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Multiplus-II and Onan QG 5500 design questions/validation

Brother_Bluto

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Jul 23, 2021
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Looking for some help and or validation in ways to deploy the Multiplus-II in a 50A RV Toyhauler that has the Onan QG 5500 on board. Unfortunately, the Onan outputs two 120V legs in a single phase, which is no bueno with the Multiplus-II as it will see the single phase and drop L2 from the genset in that scenario leaving me hamstrung with half of the generator potential output. I want full use use of the ~46A output of the generator (run all 3 A/C's, etc). I was thinking I could remove the ATS and instead run the shore line directly to the Multiplus-II. Then install a manual switch (Blue Sea #9093?) on the output side between the Multiplus-II and the 50A panel, connect the generator output to the other side of that manual switch. This has the generator completely bypass the Multiplus-II and should let the Multiplus-II power the whole 50A panel and also provide the ability to run the generator when needed utilizing the full ~46A. Does this route make (electrical) sense? I was thinking I could also leave the existing 60A converter in place as well which will boost the charging potential to the (4) 100Ah BB's as well as ensure I can charge off of the generator if no solar is happening. Thoughts? If a sound design, is the Blue Sea #9093 the correct switch? Kinda sucks having to manually throw a switch... but seems like it is the only option to provide the best of both worlds. Am I missing anything.
 
I helped a friend install a Multiplus II into a 50 amp trailer with four 105 amp LiFePO4 batteries. We disabled (with future removal expected) the existing converter. The Multiplus produced plenty of amps to charge the battery bank.

I can't speak to how the two 120 volt inputs to the Multiplus from the ATS works. I didn't work on that part of the install.
 
Thanks. If the generator is run through the MP-II, the MP-II will shut down one of the 120V legs from the generator since it would come in as two 120V legs in a single phase as opposed to 240 split phase. That unfortunately leaves only ~23A 120V of output on a generator that can output ~46A when both 120V legs are used. As far as leaving in the old converter... adding the PD9160ALV into the mix gives a total of 180A of charging... which is just shy of the Battleborn recommended 50A per battery (4-100ah BB's). I really can't see anything wrong with this setup assuming I have called out the correct switch.
 
If you're comfortable with the charge profile of your converter, that's OK. In the case of the install I helped on, the charge profile was not acceptable for LiFePO4. My preference is to use a lower charge rate from a device that is programmable than take a chance with a higher charge rate from a device that may not be as friendly to my LiFePO4 batteries.
 
On a stand-alone basis the PD9160ALV is recommended by Battle Born for use with their batteries - it is a direct swap out of the stock WFO 55A unit that came in our 5th wheel. What I wasn't sure is if any considerations are needed when combined on the buss bar with the MP-II charging. From an Amp perspective the combined charge is still under the (per battery) recommendation, but I have reached out to BB for their advice on that one. Otherwise I may just wire the PD9160ALV converter on just the generator feed so something is still charging the batteries when the switch is in the Generator position (bypassing the MP-II).

FWIW - I am also looking into using the Victron Auto Transformer as a way to eliminate a switch and keep both legs of the generator going through the MP-II, but in a 120/240V split phase configuration which the MP-II would then accept both L1 & L2 from the generator. Seems like another failure point though and would have a ~5% loss of volatage on one leg from the Auto Transformer (not sure an issue).
 
I just jumpered both legs together at the transfer switch and I have pulled over 40 amps on l1 without tripping one of the 30 amp Onan breakers.
 
I just jumpered both legs together at the transfer switch and I have pulled over 40 amps on l1 without tripping one of the 30 amp Onan breakers.
That is an option, but then the generator only powers half of the panel through the MP-II passthrough of L1, and other half of the panel would be provided by the inverter on L2 of the MP-II. I'm still leaning towards either 1) removing the ATS, feeding the MP-II only via shore power, installing a manual transfer switch on the output side of the MP-II so if I don't have shore power I switch it to generator power and can feed both sides of the panel then directly by the generator. -Or 2) Using the Victron Auto Transformer for the generator output just before the ATS to change the Onan's (2) 120v single phase to a 120/240v split phase which will then passthrough both output legs of the MP-II.
 
At the risk of hijacking the thread because I have a regular Multiplus not the Multiplus II...

I have the same generator and an OEM ATS in a 30 amp trailer. I know there are two circuit breakers at the generator. Does that mean that there are two sets of wires coming into the ATS and then two sets coming out? I haven't given my ATS much thought, so I'm not familiar with it.
 
At the risk of hijacking the thread because I have a regular Multiplus not the Multiplus II...

I have the same generator and an OEM ATS in a 30 amp trailer. I know there are two circuit breakers at the generator. Does that mean that there are two sets of wires coming into the ATS and then two sets coming out? I haven't given my ATS much thought, so I'm not familiar with it.
Holding out the question of the Multiplus... Typically on a 50A transfer switch, the two Onan 120v single phase outputs from the Onan QG 5500 HGJAB would have the Neutral bonded on the ATS with one hot on L1 and the other hot on L2. Basically the RV panel doesn't care that they are single phase vs split phase. I am not familiar with the 30A wiring for this unit or a 30A ATS, but pulled up Onan's RV installation guide for the HGJAB and it shows the primary leg hot & neutral from the generator running through the ATS, and the secondary leg hot & neutral running directly to an outlet (in their diagram it ran directly to an AC unit). I believe there are a couple of different breaker configs of the 5.5 HGJAB and suspect yours has a 30A breaker for main leg and a 20A for secondary leg? Maybe others can confirm.
 
