Charging battery bank with automotive charger

[ollkorrect]

Anybody ever tried charging their 12V battery bank en masse with a 12V automotive battery charger?

My charge controller took a crap when my batteries got too low over night, charge controller disconnected, sun came up, and fried my charge controller in 3 seconds because of the disconnect. Just trying to figure out how to charge the batteries, in their current box, en masse and not individually, with what I have on hand, until my new charge controller gets delivered.

And don't worry, I'm also replacing the batteries with high internal resistance since they are what kick started the disaster.

 

[VanLife Jake]

I just dealt with a situation like this.
Search "Mighty Max" in this forum and read those posts.
I don't recommend it.... I'm sure its not the approved method.
But, it did get me past the BMS shutoff. So, i could start charging the batteries with the appropriate Lithium Charger.

 

[ollkorrect]

Thank you. I checked out the "mighty max" thread. Surprisingly the batteries aren't dead. They read 12.04V (on average). Renogy controller disconnected at 12V [seems a little excessive]. So, the batteries will take a charge alright. Just wondering if I should charge them in parallel if possible or if necessarily individually with a cheap automotive charger... If anyone has ever tried that with any luck.

Because of their high internal resistance, I'm not expecting them to overcharge (sealed AGMs).

I guess if no one has had any bad outcomes, I can give it a shot and report how it went.

 

[VanLife Jake]

I think it depends on the output of the automotive charger.
My cheap Lithium charger is rated for 60ah or 80ah batteries.
But it works on my 100ah batteries when I am in a jam.

 

[chrisski]

Not really an automotive charger, but I tried an undersized charger and it did not put enough juice in it.

I tried charging a 458 AH 12 volt battery bank with a 26 amp NOCO charger. Charging amps are supposed to be close to 60 for that size, so it never really read full.

Since it was four golf cart batteries 2S2P, I removed the parallel set to charge only two in a series at a time and the 26 amps it received was enough to charge the batteries. 26 amps is close enough to 30 amps two batteries want, but not close enough to 60 amps all four wanted hooked together.

I had the bright idea since its a 24 volt charger to hook the batteries up in series to charge them. Unknown to me and in small print in ione of the documents, 24 volt charging was limited to 13 amps, so. I had the same problem of it not filling up.

I also found a lot of cheaper battery chargers that claimed 30 amps, was a special mode that just delivered that amperage for a little as 5 minutes to rejuvenate a battery and the normal charge amperage was around 10 amps.

THere’s all sorts of write ups about charging profiles for automotive battery chargers, and they are just so different if even published. NOCO does a good job at giving a graph that covers three of their seven phases of charging.

For home charging next year, I may actually use a Powermax RV AC to DC converter. There’s a rating pretty close to the 60 amps my battery bank needs.

 

[RCinFLA]

Biggest risk is with 'smart chargers' that decide on their own if equalization is needed. They seem to decide this based on rate of voltage rise during charging.

Most auto chargers assume battery is lead acid in the 60-90 AH size range. They will go to absorb voltage of 14.2-14.5v and drop to float voltage of about 13.2-13.6v. The 15+ volt equalize phase is the situation you do not want to happen.

Old chargers with only transformer and rectifiers I would not use to charge any kind of battery..

 

[Bud Martin]

May I ask what is the make and model of the Solar Charge controller?