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brother-bluto avatar image
brother-bluto asked

Multiplus-II on a 50A RV (US - 120/12V) with onboard Onan 5500 Generator

An Onan 5500 generator output is two 120V legs that total ~45A combined but are in single phase. I am finding out this is problematic for Victron products. I was thinking the Multiplus-II was the ticket to cover the entire 50A RV panel when on shore/generator/solar, until I found out that that when the Multiplus-II sees both L1 & L2 from the Onan 5500 in single phase it will shut down L2... and thus only provide the RV with L1/30A of the 45A the generator is capable of. Space is an issue, so trying to stick with a single inverter/charger combo and don't want to hamstring the generator output. Seems the only route I can go is to only power half of the panel (or a sub-panel) through a Multiplus instead of attempting to run everything through a Multiplus-II. Am I correct in this assumption?

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brother-bluto avatar image brother-bluto commented ·

Another thought... could I stay the course with a Multiplus-II and instead of having the current ATS on the input side, remove that and install a manual switch (Blue Sea #9093) on the output line between the Multiplus-II and the 50A panel so the generator completely bypasses the Multiplus-II. When I want to run the generator, just switch from Shore to Gen and get full use of the generator? Has anyone done this with the Multiplus-II and the Onan (or similar single phase, dual 120V output genset)? Seems I could keep my existing converter in place on the Generator side as well and provide a faster path for charging batteries when on generator power as the Multiplus-II would also continue to charge. Nice to have an ATS, but perhaps this outcome is the best I can get if I want to power my entire panel and still have full use of the Onan 5500 generator. Am I missing something?

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snoobler avatar image snoobler brother-bluto commented ·
Saw you over on DIY Solar. I think you're on the right track with the Blue Sea #9093 to simply select whether you're pulling from the MP-II or the generator.


I'm not sure I follow you on the MP-II charging from the generator unless you're also routing both legs of the generator to L1/N input on the MP. Would the transfer switch do this?

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brother-bluto avatar image brother-bluto snoobler commented ·
Thanks for the response - I may not have worded it properly, but using the switch to determine what feeds the RV panel (MP-II or Generator) means that when switched to generator I wouldn't have anything charging the batteries (since no power going to the MP-II). I think however I can work in the old PD9160ALV converter into that generator feed to accomplish charging when switched to generator. I was originally thinking of just leaving the PD9160ALV plugged into the panel which would provide charging regardless if the switch is on MP-II or Generator... but BattleBorn responded to my inquiry and didn't like the idea of supplementing the MP-II even though the per battery charge would be below their 50A recommendation.
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tmillsap avatar image tmillsap commented ·
Check out Changing Lanes on Youtube. Chad got the ok from electrical experts to combine L1 and L2 on the generator output (transfer switch input) since L2 gets dropped in single phase. It's basically paralleling the 120 circuit to give you 120V and 45 amps instead of 120v with 2-30 amp which is problematic for 50 amp RVs. I had this same problem and this fixed it.
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2 Answers
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Kevin Windrem answered ·

I believe the MPII 120/240 will accept a single phase input and power both output legs in phase if you connect only L1.

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brdcrtr avatar image brdcrtr commented ·

But L2 would be connected with 120v as well but it will be the same phase as L1. It's how the Onan QV 5500 works. It's a dual 30A output single phase. You can not make 240v from it.

How would the Multiplus handle that situation?

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Kevin Windrem avatar image Kevin Windrem brdcrtr commented ·
I don't know what happens if L1 and L2 are in phase. I agree that this would be a typical scenario in an RV with 50 amp 120/240 inlet in the US because often a TT30 to 14-50 doggone adapter is used and it feeds both legs off the one hot in the TT30.

You may need to try it to see what happens.

If L1 and L2 are in phase from the generator, you'd either need to connect them together (if you can and the generator doesn't complain), or disconnect L2 from the generator and only 65% of its output available (30 amps vs 46 amps). Some Onan generators can be rewired to produce 120/240.

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dennis16 avatar image
dennis16 answered ·

Looking for a verified answer on this, appreciate any help, hesitant to combine my L1 & L2 from Onan 5500 RV generator, thanks!

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corn avatar image corn commented ·
I am running into this same problem on a system I had installed on our RV. The installer recommended combining L1 and L2 from generator input to ATS. 45amps over a 6 gage wire makes me nervous. Has anyone done this successfully or figured another solution?
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tmillsap avatar image tmillsap commented ·
Jump L1 and L2. Check Changing Lanes on Youtube under his electrical fixes. Works like a charm.
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derrick thomas avatar image derrick thomas tmillsap commented ·
Be mindful when doing this. There have been a few reports lately on newer Onan generators that this now causes an output error and disabled the output. It doesn't appear to have any adverse effect however, once the jumper is removed and the error is cleared. Some of the newer small Onans are changing to inverter output and this seems to be cause.
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