Skip to main content ↑ ↓
Topic: Mains vs Genset Problem (Read 2188 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Mains vs Genset Problem

Yahoo Message Number: 73362
We have a Onan 8HDKAK in our 07 Allure and the following problem. When we run the genset the forward AC unit dosn't run.
When on the mains all is normal. The voltages at the pedestal, transfer switch and breaker box all measure L1 to ground 120V, L2 to ground 120V, L2 to L2 240V.
On the genset the voltages are, L1 to ground 120V, L2 to ground 120V and L1 to L2 0V. These voltages are the same from the genset terminal block through the system.
The EMS panel shows Gen and all lights are lit but there's no voltage to several of the breakers including the front AC.

Thanks for your thoughts,
Jim

07 Allure #31570

Re: Mains vs Genset Problem

Reply #1 –
Yahoo Message Number: 73390
Your generator does not produce 240 volts across L1 and L2. It has 2 120 legs in phase so the voltage across them will be 0. The voltage readings you have posted are the way they should be for both shore power and generator. You need to look a little harder at the Load Shedding device and breakers.

Mikee

Re: Mains vs Genset Problem

Reply #2 –
Yahoo Message Number: 73397
Thank you Mikee,

With that information I'll look further at the Intellitec 50 Amp Smart EMS. It correctly shows "GenSet" with all lights lit when the gen is running but, it is shedding loads including the front AC unit.
Me-thinks I may have a failed component on the EMS board. Where to get a rebuilt and/or new board?

Thanks again,
Jim

07 Allure #31570

Re: Mains vs Genset Problem

Reply #3 –
Yahoo Message Number: 73398
I. Agree the gen can produce 240 volts but in a MH application it provides two 120 volt legs in phase. Bob 06 intrigue 12047

Re: Mains vs Genset Problem

Reply #4 –
Yahoo Message Number: 73401
Buck,

They come in both flavors. In coaches that do not have any 240 volt appliances it makes no difference to the coach wiring, In fact a 50 to 30 amp pigtail creates the same condition for a street hookup. L1 to Neutral 120, L2 to Neutral 120 and L1 to L2 0 volts.

Don Seager

2004 Allure 31046

Re: Mains vs Genset Problem

Reply #5 –
Yahoo Message Number: 73406
Freind I agree with you, Rarely on smaller RV Generators 25 kw and under Single Phase will you have 240 volts across the Two Generator Mounted Breaker's, One way to find out as many times repairing them and removing them from a coach/Building etc. is a Jumper on the Generator side of the Two Gnnerator Breakers connectong L1 and L2,The other end of the Marked L1 and L2 coils are tied to eather a Neutral Bar/Bolt and or are Tied to the generator Stator Housing. Our 7 kw power tech had two breakers and each one allow's about 25 A/C Amps at 120 pass. Added total of Plus or Minus 50 total Amps. Yes you would and should get zero volts between L1 and L2! Keep us posted Ken Retired Cat Power Statems Tech. 99 Allure 30356

Re: Mains vs Genset Problem

Reply #6 –
Yahoo Message Number: 73412
UpDate. To further test the system I moved the power cord from the 50 amp plug on the park pedestal to the 30 amp plug. The system came up normally with the EMS announcing 30 amps and all circuits active. As I applied loads the EMS shut down as necessary to stay in limits. The front AC unit worked normally.
Does this juggest our house system, EMS etc., is set up with the expectation of multi phase, ie 240V across L1 & L2, input from the genset?

Boy this is fun!

Thanks,
Jim

07 Allure #31570

Re: Mains vs Genset Problem

Reply #7 –
Yahoo Message Number: 73417
What this suggests to me is that there is something wrong with your 50 amp shore power. Have you checked your surge guard? They can do wierd things when shore power is bad.

Rich 2002 Magna

Re: Mains vs Genset Problem

Reply #8 –
Yahoo Message Number: 73423
Hi Rich -

Yes we've checked the shore power 50 and 30 amp and all is well. The surge guard is working fine, the problem(s) only occur when we run the genset. I checked the specs for the Onan 8-HDKAK and it's only rated for single phase 120 on each leg so it should not yield 240 L2 to L2.
The best I can come up with now is a failed component on the Intellitec EMS board.
When we run the gen all of the "shed loads" are dumped - any other souce, 30 and/or 50 amp and the system works OK.

