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

Sorry mate but unless.You.buy a dedicated.24v panel.and regulator that will let you run.that panel.to.charge a 12v system, thats unlikely to work.


What you could.do is buy a small 12v-24v dc/dc charger and wire that to the switch so you can boost the 24v batteries a little.while.the panels are getting full sun. Realistically though I don't think your be taki.g that much out of the truck batteries that you'd. Have to worry about charging them.

You could also just look at pairing a small pair of 25w panels with a cheapy regulator just to keep the trick batteries up.

Uh - ok. My diagram is a simplification. Each panel in my diagram is a pair of panels in real life. So there are 3 pairs of panels, of 2 each in series = 6 panels altogether, 100w per actual panel. From a wiring point of view, the are effectively just 3 panels though.

For each panel pair:
- VOC is 45v
- VMP is 38v
- 200 watts combined

The MPPT will take the 38v and convert it back to 24v no problems. The other MPPT will also take 38v and convert it to 12v. That's how come I can switch from the 12v to the 24v system. Seemed like the simplest solution to me.

These are similar to the panels I am using - flexible (although that is irrelevant in my application) and very light weight: 100w-flex-solar-panel

Hope that clarifies things.

Thatd work.

But..

My advice on flexi panels is "unless your going to mount them on a surface permanently.... Don't".

I have used industrial double sided tape from Germany + 4 rivets to hold each panel down. They ain't never coming off

Originally Posted by spudboy

I have used industrial double sided tape from Germany + 4 rivets to hold each panel down. They ain't never coming off

Challange accepted, where will you be parking.this thing?

The earth line went in on Saturday. No smoke

Everything is working very happily, on both the 12v side and the 24v side. Both MPPT's are charging as expected, and after only 1 days charging both battery banks are running at 'full' voltage.

Thanks all for your assistance. Much appreciated.

Now that Spudboy's original question has been answered, may I ask a slight variant to the question?
I have read the thread but am a bit lost in converting the wisdom given to my system.

I have a 24v system in my FFR, which has its own alternator/generator (unsure), is shielded to run sensitive electronics and hence I reckon doesn't use a common ground with the 12v vehicle system. I could well be wrong though.

I wish to run a pair of 12v Engel fridges from this 24v system. If I purchase a 24v-12v DC converter of around 15 or 20 amps, and run my fridges direct from this (perhaps with fuses?) will I run into this floating circuit short risk?


I would also have other 12v items running from this system, such as phone chargers, UHF radio and camp lighting.
I know I could purchase one or two 12v/24v/240v fridges but already have two perfectly good 12v/240v fridges and a small budget.

I would personally have a 12v battery in the system charged by a 24v-12v Dc-Dc charger and run your gear off the 12v battery.

However what you have described would work but irrespective of whether you run my system or the one you propose you will need to have something in place to protect your starter batteries from discharge. In my system the 24v-12v system would only work when the ignition is on - but then I have the extra storage capacity of the spare battery.

Oops - just reread your post - I assume your actual car systems, starter, lights etc are 12v so you also have a 12v alternator and 12v battery.

If so then yes your system will work as you have outlined - treat your 24v system as an aux battery system and manage accordingly - get a solar system with a 24v capability as a backup.

Cheers

Garry