120v Generator -> AT 240v-> 240v Quattro -> AT 120/240 creates ghost load on AC1 out

DIY
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1

OK So I have my system set up in my motorhome. I have a 48v 15kva Quattro 230v (configured for 240v, 60hz) outputting to a 100A auto-transformer to take the 240v single phase off AC Out1 and convert it into 120/240v to my 50A panel. I also have an onan 8Kw QD 120v (2 legs, 120v in phase 30A ea and I have the bonded together at a bus bar) going to a second 100A autotransformer to step the 120v 60hz single phase to 240v 60hz single phase. This goes into AC-1 IN configured as a generator, then outputs to AC Out - 1 which goes to the AT being used to create split phase.

When in inverter mode running off the solar and batteries, the quattro and autotransformer kick the ground relay on the AT on, and provide power, no issues everything works, no ghost loads.

When I turn on the generator, the AT1 energizes, the ground relays kick off, but only half the load goes to charging the batteries, the other just dumps into AC out1 when there is no load there. Example. When the inverter is running, then I have 588watts going to AC out. Once the generator comes on, and say I’m generating 4kw on it, 1800watts will start loading up on AC1 out, though nothing changed on the load side, and the rest will go to the batteries.

I have removed the neutral ground bond at the genset, and I have checked continuity. no tone, and reads zero. Voltage going into the first AT is 120v, coming out is 240v and it reads 240v going into the quattro from VRM. If I reduce the amp limit, and I’m producing 2kw on the generator, then the load going to AC-1 will scale down accordingly, to about 1kw. Can someone please help me figure out what is going on? If i put it into charger only mode, and shut off AT 2, then all load goes to charging the batteries.

Long term, I’m going to try to sell the generator, and pick up a 12.5kw onan that is 120/240 and then I can just connect the two hots directly to the quattro and bypass the AT. But in the interim, I would really like to figure this out and have it work.

2

I had a similar setup on my RV in the past. You should be able to get this to work. Except that, if you’re using a Victron AT as the step-up transformer for the genset, you really don’t have 100A: you have 32A peak or 28A continuous (or less if the bay gets warm). So the maximum you could expect from your Onan is around 3.3kW continuously.

Anyway, the first thing I’d do is get a clamp ammeter and start measuring current directly. And the first test I would do is to leave both ATs in circuit, but turn off all loads on the output. Do you have a main input breaker at the distribution panel you can use to do that?

Then, go measure the current with your meter on each wire and let us know what you see.

3

Some 120V gensets can be trivially rewired to produce 240V, you might check into it. Others can be repowered with a new generator head. Or, you could swap it out, as you mentioned.

Separate from your problem, I’d do one of those. The step-up adds heat and copper and limits the system’s capacity.

4

Onan 8000qd generators are inverter generators. No way to rewire, or re-power. The engine rpm will scale with load. The neutral ground bond is created on the backside of the inverter/control box. Which I disconnected the jumper for.

5

If I disconnect the main panel I get all load going to the batteries. But then I have no power on the bus, and we are full timing it atm. I will try limiting it to 20 amps or under. 3kw of battery charge is better than no battery charge.

I will go pick up an ampmeter clamp today and get back to you. We have an octoberfest thing to go to, but i can stop by a hardware store on the way home.

6

Ok, so coming going into the AT to step up I was getting 30 Amps when I hooked to the L1 or Neutral, Neutral to ground was 0v, neutral to L1 was 120v, L1-G was 120v. I get 240 to the quattro.

So I did some additional testing at the second autotransformer. When its coming from the inverter, and the ground relay is lit up, I get (from ground) 116v on L1, 0 on N, 122 on L2. When I turn on the generator, I get (from ground) 230 on L1, 115 on N, 0 on L2. with the ground relay light off. So am I needing to figure out how to keep the ground relay on, when the generator is active?