MEP-802a Low Voltage and Quad Winding Help?

[Crabbie]

I picked up an 802a and have 60 hz but only about 20 volts output. It will make 120 volts if the master switch is held in the start position, but drops back down to 20 volts in the run position. The genset did not have the quad winding fuse modification, but does now. The some of the diodes in the voltage regulator quad winding circuit were fried. I replaced the voltage regulator with a known good regulator and still have the same problem. The quad winding resistance is low at 0.5 ohms versus the 0.9 to 1.2 as stated in the manual, so i presume the quad winding is shorted and not supplying voltage to the regulator.

My questions are 1) What voltage does the quad winding supply to the regulator, if it is in the manual I have not found it? 2) Has anyone bypassed the quad winding to supply an alternate source of AC voltage to the regulator either temporarily to test everything else or permanently? 3) Am I correct in subtracting the multimeter's wire resistance of 0.7 ohms for the multimeter I am using, from the displayed resistance reading (1.2 ohms) of the quad winding. 1.2ohms (reading) -0.7 ohms (multimeter wire resistance) to give me the 0.5 ohms I am using for the actual quad winding resistance?

Thanks

 

[m-35tom]

you zero the meter you are using, then measure the resistance. no further math needed.

 

[BadBrad1]

Some digital meters do not have a ZERO function, some have nothing and some have a OFFSET function where you short the leads and hit a offset button...this nulls the meter removing lead induced error..functionally the same as the ZERO function..

DMM"s that do not have a zero or offset function should read 00.0 or 00.1 when set to OHM's and leads shorted. Leads or meter should be suspect if over this. Note that some cheaper meters can be quite inaccurate at low resistance readings.

 

[zarathustra]

What I have found with my Fluke digital meter is that if I set the meter to continuity -- makes a tone when continuity is detected, and hold the leads together whilst I switch to ohms that it will register 0 ohms. If I just short the two leads together under ohms without doing that first I get .1 ohms.

As a note...

Here are the leads that you want to test. The numbers are based on the numbers on the terminal strip.

1 and 4
2 and 5
3 and 6
7 and 10
8 and 11
9 and 12

You'll have to disconnect the wires from the terminal strip to make sure that external circuits are not affecting the resistance reading. I also check the continuity ( not resistance) of the disconnected wire to every other wire on the terminal board. The only one that should have any continuity is the one that it is paired with in the above table. Any continuity other than that indicates a short between phases in the stator.

In order to eliminate an "opportunity for error" I only disconnect and test one pair of leads at a time and re-connect them before I start on the second pair.

zarathustra

 

[zarathustra]

I just re-read your post and saw that you think that the quad winding is no good.

If the quad winding is bad then there is no need to test the other windings. The stator needs to be replaced.

Think of the quad winding as a "fusible link" or "shear pin" to prevent fires. Fire prevention is why the ONLY DC powered item in the generator that is NOT powered by the +24 volt batteries is the voltage regulator. That is so that if there is a major internal problem within the generator the quad winding goes out, eliminating the power to the regulator and thus reducing the AC generated to near zero. If the regulator kept trying to pump out electricity when there is a major stator problem a fire would be the end result.


That is why you get to see some smoke when forcing the system to generate power by holding the start button on. The gen head is getting hot enough to begin cooking the stator windings.