Power on Multiplus: immediate battery voltage drop

[Atomic_13]

I’m installing a modern electrical system in a renovated vintage Tradewind. I attempted to provide 12VDC power to a Victron Multiplus (12/3000/120) via its dual DC +/- terminals using a single battery. I was trying power on the unit to update the firmware and adjust the settings for a 400 Ah LiFePO4 battery bank.

During this I experience an odd and rapid drop in battery voltage (from 13.3 to 4.0) the instant I power on the Multiplus. The few DC appliances running also shut down when this occurs. I’ve triple checked the wiring, fuses, and voltage at various locations along the electrical system and all seems normal. If I remove the negative cable from the battery and reattach it, it “clears the fault” and the voltage once again measures 13.3VDC.

Strangely, If I supply power the unit using “AC in” it works fine and the battery accepts a charge. It’s only when I disconnect the AC power and only supply the Multiplus with DC does the battery drop it’s voltage instantly. I was able to update the Multiplus firmware and this didn’t resolve the problem.

Any ideas? If it helps, I’ve provided my wiring diagram below.

I’m curious if perhaps I have a bad BMS in the battery? I’m going to give Battleborn a call Monday but I’m the interim I figured I’d toss this out here.

[fran&frank]

Do you have any AC loads on the inverter? it sounds like the Multiplus is pulling too much power from the one battrery you have hooked up. Does it work ok if you just put the Multiplus switch on charger instead of inverter? Is your battery fully charged?-- Frank

[Atomic_13]

Good questions, Frank.

No AC loads are on the inverter when this occurs. I’m fairly certain this happens in either the “on” switch setting or the “charge only” setting. I’ll double check that this morning. I purchased the batteries a few months ago and they’ve been sitting indoors and are discharged to 13.3 volts.

It’s my understanding that I should be able to connect a single battery to the positive and negative terminal connections inside the Multiplus and then update the firmware using the MK3 to USB cable. I’m experiencing the rapid (but reversible without charging) voltage drop during this process. When I test the voltage with my Fluke 115 multimeter, it originally reads 13.3 VDC. After I turn on the Multiplus via the switch the battery reads 4 VDC, instantly.

I’m confident it’s not actually draining the battery because when I disconnect the battery cable and reattach them, the voltage returns to the resting state of 13.3. This makes me believe it’s a battery issue, not a Multiplus issue. I could be wrong. I’d hook up a separate battery but didn’t want to damage a second battery if it’s a Multiplus issue.

Of note, when I power the Multiplus with 120 VAC via the “AC in” connection, both “AC1 out” and “AC2 out” are performing as expected. That is, the pass through functionality of the Multiplus is working.

Also, when this specific battery is used to energize the + BUS bar, various 12 VDC devices work fine (BMS 712, CCGX, solar charge controller, tank monitor display, etc). As expected, these items shut down instantly when the Multiplus switch triggers the voltage drop I describe above.

[Atomic_13]

Ok, here is another (likely) possibility...

When the inverter is connected to DC only, power from the battery rushes into the capacitors in the inverter. As the capacitor voltage rises quickly, Battleborn’s battery management system (BMS) detects current above its trip threshold. As a result the BMS operates a safety switch and disconnects the battery. This would explain why the battery can be “reset” by removing the negative connection and also why it works just fine if connected to AC power.

Evidently, Battleborn sells a $280 (ouch) current surge limiter that does the following:

“The CSL500 Current Surge Limiter is a FET-based current limiting device that is to be used with Battle Born Batteries LiFePO4 battery packs when they are used in conjunction with large (greater than 4kW) inverter/chargers. The device is mounted permanently in series between the negative pole of the battery bank and the negative DC input terminal of the inverter/charger. The device protects the battery management system (BMS) from damage caused by the initial current spike that is created when connecting directly to the large capacitors (> 5 milliFarads) that are typically on the DC input side of the inverter/chargers. The device allows the batteries to slowly charge the capacitors (within 1 ms). This soft start avoids the high-current shutoff inherent to the BMS of the batteries.”

[uncle_bob]

Hi

Simple answer is that the Multi's turn on surge *is* more than one 100AH lithium will handle. You need at least two in parallel and three would be better.

Bob

[fran&frank]

I agree with Bob, hook up a couple more of your batteries.--Frank

[hotfoot88]

or maybe just charge the one, these new gen batteries are known for holding same voltage until out of power then shutting down which is bad for the longevity of the battery. above replies good along with making sure fully charged before putting in service.

[GMFL]

Originally Posted by hotfoot88

or maybe just charge the one, these new gen batteries are known for holding same voltage until out of power then shutting down which is bad for the longevity of the battery. above replies good along with making sure fully charged before putting in service.

That’s it. Battery is low. On lithium, just because it says 13.2 volt does not mean it’s good.
I use a Battle Born all the time to program MultiPlus inverters and have never had an issue ( other than the initial spark when the capacitors charge up). ( I recommend in inline switch to prevent).
Charge the battery you should be good to go.

[Atomic_13]

Thanks all! That did the trick. I connected all four batteries and charged them (doesn't take long at 120A/hr). Once that was done, the Multiplus powered up using "DC power only" just fine. Feeling pretty fancy sitting here charging my laptop on inverted DC power and chilling down a few beers in my isotherm fridge Relieved to have the electrical system now functioning as planned. Yeehaw! All that's left is to get the 480W of solar panels on the roof. I'll tackle that once I receive a few more panel mounting brackets from AM Solar.