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Ambot avatar image
Ambot asked

Battery BMS Triggers Short Circuit Protection when connecting Multiplus

tldr: When I turn the battery on with the Multiplus connected it registers a short circuit protection event. Help!

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I've read thru the Battleborn thread and wondering if I'm suffering from the same issue, but its a little different.

https://community.victronenergy.com/questions/34055/multiplus-is-tripping-battle-born-battery-bms.html

I have 3 RJ Lithium 24V 300AH 150 cont/300 peak batteries and a Multiplus 24/3000/50/120

I wanted to use the multiplus to charge them up equally to parallel them.

I wired everything with a single battery powered "off" (charge and discharge disabled, FETs Locked)

The battery cable is 2ga and 26 inches long and feeds to a Lynx Distributor ->Lynx Shunt -> Lynx Distributor 2

I installed 150 mega fuses everywhere that needed one just to get the Multiplus configured and the batteries charged and paralleled.

The inverter cable is 1/0 and 5 feet long

When I turn the battery on without the multiplus connected, I measure 26.4v at the Lynx Distributor 2.

When I turn the battery on with the multiplus connected the BMS registers a short circuit protection event and shuts down.

The Multiplus is OFF.

I've attempted to precharge the Multiplus by hooking up AC as in the Battleborn thread and this did NOT change things.

I have not tried a different battery.

I have not tried connecting the multiplus directly to the battery using the 1/0 wire.

In general the "short circuit" has me freaked out.

Anything glaring above that would help sort this out?


Thanks for reading.


MultiPlus Quattro Inverter ChargerLithium BatteryBattery Protect
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5 Answers
Ambot avatar image
Ambot answered ·

I obtained a 30w resistor and charged the caps using the resistor between the battery and negative cable.

It indeed no longer sparked when connecting the negative to the buss bar.

I then turned on the inverter, it made a buzzing noise, then a popping noise, then smoke came out the top vents

a758211a-6697-4acf-9e33-7de43af6a80a.jpeg


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alan avatar image alan commented ·

Is this picture showing the resistor you wired in?
1612402305855.png

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Paul B avatar image
Paul B answered ·

you are seeing this as the INrush current is to high for the batteries.

you will need to precharge the Multiplus, you may get away with it by trying this

1.Turn the batteries on both on and both connected in parallel

2. turn the multi to off

3. connect the multiplus negative wire to the Batteries Neg terminal

4. VERY quickly touch the multis positive wire to the batteries positive connection do a - on /off / on /off and keep repeating this until there is no more sparking you must do this on/off/on/off VERY quickly.

5. once the sparks stop you can leave the positive connected and all should work fine. this is basically pre charging the multiplus capacitors in small steps



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Ambot avatar image Ambot commented ·

Thanks for the reply. I gave that a go and the Bms shut down after a really impressive spark. It was in a more severe state than before requiring a harder reset to clear the short circuit protection event.

At this point there’s no way I can use this inverter and battery combo as it stands.

I suppose the battle born device is the way to go, but how can I rule out a defective multiplus that is shorting out the battery for real?

Just seems hooking an inverter to a very capable battery shouldn’t cause a meltdown. 6b2c9dfc-64bb-4f80-b710-b7cb289b398f.jpeg

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seb71 avatar image seb71 Ambot commented ·

If precharging the inverter capacitors is the cause, a safer method is to use a resistor or an incandescent light bulb (in a bulb base, with wires attached) and connect the positive wire through that first.

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alan avatar image alan seb71 commented ·

Yes, I agree with this. It’s the capacitors charging triggering an over current. Wire a resistor in the circuit initially, then disconnect it and reconnect the batteries shortly after.

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Fideri avatar image Fideri seb71 commented ·
@Seb71

Should I use a 48V DC bulb since my batteries and entire system are 48V? Someone is using an AC bulb successfully which I find strange.

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Alexandra avatar image Alexandra ♦ Fideri commented ·

@Fideri

An incandescent AC bulb will work. You just need the resistance to slow the inrush.

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Fideri avatar image Fideri Alexandra ♦ commented ·
@Alexandra thank you.
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seb71 avatar image seb71 Fideri commented ·

As Alexandra said, an incandescent light bulb is basically a resistor.

So a bulb like this, with a Wolfram/Tungsten filament:


incandescent-light-bulb.png


Do not use LED light bulbs.

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Fideri avatar image Fideri seb71 commented ·
@Seb71 thank you.
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rslifkin avatar image
rslifkin answered ·

If you have AC power available to the Multi, bring it online with AC power first and let it start "charging" the not-connected batteries. This will charge the DC input caps, so you won't get the huge inrush when you close the contactor feeding the multiplus.

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Stan avatar image
Stan answered ·

My batteries are 2x12v 200ah with a 100a bms. This is how I precharge the my Multiplus II 24v3000..How to Pre-charge Large Off-grid Inverters SAFELY. Save your eyes and your bank account - YouTube

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alexben avatar image
alexben answered ·

I found this thread before posting similar question. I’m just starting my RV electric system off simply. I have a EEL 24v x 305ah prefab box with its JK BMS. I had my Multiplus 24/2000 50 amp unit repaired under warranty, bought used and bricked.

Installed last week for first time, and after minor hiccups appeared to be working. No solar yet, no 24-> 12 transformers added yet, just smart shunt, BMV712, and Multiplus. I had AC output. When I plugged it in to 110 AC power to charge the battery, it initially worked, but then the BMS shut down as I had accidentally left default charge limit from factory at 25 amps on the JK. I packed it up to work on it this weekend, shut it all off.

Upon return, the BMS would register short from the Multiplus immediately, and the BMV showed rapidly decreasing voltage from (?) 24 Maybe start.

I was able to get it to all work by plugging into 110 AC from my home. Did this with battery off at first. Multiplus showed red at first, then yellow after a few moments. Then I was able to turn on the battery and not see a short.

I fear being out boondocking without AC current to reset the system.

Just leave it on all the time, unplug or turn off loads?

Short cut to safely easily precharge the caps? That lightbulb technique sounds like work if I have to do it everytime I’ve left RV in storage and off…


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nickdb avatar image nickdb ♦♦ commented ·

Don't precharge via grid and a disconnected battery, that moves the stress to the relays and it is a great way to ensure they fail later or weld themselves shut. This method is in no way supported.

Either buy a precharge device (rumour has it victron may just be making one), or a workaround is to precharge by first starting solar chargers, and then starting the battery.

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