MAX rate of charge for Flooded Lead Acid Batteries?

ligwyd · March 2020

My 630 amp hour battery bank (3 strings of 4-12volt batteries) is currently set at 10% MAX charge rate. So 63 amp MAX in bulk.

The labels on my 12 volt batteries state 10-15 amps Bulk.

So, according to my battery labels the max charge rate should be 45 amps max for all three strings, however I realize that with solar you have to make hay while the sun shines and get the batteries charged up as fast as you can with the avail sunshine.

My question is what max charge rate is common for FLA banks? I know it is a ballpark question, relative to many other factors, however just looking for some feedback none the less......

I have read that 10-13% (of 20 hour capacity) max charge rate is a min recommendation. If I have enough solar could you go higher and if so what is the highest some have safely and successfully used?

mike_s · March 2020

ligwyd said:

I have read that 10-13% (of 20 hour capacity) max charge rate is a min recommendation.

What does that even mean? If they thought higher was good, they'd spec 10-25%, or whatever.

Trojan is quite clear - 13% "Maximum Charge Current" (for FLA), with the note "If charging time is limited contact Trojan Technical Support for assistance." But different manufacturers have different recommendations, and you haven't bothered mentioning which batteries you have.

Raj174 · March 2020

That would be true if the batteries were 100 amp hour, but they are 210 amp hour, right, so up to 81 amps (13%) should be ok for bulk charging.

BB. · March 2020

Usually, it is GEL type batteries (at least in the USA) that end to have a 5% or C/20 limit on the rate of charge.

Another issue could be is if the capacity (AH) of the battery bank is defined at C/100 discharge rate (makes tattery appear larger AH capacity vs the normal C/20 discharge rate battery capacity number we use).

-Bill

Marc Kurth · March 2020

The best source of information regarding how far you can push something - is from the manufacturer. Yes, there is a huge amount of field experience here, but a decent guess cannot be offered without knowing what you have. All flooded batteries are not the same.

Dave Angelini · March 2020

Fast charging for offgrid is a balance of the manufacturer and a lesser amount that will often yield the longest life. What is the rush? Go for a walk or a boat ride

ligwyd · March 2020

Pic of the batteries used in this application and pdf of the spec sheet. C20 discharge rate of 630Ah (210 Ah per string).

I'll fire off an e-mail to the vendor and manufacturer and post what I find.

Any other feed back is appreciated.

Thanks.

Image: https://us.v-cdn.net/6024911/uploads/editor/aa/c6ju497oausb.jpg

mike95490 · March 2020

The recurring story I've heard, is that flooded and AGM lead acid, can take a pretty beefy charge rate, well above normal rate, till the battery is about 80% full. Then you must reduce to factory specs or heat damage occurs .

Marc Kurth · March 2020

Discover put the specs on the battery label for a reason so I would let them tell me what they want and why.

I realize that you know this, Mike, but for less experienced people I will point out that around 80% to 85% SOC is where the battery naturally increases in resistance and starts reducing its current draw on its own. That is the definition of going into the Absorb phase of the charging cycle.

Dave Angelini · March 2020

It is actually the opposite of what Mike said and reducing this huge current is what can make a battery last well past warranty.

If there is not a rational reason to hit a battery with all of the power you have, you can lessen the thermal shock of internals and get longer life.

I really have never had a FLA not last long past 10 years and the only reason to replace was loss of capacity. I also am not just talking about my 30+ years but hundreds of clients offgrid.

mike95490 · March 2020

It's all about a balance of available sunlight, loads and generator fuel. When the battery gets warm, slow down.

And of course, the factory specs are very important.

And maybe late at night I inverted my logic and memory, so the rest of the innertubes will set you straight when I foul up.

ligwyd · April 2020

Thanks for you all comments. Very much appreciated. Love this forum. My system is up and running and in service and performing well:)

mcgivor · April 2020

ligwyd said:

Pic of the batteries used in this application and pdf of the spec sheet. C20 discharge rate of 630Ah (210 Ah per string).
I'll fire off an e-mail to the vendor and manufacturer and post what I find.
Any other feed back is appreciated.
Thanks.

This is a link to a cut away of that battery https://forum.solar-electric.com/discussion/353896/tubular-lead-acid-battery-cutaway

mike95490 · April 2020

Label says to me, 15A max

MAX rate of charge for Flooded Lead Acid Batteries?

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