Generator – voltage shifts under electrical load


Old 09-05-13, 07:00 PM
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Generator – voltage shifts under electrical load

I am having problems with my Generac PP5000T generator. This is a dual voltage 115V/230V, 5000 W generator. It hasn’t been used in quite a while (like 9 years). The last time I used it, it generated electricity as expected.

The engine starts and runs very well, but a halogen work lamp does not light when plugged into any of the 115V receptacles. A 115V drill also does not work when plugged into any 115V receptacle.

With no electrical load, the receptacles measures about what they should – each 115V outlet measures about 115V (one measures 120V and the other measures 110V). The 230V receptacle measures 253V (a bit high). The frequency measures 60Hz. Again, these readings are with no electrical load - just the multimeter probes inserted into the receptacles.

Interestingly, when I plug the halogen work light into either 115V receptacle, the voltage at the other 115V receptacle goes up from 115V or so to 253V. It is like the applied electrical load causes the all the voltage to “shift to the other side of the power windings”.

I changed the bridge rectifier / brush assembly and this did not help. I tried flashing the field once using 12V per the Briggs & Stratton troubleshooting guide (B&S apparently makes this generator). Neither of these helped.

I measure correct resistance on the rotor winding (measured 25.2 ohms, should be 24 – 29 ohms) and correct resistance on the excitation field windings (1.43 ohms, should be 1.26 – 1.67 ohms). The stator power field winding overall resistance was a bit high 0.34 Ohms /0.41 Ohms (if I read the B&S troubleshooting chart correctly, these should be 0.23 - 0.29/0.24 -0.34). There were no shorts to ground in any coil.

I am confused. I don’t believe this unit has a voltage regulator, just the brush / bridge rectifier assembly.

Any ideas what is going on?

Has anyone else seen this before?

Thanks for your help.
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Old 09-05-13, 07:58 PM
Join Date: Mar 2006
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Purely off the top of my head but it sounds like a high resistance connection where the "neutral" leads of the 115 volt receptacles connect to the main stator coil center tap.
Old 09-06-13, 03:52 AM
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When you measure low resistance values, you check the value you read first by shorting the test leads. Then you have to subtract that reading when you measure the value you're trying to read. So your subtracting the test lead resistance.
Old 09-06-13, 01:23 PM
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Update - tried something else

Last night I had a thought to plug 2 halogen work lamps in at the same time - one on each 115v "side". When both lights were plugged in, both lights became illuminated.

When one light was unplugged, the other light (that was still plugged in to the "other side") went dark.

Does this help stimulate any ideas?

At least it is generating to figure out how to use it!
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