MadModder
The Shop => Electronics & IC Programing => Topic started by: 75Plus on September 27, 2010, 02:49:41 PM
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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
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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
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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
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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
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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
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I was looking for this information.Your post solve my Problem!!!