48 V Forklift Battery

CoolWill

Solar Enthusiast
Joined
Sep 21, 2022
Messages
45
This is a follow up to my post in the newb forum.

The battery is a 24-125-13, rated 1182 AH at the 20 hour rate. My concern was that I wouldn't be able to push enough amps into with my 6 kW solar array. Question is, if I only ever discharge to 50%, how important is the charging current? So let's say I discharge it down to 70%. Does it matter if I push 100 amps into it, or could I push 20 amps into as long as the voltage gets back to full?

Another way to phrase it may be ask if charge rate matters as along as I get it topped off in a reasonable time?
 

OzSolar

Whatever you did, that's what you planned.
Joined
Jan 5, 2021
Messages
859
Location
Southwest MO
Another way to phrase it may be ask if charge rate matters as along as I get it topped off in a reasonable time?
It matters.

IMHO, you're going to have keep a close eye on SG and equalize with the grid or a generator every few months.

With the big 2V FLA it takes X amps to get the charging process started and until you get above X there's no useful charging. X is function of battery size, age, temperature and other things that I'm not able to remember at the moment.

1,182 x 10% = ~120 amps recommended charging rate which some might say is a bit low.

My back of the napkin maths says your array probably won't spend more than 2 hours a day at ~100 amps.

The best battery meter is shunt type amp hour counting type but even they have a very hard time staying accurate for a more than week in these conditions. The cumulative error from never fully recharging the battery (finishing charge reset) leads to the AH meter grossly understating the battery's actual state of charge while the whole time you think things are fine.

I predict you're going to see the SG of the battery drop over the course of weeks but it may take months.

I learned the above lessons the hard way.

There is some great information in the Rolls Surrette Battery User Manual.
 
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CoolWill

Solar Enthusiast
Joined
Sep 21, 2022
Messages
45
Thanks for the link! It says charge rate is between 5-20%. So as long as I don't pull more than 20% out of it, I can get it topped off in a couple of hours of sun. Looks like I should work on getting more PV in order to take advantage of this battery.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
12,121
If FLA wet cell, it cares about minimum charge rate. I've read 0.12C is preferred. Something about stirring the electrolyte.
I think some systems may use an air bubbler to stir.

VRLA, like my AGM, doesn't require higher rate for that purpose. Still, spec sheet says prefer 0.2C minimum, otherwise a different charge cycle with longer absorption is needed to fully charge.

PV is cheaper than a good battery. Buy more PV.
With multiple orientations, you should be able to get longer, flatter, charge cycle.
It is best (for FLA) to have a charge controller that regulates its output to maintain target current into battery (vary output to provide for loads in addition.)
 
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