Can I reduce output voltage of battery charger?

[cygnusv]

I've bought (cheap!) a 24 volt 30 amp heavy duty battery charger. It's basically meant for deep cycle truck batteries. The output voltage is 34 volts. I'd like to reduce this to 28 volts if possible to avoid damaging the batteries I want to use it on.
For simplicity I wondered if some kind of resistor could be used in the positive charger output cable?
On the face of it this question doesn't sound very boaty I know....... But it is.
Many thanks. Stu

 

[pvb]

I've bought (cheap!) a 24 volt 30 amp heavy duty battery charger. It's basically meant for deep cycle truck batteries. The output voltage is 34 volts. I'd like to reduce this to 28 volts if possible to avoid damaging the batteries I want to use it on.

Have you measured 34v when it's connected to the batteries?

 

[lw395]

Simple answer:
No!

If the 34V is open circuit voltage, then it may be fine for short term charging, the load on it will bring the volts down. But it sounds like something entirely unsuitable for leaving connected more than a few hours.
Is it by any chance a big heavy thing with a simple transformer in it?

There may be more to it than meets the eye, but from what you've said I would advise caution!

 

[cygnusv]

The voltage, at the batteries, is actually 34.5. The unit is a Nueva Elettra 24/30. I believe that it's electronically controlled rather than a simple transformer. It certainly seems very modern. It's described as a fork truck charger.

 

[pvb]

The voltage, at the batteries, is actually 34.5.

That's too high for boat batteries. Can you return it for a refund?

 

[Lon nan Gruagach]

You could use diodes to drop the voltage... Would need to know the current though.
This https://cpc.farnell.com/stmicroelectronics/stth6012w/diode-ultrafast-60a-1200v/dp/SC11403 would probably do. Well, 8 of them in series.

 

[lw395]

The voltage, at the batteries, is actually 34.5. The unit is a Nueva Elettra 24/30. I believe that it's electronically controlled rather than a simple transformer. It certainly seems very modern. It's described as a fork truck charger.

To raise a decent size bank of nominally 24V batteries to 34.5V would imply a lot of current flowing.
Do you hear lots of bubbling/fizzing?
I'd suggest checking everything from the basics.
Disconnect charger, measure battery voltage and charger open circuit voltage.
Trust nothing!
Your meter could be broken, your charger could be faulty.
Your batteries might be connected wrong.
Measure the current.

 

[William_H]

To raise a decent size bank of nominally 24V batteries to 34.5V would imply a lot of current flowing.
Do you hear lots of bubbling/fizzing?
I'd suggest checking everything from the basics.
Disconnect charger, measure battery voltage and charger open circuit voltage.
Trust nothing!
Your meter could be broken, your charger could be faulty.
Your batteries might be connected wrong.
Measure the current.

Agree completely. Digital multimeters start to read excessively high when battery gets low. Check with another meter. Make sure you are measuring voltage at the actual lead post of the battery. Make sure the connection between the 2 12v batteries is good. (check voltage across this lead terminal to terminal). As said check actual current going in to the batteries.
If indeed the charger is pushing 30 amps or so into your batteries at a terminal voltage of 34.5 then you need to disconnect as it will boil the batteries. This would one might imagine indicate a bad charger.
If you want to reduce the voltage then a regulator like this would enable you to set the charge voltage and limit current which would mean you could leave the charger on 24/7 but would mean a much lower charge current fro recovering from discharge. https://www.ebay.com/itm/10-50V-to-...905831?hash=item5b016c68a7:g:HfQAAOSw7FRWXUFe or perhaps you can find a higher current buck regulator but check capability for higher input voltage. ol'will

 

[penberth3]

To raise a decent size bank of nominally 24V batteries to 34.5V would imply a lot of current flowing.
Do you hear lots of bubbling/fizzing?
I'd suggest checking everything from the basics.
Disconnect charger, measure battery voltage and charger open circuit voltage.
Trust nothing!
Your meter could be broken, your charger could be faulty.
Your batteries might be connected wrong.
Measure the current.

Also check you've selected DC volts on the multimeter.

 

[Bilgediver]

I've bought (cheap!) a 24 volt 30 amp heavy duty battery charger. It's basically meant for deep cycle truck batteries. The output voltage is 34 volts. I'd like to reduce this to 28 volts if possible to avoid damaging the batteries I want to use it on.
For simplicity I wondered if some kind of resistor could be used in the positive charger output cable?
On the face of it this question doesn't sound very boaty I know....... But it is.
Many thanks. Stu

You describe this as a cheap charger then refer to it as a fork lift charger later on. Is it possible that when used in its former life it was used as a a plug in device to the fork lift. Do you have this plug and can you confirm if it is two or three pole. If three pole then the third pole maybe voltage sense might be worth investigating. It sounds as if it is not regulating if your readings are correct.