??
5. I stopped the generator then restarted to take a video and no longer smoking
6. The control panel indicates around 240v and 61 hz (which seems to work but may not be generating??)

Can a capacitor "partially" work? I thought a capacitor can either work or not work....I am going to replace the capacitor but out of stock for now (as my generator seems to require a rectangular one vs. a half-moon shaped).

View attachment 266512
Click to expand...
I work on generators like that almost every day in the winter. Any capacitor that's the same uf as what it's supposed to have works. It doesn't have to be a square 450v 45uf capacitor with its own wires. You can make a round capacitor with spade terminals work as long as it will fit. As long as the voltage is at least 450v. The capacitance is what needs to say the same.
I'm not sure what putting a larger capacitor in will do, I've been meaning to test it.
Might have better luck finding a 480v 40uf motor run capacitor.
I used to sell electrical salvage on ebay.
480v capacitors are pretty common.
 
Cujet said:
Typically, in conventional generator heads, the capacitor simply smooths out the excitation power. Without it, the output current looks a bit ugly on an O-scope.

There are more complex systems that actively manage voltage, in these there are nearly always capacitors that smooth out excitation power and others used as filters for accuracy, in the circuitry to manage voltage.

As I am sure you know, many of today's capacitors have a very limited lifespan due to poor quality. A 250V capacitor is too low for a 240V generator. I understand the point above, but the RMS voltage produced is 240, not 170. The 170 number is the 'peak' voltage of a 120V circuit. The 240V circuit has a peak voltage of 340 or more in generators.

EDIT: If one were to rectify 240VAC, using a simple bridge rectifier (4 diodes) the resulting voltage is 325VDC. This is what that capacitor must deal with.
Click to expand...
On those little capacitor regulated generators the output voltage always looks ugly on an oscilloscope.
 
I know nothing about capacitors on generators - sorry.
It might help if you look on YouTube to learn how to check a capacitor using a multimeter.
Yearly, I check the capacitors on my furnace and refrigerator (using multimeter).
The micro-farads number is on the capacitor and has a tolerance.

My neighbor had an air-compressor that kept tripping the breaker.
I checked the two capacitors on the motor, and one was bad.
I replaced both (start and also run) and no more problems.
 
MasterSolenoid said:
I know nothing about capacitors on generators - sorry.
It might help if you look on YouTube to learn how to check a capacitor using a multimeter.
Yearly, I check the capacitors on my furnace and refrigerator (using multimeter).
The micro-farads number is on the capacitor and has a tolerance.

My neighbor had an air-compressor that kept tripping the breaker.
I checked the two capacitors on the motor, and one was bad.
I replaced both (start and also run) and no more problems.
Click to expand...
You can get a meter with a capacitor test function.
 
So the org. cap blew.. now the replacement cap blew.. maybe something is blowing up the capacitors?
 
Sometimes capacitors don't blow entirely and will still partially work. See that a lot in electronics with swollen electrolytic caps, especially certain years and models of motherboards. You will get all sorts of weird things going on with the computer, like errors and crashes. Open the case to find a bunch of swollen caps that need to be replaced. Then you get the fun time of desoldering a bunch of caps and replacing them, assuming they haven't started fully leaking and ruined the board entirely.

In this case though, I'm going to say the use of a 250V cap where a 450V cap should have been used is the issue. Its normally fine to go to a higher voltage rating for the cap but lower is going to cause issues. Make sure the new cap you put in has at least a 450V rating and the same uF and you should be good to go.
 
450v 45uf capacitor
Rand said:
So the org. cap blew.. now the replacement cap blew.. maybe something is blowing up the capacitors?
Click to expand...

That is a very common line of reasoning. I was working on an 115V, 400HZ aircraft power cart that kept failing after
'professional repairs' by blowing the rather large capacitor bank. Often rather explosively, with lots of noise, smoke and some flames. After getting chewed out by the big boss, who insisted something else was wrong as he thought he knew his stuff... I purchased 35 capacitors from the manufacturer. Worked like a champ.

The thing is, the output was spot on 115V, 400HZ. Exactly what the 35 capacitor bank was designed to filter. There was nothing wrong with the power produced. Put another way, it is very unlikely your generator is producing say, 700V and frying the capacitor.

Quality control today is terrible, especially with imported parts. Knowing what and where to purchase from is next-level information.
 
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