Author Options:

How to Limit Current on a 24V DC Battery Charger? Answered

Due to what I feel is a Bad design on the charger. I'm trying to limit current coming from a 120V AC to 24 Volt Dc Battery Charger. 

The Charger Is what is supposed to be a  Plain 10 Amp Only 24 Volt Charger. However when hooked to a dead set of batteries the current skyrockets up to 30-35 Amps and it trips the internal 20 Amp Breaker. 

Is there something I can do to regulate the current down to a better amperage ? 

Thanks In Advance. 



Best Answer 1 year ago

Generally speaking, you can use PWM to control the current, increasing the duty cycle (from 0%) as the draw decreases after the battery has begun to build a charge reservoir., or said another way, reducing the duty cycle (to 0%) as the draw approaches a threshold setpoint (I max)

One would use the output of a current measurement circuit to control the duty cycle.

One would choose a current threshold well below the rated output of the charger

Having said that, "dead'" is a relative term. Do you mean a lead acid type, where literally dead ( Vbattery(now) < ~0.75xVbattery(new) ), or (like, it's dead man) ie, depleted (Vbattery(now) > ~0.75xVbattery(new) )?

If the former, you're probably done. If the latter, see the beginning of my post


Answer 1 year ago


This is exactly what I needed. I Found a pulse width modulator that is already set up with a potentiometer. (http://a.co/9RpYQPt )Wired it in series with the amp meter on the charger. Now I can Manually "turn down" the charger and keep the charger running without over powering the breaker.


1 year ago

Use an old incandescent light bulb in series to reduce power transfer current...

You can use it on AC power in side, or DC power to battery side..

When battery voltage begins to return increase wattage or short the lamp..

If battery voltage never returns, then the battery is a dead short, probably caused by falling lead flakes touching both cell plates in a lead acid car battery...

Click the pic to see the whole image..


Answer 1 year ago

What About a dimmer switch installed on the AC Power in Side?


1 year ago

Batteries are good, they are just dead. The system I'm trying to charge is an engine that has had the status panel left on and drained the batteries to a low low voltage. Instead of using the truck to charge one battery at a time. The idea was to throw a 24 volt charger on the system and charge the batteries together, getting the engine back running faster and back to normal.

But this Current charger just skyrockets on Amps when the Voltage is low. With a Clamp on Amp Meter I'm getting 30+ Amps for a minute before the breaker kicks out. Then the longer it runs the faster the breaker trips from the amps and heat. I've tried another charger of the same brand and Model and it does the same.

Really I think the charger would only work well with batteries of 9-10 volts each. Then it might self regulate and not trip the breaker.


Answer 1 year ago

There is NOgood dead battery !

Once the battery is discharged well below 40% it will never function as a battery for more then a few minutes if at all...


Answer 1 year ago

0 volts your going to need a constant current charger to even try to revive them.

From the link:

"Now, if you go near 9V, it will become 0V very quickly. You'll easily be too late.

Many manufacturers tell us "Consider your battery empty at 11.8V", some people (me included) assume 11V. Those who use 11V often (but not always) take care to know that this is the lower limit. This is exactly for that reason."


1 year ago

Does the charger work correctly on other batteries?

Can you take a volt meter and check to see if there is any standing voltage in the battery now?

If there is no voltage showing on the volt-meter now can you do a continuity check to test for a short?

My thoughts are if the charger works on other batteries then it most likely is not the charger. Next, if the battery is not showing any voltage at all then it is most likely safe to check it for a short. It sounds as if you have a dead short which could happen under the correct circumstances. You might want to look at the sides and ends of the battery to see if there is any bulging which could indicate the battery got really hot. What kind of battery is it?


1 year ago

That sounds like either a dead short or a badly damaged battery.
Of course this all depends on the size and capacity of the battery in question.
Assuming all is indeed correct the only real way to limit current of that scale is quite costly or quite dodgy.
IMHO it might be best to salvage a transformer from a microwave.
Remove the secondary coil - the one for the high voltage with the thinner wire.
Then use the primary of the microwave transformer in series with your charger on the mains side.
This should limit the output to under 10A but might also limit the output voltage to below 27V, so best to check with a multimeter.