partial charges
 

Can you partially charge an SLA battery and then ride without doing damage? I'm talking about going to work, charging for a while, and then going off to another site before hitting maximum charge. I've just been all over the internet trying to find an answer to this question, and I can't find one.

It's bad to partial charge lead acid batteries. I can't remember why exactly, and no longer have access to the book which explained it.

I'm thinking it also causes sulfation.


Here's something to back up my memory:
http://209.85.173.132/search?q=cache...ient=firefox-a

Look at page 4, first two paragraphs.

Hope this helps, not too much on the internet on the subject.

I can't get page 4. It ended after page 3.

What kills SLAs are deep discharges. Sulfation starts in the discharge state. You need to charge the battery asap after every use.
Shallow discharge/charge cycles are ok. Bottom line you should charge them after every use as soon as it is possible.

INTERMEDIATE FULL CHARGE CYCLES
An observation early in the testing required a change
in the test procedure. The original intent had been to
perform several partial charge/discharge cycles in
sequence. For example, charge to 68Ah input, discharge,
then charge to 68Ah input and so on until the four
complete cycles at 68Ah input were complete. Then fully
charge and discharge the battery before proceeding with
the next level. It was seen early in the testing that this
was not going to work, as the capacity resulting from
68Ah input dropped with each succeeding cycle when no
full charge cycles were performed between partial charge
cycles. Therefore a full charge and discharge cycle was
added between each partial charge/discharge cycle.
This result has important implications to operational
PV systems. That is, if a battery is partially charged for
several consecutive cycles (for example, the array is
marginally sized and there is a series of less than full sun
days in the winter) the useable battery capacity decreases
each cycle, even though the same amount of energy has
been presented to the battery each day. This is the result
of battery inefficiencies, electrolyte stratification, and
sulfate buildup during these partial charges.
An
associated full charge, with its attendant gassing, is
needed to destratify the electrolyte and remove the
residual sulfate. This sulfate buildup can become a
problem if this pattern continues for several months. In
the short term it can be reversed by a full “equalizing”
type charge, which, in most cases is not possible in small
PV systems. Battery equalization requires a PV charge
controller that has been specifically designed to include
this function. At low charge rates (for example, less than
C/40) equalization may not be possible because of
charging time limitations. In any case, this reduction in
useable capacity will impact system availability and
should be understood....

Even though you are talking about doing something a little different (a partial charge and then a full charge, instead of consecutive partial charges), I think the advice still applies. Once the battery is sulfated, it is difficult to break the crystals off and would require an equalizer battery charge or a sulfation circuit to get it back to normal again. But then considering that SLA don't live that long, maybe we're only talking about shortening the life from 200 cycles to 175 cycles. It might be worth the convenience to lose 25 cycles. Or maybe it's 10 cycles. Or 50?

Here's one way to think about it -

it appears that sulfation is likely to result, to some degree.

But how much?

Looks to me like if you use 10 amp hours and do a full recharge, you get a certain amount of sulfation.

If you use 5 amp hours, recharge 2 of them, and then use another 5 amp hours, you probably get LESS harm to the battery than if you had just used the 10 amp hours without a recharge in between... but more than if you had just used 5, fully recharged, and used 5 again.

With SLA - you should always apply a charge (small or large current, long or short) to this chemistry as soon as possible after drain - within proper temperature limits of course! Doing so will help minimize plate sulfation. So yes, you can partially discharge and apply repeated charge cycles and no excessive damage will occur. In fact, your SLA will last longer if you do apply a charge - even a trickle charge - immediately following use.

However, if doing this puts the battery into deep discharge condition - you will cause damage but only as a result of draining too much current from the battery during your duty cycle. Having nothing to do with repeated charging.

I have gone through several sets of SLA with my GoPed ESR750EX and during errands I'm always looking for an outlet to plug-in if even for a moment because of the increased battery life I get from this practice.

Yes, yes, yes - I missed this before posting my long reply but he's saying the same thing I said.

The article is talking accumulative discharge condition within a PV system. In other words, deep discharge of the battery without enough recharging. Different animal.