lead acid sla agm 36v.

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ssss25
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lead acid sla agm 36v.

hi..

I have got a modified bike with a front wheel running on 36v sla agm batteries. 3 x 12v.

I used the charger that came with it and one time I forgot it.. it over charged. batteries expanded and I think I got hydrogen. they were very hot.

I was very scared. I replaced Bart's with news ones. got a 36v soneil charger.

I put a voltimetre on the 36v terminals when its charging. I read 43.3.. still charging. isn't that a high voltage when a full 12v charge is about 12.8v?

also. when I measured across each of the batteries while they are charging using the 36v 2a soneil. I got 14.79 14.23 14.14..

why each battle has a different voltage..

I if anyone can explain any of this... please do..

thanks a lot.. :-)

colin9876
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Re: lead acid sla agm 36v.

43.3v is ok for Total charging voltage BUT your Batts are out of Balance. This is why one can overcharge, it shouldnt have mattered that 'u forgot and left ur charger on' as it should stop at the final voltage. However with unbalanced cells a batt can get too highly charged.
get a bulb and discharge a bit from the highest ones.

ssss25
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Re: lead acid sla agm 36v.

just before I I get that charged they were all connected in parallel for days so I am sure they stabilize. am I not right that if they were all connected in parallel the higher charge will charge lower charge one and they all get to same level?

my other concern is that I have one of the batteries bad from the store.

thanks for ur advice.

ssss25
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Re: lead acid sla agm 36v.

I just did some more testing.

When I take disconnect the charger. I get 13.6,13.5,13.5 on each battery, looks close, as I said they were in parallel for few days. When I connect the charger, I got 15.1v,14.1v,14.1v

Why is one voltage higher? Does that mean it's taking less or more than the rest? Is it maybe a battery that is in a better or worse case than the rest? If so, I need to contact where I bought it and ask them to replace it.

Please help me understand this strange behavior.

Thanks,

fivari
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Re: lead acid sla agm 36v.

I just did some more testing.

When I take disconnect the charger. I get 13.6,13.5,13.5 on each battery, looks close, as I said they were in parallel for few days. When I connect the charger, I got 15.1v,14.1v,14.1v

Why is one voltage higher? Does that mean it's taking less or more than the rest? Is it maybe a battery that is in a better or worse case than the rest? If so, I need to contact where I bought it and ask them to replace it.

Please help me understand this strange behavior.

Thanks,

I am not a specialist though I read a lot about batteries lately for the same reason: I bought some E-scooters and the batteries are not performing as they should. I have one functioning perfectly. The four batteries are perfectly balanced up to 0,01V. Amazing. The other scooters don't. One battery is broken. Even just after charging it reads only 11,2V. I don't think I can recover that one. So the second scooter is lost without a replacement battery.

The third was somewhat OK: some weak batteries, but holding charge. I put the four best batteries together in the third one. There I notice the same problem as you do: batteries are not balanced during charging. After a night of serie charging I read 13,3V for all four but during charging and when loaded I read big differerences. For instance during bulk charging: total voltage about 57V but big individual differences: 13,3V; 13,5V 15,4V and 14,7V. I think it has to do with the internal resistance of the batteries. During charing one pushes the same current through all the batteries in the string. The ones with higher voltage show a higher internal resistance, so there voltage is rising. When discharging the opposite is true. The weak battery with the higher internal resistance will show the highest voltage drop. Normally, when the batteries are not too far gone, they will recover somewhat by desulphating or over charging. However, in order to help things to improve, I bought a 48V Forklift Battery Pulse Desulfator Recover Capacity. It didn't arrive yet, so I am not using it yet. If other members of this forum have some experiences with electronic desulphators, I am curious reading them. Anyway, I will post my results here.

Two e-scooters 1500W 48V 30 Ah LiFePO4

ssss25
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Re: lead acid sla agm 36v.

Thanks for the reply. You are right.. after charge the one with the higher voltage during charge has less voltage after charge. That leads me to believe that this battery is not in the same condition as the other two and thus afraid it will cause problems when charging.

I read the ebay posting for the battery pulse.. not sure how sound what they are saying and if its true or not. Need an expert opinion.

Any one can comment?

Any one can say if we are reading too much into this or if I have a valid concern to try to replace that battery with high voltage during charge?

