48 V Forklift Battery

[CoolWill]

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]

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.

 

[CoolWill]

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.

 

[xjaw4]

What brand of battery is it and how much did it cost?

The folks over at GB battery recommend a charging rate between 68 and 136A for that size of cell.

https://gb-battery.com/products/ols/products/6-125-15-sb-slash-1379ah-solar-battery-module

 

[Hedges]

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.)

 

[Vigo]

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.

Yeah, the thing is that if 100amps is the max your system can put out, that also means you'd have a 2hr period where you couldn't use the system for anything else. That's iffy, so i agree that getting more PV is your next move.

 

[Hedges]

Ideally your hardware will varying power harvested from PV, to maintain constant battery charge current (measured by shunt) and supply varying loads by inverter. That way you can give FLA forklift battery steady 0.12C charge followed by absorption voltage for a few hours (given sufficient PV.)

Victron SCC together with Cerbo, I think, can do that.
Midnight Classic with Wiz Bang Jr.
Sunny Island or other battery inverter supporting AC coupling to GT PV with frequency-watts.
I would think any all-in-one, low end or high end brand, ought to.

But separate SCC and inverter with no communication would not.

PV panels cost a lot less per kWh than a lead-acid forklift battery, about 1/20th as much. So put in enough to always properly charge. At the very least, use an SCC that can be over-paneled and programmed for desired current output. Preferably, regulate battery current not just SCC output current.

 

[CoolWill]

Ideally your hardware will varying power harvested from PV, to maintain constant battery charge current (measured by shunt) and supply varying loads by inverter. That way you can give FLA forklift battery steady 0.12C charge followed by absorption voltage for a few hours (given sufficient PV.)

Victron SCC together with Cerbo, I think, can do that.
Midnight Classic with Wiz Bang Jr.
Sunny Island or other battery inverter supporting AC coupling to GT PV with frequency-watts.
I would think any all-in-one, low end or high end brand, ought to.

But separate SCC and inverter with no communication would not.

PV panels cost a lot less per kWh than a lead-acid forklift battery, about 1/20th as much. So put in enough to always properly charge. At the very least, use an SCC that can be over-paneled and programmed for desired current output. Preferably, regulate battery current not just SCC output current.

Forgive my ignorance. Can you elaborate the theory here, re: using a Whiz Bang Jr. and shunt? Is it that the true state of charge for the battery is unknown unless the total amount of energy taken out of it is known via the shunt? I suppose the battery capacity is setup in the CC?

 

[Hedges]

A shunt can be used to monitor SoC. That is a good way to know; voltage by itself doesn't tell you. Unless you let it rest with zero amps for a while.

But what I'm referring to is measuring charge current. If SCC, inverter, and battery are all wired together, SCC doesn't know how much current goes into battery. Maybe SCC produces 50A, inverter takes 40A, battery gets 10A. Or inverter takes 0A, battery gets 50A.

For FLA, there is an optimal charge rate (e.g. 0.12C). I think it stirs electrolyte through bubbling, among other things. For FLA and AGM, the charge current as it approaches full voltage influences how long it should be held at full voltage for absorption.

A system that has a shunt with battery current reported to SCC can allow SCC to vary its output current such that battery gets desired charge current regardless of how much or little inverter draws. (unless PV & SCC can't keep up with that.

Although Midnight's description of WBjr doesn't say it supports that function, only mentions monitoring capability, their members on the forum have said it does (at least with Classic as I recall.)