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Charger for SLA 12V / 7Ah battery

Started by gm July 2, 2015
On 03/07/2015 05:35, dakupoto@gmail.com wrote:
> On Thursday, July 2, 2015 at 4:35:02 PM UTC-4, gm wrote: >> The subject says all :-) >> I connected 3 x 12V / 7Ah battery's is serial and start to charge them >> with my ebike 36V/1,2A charger. After cca 30 minutes battery pack was >> getting hot, so i disconnect the whole stuff. >> >> What is the highest charging current for such battery's ? >> >> The funny thing is that i use the same charger to recharge my 36V ebike >> battery pack, and there was no problems whatsoever. The charger was >> shipped with ebike and the ebike battery pack is also a lead acid pack... >> >> GM > > A simple rule of thumb is that the maximum > charging current must be AH/10, where 'AH' > is the rated Ampere hour. The maximum charger > voltage should be alightly higher than the > rated maximum voltage of the battery to be > chargrd.
C/10 is relatively safe for manually operated dumb chargers. Fast chargers with the right algorithms and safeguards can do C/3 or much higher into modern SLA battery packs. Even prehistoric dumb as a rock car battery chargers offer to put ~6-8A into a 40Ah battery. Some makers claim 1.5C as the practical upper limit - seems a bit high to me. Anyone with direct experience of this kit care to comment. http://www.powerstream.com/SLA-fast-charge.htm Overcharging is bad for them. The right terminal voltage/current profile is temperature sensitive. Charging them in series is asking for trouble since the weakest pack will put the others under stress. It is a great way to ruin batteries in the longer term. -- Regards, Martin Brown
On 03.07.2015 14:17, Martin Brown wrote:
> On 03/07/2015 05:35, dakupoto@gmail.com wrote: >> On Thursday, July 2, 2015 at 4:35:02 PM UTC-4, gm wrote: >>> The subject says all :-) >>> I connected 3 x 12V / 7Ah battery's is serial and start to charge them >>> with my ebike 36V/1,2A charger. After cca 30 minutes battery pack was >>> getting hot, so i disconnect the whole stuff. >>> >>> What is the highest charging current for such battery's ? >>> >>> The funny thing is that i use the same charger to recharge my 36V ebike >>> battery pack, and there was no problems whatsoever. The charger was >>> shipped with ebike and the ebike battery pack is also a lead acid >>> pack... >>> >>> GM >> >> A simple rule of thumb is that the maximum >> charging current must be AH/10, where 'AH' >> is the rated Ampere hour. The maximum charger >> voltage should be alightly higher than the >> rated maximum voltage of the battery to be >> chargrd. > > C/10 is relatively safe for manually operated dumb chargers. > > Fast chargers with the right algorithms and safeguards can do C/3 or > much higher into modern SLA battery packs. Even prehistoric dumb as a > rock car battery chargers offer to put ~6-8A into a 40Ah battery. > > Some makers claim 1.5C as the practical upper limit - seems a bit high > to me. Anyone with direct experience of this kit care to comment. > > http://www.powerstream.com/SLA-fast-charge.htm > > Overcharging is bad for them. The right terminal voltage/current profile > is temperature sensitive.
------------------------------------------ Charging them in series is asking for trouble since the weakest pack will put the others under stress. *** Of course, i agree with you, but how to make / test some 36 or 72V charger ? I got one 10A 72V Chinese charger that i used to charge 6x12V battery pack. The pack was charged OK but the charger was so hot that i need to wait cca 20 minutes until i could move him....
On 7/2/2015 10:45 PM, DecadentLinuxUserNumeroUno wrote:
> On Thu, 02 Jul 2015 22:21:43 -0500, John S <Sophi.2@invalid.org> Gave > us: > >> On 7/2/2015 10:18 PM, John S wrote: >>> On 7/2/2015 3:34 PM, gm wrote: >>>> The subject says all :-) >>>> I connected 3 x 12V / 7Ah battery's is serial and start to charge them >>>> with my ebike 36V/1,2A charger. After cca 30 minutes battery pack was >>>> getting hot, so i disconnect the whole stuff. >>>> >>>> What is the highest charging current for such battery's ? >>>> >>>> The funny thing is that i use the same charger to recharge my 36V ebike >>>> battery pack, and there was no problems whatsoever. The charger was >>>> shipped with ebike and the ebike battery pack is also a lead acid pack... >>>> >>>> GM >>> >>> Keep the charging current below about 2 amps. >>> >>> Were all three getting hot or just one of them? They usually only get >>> hot when they are fully charged and are throwing away the excess. Are >>> you sure they need charging? >> >> For example, suppose one of them is essentially shorted. It will not get >> hot. The other two will try to charge to 36V even though they should >> charge to only 24V and they might get hot. Does this make sense? >> > > They should be charged individually. Ever heard of "memory effect" as > it relates to battery pack assemblies? You essentially just described > one scenario of it. > > Does this make sense? (rhetorical question)
Yes. However, I was unaware that SLAs have a "memory effect" similar to NiCd, etc. The elephant in the room is that a 12V SLA is actually 6 series-connected 2V cells in one box. You can't charge the cells individually and, in fact, they fail for the same reasons rendering the entire battery useless. I agree that it is better to charge each 12V battery individually because there is a better chance that the cells are balanced and manufactured for this purpose.
 John S wrote:

