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Gel cell charger

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Firnagzen

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Yes, I know this has been asked recently, but my question is different.

Could someone offer an opinion between these two circuits?
http://www.aaroncake.net/circuits/charger1.htm
**broken link removed**
As in, which one would be better?

As I understand it:
-The first one adapts to any battery you plug in? Regardless of voltage/Ahr rating?
-The second one is simple, but slightly slower? Given similar batteries, say 6v 1.2Ahr ratings, what would the difference be like?

Thanks in advance.
 
Not much to chose between them. The more complicated one reduces the charge to a trickle which is only important if you want the charger to be connected 24/7.

Both will handle a range of batteries up to about 15V, but both are unnecessary if you just want to do occasional charging.

Lead acid batteries can be charged from a constant voltage and will adjust the current by themselves.
If you have a variable dc power supply, just set it to about 1.2 x the nominal battery voltage and connect up (eg 7V for 6V battery, 14V for 12V battery).
You won't be able to hurt a car battery, but sealed lead-acid batteries have a maximum charge rate so set the current limit on the power supply to this.
 
I see, but doesn't the second circuit reduce the current to a trickle too? The difference, as I understand it, is that the second circuit is more like a straight line graph with a downwards slope, but the first circuit is more like a straight step from max charging current to a trickle. Is that right?

Thanks.
 
Lead Acid Charger

Hi,
You are correct that the first circuit has a step change to trickle charge. The second simply has a maximum current limit. The first will charge you battery slightly more quickly. The second is infact over complicated, you can limit the current from an LM317 by simply adding a low value resistor at the output pin, before the voltage setting resistors. see "12v battery charger" on page 20 of the LM317 datasheet, https://www.electro-tech-online.com/custompdfs/2007/01/LM117.pdf
ore info is given on page 8 figure 2.
This circuit works very well.
Robert.
 
My understanding is that gell cell batteries require very different charging parameters than lead acid batteries. Do these charges take that into account?
 
I see.

But neither will harm the SLA in the long run by overcharging, correct? As in, I can leave the battery in the charger indefinitely?

And anyway, according to this other website I found with the same circuit, the second eventually drops the current to the minimum too?
http://www.myra-simon.com/bike/charger.html

Thanks for your help!
 
Use an LM317 power supply set to 7V to charge a 6V battery; it really doesn't need to be any more complicated than that.
 
I find battery terminology fairly confusing. :) Some consider a SLA to be a maintenance free lead-acid. Some consider it a form of gel or AGM. Some consider gels and AGMs the same. They're not, and for charging purposes you need to know which you have.

AFAIK any sealed battery should be protected from being overcharged, as that will significantly shorten its lifespan.

My reading says gels should be bulk phase charged at no higher than 14.3v. Float charge at 13.8v. AGMs can be a bit higher.

So, do you have a gel, an AGM, or a maintenance free lead-acid?? :)
 
Firnagzen said:
But if I it to charge overnight, won't that harm the battery?
As I said in my PM to you, providing the charge voltage doesn't exceed 7V the battery can be left connected indefinitely, if doesn't matter whether you leave it overnight or over a year, no damage will be done to the battery.
 
It's a valve regulated lead-acid battery, 6v 4.5Ah.

Thanks for all your help, I understand it now. Thank you very much!
 
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