Wiring neutral/ground when splitting panel for MultiPlus?

[joe6789]

Trying to install a Multi Plus Compact 2000w inverter/charger in my RV. The shore power connection has four wires: two 50A hot legs (red and black), neutral, and ground. Since the Multi Plus inverter will only power one hot leg, my plan is to "split" my existing breaker panel so that one leg (about half the panel) is powered direct from shore power and the other leg runs through the Multi Plus.

Let's say I leave AC line 1 as the non-inverter side, going straight from shore power into the breaker panel. Then AC line 2 would go from shore power, to the Multi Plus AC-in, then from the Multi Plus AC-out to the second leg of the breaker panel.

But how do I wire the neutral and ground?

Normally AC line 1 and 2 share a neutral and ground (since 1 and 2 are out of phase, their currents cancel each other out on the neutral). But now line 2 gets sent to the Multi Plus while line 1 goes straight to the breaker panel. Is it fine for the neutral and ground wires to simply follow line 2 through the Multi Plus before arriving at the breaker panel? Or does line 1 now need its own neutral/ground? Do I need to split the neutral so that one neutral wire follows AC line 1 into the breaker panel and another neutral wire follows AC line 2 through the Multi Plus? If so, do I need to isolate the two neutrals by cutting the existing neutral bar in the breaker box?

I've read that a better solution is installing a sub-panel, but I'm trying to go for the simplest solution, which I believe would be keeping everything in the existing breaker panel.

Advice would be much appreciated.

[3_tons]

joe6789 wrote:
After a long day of splicing wires I finally have the entire setup installed. The Victron inverter/charger is both inverting and charging. Thanks everyone for the help in determining the right setup.

It was not without more hiccups today though. The batteries were again dropping to near zero voltage. I called Battle Born, who said the battery management system could be causing this, but they didn't know why. They suggested that the switch (Blue Sea Systems 350A on/off switch) could be bad. I completely removed the switch from the circuit, and that fixed the issue (at least for now). Maybe the switch was falsely tripping the BMS. I may experiment some more with different configurations for the switch.

Nice, Looks like you’re on to something, Glad you’ve persevered (via process of elimination) and found a path forward...Please keep us posted as to the possibility of a BMS issue!

3 tons

[joe6789]

After a long day of splicing wires I finally have the entire setup installed. The Victron inverter/charger is both inverting and charging. Thanks everyone for the help in determining the right setup.

It was not without more hiccups today though. The batteries were again dropping to near zero voltage. I called Battle Born, who said the battery management system could be causing this, but they didn't know why. They suggested that the switch (Blue Sea Systems 350A on/off switch) could be bad. I completely removed the switch from the circuit, and that fixed the issue (at least for now). Maybe the switch was falsely tripping the BMS. I may experiment some more with different configurations for the switch.

[3_tons]

Sorry, double post...

[3_tons]

joe6789 wrote:
I'm fine ditching the switch. You're right that Victron did not call for it. The purpose was simply to be a master battery disconnect, so I could disconnect ALL loads (not just the inverter) on the battery when the trailer is not in use. But I may have to live without the switch, and manually unhook the battery instead when the trailer is not in use.

It would still be good to know what is happening though. I doubt the issue is the switch itself, as it seems to be functioning normally with only the inverter connected through it. My best guesses right now are either:
a) Some sort of feature on the inverter, but I'm still not sure how the inverter could possibly be dropping the battery terminal voltage to zero
B) Some sort of feature on the Battle Born batteries. They have a built-in battery management system, so maybe the batteries are shutting themselves off for some reason when the switch turns on.

I have the workaround for now (only hooking one component through the switch), so I'll proceed with the installation while I'm still figuring out what was going wrong.

First off I must have missed the fact that you have Li batteries (how many??), and know that the BMS can definitely be your problem... Do you have another battery which you can temporarily substitute for the Lithium ??

I recently installed a single 100a LiFePo4 Lithium in a camper conversion, and was able to see during start-ups of the Coleman Mach 1 P.S. ‘momentarily’ as high as 400 dc LRA amps via the Victron meter, thus one might assume that the BMS was tolerant of this sudden but momentary loading, though the mfg. surge specification was rated at only 200amps for 20 sec...

The voltage drop you’ve described is a red flag, thus I believe your BMS might somehow be the root cause...

3 tons

[joe6789]

I'm fine ditching the switch. You're right that Victron did not call for it. The purpose was simply to be a master battery disconnect, so I could disconnect ALL loads (not just the inverter) on the battery when the trailer is not in use. But I may have to live without the switch, and manually unhook the battery instead when the trailer is not in use.

It would still be good to know what is happening though. I doubt the issue is the switch itself, as it seems to be functioning normally with only the inverter connected through it. My best guesses right now are either:
a) Some sort of feature on the inverter, but I'm still not sure how the inverter could possibly be dropping the battery terminal voltage to zero
B) Some sort of feature on the Battle Born batteries. They have a built-in battery management system, so maybe the batteries are shutting themselves off for some reason when the switch turns on.

I have the workaround for now (only hooking one component through the switch), so I'll proceed with the installation while I'm still figuring out what was going wrong.