> > Yes. However, I was unaware that SLAs have a "memory effect" similar to > NiCd, etc.
** Stay unaware - it's nonsense. .... Phil
On Fri, 03 Jul 2015 14:53:36 +0200, gm <notMyMail@mail.not> Gave us:

>I got one 10A 72V Chinese charger that i used to charge 6x12V battery >pack. The pack was charged OK but the charger was so hot that i need to >wait cca 20 minutes until i could move him....
If you didn't assemble the pack, it may have had individual "watchdog" circuits on each cell element, making for an evenly balanced charging session management schema.
On Fri, 03 Jul 2015 08:40:32 -0500, John S <Sophi.2@invalid.org> Gave
us:

>Yes. However, I was unaware that SLAs have a "memory effect" similar to >NiCd, etc.
Purchased "packs" (batteries were what they were once called) generally have individual cell management circuitry these days, negating such 'effects'. A hand assembled conglomeration typically does not, and almost certainly not when the assembler is asking here about charging methods.
On 7/3/2015 10:59 AM, DecadentLinuxUserNumeroUno wrote:
> On Fri, 03 Jul 2015 08:40:32 -0500, John S <Sophi.2@invalid.org> Gave > us: > >> Yes. However, I was unaware that SLAs have a "memory effect" similar to >> NiCd, etc. > > Purchased "packs" (batteries were what they were once called) > generally have individual cell management circuitry these days, negating > such 'effects'. A hand assembled conglomeration typically does not, and > almost certainly not when the assembler is asking here about charging > methods. >
Have you noticed the Subject line? It says SLA which is an acronym for Sealed Lead Acid. These are not "packs". They are still called batteries. Do a search. Why do you insist on being always wrong, AlwaysWrong? Is it hereditary or did you manage it on your own?
On Fri, 03 Jul 2015 11:42:24 -0500, John S <Sophi.2@invalid.org> Gave
us:

>Have you noticed the Subject line?
Are you daft?
> It says SLA which is an acronym for >Sealed Lead Acid.
I didn't need a primer, thanks.
> These are not "packs". They are still called >batteries. Do a search.
When a person places an array of them together, the finished product is known as "a battery". Check your dictionary. Context is everything.
On Fri, 03 Jul 2015 11:42:24 -0500, John S <Sophi.2@invalid.org> Gave
us:

>Why do you insist on being always wrong, AlwaysWrong? Is it hereditary >or did you manage it on your own?
Someone should come find you and upgrade your manners, idiot. Remember, it was you that brought bullshit into this thread with this baby bullshit childish non-sense. Grow the fuck up, child.
On 7/3/2015 12:15 PM, DecadentLinuxUserNumeroUno wrote:
> On Fri, 03 Jul 2015 11:42:24 -0500, John S <Sophi.2@invalid.org> Gave > us: > >> Have you noticed the Subject line? > > Are you daft?
I don't think so. Why do you ask?
> >> It says SLA which is an acronym for >> Sealed Lead Acid. > > I didn't need a primer, thanks.
Apparently you do because of the following...
>> These are not "packs". They are still called >> batteries. Do a search. > > When a person places an array of them together, the finished product > is known as "a battery". Check your dictionary. Context is everything. >
Can you read what I typed in the paragraph just above your last one? I say "batteries" and you say "a battery". I say tomato and you say tomato. Let's call the whole thing off. Take your meds.