Thanks.

mf70
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Re: lead acid sla agm 36v.

Indeed, during charge, you are seeing what each link in the series is putting in to that total voltage. It is clear why that 15V battery is being cooked. Each electron that is needed to charge the batteries with larger capacity must also travel past the one that is already filled. This is only possible by electrolyzing the electrolyte. A "36V" series charger is looking for a termination voltage of 44.1V. If your pack voltages are 15, 14, and 14, the total is only 43, and the charger will still be merrily dumping electrons into the bin.

If the voltage was presented in parallel, the higher internal resistance of the weak battery would divert the electrons to the batteries where they were needed, and the charge would be terminated when ALL were at 14.7 and not accepting any further charge.

NB: this would NOT "restore" capacity in the weak battery, but it would allow all batteries to accept their full capacity without further damaging the weakest cell.

A Series/parallel plug is the simplest way to ensure quick parallel charging of a pack that is DIScharged in series.

Mark

fivari
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Re: lead acid sla agm 36v.

The series/parallel plug is indead a simple way to ensure the parallel and balanced charging. Anyway it needs rewiring and one has to make sure the connections are as good as possible because they might increase the resistance of the current path. If the connections resistance is too high, they might heat locally and burn. Personnally I added 5 additional wires, leaving the original wires inplace, in order to be able to check for inbalance and to be able to charge the batteries individually. But even if all batteries are fully charged individually, they still are out of balance after loading because of different capacity. Another possibility is to make use of a 48V equalizer such as the HDM-device or this ebay-offer. Has anyone used these kind of electronic devices for balancing strings of batteries?
The desulphator is now connected for two days. So far I don't see much difference, but these things take effect only after several charge-discharge cycles. So I am still hoping.
The other possibility is that the high voltage battery is over charged. This would mean that it has dried out. I red at the end of this article that even for gel batteries, adding some water is a way to overcome this problem. I opened the weakest battery and noticed some white powder (lead sulphate) around the sealings of all six cells. I am still hesitating to add distilled water since after that it would require regular maintenance.
Same question: Does anyone know about a good way of reviving gel batteries that show symptoms of overcharging or that are being cooked as mf70 says?
Thanks,
Filip

Two e-scooters 1500W 48V 30 Ah LiFePO4

mf70
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Re: lead acid sla agm 36v.

A few points:

it needs rewiring and one has to make sure the connections are as good as possible because they might increase the resistance of the current path. If the connections resistance is too high, they might heat locally and burn. Personnally I added 5 additional wires, leaving the original wires inplace,

Since the "stock" wiring in my XB-600 was crimped-on 14GA, I replaced all source wiring (upstream of the controller) with 10GA with soldered termination. I believe it was worth the effort. Installing the Anderson plug involved cutting an access port in the lower side of the scooter body.

But even if all batteries are fully charged individually, they still are out of balance after loading because of different capacity.

The capacity of a battery is a physical fact, based on the number of available atoms. This can be limited by sulphation or by lack of electrolyte. AFIK, equalizers cannot replace battery capacity, so they cannot create a balanced pack with unequal batteries. For some very mild discharge uses, they claim to redistribute power between batteries, but I don't see how they could do that for a heavy load. (Look at the wire size between the balancer units!)

Does anyone know about a good way of reviving gel batteries that show symptoms of overcharging or that are being cooked as mf70 says?

Again AFIK, there are two (+1) basic failure modes in SLA's:
  • Lack of electrolyte -- Cooking: Some (including me) have tried opening the cells and adding distilled water as though they were regular floodies. I believe that they can be treated as regular SLA's after that if the caps and pressure seals are replaced. However, I have not seen much improvement in capacity after this treatment.
  • Sulphation: I believe that the symptom of this is swelling of the battery. As mentioned earlier in this thread, there are devices advertised that claim to reduce or reverse sulphation. I have not seen consistent successful feedback on this list; if you are trying one, let us know how your batteries' capacity changes. If they worked, I would expect that they would be all over the place. They aren't.
  • Shorting: As a final extension of sulphation (AFIK), sometimes a cell may develop a physical metallic lead trace between plates in a cell. I have heard that this can sometimes be repaired with a strong reverse polarity pulse of electricity. I've never tried this.

Mark

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