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Madscientist267:
Seriously.

Thanks to Peukert factor, full capacity can't realistically be expected. This is understood.

But I have a 'brand new' SLA here that is (by my calculations) under-performing.

WTF, I ask you?

Thanks for the insight ahead of time, because I'm apparently off on this, or SLAs are just clearly pieces of $#!+ from the git go.

My FLAs don't seem to behave this way.

Steve

Madscientist267:
According to 'average' performance (generic numbers given to a Peukert calculator), the time to 100% discharge SHOULD be 4.5 hours.

So 50% would be 2.25 hours...

Right?

Steve

dnix71:
C/6 is harsh, unless it's a battery that was designed for that. The forklift batteries I replaced last week had two ratings on them. c/5 and c/20 and those weren't much different. But these batteries were GNB Absolytes. The non-GNB brand replacements, 6v 220AH, were $250 each, wholesale in Miami, so there is a price to pay for quality.

http://endless-sphere.com/forums/viewtopic.php?f=14&t=16838&start=0  Kind of a long winded thread on this. If you don't go below 80% DOD, at c/5 or c/6 there can be a LOT less usable AH than what's printed on the label. But this only applies to SLA's, not lithium or nicads.

Madscientist267:
What I don't understand is why the SLAs behave this way, and FLA, while still affected, seems to be a lot more robust.

Been reading up on it, and from what I can tell, FLA has a lower effective Peukert number than SLA does.

Damn shame, because I'd rather use them, with that whole liquid acid thing being a factor, but their performance always seems to disappoint. :(

I've come to the conclusion too that they should not be brought as high up as FLA in terms of charging voltage, and especially not floated as high...

I've recently trimmed the dump controller on the new battery back to 13.7V, and although I realize I'm not hitting 100%, the pros of doing so seem to outweigh the cons.

I learned that watering an SLA doesn't get me very far, and so my next strategy is to avoid the gassing as much as possible instead.

My conclusion about SLA at this point is that they are much more finnicky in many ways than FLA, and so as (I believe) DamonHD put it, "they need to be babied". Pushing for that final 10% of charge seems to do more harm than good most of the time, and maybe should be considered as the 'equalization' for SLA, only going above 13.8V occasionally.

I'm also finding that the constant current mode should be extended somewhat, providing gassing protection toward the top of the charge. Once the threshold is reached, it seems as though they like to be let go and returned to a lower constant voltage charge than FLA does.

Then if that wasn't enough anal-retentiveness for one chemistry, resting appears to be key to obtaining maximum capacity from them. I think this is probably due to the bubbles being trapped in the matting, unable to escape as easily, resulting in an insulating effect on the plates. Once they have rested, I've noticed that the internal impedance is much lower, and they handle loading better.

The part about that which I can't seem to figure out, is this appears to be an issue on discharge as well. They 'grab' the charger better and show a lower impedance if they are allowed to sit after being discharged. This is most apparent after a heavy load. Light loading (<C/20) doesn't seem to bother them as much in this area.

I want a portable solar 'plant', but with SLA I can't get the capacity I need, and with FLA there are other problems to consider, namely the liquid spill potential. I've considered Lithium, but my preliminary encounters with smaller lithium phosphate didn't exactly leave me creaming.  :-\

NiCd, maybe. If I could get my hands on some really high capacity cells that are all in good shape. Problem there is, there's almost twice as many cells for the same nominal system voltage, and that brings it's own set of problems to the table.

NiMH is out of the question. They are crap.

So my options here are limited... Damn this is frustrating! :(

Steve

dnix71:
Being starved for water is what messes up SLA's. Allowing them to sit a short time before recharge allows the electrolyte to even itself out. I noticed that when recharging my ebike.

I would love to have them, too, but they are a lot more expensive and less tolerant of abuse. They are 2 or 3 times the price of FLA's of the same capacity here.

I would love to be able to put a big FLA on my bike because of the extra range it would get me, but the water weight and sloshing acid isn't something I want to risk. If I had 3 or 4 wheels on the ground, golf cart style, FLA would be the way to go. Sam's club has $80 6v 200ah FLA's

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