Author Topic: Generator Problem (Solved)  (Read 6590 times)

Offline 75Plus

  • Hero Member
  • *****
  • Posts: 624
  • Country: us
Generator Problem (Solved)
« on: September 27, 2010, 02:49:41 PM »
I am trying to repair a 5.5 KW portable generator for a friend. It has only 8 hours running time since new. The problem is in the exciter circuit.

The exciter winding feeds a bridge rectifier circuit that is made up with 8 discrete 2.5 amp 1000 piv diodes. The diodes are paralleled which is the reason for it using eight. There is also a 460 mfd. 200 wvdc. capacitor.

The field has a resistance of approx. 40 ohms and when flashing it with a 12 volt battery it draws about 250 ma. However, when running the current draw starts at approx. 6.5 amps cold and goes up to 9.5~10 amps as the temperature rises. The diodes get hot enough to melt the solder and fall off the circuit board or will short out sending AC to the capacitor causing it to swell up and burn open.

I spent a lot of time rigging up a 35 amp 100 piv. rectifier module and 2 1000 mfd 200wvdc capacitors wired in series to half the capacitance and double the working voltage. The circuit was placed in an enclosure with a heat sink in an attempt to keep it cool. I wired it to the circuit board that previously held the discrete components and brought it out so I could monitor the operation. After about 20 minutes of operating at approx. 15% load the output failed. This failure was due to the AC input connector on the rectifier board melting the solder.

I have worked with electrical equipment, both AC and DC including HF, VHF and UHF, for over 50 years but this problem has me stumped. Anyone have any ideas?

Joe
« Last Edit: September 27, 2010, 05:10:09 PM by 75Plus »

Offline John Swift

  • Sr. Member
  • ****
  • Posts: 344
  • Country: england
Re: Generator Problem
« Reply #1 on: September 27, 2010, 04:31:07 PM »
Hi 75plus

 I have not worked with portable generators , but  expect them to work like the alternator on a car
but without the output  being rectified

the dc voltage to the field winding must be too high
whats the AC output  ,is it correct ?

I would expect an electronic  regulator circuit to control the field current

if not some kind of non linear magnetic control of the exciter winding




                      John
« Last Edit: September 27, 2010, 05:05:39 PM by John Swift »

Offline 75Plus

  • Hero Member
  • *****
  • Posts: 624
  • Country: us
Re: Generator Problem
« Reply #2 on: September 27, 2010, 05:09:23 PM »
Thanks for the reply John. I just found the problem in the stator not the rotor. It appears to have been damaged prior to or during assembly. One of the laminations was bent and the varnish insulation on the wire failed grounding a good part of the winding. Naturally it was on the end next to the engine so it had to be completely disassembled to find it.

Now to locate a new part.

Joe

Offline John Swift

  • Sr. Member
  • ****
  • Posts: 344
  • Country: england
Re: Generator Problem (Solved)
« Reply #3 on: September 27, 2010, 05:49:46 PM »
Hi Joe ,

that explains the high current


 as a matter of interest whats the output voltage 110v or 110 / 220v 
and is it normally  floating or connected to the chassis

 good luck with the repair

        John

Offline 75Plus

  • Hero Member
  • *****
  • Posts: 624
  • Country: us
Re: Generator Problem (Solved)
« Reply #4 on: September 27, 2010, 06:07:16 PM »
It's a 120/240 VAC unit with floating output. The last thing I tried was to disconnect the output harness from the receptacles and start it. There was no output until I flashed the field at which time I heard the engine load up. With no load present there had to be a problem outside the rotor.

I found a new stator for $260 USD delivered.

Joe

Offline Dannywilson

  • Newbie
  • *
  • Posts: 1
Re: Generator Problem (Solved)
« Reply #5 on: February 16, 2011, 07:52:00 AM »
I was looking for this information.Your post solve my Problem!!!