Holding out the question of the Multiplus... Typically on a 50A transfer switch, the two Onan 120v single phase outputs from the Onan QG 5500 HGJAB would have the Neutral bonded on the ATS with one hot on L1 and the other hot on L2. Basically the RV panel doesn't care that they are single phase vs split phase. I am not familiar with the 30A wiring for this unit or a 30A ATS, but pulled up Onan's RV installation guide for the HGJAB and it shows the primary leg hot & neutral from the generator running through the ATS, and the secondary leg hot & neutral running directly to an outlet (in their diagram it ran directly to an AC unit). I believe there are a couple of different breaker configs of the 5.5 HGJAB and suspect yours has a 30A breaker for main leg and a 20A for secondary leg? Maybe others can confirm.

I do have a clothes dryer plug in the trailer. I've never used it, so I don't know if it's active with both shore power and generator. If the circuit for that bypasses the main AC distribution panel then I think my system may be fairly simple. But that would mean that the ATS has two shore power inputs and two generator inputs, then two outputs. The last time I had the ATS and main distribution panel out I didn't look at it with a new inverter in mind.
 
which is no bueno with the Multiplus-II as it will see the single phase and drop L2 from the genset in that scenario
If the generator is run through the MP-II, the MP-II will shut down one of the 120V legs from the generator since it would come in as two 120V legs in a single phase as opposed to 240 split phase

The Multi should have no problem with accepting in-phase power on L1 and L2, the internal jumper relay will not close in this scenario and L2 is purely a pass through, where as L1 gets powerassist functions and is the leg that the charger pulls from.

You should get L2 pass-through even if voltage from L1-l2 is 0 as long as l2-N is 120
 
The Multi should have no problem with accepting in-phase power on L1 and L2, the internal jumper relay will not close in this scenario and L2 is purely a pass through, where as L1 gets powerassist functions and is the leg that the charger pulls from.

You should get L2 pass-through even if voltage from L1-l2 is 0 as long as l2-N is 120
The generator produces a single phase output of two 120V lines (not split phase). What others are reporting in various groups including Victron's user group is that if L1 & L2 come in on the same phase, then the MP-II will shut down L2 (MP-II thinks there is an issue) and puts L2 into inverter mode only output to the panel. My RV panel doesn't care if it is same phase or split phase, but it sounds like the MP-II designed to only work with 120/240V split phase to pass-through both L1 & L2.
Even in the MP-II manual under "Power Flow Diagrams" it confirms L2 shut down in a "Power Flow Single Phase" scenario and pushing inverted power to L2 instead..
 
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It's a bummer that the Multiplus II 2x120v won't pass L2. I'm in the same situation as you and redoing my trailers setup with a new inverter and switching to lifepo4 batteries. I just bought the Multiplus 12/3000 but haven't installed it yet because I learned of the Multiplus II and it would have simplified a lot of my install. It seems like a simple enough problem that could be fixed via a firmware update.

I'm currently using a breaker output to feed my inverter and the output of that goes to a Blue Sea manual switch so I can power a set of outlets and microwave off the inverter or generator. I did it this way because we camp in the cold weather a lot so I run a space heater in the mornings. If I run the space heater through the inverter while on generator the battery charging slows to a crawl.

SCR-20220213-jsp.png

I had one set of outlets on the L2 side of the breaker panel that would always be shore/generator power but it always ended up being the one I wanted inverted power from so now I have all outlets on the inverter.

What would have been nice with the Multiplus II would be using power assist when I'm using the trailer to visit family. My air conditioners are 15k BTU units and won't stay running off a 15A outlet. I was thinking I could set the inverter input to 13A and let the inverter power assist help with power the air conditioner in the bedroom. Again the Multiplus II would have made all this simple, I could run any one of the air conditioners if I wanted, etc.

What about splitting the breaker panel? I don't know enough about electrical code. I read somewhere that I need to break the neutral between L1 and L2 at the breaker panel if I was to do this? Maybe this should be a different thread...

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That is an option, but then the generator only powers half of the panel through the MP-II passthrough of L1, and other half of the panel would be provided by the inverter on L2 of the MP-II. I'm still leaning towards either 1) removing the ATS, feeding the MP-II only via shore power, installing a manual transfer switch on the output side of the MP-II so if I don't have shore power I switch it to generator power and can feed both sides of the panel then directly by the generator. -Or 2) Using the Victron Auto Transformer for the generator output just before the ATS to change the Onan's (2) 120v single phase to a 120/240v split phase which will then passthrough both output legs of the MP-II.
Your assumption that when only a 120v input is on L1 and no input on L2, the Multiplus makes L2 from the inverter is incorrect. L1 input is put into parallel with L2 and the inverter as well. So if you had say a 3000w shore power connection the MPII would passthrough to both L1 and L2 as well as power assist with the inverter. As long as the input from the generator does not exceed 50amps, combining L1 and L2 at the ATS would be an ideal solution. However a lot of onan 5500s are labeled as NON-RECOMBINABLE.
 
Engine RPM2400

Anybody know how does a 2400 rpm generator make 60hz alternating current?
The 2400 rpm generators have 3 physical poles. So the formula for frequency, Generator Frequency (f) = Number of revolutions per minute of the engine (N) * Number of magnetic poles (P) / 120.

2400*3= 7200/120=60
 
And just to confirm, L1 and L2 have no potential/no voltage between them.
Correct, they are in phase with each other, bridging them just gets around the limitations of the breakers for each leg and allows you to use the full power of the generator. Not sure why they designed the mpii to reject l2 power when in phase with l1. I am sure there is a reason...
 
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