[time2roll]

0.9 amps should have only a tiny effect if the batteries and cabling are in proper shape. This is not a chassis ground or inverter issue.

[3_tons]

joe6789 wrote:
Well the switch is actually rated for 350A, there's a 300A fuse at the positive terminal, and I'm using 0000 cables that are all very short. So theoretically all these components should be able to manage the current just fine. And right now the inverter isn't even hooked up to any AC loads, so it's only idling at about 0.9A draw.

In my limited world view (from the few inverters I’ve installed...) I’ve yet to install one that suggested a master switch, nor do I believe that Victron calls for one, but considering your present scenario from afar, I would proceed to ditch the switch..

[joe6789]

Well the switch is actually rated for 350A, there's a 300A fuse at the positive terminal, and I'm using 0000 cables that are all very short. So theoretically all these components should be able to manage the current just fine. And right now the inverter isn't even hooked up to any AC loads, so it's only idling at about 0.9A draw.

[3_tons]

If you are saying that the battery supply to the inverter passes thru a master switch, I would suspect the switch...Leave dc loads connected to the switch (per former scheme) and connect inverter directly to battery positive terminal...The inverter needs to be connected directly to the battery with a 300a fuse in the positive cable.. Hopefully you’ve chosen cables of an adequate AWG size and a relatively short round trip cable run. It’s doubtful the switch could handle the kind of dc current the inverter will demand.

I’m using 0004 aught AWG for my 2,000w ProSine with a RT cable run of about 7’.

[joe6789]

I'm pretty sure polarity is correct.

After experimenting today, I found a workaround to the issue, and I'm able to run both the inverter/charger and the DC loads simultaneously. But I still have no idea why the issue (drop to 0 voltage) was happening.

There is a master battery disconnect switch connected to the battery positive terminal. Both the inverter/charger and the DC loads were connected to the output of this switch. So when the switch was turned off, there were no loads, no DC current flowed, and the battery terminal voltage was 13V. When the switch was turned on, power should have been supplied to both the inverter/charger and DC loads, but instead the terminal voltage would drop to almost 0 and neither the inverter/charger nor the DC loads would receive power.

What I tried today was to connect the DC loads direct to the positive terminal of the battery instead of the switch, while leaving the inverter/charger connected to the switch -- and the problem went away. Now, when I turn on the switch, the inverter/charger powers on fine, and the DC loads are also running since they are no longer controlled by the switch.

In summary, if the inverter/charger and DC loads are switched on together, neither received current and the terminal voltage drops to 0. But if instead the inverter/charger is switched on while the DC loads are already receiving power, then everything works fine.

What could be causing this? Is it just a fluke? Perhaps some sort of advanced "feature" inside the Victron inverter/charger?

Note the DC loads are only about 0.9 amps and the inverter/charger only draws another 0.9 amps, so the total draw of 1.8 amps is very small.

[3_tons]

“My understanding is that the negative DC bus bar is connected to the chassis for grounding, and the inverter/charger is also grounded to the chassis. Maybe that common ground is causing an issue.”

No, the inverter AND the dc bussbar grounds both go to the common chassis ground... Something else is amiss...

If you’re empirically confident that the battery is up to snuff, and all the dc loads are easily accommodated via the battery (converter-charger OFF) when inverter is not in the loop, then I would begin to suspect (per Occum’s razor) the inverter...This assumes (??) that everything works just fine until you insert the inverter into the loop...JMWAG

[enblethen]

Have you verified the polarity?

[time2roll]

May need to post a picture of the batteries.

[joe6789]

3 tons wrote:
Well, per your previous (after hooking up the inverter dc side cabling only - ac side not yet connected) and with the battery voltage initially reading 6v then rapidly dropping to 1 or 2 volts within 10 seconds dropping, that seems like a whole bunch of current going somewhere??

How much current does the victron read when doing this, and does this only occur when you hook up to the dc bussbar ??...(just trying to isolate this a bit).

Unfortunately, the Victron shunt does not give a reading when the voltage is at 1-2 volts (nor when the voltage is rapidly dropping from 6, 5, 4...) because the shunt requires some minimum voltage to operate, so it just turns off.

Yes, this problem only occurs when I hook up the DC bus bar AND the inverter simultaneously. With only the DC bus bar hooked up (and no inverter), everything looks and works normally. So when either the inverter or the DC bus bar are hooked up, all is good, but when both are hooked up something causes the voltage to drop to almost zero.

My understanding is that the negative DC bus bar is connected to the chassis for grounding, and the inverter/charger is also grounded to the chassis. Maybe that common ground is causing an issue.

Also, while the DC bus are is connected, as soon as I hook up the inverter, about a quarter of a second later I hear a click from inside the inverter, like a relay or switch is tripping. This could simply be the inverter recognizing that it has too low of voltage (requires minimum of ~10 volts to power on), or maybe it could be a relay that's diverting the power to ground/chassis.

Regardless, I still don't fundamentally understand what can cause voltage between battery terminals to temporarily drop to almost 0, and then have it return to normal 13V as soon as a wire is disconnected.