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Forum Index : EV's : Sealed Lead Acid battery

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larny
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Joined: 31/10/2011
Location: Australia
Posts: 320
Posted: 08:39am 13 Aug 2018
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My daughter has a 36 Volt electric bike, but the batteries are dead (I measured 0.7 Volt across the terminals of each 12 Volt battery). So I assume that there is no hope of recovery. Each battery is 12 Volt, 12 AH.



Thus I'm looking for replacements. I have attached a photo of the info on one of the batteries. Could someone please tell me what 0.1c & 0.25c means?


 
Tinker

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Joined: 07/11/2007
Location: Australia
Posts: 1904
Posted: 08:58am 13 Aug 2018
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Larny, AFAIK your 12Ah = C. So 0.1C = 1.2Amps, 0.25C = 3 Amps.
You cannot charge sealed batteries too fast hence they show the max charge current. Do use a proper regulated charger.
Klaus
 
larny
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Joined: 31/10/2011
Location: Australia
Posts: 320
Posted: 09:42am 13 Aug 2018
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Thanks Klaus,
That's what I thought but could not confirm it with internet searches.

I understand that charging batteries in series is not a good idea as one battery can be overcharged (or possibly under charged) so I am intending to use 3 chargers - one for each 12V battery.

The reason I wanted to know the meaning of C is so I can design a current limiting circuit that will not allow the current to exceed the safe threshold.

So it appears to me that I should set the limit at a little less than 3 Amp. Is that correct?

By the way, what does "AFAIK" mean?

Len
 
Boppa
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Joined: 08/11/2016
Location: Australia
Posts: 807
Posted: 10:23am 13 Aug 2018
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As Far As I Know...

there is no issues with series charging SLA batts, apart from finding a 36v charger in your case (12 or 24v are far more common as is 48v)
Although you can indeed use 3 (identical) 12v chargers as well

They would have to be SLA chargers (NOT standard car battery chargers unless they have a SLA setting) max of 14.4v, 3A
 
larny
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Joined: 31/10/2011
Location: Australia
Posts: 320
Posted: 07:43am 14 Aug 2018
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Thanks Boppa,
I'm building my own 36 V charger by modifying a Silicon Chip 12 V charger to work at 36 V.

I found the Battery Balancer I had in mind in the May 2018 issue of SC.

But it is for LiFePO4 batteries, not for Lead Acid. See below.



 
Boppa
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Joined: 08/11/2016
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Posts: 807
Posted: 08:00am 14 Aug 2018
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SLA really doesnt need a balancer in most situations, the different chemistry is really quite tolerant of variations as long as its close enough (ie replace batterys at the same time, same make etc and they will be fine), Liions on the other hand have a different chemistry and rather than self balancing as LA batterys do, they tend to get more and more out of balance, hence the need for balancers, monitoring etc

LA technology has been around for a loooong time, and has survived all this time without needing balancing units, so you are adding an extra level of complexity and possible failure points for no real reason
 
larny
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Joined: 31/10/2011
Location: Australia
Posts: 320
Posted: 08:39am 14 Aug 2018
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Boppa,
I did not explain myself very well in the previous post.

Now that I have re-read the BB article, I now realise that it does not apply to Lead Acid batteries.

So I have no intention of building a BB.

Thanks for your input.

Len
 
Boppa
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Joined: 08/11/2016
Location: Australia
Posts: 807
Posted: 09:01am 14 Aug 2018
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No worries, just though it would be good to clarify
;-)

LA 'can' have balance issues, but its pretty rare (I have modified many truck battery installations with a piece of wood to 'shelter' the leading edge of the front battery, as the cooling effect of the air over the batterys at highway speed at night did cause issues long term with the coldest cell not getting charged properly) but I doubt that will be an issue in your case LOL

eta- is the SC charger a SLA charger, or just for standard LA batts?
Edited by Boppa 2018-08-15
 
M Del
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Joined: 09/04/2012
Location: Australia
Posts: 155
Posted: 10:50pm 14 Aug 2018
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Boppa, I have a patent on that wood mod , 12mm ply in most cases.

The charger in question is standard LA unless there is a new one out.

Mark
 
Boppa
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Joined: 08/11/2016
Location: Australia
Posts: 807
Posted: 11:53pm 14 Aug 2018
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  Quote  To charge an SLA battery, a DC voltage higher than the open circuit of 2.15 volts per cell is applied to the terminals of the battery. Any of the conventional charging techniques may be used, but to obtain maximum service life and capacity, along with acceptable recharge time, constant voltage-current limited charging is recommended.

During constant voltage or taper charging, the battery's current acceptance decrease as voltage and state of charge increase. The battery is fully charged once the current stabilizes at a low level for a few hours.

Cycle Applications: Limit initial current to 0.20C (C is the nominal A.H. capacity of the battery). Charge until battery voltage (under charge) reaches 2.45 per cell at 68 degrees F (20 deg.C). Hold at 2.45 volts per cell until current drops to approximately 0.01C ampere. Battery is fully charged under these conditions, and charge to "float" voltage.

"Float" of Stand-By Service: Hold battery across constant voltage source of 2.25 to 2.30 volts per cell continuously. When held at this voltage, the battery will seek its own current level and maintain itself in a fully charged condition.

(pinched it from BatteryWholesale.com)

A standard car battery charger (unless 'intelligent') is unlikely to be the best charger for a SLA battery- I found several circuits from S.C, some may be suitable, others definitely not, if larny could confirm which is the one being looked at?

An unsuitable car battery charger could cause overcharging on an SLA, which at best would cause permanent capacity loss through venting
at worst this




 
larny
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Joined: 31/10/2011
Location: Australia
Posts: 320
Posted: 09:18am 15 Aug 2018
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Thanks Boppa,
Some time ago, I bought the PCBs & parts to make 2 chargers. See the Silicon Chip April 2008 issue. I have posted the first page & the spec page

of the article below. I've been using one to charge my car battery & intend to modify the other one to charge my daughter's 36 V bike battery.

They appear to have done a thorough job. Let me know if you want to see more of the article.







 
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