SLA pack losing apparent capacity fast

M

magnuznilzzon

1 mW
Joined
Jul 27, 2013
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17
Location
Gothenburg, Sweden
Hello

I wonder if someone can give me advice on why my AGM-SLA pack is losing capacity as fast as it (apparently) is:

The pack is 2*4 hzb-ev12-18 (http://www.ieeco.net/Documents/Batteries/HazeVehicleHZB-EV.pdf), giving 48V. Whenthe pack was new (2 months ago) the range of the electric scooter they are in was easily 20 km (the needle was down to half at that point). Now the range (to empty) is closer to 5 km.

At after running it to indicated emtpy (and seeing that it really was empty, didn't have any power) I let it rest overnight and measured. It showed 50.8 for both the parallell strings. This would mean over 90% charge if I understand things correctly. However, as soon as I load the pack (with an acceleration on flat ground) the voltage drops to less than 45V. Measuring on individual cells I see that all of them drop to around 11V at load.

The question is, what could be the reason for this? Could it be manufacturing problems?
 
One easy way to tell would be to charge the battery and see how many amps go into it. For this task you would need a Wattmeter. Full charge hot would be about 58-58 amps. The Turnegy meters are cheap and do the job. EP Buddy as them in this country.
otherDoc
Also, to quote dnmun, put a meter on the cell terminals during the charge and write the voltage for each cell. This will help to determine the ability of each cell to charge up.
 
Check the individual battery voltages (let's say, when the pack is drained), they can unbalance and you loose range.
 
It sounds like what happens if the batteries lost water. This can happen if the charging voltage is too high.

What is the peak charging voltage at end of charge?
 
Buy another pack from the same company. Your problems will most likely resolve and you'll be on your way. :mrgreen:

If they want their original battery back. Oh well...Life goes on... :mrgreen: :mrgreen: :mrgreen:

It's not that much. They are SLA and are cheap LoL
 
The sulfur ions move during charging and discharging. When it's allowed to sit in a discharged state for a period of time. the ions harden on the plates and won't release back into the electrolyte during a normal charge thus reducing capacity. That's hwy it always advised to recharge as soon as possible for lead batteries. Desulfication (sp) will most times loosen those ions and bring your batteries back to full capacity if they haven't sat too long. Some newer battery chargers have these modes usually referred to as recondition mode or something similar. Read up on lead acid batteries to learn more. My terminology may not be spot on, but hopefully you get the point.
http://en.wikipedia.org/wiki/Desulfation#Sulfation_and_desulfation
 
fechter said:
It sounds like what happens if the batteries lost water. This can happen if the charging voltage is too high.

What is the peak charging voltage at end of charge?
Click to expand...

The charger floats the pack at 53V. It might be a bit high, but I've never felt them get warm at that level. Also, how can a sealed battery lose water?
 
Lead batteries don't like to be fully discharged they lose ah's if fully discharged after each ride and worst if not charged after a short cool down and recharged and keep at a full rate of charge. If you like what you got as a bike save money and spend on a lifepo4 battery strong enough for your controller.
 
My guess is that you ride it till a battery indicator on the bike says empty. Thus, discharging it far deeper than you should be doing.

Took me a month to wreck the sla's I started out with. A bit less than the two year lifespan I was told to expect.
 
Mine are 2 years old, but only discharged completely a couple of times. Kept them on a Save A Battery charger for over a year now and they still work well for commuting 10 miles at half throttle with pedaling. Recently got 4 used sla from discard pile of which 3 seem to hold a charge. I'm going to assemble another pack from those. I should of pedaled more from the start. On a scooter could one extend the range by reducing speed and cruising?
 
magnuznilzzon said:
I wonder if someone can give me advice on why my AGM-SLA pack is losing capacity as fast as it (apparently) is:
Click to expand...

Discharging SLAs until they give up is a good way to kill them quickly. If you have run the thing to empty more than a couple of times, that's probably the deal.
 
I hope not, since these are specified to be reisistant to deep discharges. According to the spec, they should be goof for 300 complete cycles, and I have maybe done three.
 
