Rewiring a battery charger

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dacflyer
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Rewiring a battery charger

Post by dacflyer » Fri Sep 25, 2020 4:11 pm

Found a shop style battery charger that got crushed, The transformer and rectifier are still salvageable.
It is a 6v-12v charger Old school brute force type. i couldn't read any of the info on the charger..it's been painted over and over sprayed with paint
but i'm guessing it had a good high amp boost for starting.
the voltages i get from the 4 settings are (AC) 7v, 9v, 14v 17v
it has a big a half bridge rectifier 12-0-12 center tapped.
Is it possible to use a full bridge rectifier and not using the center tap to achieve a 24v charger ? Or am i missing something ?
I'm guessing it can be done, I just don't know if the voltages will be right.
I'm going with a full bridge, I'm only limited to 25-45 amps. Wouldn't be using it for any start function,,, just charging SLA batteries.
I just thought too, i could use the same half bridge, just parallel them up..then I'd have the full use out of the rectifier for the current.

gerty
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Re: Rewiring a battery charger

Post by gerty » Sat Sep 26, 2020 1:35 am

You could use a bridge to get the 24 volts, but you would get screwy voltages at the lower settings, Is that an issue ? Does this have multiple taps on the primary ?..If it does the way they get the higher charging rate is by stepping up the voltage, and you could use that to your advantage to dial in the 24 volt charging voltage you want.. Paralleling diodes gets a little tricky, if not properly matched, one will try to conduct more than the other.

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Janitor Tzap
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Re: Rewiring a battery charger

Post by Janitor Tzap » Sat Sep 26, 2020 9:50 am

Hey Dac,

Here's a 24V Charger Circuit, that I think meets your requirements.
https://www.electroschematics.com/24v-s ... y-charger/


Signed Janitor Tzap

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dacflyer
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Re: Rewiring a battery charger

Post by dacflyer » Tue Sep 29, 2020 4:47 am

The transformer I have is 12-0-12 capable of over 100A.
I've decided that it's not going to be feasible to try and get it rewired for 24v
I'm just going to go and order the parts i need to rebuild it back as a 12v shop charger.
I have leads on getting my mitts on an old style 24v 20A charger... looks like a lester golf cart charger, but it was used for a battery powered floor buffer.
the guy might have 2 of them,,
Thanks anyway..

Jastreb_J21
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Re: Rewiring a battery charger

Post by Jastreb_J21 » Tue Oct 27, 2020 8:46 am

Yes, you've made the right choice, it's better to go for a dedicated 24v charger, as as gerty said, the result of a conversion would be unreliable (and potentially dangerous, as with every unstable electric appliance).
I mean, not earlier than a year ago, I was accompanying as an interpreter a commercial partner who was visiting some of this property in Latvia, and while there, I relied on a cheap 110v to 220v converter found on the market, and it ended up melting my phone charger off... Since then, I've decided to use strictly reliable, verified electric hardware, and I can not recommend you enough to do so.

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dacflyer
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Re: Rewiring a battery charger

Post by dacflyer » Wed Oct 28, 2020 4:46 am

well this shop charger i have is too hefty to toss out,, so i ordered the new parts i need to make it back into a nice shop battery charge, I just need to find me a suitable case for it now.

I have since acquired 2x 24v 25A battery chargers ( Lestermatic II ) But they are designed for FLA batteries.
I need to try and see if i can modify it so that i can use it safely for SLA/AGM
they have a board in them, that cuts them off once the battery is full. maybe i can modify this for a lower voltage.
I just need to see if i can find a schematic.

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