My battery exploded!

[AlexanderKristiansen]

I'm having trouble with my lifepo4 battery (waiting for new BMS) and decided to build a 24v battery from some old 12v batteries I have laying around from the pre-lifepo4 days. I used this diagram to connect 4x12v 100Ah batteries to what should be a 24v 200Ah battery, but sparks and smoke flew all over the place when I connected it. I must obviously have done something wrong.


The red ring indicates where I connected the 3 cables when the spark and smoke happened. I did this as the very last step, everything else was connected. I expected the normal spark when you connect the last cable to a 24V battery, but there was a BIG spark, loud noise. smoke and the terminal on the battery was severely damaged and probably the entire 12V battery as well.

I have still 4 working 12V batteries and would like to build a 24V battery out of them, but can somebody give me a blueprint of how to build it? And what did I do wrong?

 

[curiouscarbon]

Hello Alex hope you are well and safe

Did you take note of the voltages of the two parts before attaching the wire?

 

[AlexanderKristiansen]

No, I didnt, ould that be the isssue?

 

[mikefitz]

Charge up each battery with a 12v charger and test with a meter to ensure each is at 12.6 volts or higher. Note and clearly mark the positive and negative terminals. Connect up to make two 24 volt batteries and confirm with a meter.
Next parallel connect the two 24 volt batteries and add the connection to the controller via a fuse or citcuit breaker.

To be ultra safe from possible problems add a fuse/breaker between each 24v positive battery terminal and the parallel connection.

You problem with the short and damage may have been caused by incorrect connection of the batteries, possibly confusion between the positive and negative terminals. The issue could also be caused by one or more of the batteries being faulty.

Mike

 

[svetz]

...could that [voltage difference] be the issue?...

The spark and damage are from a lot of current flowing, current only flows when there's a voltage difference. In addition to what's said above, if the controller was in the circuit at the time I'd also test it to make sure there's no dead short across it.

 

[Sverige]

What was the 3rd cable attached to? Diagram only indicates 2 Cables and if there was a 3rd, there would have to be a 4th somewhere to make another circuit.

The only way you are going to get enough amps to blow a chunk out of the terminal is if you created a dead short somewhere. My guess is you wired something backward or 2 Poles together.

He maybe took the cable which should have been on the negative pole of that battery and connected to the positive, so when connecting his 2S (24V) Bank, it was then across the single 12V battery, which blew.

@AlexanderKristiansen as you can see, it’s dangerous making mistakes when connecting up these powerful batteries. Far better to use a voltmeter to check that the voltages on your cables are as expected, before you touch the cable to the battery terminal. You could have connected each pair of 12V batteries in series with each other and checked to see there was 24V present on each pair before you then connected those cables to put the two pairs of batteries into parallel.