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dbow32 avatar image
dbow32 asked

My 12/3000/120 won't run either AC on shore power why?

I have a 2019 Heartland Fuel 335 Toy Hauler. I just installed my multiplus 3000. My trailer is 50 amp. So I installed a manual transfer switch to be able to feed phase 1 or 2. Attached is a diagram of my exact setup.

The problem is that now when I turn on one of my AC's on shore power, it trips either one of the 30 amp breakers on my Onan 5500 watt generator. Prior to installing the inverter, I could run both AC units of that generator at the same time. Now, I can't run one.

I tested the 120VAC coming out of the generator and going all the way to my 50 amp breaker. So why would it not run the AC on 120VAC?

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5 Answers
snoobler avatar image
snoobler answered ·

Does this occur when the inverter is off and it isolated from DC power?

Does it occur with the inverter AC out ground disconnected from common ground?



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dbow32 avatar image dbow32 commented ·

I've only tried to run the AC while the Inverter is on. Should i trun it off? The AC out ground is connected through the common ground bus.

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dbow32 avatar image dbow32 commented ·

I tried and nothing works with the inverter off. I have not tried to disconnect the AC out ground yet. What would that do?

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Kevin Windrem avatar image
Kevin Windrem answered ·

It looks like the Muilti is in the red hot circuit between the shore/generator auto transfer switch and the manual transfer switch. Keep in mind the Multi isolates the neutral between AC in and out. This means the RV breaker panel is receiving shore/generator power on the black leg referenced to the Multi's neutral instead of the shore/generator neutral. Not a good thing in general since the voltages generated between Multi neutral and shore/generator black hot could vary between 0 and 240 volts when the Multi is inverting and the AC input relay is open.

This could be the source of your breaker trip since the Multi will most likely open the AC input relay (hot and neutral) when you switch from shore power to generator. The Multi may also open it's AC input relay when the AC starts due to a drop in generator voltage or frequency.

The only way I can think of to solve this is to put an isolation transformer on the output of the Multi and connect the output neutral to the shore/generator neutral. That way the RV breaker panel always gets 120 volts on both hot legs referenced to the same neutral.

The Multi's input and output neutrals should NOT be connected together.

The cost and weight of a 3000 VA isolation transformer could easily greater than the cost of a second Multi.


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dbow32 avatar image dbow32 commented ·

The AC in and out neutral's are NOT connected. The neutral comes in and then goes out to the breaker. The black wire bypasses the inverter and goes into the manual switch. The red wire goes through the inverter and then into the manual switch. Position 1 on the switch is the black and position 2 on the manual switch is the red. This is starting to go over my head. I don't know what to do. I called inverters r Us where I purchased the inverter and they said it was because the pass-through voltage was too much for the inverter and that I needed a soft start on each of my AC units to work.

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Kevin Windrem avatar image Kevin Windrem commented ·

The issue is you have two neutrals, one from shore/generator power and one from the inverter, AND only one neutral in your breaker panel. You can't connect the inverter neutral to the shore/generator neutral so regardless of which neutral you use in the breaker panel you have voltage (on the red or black) that is referenced to the OTHER neutral.

I did think of another solution:

Add a second neutral bar to your breaker panel and route the neutrals for all loads on the black side to one and all loads on the red side to the other.

Route the inverter neutral and hot to the red hot and neutral in the breaker panel. (There is no need to go through the manual switch since that side of the panel is always powered from the output of the inverter.)

Rewire the manual switch to the black hot and neutral inputs to the breaker panel. Position 1 would get shore/generator hot and neutral. Position 2 would get the inverter hot and neutral connecting both sides of the breaker panel to the inverter.

I'm attaching a diagram that may help.

RV Multi Wiring.pdf

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rv-multi-wiring.pdf (29.7 KiB)
mrseas avatar image
mrseas answered ·

Have you tried "bypassing" the manual transfer switch between the Multi and your panel?

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gbntx avatar image
gbntx answered ·

This is timely as I'll be installing a Multiplus 12-3000-120 in a RV with 50A service.

The Multiplus Neutral and RV's AC Neutral wiring would have tripped me.

The OP's drawing with the manual transfer switch appears to be one from the site all about rvs showing how to power it all, 30 and 50Amp.

It appears the drawing isn't showing the Neutrals going through the transfer switch.

Another site, mortons on the move shows a variation on the transfer switch idea and it does run the neutrals through the transfer switch so the RV's AC panel just get the shore/gen neutral or the Multiplus neutral.

The first site is also showing how to wire in the Am Solar smart phase selector, a modded Progressive Dynamics PD52V ATS. The SPS appears to work correctly as it isolates the incoming shore/generator neutral from the Multiplus' neutral,

I noticed how AM Solar used to/still has? a 50A Passthrough AC Support Panel Diagram Rev.170516 that used the PD52V ATS with a RV AC Panel with two isolated neutral bars, a bit like Kevin had mentioned above.

So I'm working on drawing up how my RV is wired and how an EMS, ATS & SPS are wired through their contactors, rather then them just being black boxes.


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dbow32 avatar image
dbow32 answered ·

So I had a friend help me and I'm pretty sure we fixed the issue. It seems that the inverter doesn't like the power coming from the Onan 5500. We changed the settings and turned Off the UPS and it ran both AC's at the same time. Just thought I'd let y'all know that it's working now.

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Kevin Windrem avatar image Kevin Windrem commented ·

I will repeat my warning: Your wiring is UNSAFE. Please this warning and the comments from gbnTX into consideration. This configuration can crate damaging voltages for your loads and also back-feed AC into the Multi AC output.

The breaker panel is receiving power from two different sources: shore/generator, and inverter. These sources have SEPARATE NEUTRALS, however the breaker panel only has ONE neutral bus. Therefore, when shore/generator power exists but the inverter is running without an AC input, it's output frequency is not locked to shore/generator. One side of the breaker panel will have a hot leg that varies in voltage from 0 volts to 240 volts as the relative phase changes.

The Multi will disconnect from the AC input under several conditions including frequency/voltage out of range from the generator. The Multi disconnects from incoming AC for several to 30 seconds when there is any disruption of the incoming AC (e.g., transition between generator and shore changeover). There are other conditions that may prevent the Multi from disconnecting from incoming AC.

Your recent changes have probably shortened the Multi's AC input disconnect when switching to and running on generator, potentially hiding the problem to some extent but there is still a risk of damaging voltages to your loads.

You MUST have separate neutrals for the two hot sections of the breaker panel in order to avoid these damaging voltage situations even if they are short in duration.

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