Thread: 12V and 24V on same vehicle. Can they share same earth (-ve)? Or keep separate?

Same neg is fine.
And yes, connect the negs on the batteries.

Am I thinking about it too much

I was concerned about some sort of voltage leak, but looks like it is nothing to worry about.

So, should I explicitly connect the -ve of both system together with some nice heavy wire? This would definitely tie the negatives to the same voltage potential.

Best practice is to have the negs on the batteries linked. Big cable is better.

No worries - I'll do it with a HD cable from 12v -ve to 24v -ve terminal (and not through the chassis).

Thanks for the advice.

Years ago it was common for batteries to have an external link on the top to link the cells.

Now if you wanted less then 12 volts you would take the -ve from the negative terminal or a point on the engine/chassis. You would then take +ve from a point along the battery top to get the required volts at 2.1 volt increments.

Same would apply to a 24 volt system.

Spuddy you are thinking about it too much. My 101 has a 24v alternator, a 12v alternator, a 24v battery bank and an aux 12v battery - all are just earthed to the nearest convenient spot as are the various 24v and 12v accessories. You just need to make sure the 24v and 12v positive systems live on different circuits as 12v systems don't run for long on 24v.

Cheers

Garry

Ok folks, you really need to stick to the correct electrical symbols, and in this case, with different positives, it is imperative to use the correct symbols.

-ve and +ve are electronic schematic symbols and are not used in automotive electrical circuits, plus they have a completely different meaning to what is being discussed here.

-ve means voltages below 0v or ground, and would be displayed with an actual voltage, EG -12v. or if no exact voltage is known or there is a variable voltage, it is marked as -ve.

So this symbol has nothing to do with this or any other automotive electrical circuit and as above, in this specific case, could lead to erroneous ASSUMPTIONS.

+ve is also a non automotive electrical symbol and in ALL DC CIRCUITS any number is automatically deemed as being volts above 0v, EG 12v and 24v.

Hi spudboy and to your question, as others have posted, the negative of all batteries and appliances would normally be connected to a common ground or earth, like the chassis.

If you do not set up a common ground or earth you will end up with one or two FLOATING circuits and in extreme cases could cause shorts to occur in the positive and negative circuits.

This is just a suggestion but if you are setting this up from scratch, try using specific colours for the two different voltage positives.

Start by using Black for all negative circuits.

Use Red for the main 12v supply and Red with a trace colour for 12v circuits.

Then say Yellow for the main 24v supply and Yellow with a trace colour for any 24v circuits.

I must be stoopid or something.

In the 12V system battery A is Neg ground and Pos for 12V.

In the 24V system battery B is Neg ground and Pos is bridged to Neg on battery C and 24V is supplied from Pos on Batt c and ground.

We used to use 24V aircraft starter motors as winches and used one Pos ground battery and one Pos ground battery. Power was supplied by a Neg ground alternator and a second Pos ground alternator (made by reversing the diodes in the alternator and having a an external Pos ground regulator. 24V was across the non ground terminals and the main vehicle system ran off one side usually the Neg ground system.