Float Charging Flooded Lead Acid Batteries?

Vic · December 2019

" ... Don't remember the "transition to float %age of capacity" being adjustable, but I'm sure it is somehow."

Historically, Schneider has NOT allowed the user to enter the desired battery charge current for the end of Absorb. SO the user needed to LIE about the battery Capacity to accomplish this EA value. THis lie might have consequences, elsewhere, though.

Perhaps, this has changed, but, we doubt it. Schneider usually tries to make things as easy on themselves, and not the customer, IMO ... (ooopppsssss, too judgmental!). FWIW, Vic

papab · December 2019

BB. said:

In theory (as I have read over the years here), as long as your lead acid battery bank is cycling daily (like 50% to 80%), you really do not need daily Float/EQ charging.

The "standard" reply is to cycle to >90% once per week. However, one major mfg (Rolls/Surrette?) had said that >90% is only needed every 4 weeks (if daily 50-80% cycling).

If the batteries are not cycling (you leave the cabin for a week at 50% SoC and bad weather)--You do really need to get upwards to 90%+ State of Charge before putting the cabin/batteries "to bed"--When there is no immediate solar charging available (days/weeks of assumed bad weather/missing sun) getting the bank charged will help reduce Sulfation (which is, more or less, permanent battery damage).

-Bill "I am not a battery engineer" B.

Do you think this is true for most AGM's also, or just FLA? All I know it that Lifeline recommends charging to 100% every day.

mike_s · December 2019

ligwyd said:

My battery specs state maximum life span 4500 cycles at 20% D.O.D. The cycles stated for 50% D.O.D. is half that. Would it not be wise to design a system based on 20% D.O.D., albeit more upfront investment, and have lots of extra power when needed?

If it were half the cycles at 40% DoD, it would be a wash - spend twice as much for a battery bank with a cycle lifetime twice as long. So you can consider that extra 25% of capacity (50% / 40% = 125%) along with the saved cost as a something to balance against whatever the extra energy storage is worth to you. If you really need more capacity on rare occasion, no reason you can't draw down below 50%.

ligwyd · January 2020

Good point. Well said mike_s. Really appreciate your comment.

I guess down side would be more batteries to maintain, upside is less generator run time. Toss up........

ligwyd · January 2020

Just spoke with Schneider today and they confirmed that the only way, at this time, to enable the absorb stage of the charge cycle to exit to float stage at less than 2% of programmed 20hour battery bank capacity, is to lower the entered capacity.

So I'll give it a shot and post how it works out.

ligwyd · January 2020

So, I reduced the Amp hours programmed into the SCP/ XW from 630 to 315 amp hours and absorb exited to float at 6.3 amps as opposed to 12.6 as expected.

The amps on the XW display where at approx. 4 amps. The float charge over night can still reduce the amps on the XW to less than 1 amp. Would this setting suffice in the field when running off solar alone? (currently I am charging from grid power)

Would you reduce the amp hour setting even further to less than 1% exit to float?

Appreciate the dialogue as always:)

Vic · January 2020

ligwyd said:

So, I reduced the Amp hours programmed into the SCP/ XW from 630 to 315 amp hours and absorb exited to float at 6.3 amps as opposed to 12.6 as expected.
The amps on the XW display where at approx. 4 amps. The float charge over night can still reduce the amps on the XW to less than 1 amp. Would this setting suffice in the field when running off solar alone? (currently I am charging from grid power)
Would you reduce the amp hour setting even further to less than 1% exit to float?
Appreciate the dialogue as always:)

Since the batteries are Flooded, the End Amp setting, and the Float voltage can each be set on using merasured SGs.

Of course, if EA is set too low, the EA will not be met, and if the charger has the capability, then, Absorb will terminate, based on an Absorb time setting.

For EA, try measuring SGs about an hour after entering Float, when the battery is still in Float.
For determination of a good Float voltage, try measuring SG early in the AM, before recharge has begun, on systems that have been Floated from the Grid.

For Off Grid systems, measure SG late in the day, just before the CCs cannot maintain Float voltage.

All IMO, Vic

Estragon · January 2020

I wouldn't reduce to under 1% unless trying to remediate a problem. Although I suspect the most common premature fail is sulfation from undercharging, getting a battery to "full" is also hard on it. A bit of a trade-off.

Float Charging Flooded Lead Acid Batteries?

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