Hope for SLAs?

Drunkskunk

Drunkskunk

100 GW
Joined
Apr 14, 2007
Messages
7,244
Location
Dallas, Texas. U.S.A.
I broke my bricks.

I did a dumb thing, I plugged in bike after a ride as I always do, then forgot to switch off the power, which I sometimes do, then managed to unplug the charger from the wall, which Is a new screw up for me. it rained for the next 3 weeks, so I didn't check on the bike. I leave it on the charger when its not in use, and it keeps the batteries toped up. Only this time they drained, all the way to zilch, then stayed there for 3 weeks.

Oh [CENSORED] says me, as I plugged in the charger. They took their charge, and managed to work after, at 50% of previous. 10 cycles now on them, and they still won't hold any more than 50% capacity of previous, or 3.5 amps... in a 10 amp battery.

Is there anything I can do to get some of the capacity back in them, or am I hosed?
 
Leave it on trickle charge for a month. :D Just plug it in though. I don't know. Probably have to get new ones. :)
 
Mr. Skunk,

I'm afraid your batteries are toast. I did the same once on a scooter. Technically, i believe your batteries have "sulfated". Chemically, i don't know what that means but it's one of the main ways SLA lose capacity. It is said that this process can be reversed by rapid, high current discharge and charge cycles but they will never be the same. At best, this reconditioning can bring them back to maybe from 50 to 80%.
 
Drunkskunk said:
...it rained for the next 3 weeks, so I didn't check on the bike. ....
Click to expand...

Drunkskunk decode: It was raining beer down my mouth. I was drunk off-my-butt for three weeks and forgot to turn the bike off or check on it.

??? :D
 
Don't these chargers have diodes?? How did it discharge?

:?:
 
TylerDurden said:
Don't these chargers have diodes?? How did it discharge?

:?:
Click to expand...

Some do, but even a small trickle of current will eventually kill the battery, especially after 3 weeks. I'm surprised that came back at even 50% capacity.
 
Actually to prevent this problem, you need a controller that understands when it's on for a long time (maybe 10 minutes) without the throttle being engaged and decide that it needs to turn off before ruining the battery. My goped scooter has this feature. It should be standard for all controllers.
 
jondoh said:
Actually to prevent this problem, you need a controller that understands when it's on for a long time (maybe 10 minutes) without the throttle being engaged and decide that it needs to turn off before ruining the battery. My goped scooter has this feature. It should be standard for all controllers.
Click to expand...

Ah I see... I missed the critical "forgot to kill the power" part.

Yeah, that auto-off feature should be on all of em. I have no idea if Ananda includes the feature. Maybe there is a way to add it...
:?
 
Do the batteries get hot when you charge them now?

Frequently when SLAs are left to die, the sulfate builds up enough to cause the separators to short in some of the cells. I've never been able to clear a shorted cell.

If none of the cells are shorted (charging current is at or below normal), then leaving them on charge for a month is not a bad idea. You might be able to convert some of the sulfate back into active material.

I don't think you can ever get them back to full capacity, but you can make an improvement.

Perhaps this is an excuse to go for LiFePO4 batteries :wink:
 
Some fancy SLA chargers can detect sulfated cells and apply a "desulfate mode" to the cells. I have one 12v charger that does this. You could give that a shot. The company rep (I used to carry these at our store) said it feeds in high voltages for extremely short bursts in specially shaped pulses. Or something.
 
Hey Mr Redneck,

So what's the plan for your broken bricks? You going to charge the crap or acid back out of them or what? You have a great experiment on your hands here. Going to get a de-sulphator? What's the deal?
 
State Of Health

The lifespan of your SLA battery depends a great deal on the relative size of your battery compared to your current limit. However, time defeats even the largest battery. Using some intelligent decision making you can determine the IDEAL size battery for your bike so that you get the longest performance while carrying the lowest weight.

Looking at the chart we see that:

A 10 Ah battery effectively "dies" in about a year or two. (80% SOH)

All the larger battery sizes (20, 30, 40, 50 Ah) will die from old age before they lose their ability to deliver current and so as long as you don't seriously damage them from misuse they should all last up to five years before needing replacement.

:arrow: So now you know...

If you demand a 40 amp current you need AT LEAST a 20 Ah battery if you are using SLA. But beyond 20 Ah all you are gaining is longer range.

(or a more energetic "half ride" like what I do)

:arrow: The irony is that buying LESS battery is wasting money!!!

:arrow: Buying too much battery is wasting money.

:arrow: Only buying the right amount of battery will yield the best cost performance... :wink:
 
safe said:


If you demand a 40 amp current you need AT LEAST a 20 Ah battery if you are using SLA. But beyond 20 Ah all you are gaining is longer range.

[/i]
Click to expand...


