EG4 12v 400ah battery goes into fault under mid loads

[Col. Spigot]

Hi,
First time poster here. I built a solar and battery system in my travel trailer at the beginning of the year. I think I used good parts and it has worked really well until our last trip out. Total of 1100 watts of solar on the roof. Victron solar charge controller. Victron Shunt, Victron multiplus 3000 watt inverter and an EG4 12v 400ah battery.

The issue we had was that the battery would fault about once a day when the microwave was used. Microwave generally draws about 1500 watts. There were a few LED lights on the few times it happened and one time the heater blower was running. The heater generally draws about 75 watts. Total load wouldn't have been over 2000 watts which should be well under what the multiplus and battery can handle. The other weird thing is that the battery wouldn't come out of fault until I provided an external power source through the inverter from a generator.

I've tried to duplicate the issue to rule out some variables and nail down an issue but I can't re-create it. Happens when it wants to. I've gone through all the connections and wiring to look for a short.

Wondering if my BMS is bad or is going bad? Does that happen with these batteries much?

Thanks for any help guys,

 

[jberger]

i would plug up the battery to a PC and watch it with BMStools to see what alarms and alerts are showing. Without knowing the exact voltage levels, amp draw, etc it's hard to get a root cause.

For reference, I have (3) EG4 12v units connected up to (2) Magnum MS2812's and I can load them up with 2 rooftop AC units and run them for hours so it's more likely the battery you have is out of balance if it's low or it's simply not able to supply as much amperage as the multiplus is drawing at that given moment in time.

I think what you are seeing is just an overload of a single battery setup, the Microwave has large inrush current when the magnetron turns on and it's just pushing the battery into overload or under voltage at times. It's a serious momentary draw and might even look like a short to the battery. It's MUCH higher than you think, and it's not shown on the microwave nameplate.

If you don't have a PC available, and the inverter has shore power, you might be able to get some solid details from the victron logging, but probably not enough detail to know exactly what the BMS is seeing.

 

[Col. Spigot]

I've hooked an mk3 adapter to the Victron inverter and watched while the microwave turned on. There was a bit of a jump in draw when it started vs what at runs at but it wasn't significant. This battery should be able to discharge at 200 amps constant without tripping the overcharge. Factoring in the roughly 7% inefficiency rating of the inverter that should be about 2500 watts. The battery doesn't fault every time we use the microwave but every time it faults its while using the microwave. I can run our single AC unit off of this battery set up as well. It draws just under 1600 watts while running. AC starts fine because I installed a soft start.

Not being able to recreate the issue concerns me a bit. I'll turn on every electrical item that was on at the time the fault occurs and then start the microwave and it runs fine. Then I'll add some additional draw and it will work fine. Then, the next day, under marginal load someone will hit start on the microwave and the whole trailer goes dark.

It shouldn't be because of low battery conditions. Even when we have a few cloudy days, the battery charge rarely goes under 70%.

I haven't plugged my computer into the battery before to see what info it would share. I'll download the software and try it.

 

[jberger]

Did you put enough water in the microwave, when testing, to spin the wave up to 100% sustained? I think if the Microwave is tripping it almost every time, then it's inrush, especially if it's running the AC unit with no problems.

The specs that were in the manual for the BMS (not the battery) shows 100A discharge constant. But I take that with a big grain of salt since it talks about 48V nominal even for the 12V pack. . . (check page 5, wait that chart is missing in the latest manual at EG4electronics.com)
Now it says 200A max, 60A recommended in the current version.