Electrical problem with camper control unit, lights, fridge after short circuit

[yossarian]

There is a brown cable coming off the rear battery negative terminal and going somewhere unknown, goes up behind the inverter and behind the cupboards. If we disconnect it the control panel gives a voltage error, even though the accessories keep working. Do you think this goes to the shunt?

This sounds like the cable indicated by the rightmost green arrow on the screenshot I posted. The colour matches too.

 

[yossarian]

The resources section has a shunt repair guide. It involves putting up the roof and taking out the fridge.

 

[yossarian]

That brown cable is an odd size too considering it will carry the full leisure system current.

 

[benArrayx]

Do you see instant voltage fluctuations that tie up with the current draw increasing from 5A to 20A? If so then your shunt is probably ok

At the moment it's only draining 6A, no massively visible voltage fluctuation at the mo. There's no rhyme or reason that I can see for when it goes up to 20A drain, but anyway it's not happening at the moment. I'll keep an eye on it and the voltage readings...

 

[sidepod]

sounds like it yes, probs this link

 

[yossarian]

At the moment it's only draining 6A, no massively visible voltage fluctuation at the mo. There's no rhyme or reason that I can see for when it goes up to 20A drain, but anyway it's not happening at the moment. I'll keep an eye on it and the voltage readings...

The ammeter must misread if you have connected an alternative path to ground.

The reading is based on a small voltage appearing across the shunt when current is flowing through the shunt. Bypass the shunt (which you have done) and the readings are probably meaningless.

The brown wire is supposed to connect to the shunt and the shunt to the left wheel well earth point.

As you have no continuity to chassis ground one of those three things, brown wire, shunt or wire from shunt to earth must be faulty.

 

[sidepod]

That brown cable is an odd size too considering it will carry the full leisure system current.

sized for voltdrop so the shunt remains accurate?

 

[yossarian]

sized for voltdrop so the shunt remains accurate?

Could be.

Rambling a bit here I know but:

The 'voltage fault' with brown cable disconnected proves that the brown cable is not totally open circuit. So the most likely break in the path is probably the shunt.

 

[benArrayx]

The ammeter must misread if you have connected an alternative path to ground.

The reading is based on a small voltage appearing across the shunt when current is flowing through the shunt. Bypass the shunt (which you have done) and the readings are probably meaningless.

The brown wire is supposed to connect to the shunt and the shunt to the left wheel well earth point.

As you have no continuity to chassis ground one of those three things, brown wire, shunt or wire from shunt to earth must be faulty.

Ok I'm going to assume it's the shunt for now and try and find a replacement before starting to open everything up.

Thanks so much for the help guys, it's really very much appreciated!!! I'll let you know how I get on

 

[benArrayx]

I just checked and after an hour of having the extra earth bridge connected and reading 4-8A drain with no appliances switched on, voltage has not dropped at all. The other day when it drained to 10.5V I had the fridge on. So I can definitely assume that amp usage reading as erroneous.

 

[benArrayx]

I just checked and after an hour of having the extra earth bridge connected and reading 4-8A drain with no appliances switched on, voltage has not dropped at all. The other day when it drained to 10.5A I had the fridge on. So I can definitely assume that amp usage reading as erroneous.

I just realised that I've got the solar panels connected and it's charging so that wasn't a good test either! Anyway, I still think it's the shunt so heading off to find a VW dealer now!

 

[benArrayx]

It was the measuring resistor at the earth shunt (N162 in the wiring diagrams), replaced yesterday and all working perfectly again

Thanks again for the help guys, really appreciated!!

 

[kurienp]

View attachment 98380
It was the resistance measuring thing at the earth shunt (N162 in the wiring diagrams), replaced yesterday and all working perfectly again

Thanks again for the help guys, really appreciated!!

Well, the safety systems worked as they should.

How did you/the dealer get to that location? Did you remove the fridge, or did you use the "cut a hole behind the rear leisure battery" method?

Any after repair pics?

 

[benArrayx]

I fixed it with a mechanic friend, we removed the fridge and it's directly accessible there, was surprisingly easy to remove the fridge. It took us 40 mins in total from start to finish.

I didn't take an after repair pic no, this one is from the earth shunt repair guide and shows what it's supposed to look like when intact:

 

[sidepod]

Well done. Good work. Try to "keep the smoke in the box" next time.

 

[Kernowboy]

Great thread for all the right reasons. Well done all, the team works.