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Backfeeding?

Kimbo

New Member
Joined
Sep 14, 2018
Messages
42
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czech_republic
Hi all. I have a little problem that I’m finding quite interesting, if not frustrating.
My electrical setup in my HZJ78 is a lead acid cranking battery under the bonnet, connected to the CTEK smartpass DCDC system, connected to a 110aH AGM located in the cabin. From the AGM I have a feed powering a 6 way fuse box all leading to hella and usb plugs. So far so good.
On the rear view of the car I have mounted a small LED light bar, which is used for setting up camp and cooking etc. But recently I decided this would also make an excellent ancillary reverse light in difficult locations. My idea was to use the wiring from the fog light (fog light since disconnected and dismantled,- I disagree with their concept), which is activated by a switch in the cabin, connected to the cranking battery. But I also wanted to be able to manually activate the LED bar from the switch on the fuse board panel at the rear of the vehicle, which derives its current from the service battery.
So, one feed from the cranking battery via a dashboard switch to the LED bar, and one feed from the service battery via a switch on the rear of the vehicle. However the fuse in the 6 way fuse box immediately blows when I join the feed from the cranking battery to the feed from the service battery.
I have double, triple checked all polarity. Is it possible this is an issue called Backfeeding? Any experts care to weigh in?
Best regards to all who have read this far!
 
Are you sure you are not connecting them in series somehow so making up a 24volt circuit?
 
The very interesting thing is, the fuse blows even when the cabin switch is in the off position. So it would not be possible to be in series. I’m convinced it’s a short circuit but I have been over the dam thing top to bottom with a multimeter and not detected anything to indicate a short.
 
Ok it’s all sorted out. I’ll post the answer here so it may help somebody else in the future. The switch in the cabin (one of those illuminating LED switches) in the off position was earthing the positive = short circuit. Simple fix by disconnecting the ground from the cabin switch, which means it no longer illuminates, but no big deal.
 
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