Thanks,

Jim 07 Allure #31570

Re: Mains vs Genset Problem

Reply #9 –
Yahoo Message Number: 73425
Sounds like the shore power is either wired wrong or missing a neutral. I have seen that in the campground that I am at. The neutral was intermittant and corroded at a bad junction at the meter.

Jon Baum
Magna 5923

Re: Mains vs Genset Problem

Reply #10 –
Yahoo Message Number: 73426
Guys the shore power is OK, my problem only happens when we disconect it and use the genset!

When on the GENSET all the shed loads are dumped.

Jim

Re: Mains vs Genset Problem

Reply #11 –
Yahoo Message Number: 73432
Buck,

The generator can be wired either way, 2 120 volt legs in phase or 2 120 legs 180 apart in phase. A lot of coaches use 240 volt appliances, dryer, stove, etc that require a generator that will provide 240 volts. Most coaches, with onan have 2 120 volt legs in phase. It is not an absolute, if you measure 120 on each leg to neutral, but 0 across L1 and L2 they are in phase, if you measure 240 across L1 and L2 they are 180 apart in phase. 180 apart in phase gives 240 volts, 2 120 legs in phase give 0 volts across L1 and L2 .

Mikee

Re: Mains vs Genset Problem

Reply #12 –
Yahoo Message Number: 73433
Jim,

Have you measured the voltage after the transfer switch when on generator? The easiest place would be the main panel in the coach. If you have 120 on both legs there the problem if after that if not it is before, move back towards the generator until you find the loss. It may be one contact in the transfer switch is failing, or one leg on the generator is dropping out. Let me know the results of these measurements.

Mikee

Re: Mains vs Genset Problem

Reply #13 –
Yahoo Message Number: 73455
Mikee and others,

Thanks for all your help.

Here's the latest - I have 120V out on each side, L1 & L2, at the genset. On the input of the transfer switch I only have 120V on L2.
Something has gone open on L1 between the genset and the transfer switch. This wiring is buried in the ceiling(s) of the bays. Does anyone know if there are connections and/or devices in that line?

Thanks to all again,
Jim

07 Allure #31570

Re: Mains vs Genset Problem

Reply #14 –
Yahoo Message Number: 73456
Jim,

I don't believe I have seen the answer to Mikee's question below. Have you measured the voltages (L1 - Neutral and L2 - Neutral) AT THE TRANSFER SWITCH -- both input to the transfer switch and output from the transfer switch. Maybe bad contactor on one one of the two lines from the generator. If the input to the transfer switch from the generator does not look right, then search back to the generator. I vaguely believe the breaker on the generator is TWO-POLE, even though the potential between L1 and L2 is zero volts -- bad breaker or generator.

Herb

Forum Moderator

Re: Mains vs Genset Problem

Reply #15 –
Yahoo Message Number: 73457
Jim,

While posting, I missed the post 7 minutes before mine -- about the time I started typing my previous reply!!!! Glad you have confirmed that it is before the transfer switch. Where did you measure at the generator? Before or after the breaker on the Generator?. Even though the breaker has only one handle, I seem to recall that it has L1 and L2 separated. I'll bet on the breaker.

Herb

Re: Mains vs Genset Problem

Reply #16 –
Yahoo Message Number: 73458
Hi Herb -

I measured the output of the genset after the breaker(s) at the connection block on the top right front of the unit. Got 120V on each side, one side is missing however at the input of the transfer switch.

This tells me I've lost continuity between the genset & the switch.
Before I dig in to the bays I'd like to know if there are any connections or other hardware along that line.

Thanks,
Jim

Re: Mains vs Genset Problem

Reply #17 –
Yahoo Message Number: 73461
On my coach, there is a 120 volt conduit junction box, above and behind the genset. Inside, the stranded conductor, flexible conduit from the genset is connected to solid conductor Romex wire with wire nuts. The wire nuts in mine were not very tight. If you have this junction box, it is a likely source of your problem.

