Engine Altenator and Battery 12 / 24 VDC

[aarotech]

I have a situation that my altenator is 24 VDC and I have two 12 VDC Batteries. I also have equipment that needs 24 VDC power and some that requires 12 VDC. I understand to series the batteries off the altenator for charging 24VDC. I want to use a common DC GND and between the two batteries use the 12 VDC for the devices needing 12 VDC. Others say I need a DC to DC converter. Why?

 

[gerty]

Are the 12 volt loads isolated from the vehicle ground? How much current do you need for the 12 volt loads ? some 24 volt systems are positive ground what is yours ?

 

[crutschow]

The problem with tapping off between the two batteries is that it unbalances the charging current (and battery charge) between the batteries. Thus if the 12V current required is more than a probably a few hundred mA you will need to use a 24V to 12V converter.

 

[aarotech]

24 VDC System

The 24 VDC is negative gnd, and no the GND is common chassis ground.

 

[aarotech]

Charging Current

Is this an issue Charging current? Current is same in series circuit.

 

[gerty]

If the load is small a dc -dc converter is probably best. If you had a pos ground your 12v stuff (neg ground ) would have to be isolated from it, if it were a radio or such. If you wanted to put on half a dozen KC HIGHLITERS then your load would be sizable , but the polarity wouldn't matter.

 

[aarotech]

24 VDC Charging

The load is actually significant on the 12V but not so much on the 24V. 24V is AB PLC's and some of the control circuits. 12V is Lighting, valve actuators, and lights panel meters.

 

[ronsimpson]

battery equaliser

This problem is very typical in 24 volt systems. Bus, tractors, etc. The alternator charges both batteries with the same current but the load is more on the bottom battery. This overcharges the top battery and undercharges the bottom battery.

**broken link removed**

Years ago I helped design a product like the above. It takes power from the overcharged battery and transfers it to the undercharged battery.

If you can’t get a battery equaliser, you could use a 24 volt alternator for both batteries and a second 12 volt alternator to top-off the bottom battery.

 

[Hero999]

Use a DC-DC converter, I can get you a 100W one for the cost of shipping if you like.

 

[crutschow]

Use a DC-DC converter, I can get you a 100W one for the cost of shipping if you like.

Does that operate from 24VDC?

Otherwise, I think the best would be to use a battery equalizer such as ronsimpson suggested. Several companies make such devices for various power levels.

 

[Hero999]

Yes, if I remember rightly the input is 18V - 32V and the output is 13.8V.