[Discussion] Paralleling (2) MultiPlus II 12v/3000va (2 x 120v) units

[starboat]

I was reading about dual Multiplus ii 2 x 120 on DIY solar forum last night and they said that you should never plug this system into 30A. Do you have any knowledge of this??

https://diysolarforum.com/threads/ac...ltiplus.22200/

[Second Chance]

I was reading about dual Multiplus ii 2 x 120 on DIY solar forum last night and they said that you should never plug this system into 30A. Do you have any knowledge of this??

https://diysolarforum.com/threads/ac...ltiplus.22200/

@starboat -

It's not really clear who you are asking... here are a few forum tips:

1) If you use "Reply With Quote" (to the right of "Reply") as I have here, folks will know to whom you are responding and that person will get a notification.

2) You can also tag folks using the "@" symbol and their user name (as I have done yours) - they'll also get a notification that way.

3) You can create a signature block with your RV and tow vehicle information (see mine below). That way you won't have to repeat that information whenever you post or ask a question - and others won't have to ask. You can create a signature by going to:

Forum Actions (on menu bar) -> Edit Profile -> Edit Signature (under My Settings on the left)

Note: you'll need to have a paid subscription to add an image to your signature.

Rob

[houlster]

I was reading about dual Multiplus ii 2 x 120 on DIY solar forum last night and they said that you should never plug this system into 30A. Do you have any knowledge of this??

https://diysolarforum.com/threads/ac...ltiplus.22200/

That's for wiring the 2 MP to work in split-phase. I am not sure what happens if you plug into single phase power set up like that. I always thought you'd end up with the L1 MP working as normal and drawing power from shore and the L2 MP inverting, but that may depend on if your 30A->50A connector joins L1/L2 or not. Would def do some more research before trying though.

That said, if the MP are wired in parallel / single phase. There are no issues with single or split-phase shore power, generator, etc. It all works so long as you set your input current limit appropriately.

[starboat]

That's for wiring the 2 MP to work in split-phase. I am not sure what happens if you plug into single phase power set up like that. I always thought you'd end up with the L1 MP working as normal and drawing power from shore and the L2 MP inverting, but that may depend on if your 30A->50A connector joins L1/L2 or not. Would def do some more research before trying though.

That said, if the MP are wired in parallel / single phase. There are no issues with single or split-phase shore power, generator, etc. It all works so long as you set your input current limit appropriately.

@houlster

Thankyou for your answer. I guess I assumed this was only a parallel system. My understanding was that the only time it could be split phase would be when you had 50 amp shore power that was split phase running it,. Most Inverter generators, with a 4 prong outlet, have two identical legs which causes L2 to shut down. My knowledge level is low so in seeking to understand what situation might place me or my system in danger?

[LMagelitz]

@houlster

Thankyou for your answer. I guess I assumed this was only a parallel system. My understanding was that the only time it could be split phase would be when you had 50 amp shore power that was split phase running it,. Most Inverter generators, with a 4 prong outlet, have two identical legs which causes L2 to shut down. My knowledge level is low so in seeking to understand what situation might place me or my system in danger?

I have two 5kva Quattros set up split phase, and I tested presenting them both with the same 120v leg today (like a 30a campground hookup). They reject the input, and both remain inverting from the batts. Neither one accepts the input. If they are set up split phase, they only accept split phase.

The way I get around this at 30a campgrounds, or when I have to run the genny (120v only), is by using a 120 - 120/240 transformer on board.

[houlster]

@houlster

Thankyou for your answer. I guess I assumed this was only a parallel system. My understanding was that the only time it could be split phase would be when you had 50 amp shore power that was split phase running it,. Most Inverter generators, with a 4 prong outlet, have two identical legs which causes L2 to shut down. My knowledge level is low so in seeking to understand what situation might place me or my system in danger?

I think you've got it right. That's fine if the generator has only one circuit breaker for both L1/L2. The 2x120 would still pull full, rated power (up to 50 amp) from the genny L1 and provide on L1 & L2 of the RV.


My Onan 5500 generator (~45a total) has 2 30 amp circuit breaker outputs connected to L1 & L2 of the RV. They are in phase with each other and the 2x120 shuts the L2 input off when running on genny. This means the MP can only draw from L1 and if it goes over 30 amps the circuit breaker on the genny trips. To solve this, (this may be controversial) I've joined L1/L2 outputs from the generator inside the transfer switch, before it gets to the inverters. Now the inverters are pulling from L1 & L2 on the genny, but can pull the full 45-ish amps it can provide without tripping breakers & still be well within the power capabilities of the wires.


Wired in single phase...

If inverting, the RV gets single phase. L1 & L2 are joined inside the inverters so you get full inverter power regardless of which line the load is on.
If plugged into single phase, RV gets single phase on L1. L2 input is shut off. L1 & L2 outputs are joined inside the inverters and both inverters are able to power boost up to their maximum amount regardless of which line the load is on.
If plugged into split phase, inverters sync with that and RV gets split phase. L2 is passed directly through to the RV. No power boost on that line. L1 runs through the inverters, is the line used for charging & the inverters will provide power boost on L1 loads only.

Some considerations:
In single phase, IN THEORY, with 2 inverters and 30 amp shore power, you could draw as much as 50 amps on L1 and 50 amps on L2. That means the common would be hauling the whole 100 amps for the short section of wire from the RV panel back to the inverters. But, I can't imagine an RV using anywhere near this amount of power. Even with 3 ACs, toaster, microwave, coffee machine all running at the same time it's nowhere near this. Again, it makes a difference how the inverters are wired in. If they're each wired individually to the panel, then there's 2 common wires handling the load and no problem. If you're using a single wire from the panel to a junction box near the inverters where it splits to each, then yeah, that short section of a single common wire will carry the full amps being used by the RV, but still unlikely to be more than the common can handle. This is all assuming the RV A/C side to the panel is using 6ga that a 50 amp RV should be using. I think some may use 8 ga inside though. Regardless, it'd be easy to just add an additional common wire from panel to inverters if needed for peace of mind.