Agreed. Fresh out of the box I doubled-up on my Currie's SLA's (12ah --> 22ah) in part because of the excessive voltage sag at full throttle (35 amps). Problem is, of course, all the extra weight. In the long run, the more expensive chemistries are actually less expensive for anything but very heavy 86lb packs like yours'.
 
vanilla ice said:
So the ah has to half your current at minimum? So you're drawing only 30 amps 15 ah min SLA?
Click to expand...

Doesn't have to. But voltage sag, run-time, and longevity all suffer exponentially with decreased SLA rated-capacity. Safe's suggested line is by no means a hard-and-fast rule, it's just a guideline for obtaining acceptable performance from SLA batteries.
 
xyster said:
Safe's suggested line is by no means a hard-and-fast rule, it's just a guideline for obtaining acceptable performance from SLA batteries.
Click to expand...

:!: Agreed.

You can look at that chart and make up your own mind what to do, it's relatively easy to understand. All I did was use the established 5C maximum for peak current on a new SLA battery. As the State Of Health (SOH) declines as a percentage then the 5C peak will decline in proportion to the health... so a 50% reduction in health means a 50% reduction in peak current.

Where people seem to be getting into trouble is when they think that they want to SAVE MONEY and buy less batteries, but that actually ends up meaning that the battery's useful life is cut very short... which translates to lowered cost effectiveness.

:arrow: If your current rate is 40 amps you need a MINIMUM of 20 Ah.
(and preferably more like 30-40 Ah)

:arrow: If your current rate is 20 amps you need a MINIMUM of 10 Ah.
(and preferably more like 15-20 Ah)

I've got a 40 amp controller so I need to have my 38 Ah batteries to get plenty of power and still get about five years of use. After five years no matter how big of a battery you have won't matter because it will die of natural causes.

And don't forget about runtime voltage sag on SLA's. The smaller the battery the worse the runtime sagging, so erring a little on the larger size for battery selection is good if your bike can be configured to handle it. 86lbs of batteries is more than most people could safely carry. (so to really use a 40 amp controller you should use a custom frame or better yet switch to a lighter type of battery other than SLA)

I think what happens is that people buy a set of batteries that gives them 10 Ah and they draw a current of 40 amps at a rate of about 4C and for the first year or so things are great. Then the SOH is reduced to 80% and they start having troubles just pulling the current because even at 5C they can't get enough current. 80% of the battery is still good, but unless they add more batteries they can't get a current rate that equals full performance.


soh_vs_peak_current_vs_battery_ah_154.gif
 
Ypedal said:
Lead IS dead.. time to move on ! 8)
Click to expand...

Not so fast, three-legged Y-pedal person (as opposed to a bipedal person...:) )! Because of its low price and long standby life, lead is a good choice for small EV's the owner doesn't expect to use more than once a week or so, and doesn't expect to ever ride very far or very fast. Granted, this doesn't describe many of us here, but we're not exactly a random sample of potential ebike-riding people.
 
xyster said:
Because of its low price and long standby life, lead is a good choice for small EV's the owner doesn't expect to use more than once a week or so, and doesn't expect to ever ride very far or very fast.
Click to expand...

Hey, my bike uses SLA and I can hit 52 mph (downhill) and 42 mph on the flat. There are a lot of Lithium / NiCad / NiMh bikes out there that can't even match my current bikes performance. The trick I think is in recognizing the "realities" about SLA and adapting to them early on. Trying to "get by" with a little 10 Ah pack when you want to pump out 40 amps of power is just setting yourself up for failure. If you want your SLA's to work for you then you need (I think) about a 1C drain rate. At 1C you get a low Peukert's Effect and will have long battery life. The only negative is that you need to be a custom frame builder so as to accomodate 86 lbs worth of batteries. (assuming you want to be able to pull 40 amps)

I think if people did SLA right they would find more satisfaction than they presently do. But it's true, the more expensive batteries have better performance, less sag, better energy density, etc.

The future is probably LiFePO4...
 
If I had to do it again, I'd use the B&B EB series 20ah sla. Its good for 15ah at 1c if you look at the graph.

Xyster, if you used these instead of doubling up on the "non" EB type, you would save 3 lbs and have more capacity.

A good battery pack tester will test a pack from beginning to end and then make a statement of whether its good or not. :)
 
D-Man said:
If I had to do it again, I'd use the B&B EB series 20ah sla. Its good for 15ah at 1c if you look at the graph.

Xyster, if you used these instead of doubling up on the "non" EB type, you would save 3 lbs and have more capacity.

A good battery pack tester will test a pack from beginning to end and then make a statement of whether its good or not. :)
Click to expand...

Did it that way because my Currie came with 2, 12ah SLAs, and I had four 10ah SLAs on my scooter I wasn't using. So I didn't need to buy anymore batteries.
 
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