Dave

2000 Allure #30444

Re: Mains vs Genset Problem

Reply #18 –
Yahoo Message Number: 73464
I just looked at ours and what I can see is some sort of straight connection between the flex cable and the run aft. I don't see a box or a way I can climb in there without putting the coach up on a hoist.
If the thing I see is the junction I'll just have to wait till we get to a shop.
I wonder if the "box" may be further aft in the overhead of one of the bays, I may be able to get to it that way.

Jim

Re: Mains vs Genset Problem

Reply #19 –
Yahoo Message Number: 73466
There should be no junctions that are not in a junction box. They may have run individual conductors in conduit all the way to the transfer switch rather than using Romex in your coach. Or as you say, there could be a junction box elsewhere.

Good Luck,
Dave

2000 Allure #30444

Re: Mains vs Genset Problem

Reply #20 –
Yahoo Message Number: 73486
I think it is a direct run, with nothing else in between.

Mikee

Re: Mains vs Genset Problem

Reply #21 –
Yahoo Message Number: 73489
Unfortunately I'm afraid it is Mikee.
Dave and others have said there should be a junction box aft of the genset that connects the flex conduit, needed to accommodate the gens in & out, coming out of the genset to the rigid conduit running aft to the t-switch.
On this coach it appears they made a straight connection between the flex and the rigid and pulled a wire set all the way with no connections.
If we have an "open" in that wire set we'll have to pull new wire(s) I guess.

Jim

07 Allure #31570

Re: Mains vs Genset Problem

Reply #22 –
Yahoo Message Number: 73492
I would look for a loose connection at both ends of the wire set. That is more likely than an open wire, but anything is possible.

Happy Hunting and let us know what you find.

Thanks

Mikee

Re: Mains vs Genset Problem

Reply #23 –
Yahoo Message Number: 73493
Done that, in fact I reset all the connections at the genset and tightened them at the t-switch.
Think I'll dig into the overhead(s) of the bays today and see what I can see along that line.

We're having fun now, right?
Jim

Re: Mains vs Genset Problem

Reply #24 –
Yahoo Message Number: 73496
Jim, even though you tightened the connections at the genset, you may still have corrosion inside the connection. Remove the wire completely and wire brush the wire and the inside of the connector terminal. Do this at both ends. Then, if you still have the problem, go to a craft or sewing store and get some T-pins (get the largest ones they carry). At the genset end, follow along the wire toward the transfer switch to the last point that you can access the wire. Using pliers or a small hammer (with the genset off, the coach disconnected from shore power, and the inverter off) push a T-pin through the insulation and into the wire itself (make sure you are in an area where the pin can't touch anything). Turn on the genset and check the voltage at the T-pin. If you have voltage, remove the T-pin (the hole in the insulation should be too small to cause any problems but you can take a wrap of electrical tape over the hole to be sure). Then repeat the process at the transfer switch end. This will at least verify that the wire is indeed broken if it is. Given the size of wire that they use, I really have a hard time believing that the wire has broken without leaving bare wire exposed which should cause the genset breaker to trip if it is in contact with the frame somehere. The situation would be the same if the insulation has just been damaged by chaffing - the breaker would turn off but the voltage would still be there. Having gone through that analysis, I believe that if the voltage is 'dying' somewhere between the 'pins' then there just almost has to be a junction box buried somewhere (this doesn't mean that you can get to it - just that it exists) and that is where corrosion or loose contacts are causing the problem. If that is the case, pulling a new wire may be the simplest answer.
One last check that can be made requires some jury-rigging, but would give you one more piece of information. Disconnect the wire at the genset end and attach a long piece of wire to the power wire. Then, with your meter set on 'Ohms', measure the resistance between the end of the 'new' wire and the power wire end at the transfer switch. If you get high or infinite resistance, then the wire is truly broken or disconnected at some point. If you get low or reasonably low resistance, then the wire is not broken. However, this will also indicate that in all probability there is a loose connector somehere in the line. Many times a connection will ohm out as good, but will have enough resistance that when high current tries to flow, the resistance will be enough to cause all the voltage to drop across the 'bad' connection.

Hope this helps.

Regards,

John

'06 Inspire DaVinci #51905