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

That is exactly the same piece of kit that I have to go into my vehicle. I have the 60 amp OEX version - same piece of hardware just a different brand.

Cheers

Garry

A word of warning spudboy, take notice of what Garry posted up because as you are now adding the step-down device, if you do not setup your system with a single common earth you risk causing a fire.

With any form of step-down device, the device needs a reference point to control the output voltage.

This reference point is made through the negative circuit of both the 24v supply and the 12v output source.

If the device is not connected to a common earth for both voltage circuits, the step-down device could float and in a worst case, you could have 24v being supplied to your 12v circuit.

( EDIT ) Also note, as you had questioned the use of fuses in the negative circuits of your set up, as these devices create a common earth through them internally, do not fit any fuses in the earth circuit of either the 24v or 12v, to avoid a floating circuit situation being created.

At best this would cook your 12v batteries but at worst, it will cause a fire in the 12v circuits wiring and/or appliances connected to the 12v circuit.

Again, you really don’t know what you are doing and because of the complexity of dual voltage systems, I strongly recommend you get an auto electrician to do the work for you.

Originally Posted by drivesafe

...
Again, you really don’t know what you are doing and because of the complexity of dual voltage systems, I strongly recommend you get an auto electrician to do the work for you.

That's why I am here asking questions

The common earth will be going in this weekend.

Hi spudboy and I am not having a go at you.

Working with a single voltage circuit is easy enough to talk someone through but dual voltage systems are not only difficult but as posted, can very easily lead to damage and fires.

I was quite serious when I suggested you get the work done by someone who has an idea of how it needs to be done.

Having stated the above, if you want to go ahead and do it yourself, start by drawing up a circuit diagram and posting it up here and we can then try to make sure all safety guards are in place before you start wiring.

By the way - what vehicle are we talking about? Certainly on all my vehicles the body or chassis is the common earth but I appreciate all vehicles may not be the same.

Cheers

Garry

Originally Posted by spudboy

Thanks for all that info Garry.

BTW - I have a special 24v - 12v device from GSL that is designed to charge 12v batteries when the vehicle is 24v.

This puts you into the category of techy stuff where you need to pay attention.

In most cases the simplest solution will work without any problems. It's what happens when you have a failure that can get entertaining. And I mean that in the "oh look my campers burning to the ground with everything in it, wheres the marshmellows?" Kind of way.

Garry

What is being said is to put all the zero potential voltages -v to a common terminal in order to have 0v between the earths ---I realise what you are saying BUT there can be bad crimping of terminals ,solder joints on lugs causing high resistance ,loose connections onto chassis etc.

If all earth connections are to a common point there is less pontential for stray voltages

Originally Posted by muddy

Garry

What is being said is to put all the zero potential voltages -v to a common terminal in order to have 0v between the earths ---I realise what you are saying BUT there can be bad crimping of terminals ,solder joints on lugs causing high resistance ,loose connections onto chassis etc.

If all earth connections are to a common point there is less pontential for stray voltages

Yes agree if it is practical - in my 101 if I was to do that I would have heavy duty earth cables running up to 4 feet just to get to a common point. I have each alternator obviously earthed through the engine which has earth straps to the chassis and the body. 24v battery earthed on the gal capping behind the passenger seat and 12v battery earthed on the gal capping behind the drivers seat - both integral components of the front body which is earth strapped to the chassis.

To me - in most circumstances it is not necessary to go for a common earth with all its extra cabling as the common earth is the body/chassis - but as you have highlighted you do need to make sure it is a good earth.

However if Spudboy prefers a common earth point that is fine.

Cheers

Garry