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Old 06-19-2016, 06:19 PM   #1
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Onan 5.5 HGJAB Electrical problem

I just installed a "new to me" Onan 5.5 HGJAB in my bus conversion, along with new transfer switch and 50 amp panel. We took the bus on a weekend boondocking excursion to the races and the generator ran for approximately 32 hours in near 100 degree heat. It shut down one time, appeared to have been a cooling issue caused by the unit being too close to the ground, cleared that situation and it ran and powered fine. After we returned home my son was asleep in the bus so I left the genny on with him inside. I went out about an hour later, generator still running but AC's were off and no power to the panel. (still sleeping kid but now sweating, LOL) I let it cool down then tried again, same issue. I pulled the cover off the transfer switch to run a few tests, here is what I found:

Generator starts and runs flawlessly, still no power past the transfer switch but here is where it gets interesting.

Each hot leg of the generator reads 120v when tested between Hot and Ground at the incoming side of the transfer switch.

But, it does not read 120v when tested between hot and neutral. Neutral seems to be "lost". There is a reading but I do not know how accurate, of about 53v when tested between hot and neutral or ground and neutral with the generator running.

Big trip in a few days and the genny is our only source of AC when on the road, I'm pretty handy but having no luck troubleshooting this one. Help??

Thank you in advance
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Old 06-19-2016, 08:22 PM   #2
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The neutral should be tied to ground somewhere. Neutral to ground should always be 0. You apparently have a bad connection or broken wire on the neutral.
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Old 06-19-2016, 08:25 PM   #3
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If you have power in the transfer switch and shows half amount out the you have burnt contacts on transfer switch. You can jumper it to confirm this. It is a simple check.
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Old 06-19-2016, 08:31 PM   #4
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Thank you for the reply Paul, that was my first thought as i could swear I remembered the neutral and the ground bonded together inside the housing of the generator while I was installing it... I could be wrong about that. Then, I read on another post that the neutral and ground should never be bonded in an RV system. So, now I'm confused ��. Unfortunately I cannot remove the genset for a quick check, the install is difficult. I thought about bonding the neutral to the ground lug on the chassis where the genset ground strap is but wanted to get opinions.
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Old 06-19-2016, 08:35 PM   #5
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John, there is no voltage on the output side of the transfer switch, only on the input. Also, i disconnected the generator leads at the transfer switch and tested then alone. Still 120 with ground and hot, only 77v with neutral and hot.
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Old 06-20-2016, 06:32 AM   #6
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Information update:

Yesterday evening I disconnected the generator leads from the transfer switch and tested them standing alone. The reading was slightly higher from hot to neutral, about 77 or 78 volts, but still not 120. The reading with the generator leads standing alone was still 120 between hot and ground.

I left it sit overnight and when I started the generator this morning it read 120 between hot and neutral, and 120 between hot and ground. I hooked the generator leads back up to the transfer switch and tried it again, the voltage dropped immediately from 120 to about 56 volts between hot and neutral. Still showing 120 between hot and ground.

I do not believe the transfer switch is the problem, though I realized the voltage dropped when I hooked it back up this morning. The reason I do not believe it is the culprit, is that last night the generator was still only reading 77 volts between hot and neutral with the transfer switch disconnected.
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Old 06-20-2016, 10:35 AM   #7
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wiring diagram

I've attached the wiring schematic from the service manual, just wanted others opinion. From what I see T1 and T3 from the generator become load/hot, L1 and L2, though they appear to be jumpered together just before the breakers. (that part doesn't make sense, maybe it balances voltage at the breakers)

T2 becomes ground, this also shows tied to the chassis ground farther out in the diagram.

T4 as I see it is the neutral leg, but it's apparent that in several locations the neutral and ground are bonded, and carry through to the chassis ground.

My obvious question is this, I have a #6 ground at the transfer switch, runs from the generator output leads and from the chassis ground. Since the neutral and the ground are bonded inside the generator anyways, what is the negative impact of them being bonded at the transfer switch?

I do have a call in to the Onan help line at a local dealer, really just looking for others opinions on the subject.

Thank you for the help..
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Old 06-20-2016, 05:55 PM   #8
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As many suspected it turned out to be a burned neutral. There are five 12 gauge wires coming out of the generator, 2 hot - 2 neutral - 1 ground. That whip is about 3 foot long and runs into a J box, at that J box it changes to number 6 wire running to the transfer switch. The neutral was burned where the two number 12s connect to the single number 6.

I guess that common sense says something must have been drawing on the generator too hard, that will be the next investigation. We installed this generator to be able to run 2 air conditioners, it's very hot here in Texas. The front air is a new 15K Advent air, the rear is an older 13.5 Coleman, the only other appliance running with the refrigerator, and of course the converter.

I will have to look further into the problem and any thoughts or information would be greatly appreciated. Even if I have to pull this generator and rewire it with a heavier loop I need to be able to run both ACs at the same time.
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