I need a 6/12v switchable Lead acid Charger 20amps

Thread Starter

Khaleef

Joined Mar 22, 2017
78
Please I need a switchable 6V/12V Lead acid Battery Charger circuit?


I have an old Lead Acid charger that is 6V/12V Compatible but it has only 8amps current and a part of the label reads "suitable for up to 40ah battery" I have 6V/200ah batteries which I connect in series with a modified APC UPS (extended leads to external battery)

I need 6/12 so I can be able to charge a single battery if need arises.

I would like a 20amp charger so the batteries can charge faster. I was thinking the transformer can be used to achieve this. And also, I would like it to be current limiting (Current reduces as battery reaches full charge)

I would like it to have digital voltmeter and Ammeter displaying voltage and current used in charging the battery and maybe few LEDs to indicate FULL CHARGE.

Thanks

cc @crutschow
 

crutschow

Joined Mar 14, 2008
29,504
20Adc would require a large and expensive transformer rated for about 20V, 40Arms, along with some high power circuitry.
Price such a transformer and get back with us, if you still want to do that.

Why do you want to charge the battery so rapidly?
 
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Thread Starter

Khaleef

Joined Mar 22, 2017
78
20Adc would require a large and expensive transformer rated for about 20V, 40Arms, along with some high power circuitry.
Price such a transformer and get back with us, if you still want to do that.

Why do you want to charge the battery so rapidly?
I just need the battery to get more charge during the little time there'll be power, cause utility power ain't very stable here.

Like I said earlier the previous charger have a big transformer also but I don't know the ratings, would look closely if it was inscribed somewhere on it... And also share pictures
 

crutschow

Joined Mar 14, 2008
29,504
If the old charger was rated for 8A, then likely that's all the transformer can safely deliver.

It would likely be easier and cheaper just to buy the battery charger you need.
What's your budget?
 

Thread Starter

Khaleef

Joined Mar 22, 2017
78
If the old charger was rated for 8A, then likely that's all the transformer can safely deliver.

It would likely be easier and cheaper just to buy the battery charger you need.
What's your budget?
I have actually put so much in other chargers and they seem to charge slow. It's why I thought if I could use the transformer in a previous one to build a better ampere charger.

Besides, getting a good charger is almost impossible here in my locality except I order from overseas which which would be very costly including shipping. Not really that rich right now lol.
 

Thread Starter

Khaleef

Joined Mar 22, 2017
78
One of the chargers I have is Einhell 10amp 6v/12v. I opened it up to look inside and noticed there's not much of a circuit, just the big transformer and what seems like a diode connected to switches and the amp meter. And I was thinking, could that be how it was originally built? (Cos I got it from a used stuff warehouse)

 

crutschow

Joined Mar 14, 2008
29,504
could that be how it was originally built?
Likely.
The old dumb chargers just had a rectifier to generate the DC, and wound the transformer with sufficient winding resistance to limit the charging current below its maximum rating when connected to a discharged battery.
 

Thread Starter

Khaleef

Joined Mar 22, 2017
78
Likely.
The old dumb chargers just had a rectifier to generate the DC, and wound the transformer with sufficient winding resistance to limit the charging current below its maximum rating when connected to a discharged battery.
Could some boost converters found everywhere on eBay, AliExpress etc do any magic along with the output of the Einhell Charger?
 

Dodgydave

Joined Jun 22, 2012
10,242
Thanks @Dodgydave but seems I need a Max of 14.4v to charge the 12v LA battery.
They are adjustable upto 13.8V with an onboard preset, it can be modified to give 15V easily as they use the Ld7575 chip and a TL431 zener, i have made the 24V into bench psus with variable voltages from 5V to 35V.

LD7575PS-LP7575-PWM-Controller.jpg

This is the circuit it uses, there is a preset in series with R52 to adjust the voltage, just increase the preset resistance to get a higher voltage available.
 
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Dodgydave

Joined Jun 22, 2012
10,242
What about a current limit needed for battery charging?
RS1 sets the current limit, it monitors the primary windings through the fet Source pin, to pin 3 on the chip, this can be altered ideally set to a lower current limit.

Or alternalively use an opto and op amp sensor on the secondary side, and feed the opto output to pin 3 and Vcc pin6.
 

dendad

Joined Feb 20, 2016
4,113

Thread Starter

Khaleef

Joined Mar 22, 2017
78
If you have more than one charger, you might try connecting them in parallel to the battery.
Would this work? I read it somewhere the two chargers would conflict each other with their voltages.

What are the features to be matched for these two chargers?
 

Thread Starter

Khaleef

Joined Mar 22, 2017
78

crutschow

Joined Mar 14, 2008
29,504
I read it somewhere the two chargers would conflict each other with their voltages.
If one has a charging voltage higher than the other, it likely would provide more charging current, but I don't see that as a "conflict".
They are still likely to provide close to their maximum current when connected together on a discharged battery.
In any event, I don't see that it could cause any damage to the chargers.
One may just sit there not providing much charge current while the other carries most of the load, but that doesn't hurt anything.
 
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