What does your charger set at ? Mine was set to 56volt. I hated the sla's so much I triied to return them after 4 day's. The shipping cost stopped that. I beleived the people who sold me the kit. Now I curse them. That was 5 yrs. ago. Good batteries make a good bike. You will find out Lead is dead for an ebike. It cost me a set of sla's to find out. Sure you get 20 miles on them ???
 
magnuznilzzon said:
I hope not, since these are specified to be reisistant to deep discharges. According to the spec, they should be goof for 300 complete cycles, and I have maybe done three.
Click to expand...
Did you run them down and then not charge them for a period of time? They will sulfate fast. Only solution is to desulfate them as I stated earlier. Griping about it will do no good. If they've sulfated, just charging them will do no good. Desulfating them will. If your 12V charger doesn't have a desulfate mode, then you'll have to get one that does or forget it. I think the Battery Minder model is the gold standard in this regard, but there are cheaper alternatives.
http://batteryminders.com/
 
Read your spec again. I bet that spec states 300 cycles at a .5c rate. Your scoot could be discharging at up to 10 times that rate. So by cowboy math, take a zero off your cycles number, and you get 30 cycles. About what it took to toast my sla's.

But you could put that zero back on your cycles on the next set of lead, by discharging only to 50% depth of discharge. This is very common knowledge in the car conversion world. They learn really fast to not wreck their lead when the pack costs thousands of dollars. In general, the typical deal was they convert a car, quickly ruin the first pack, then learn to make the second try last 10 times longer.

Again, that little light on the handlebars? It's a you just ruined your lead light, when you see it turn on. They don't tell you that while trying to sell you that scoot do they? But it's true.

Save up for some lifepo4. The same treatment I gave my lead lasted 3.5 years when I switched to a 36v 20 ah lifepo4.
 
See - SLA Disadvantages
Your problem is symptomatic of a heavily "Sulfated" battery.
 
A 48V pack should charge to 57.6V (58)
Take the 4 out of the pack and rewire them for parallel then put that pack on a single cell charger for several days to balance them again in case they are unbalanced. You could try adding distilled water and epsom salts.
 
Balancing the batteries (parallel connect) might help or at least help identify a bad one in the string. Unfortunately, SLA for EV use simply sucks. It's so easy to damage the damn things with no obvious signs. Even the best HR (high rate) SLA treated like a baby will barely make 300 cycles with 80% original capacity.

Never-mind obscene weight and granny charge rates. Perhaps the biggest waste of battery money out there for eBikes, IMO.
 
Or if you just have a 12v charger at 2amp charge each one then connect all four together and charge in parelle four plus hour's with trickle or 2a charge. With a decent sla 12v charger no higher then 14.5v.. It will not stay long Watch them a bubbleing cell means a short or if one battery is getting hot. Guess what. Problem. Matbe just one weak battery ?
 
The sealed type lead batteries are supposed to have a 'starved electrolyte', which is supposed to prevent sulfation when the batteries are fully discharged. If they used a bit extra acid, AND the batteries were left sitting for a long time at a low state of charge, you could get serious sulfation.

I'm sure there's 100 ways to mess up battery chemistry or manufacturing, so could be a bad batch from the factory.

Sometimes charging for a long time at the high end of the voltage range can recover some of the lost capacity, but there is the risk of venting and water loss at too high a voltage. The float voltage measured earlier is in the safe for continuous charging range. Maybe a bit low. The charger usually goes higher than this during the charge cycle, then drops to the float voltage when the charge current drops, indicating full charge.

You could try around 58v overnight to see if that helps. Also make sure your voltmeter is accurate. If the charger voltage is too low, it will never reach full charge.
 
All lead acid batteries will sulfate, sealed or not. You can recoup capacity desulfating them in most cases. But if you leave them sit too long or continue to use them without desulfating them, it will be near impossible to bring back capacity. Desulfating is a long process. 24 hours minimum and as long as a week or more in some cases. I've had to run 5 24 hour desulfate modes on a few to get all cells working.
 
Lessss said:
A 48V pack should charge to 57.6V (58)
Take the 4 out of the pack and rewire them for parallel then put that pack on a single cell charger for several days to balance them again in case they are unbalanced. You could try adding distilled water and epsom salts.
Click to expand...
Pacific Power Batteries recommends a final (float) "full charge" voltage of 2.25V per cell = 54V for 48V pack.
"The recommended float charge voltage for the plastic SLA is 2.25 volts per cell ... Too high a float charge voltage should be avoided because it accelerates grid corrosion. During float charge, the charge current is minimal."

A higher initial charge voltage-(pressure) is used to force electrons into the battery ... more "quickly". When "full" pressure-(voltage) should be reduced.
 
Hello

Thanks for all the ideas. I just spoke to the seller and he (obviously) thinks that the cause is the charger, since its cutoff voltage for phase 1 (bulk charging) is 58.8V (2,45V/cell) while the batteries are speced for 2,35-2,4V/cell (the Vcyclic value)

Does he has a point, can this kill a battery in two months, or is it bullshit?

//magnus
 
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