Dual Victron multiplus system shut off, will not turn back on

Erik Green · March 24, 2022

Good Morning All,

We are currently parked outside okc (I am away for a few days for work) the RV is plugged in to a 30 amp service. The dual victrons are set to split phase 180 auto and not switched as group. THe power completely shut off yesterday, my wife checked primary fuses and tried resetting multiplus and power cycled everything. Power no longer passing through and Leg one will not re-engage inverting and other multiplus seems to function to charge only. I have run out of ideas. Trying to come up with something my wife can do to get power back on.

any help or ideas would be greatly appreciated

thanks!

Chad Heiser · March 25, 2022

Did it work at all when plugged into this 30 amp pedestal prior to the failure?

Erik Green · March 28, 2022

It was, I figured it out, unfortunately my wife had to go without power for two days. It over heated and melted the battery shutoff. It was passing through power on one leg and the other inverter was pulling too many amps/watts? through the other leg didn't blow the 300 amp fuse though. Upgrading to 4/0 wire but I am still not sure how to properly hook up my system on a 30 amp to prevent that in the future.

Chad Heiser · March 29, 2022

Without knowing how your system is wired, I can only speculate as to why the switch overheated. Generally though, it is caused by resistance (which generates heat). In a 12 volt dual inverter system, all your battery and inverter cables should be 4/0 cable. That switch appears to be a Blue Sea 3000 HD switch. It is rated for 600 amps. It wasn’t the amps that killed that switch, it was resistance/heat.

Erik Green · March 29, 2022

Yep totally agree Chad, I hadn't gotten to replacing the wiring from my original install. I usually am at the trailer so I was monitoring the consumption, but when I was gone my wife ran a few to many devices (dryer/elec water heater/ and then some that burnt it out. here is my new drawing with 4/0 for all battery/inverter wires. I am open to any feedback. Also any advice on how to properly set up the system to run on 30 amp would be greatly appreciated.

Lance A Lott · March 29, 2022

I would be hesitant to run as much as you indicated might have been running on 30 amps but more so if it's a 50 amp system using a 30 amp adapter. The multi plus might have been trying to make up the extra needed.

Erik Green · March 29, 2022

Yea no doubt it was a lot of power. Roughly 1500 Watts but this should be more than manageable with the system given proper gauge cabling ie 4/0. the thing I am not sure of is how the Victrons should run while connected to 30 amp. I had removed "switch as group" and it seemed to do ok, until the cables melted the switch. 6AWG cables probably the cause there. But is that the appropraite configuration for dual multis when hooked up to a 30 amp pedestal.

Chad Heiser · March 29, 2022

3 hours ago, Erik Green said:

Yea no doubt it was a lot of power. Roughly 1500 Watts but this should be more than manageable with the system given proper gauge cabling ie 4/0. the thing I am not sure of is how the Victrons should run while connected to 30 amp. I had removed "switch as group" and it seemed to do ok, until the cables melted the switch. 6AWG cables probably the cause there. But is that the appropraite configuration for dual multis when hooked up to a 30 amp pedestal.

Yes, if you are running split phase dual multiplus inverters, you need to uncheck the switch as group checkbox in the configuration. If you leave that box checked and plug into anything that does not provide split phase power (basically anything less than a 50 amp pedestal) the system won’t pass power through. With the switch as group unchecked, then power will pass through the inverter on L1 and the inverter on L2 will invert at 180 degrees out of phase to L1 to provide 120/240 volt power to the rig.

If you only had 6 AWG wire running through the blue sea switch, that is the reason it melted. I’m surprised it didn’t start a fire in your rig. As I explained above, your L2 inverter was inverting to provide power to all loads on the L2 side of the panel box because the rig was plugged into a 30 amp (single phase) pedestal. That could have been up to 3000 watts of power coming from the inverter on L2. In a 12 volt system, that is upwards of 230 amps of DC power going over those cables. That is way too much for 6 AWG wire.

When you are on 50 amp shore power, both inverters pass through 120 volt power and the only power to/from the batteries to the inverter is whatever charge current the inverters are supplying. Those inverters can charge at up to 120 amps each. Hopefully you have turned the chargers to a lower amperage setting than that until you upgrade the wiring. That much current could also cause a fire if going through 6 AWG wire. If the batteries are always at or near full, then the inverters won’t send that much charge current to them, but if they are low the inverters will send as much charge current as they can to recharge them.

You should not be using your system at all if it is wired with 6 AWG wire on the 12 volt side. It needs to be rewired as soon as possible before you have a catastrophic failure.

Erik Green · March 29, 2022

100% thanks Chad, yea luckily my wife smelled something off (heat shrink glue melting) and shut it down. All parts are delivered to our next campground so I can start the retrofit tomorrow. Also as shown in the diagram I am converting my 8 battery bank from 8 in parallel to 4 sets of two. Everything will be in 4/0 once I convery it. Also one other error I made on my initial install was putting the 12v dc out after the blue sea switch on leg two. So all DC + AC was pulling through that same 6awg wire. As I mentioned I had been keeping a close eye on consumption, this is the first time I was away that we werent on 50 amp/pass through power. glad it wasnt worse!