7.0 kw onan gen no output

jaque1 · 10-09-2011, 08:50 AM

I have a 95 winnebago motorhome with a39M 7.0 kw marquis gen. model#7HNMFA26105D serial#1943228987.It has 154 hours on it.It runs,but it won't produce AC volts.Last fall lady bugs got into the tranfer switch and fried the diodes when it was on shore power.Replaced them and it worked fine on shore power.I checked brushes,breakers,and even tried excitingit at pin 9 through a diode,and still no power.Any help would be greatly appreciated.I'm thinking it might be regulator. Thanks in advance.

Jack

Dave78Chief · 10-09-2011, 02:52 PM

Did you mean "7NHMFA26105D" vice "7HNMFA26105D"?

If so, then the Service manual is 965-0531B (http://www.cumminsonan.com/www/pdf/m.../965-0531B.pdf). A description of how the generator section works and troubleshooting it is in section 8.

Dave

Dave

Party Barge · 10-09-2011, 03:41 PM

Jaque1,

One of my gen sets had it own circit braker locaded on the unit which would trip ever so often, it would run, but not send current to the tranfer switch.

Dave78Chief · 10-09-2011, 05:19 PM

If this is a 7NHM unit, then the fact the engine runs after you release the start switch says a lot. Initial excitation is via VR1 pin 7 from the battery. This is used as field voltage across VR1 pins 9/10. This is working because your getting output from stator leads B1/B2 which generate engine run/battery charge voltage via VR2. This also starts voltage generation from stator leads Q1/Q2. When you release the start switch, B+ is removed from VR1 pin 7 therefore the source to continue field excitation is from the Q1/Q2 leads. That votage is rectified in VR1 and used for F1/F2. All that is working or the engine would not run. THis leaves you with the T1-T4 stator leads, the VR1 120VAC output voltage regulation, the harness wiring, the generator CB's, the wiring to the transfer switch or the transfer switch itself. Are you seeing voltage at the generator CB's and/or the terminal board?

Dave

wchipper · 10-09-2011, 05:23 PM

sound like the voltage regulator

jaque1 · 10-09-2011, 05:31 PM

My mistake on model#. It is 7NHM.Sorry !I'll check it out some more this week and keep you up todate.Thanks Jack

jaque1 · 10-16-2011, 10:17 AM

Dave, I checked for 110 voltage at pin 9&10 and nothing.Going to winterize it and worry about it in the spring. Jack

RTegarini · 10-19-2011, 10:19 PM

I just came across a guy with the same problem on a Onan 4000 kw just this last weekend; started right up, ran great, no a/c power. Turned out to be something very simple: the breaker tripped on the generator. A teenager actually found the breaker, as it is small in size and located down low, all but hidden. I probably wouldn't have found it without a manual pointing me in the right direction. While I doubt I would be so lucky (always costs me money to make a repair) you might check just to make sure it's not the generator breaker.-RT

mr300ce · 10-19-2011, 11:06 PM

ONE of my 2 breakers tripped. Then only 1 of the a/c units would work at a time. I found the breaker on the back side of the genset. Mine is a 7000, also. Find those breakers, and flip them. Maybe that is all you need.