Testing Condenser [capacitor?]

Jegs

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Good morning,

Got the genny diesel running but no electricity. Four wires from stator: two for output & two to condenser.

Due to location it is difficult to obtain a similar item & the rating does not appear on body.

Can these be tested &, if so, how? Would one of a similar size do the same job or is it more complicated than that? I don't think I'm going to like the answer to this!

Clamp & multimeter only.

Hopeful thanks,


John G
 

VicS

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Capacity and voltage rating are what count not physical size! Sure its a condenser even ?

No easy to test but should show open circuit on a resistance test

What generator? It may be possible to find more info on line.
 
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Jegs

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Genny

Thanks Vic,

It's a Laser genny, about 20 years old with a refurbed farymann single pot diesel.
The paperwork [in Italian] gives info re diodes but not condenser,

John G
 

cozzykim

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Good morning,

Got the genny diesel running but no electricity. Four wires from stator: two for output & two to condenser.

Due to location it is difficult to obtain a similar item & the rating does not appear on body.

Can these be tested &, if so, how? Would one of a similar size do the same job or is it more complicated than that? I don't think I'm going to like the answer to this!

Clamp & multimeter only.

Hopeful thanks,


John G

Does your multimeter have a capacitance test function?
 

cozzykim

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Capacity and voltage rating are what count not physical size! Sure its a condenser even ?

No easy to test but should show open circuit on a resistance test

What generator? It may be possible to find more info on line.

He might be able to use the higher resistance ranges to charge the capacitor one way and then observe a 'kick' on the meter when connected in reverse, at least showing that it's storing some charge.
 

savageseadog

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It will be at least 20uF rated AC working voltage continuous (very important), at least 300V AC. It's very important to use a correctly rated (voltage spec) capacitor or it could literally blow up. The capacitors tend to commonly fail and do age. To test you could connect across a 12V battery, remove and connect to a meter.
 

cozzykim

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It will be at least 20uF rated AC working voltage continuous (very important), at least 300V AC. It's very important to use a correctly rated (voltage spec) capacitor or it could literally blow up. The capacitors tend to commonly fail and do age. To test you could connect across a 12V battery, remove and connect to a meter.

Be absolutely certain that it isn't short circuit first :eek:
 

nrbx

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It is a capacitor, they are the same thing.

Cheap enough to replace, and it's just used to smooth the power.

More is more so don't worry about getting the exact same replacement, a 37 uF or around there would do just fine.

But as said make sure it's well voltage rated.


Maplin do sell them, but unsure how to test it I. Afraid
 
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cozzykim

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It is a capacitor, they are the same thing.

Cheap enough to replace, and it's just used to smooth the power.

More is more so don't worry about getting the exact same replacement, a 37 uF or around there would do just fine.

But as said make sure it's well voltage rated.


Maplin do sell them, but unsure how to test it I. Afraid

I was assuming that it's the excitation capacitor.
 

savageseadog

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It is a capacitor, they are the same thing.

Cheap enough to replace, and it's just used to smooth the power.

More is more so don't worry about getting the exact same replacement, a 37 uF or around there would do just fine.

But as said make sure it's well voltage rated.


Maplin do sell them, but unsure how to test it I. Afraid

It isn't for smoothing the power. It is used to create a magnetic field in the alternator with phase shifted excitation. I've seen suitable capacitors on ebay.
 

Spyro

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An old meter with a needle rather than a digital display is best. Connect the leads to the capacitor, put the meter on resistance scale it should show open cct then reverse the leads you should see the needle kick and then go back to zero as the capacitor discharges. repeat again to see another kick
 

Jegs

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Cap/Cond check

Good people,

Many, many thanks for all the helpful replies. My rural frog wifi is not totally reliable, hence my silence for the last couple of hours.

My meters do not have a capacitance test function. My reading of the advice is that the capacitor is used to create a magnetic field in the alternator & the rating is 37uF with a min. voltage 300v.

One more question please: the insulation on the wires was the same colour & the terminals did not appear to be marked; might reversing the connections have any effect?

John G
 

cozzykim

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Good people,

Many, many thanks for all the helpful replies. My rural frog wifi is not totally reliable, hence my silence for the last couple of hours.

My meters do not have a capacitance test function. My reading of the advice is that the capacitor is used to create a magnetic field in the alternator & the rating is 37uF with a min. voltage 300v.

One more question please: the insulation on the wires was the same colour & the terminals did not appear to be marked; might reversing the connections have any effect?

John G

No, it's not a polarized capacitor. EDIT: I hope :)

Does the generator have a pair of rotor diodes and varistors, if so have you checked that none of those is S/C ?
 

Jegs

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Genny

Cossykim,

Thank you for your input. The Italian diagram shows diodes but no mention that i can see of a varistor - do not understand 'S/C'.

It may clarify if I explain that the electricity was being produced until the engine failed. Now the motor has been fixed but no juice!

Thanks,

John G
 

cozzykim

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Cossykim,

Thank you for your input. The Italian diagram shows diodes but no mention that i can see of a varistor - do not understand 'S/C'.

It may clarify if I explain that the electricity was being produced until the engine failed. Now the motor has been fixed but no juice!

Thanks,

John G

S/C - Short Circuit.

Italian?

Is this a Mase genset, IS 2500 3500 or similar?

If so the rotor windings have a diode and varistor in parallel with the individual rotor windings, the diode to rectify the current in the windings producing a rotating magnetic field, the varistor acts like two zener diodes back to back limiting the voltage produced in the windings.

If either of the two components on either winding are short circuit (and/or open for the diodes) then the magnetic field won't be properly sustained in the rotor.

EDIT: The diode/varistor are plug in components on the rotor assembly IIRC, i.e. I don't think they're soldered on, rather screwed on.

HTH
 
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cozzykim

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The exciter capacitor is the "weak bit" of these gensets and are often replaced as part of a normal service routine. Mine is 28uf 400v on a 3.5kva, the higher the uf the more the alternator is excited and the greater the voltage produced so try to get one as close as possible to the original, 2 or 3 uf can make a lot of difference.

If most of these genset excitation capacitors are around that value then OP should be able to check whether it's charging OK using a multimeter as previously described, preferably an analogue meter as Spyro suggested.
 
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