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

[benArrayx]

Hi all, i have a problem with my T6 Ocean after having made a short circuit from the leisure battery under the front seat to the engine battery, mistakenly connecting positive leisure to negative engine. Sparks flew briefly and then stopped. After this, the camper control unit was dead unless the engine was on, or the van was plugged in to the mains.

I'm now with a mechanic friend, we found 2 blown fuses, the first one the second leisure battery in the boot (75A), on the positive terminal, we replaced this, the second in the fuse box underneath the engine battery (100A), also replaced.

We have checked every single other fuse behind the bottle holder in the centre console, underneath the seat where the battery is, and in both engine compartment fuse boxes, all are ok.

The problem we are left with, is that the camper control unit will only turn on with the engine off, if we make a connection from the under seat battery negative terminal to the van body. With this connection made and no engine on (no ignition either), the camper control unit comes on and everything works normally, except for a weird 4A-15A constant drain on the leisure batteries which obviously shouldn't be there.

Having looked at the electrical schematics available on the download section, it's clear that the battery under the seat should be connected to earth (ie the van body if I understand correctly, I'm not an electrician!), but for some reason seems not to be, given that without making an extra connection the control unit is off, and making an extra connection turns it on. The negative cable between the two leisure batteries is intact, we tested for continuity of that cable.

Does anyone have any idea of what could be the problem with the under seat battery connection to earth after having short circuited the under seat battery with the engine battery and having fixed the blown fuses?

We have connected to van diagnostics (ie via OBD) but there are no errors.

Any help really appreciated

 

[WelshGas]

Hi all, i have a problem with my T6 Ocean after having made a short circuit from the leisure battery under the front seat to the engine battery, mistakenly connecting positive leisure to negative engine. Sparks flew briefly and then stopped. After this, the camper control unit was dead unless the engine was on, or the van was plugged in to the mains.

I'm now with a mechanic friend, we found 2 blown fuses, the first one the second leisure battery in the boot (75A), on the positive terminal, we replaced this, the second in the fuse box underneath the engine battery (100A), also replaced.

We have checked every single other fuse behind the bottle holder in the centre console, underneath the seat where the battery is, and in both engine compartment fuse boxes, all are ok.

The problem we are left with, is that the camper control unit will only turn on with the engine off, if we make a connection from the under seat battery negative terminal to the van body. With this connection made and no engine on (no ignition either), the camper control unit comes on and everything works normally, except for a weird 4A-15A constant drain on the leisure batteries which obviously shouldn't be there.

Having looked at the electrical schematics available on the download section, it's clear that the battery under the seat should be connected to earth (ie the van body if I understand correctly, I'm not an electrician!), but for some reason seems not to be, given that without making an extra connection the control unit is off, and making an extra connection turns it on. The negative cable between the two leisure batteries is intact, we tested for continuity of that cable.

Does anyone have any idea of what could be the problem with the under seat battery connection to earth after having short circuited the under seat battery with the engine battery and having fixed the blown fuses?

We have connected to van diagnostics (ie via OBD) but there are no errors.

Any help really appreciated

Have you checked the continuity of the Earth connection from the front Leisure Battery to earth/chassis earthing point AND continuity from that earthing point to another chassis point.

 

[benArrayx]

We can't find the chassis earthing point for the front leisure battery, the cable just disappears off under the carpet, we can see the same cables in the inspection hatch at the bottom of the cupboard under the sink but no sight of any earthing point. Do you know where that should be?

 

[benArrayx]

Have you checked the continuity of the Earth connection from the front Leisure Battery to earth/chassis earthing point AND continuity from that earthing point to another chassis point.

I guess the point is, there is NO continuity from front leisure battery to earth/chassis (have just rechecked this), but nor do we know where that connection is supposed to be made, it not being visible underneath the front seat.

 

[sidepod]

Earth is earth is earth. Location is irrelevant.

 

[sidepod]

If everything works as it should once you’ve earthed the leisure battery then just make that connection permanent to the nearest/easiest part of the chassis.

 

[WelshGas]

I guess the point is, there is NO continuity from front leisure battery to earth/chassis (have just rechecked this), but nor do we know where that connection is supposed to be made, it not being visible underneath the front seat.

This might help. If you want to use the original Earth from front Leisure Battery then you need to follow the Earth under the carpet. Maybe the wire is burnt out.

NB, there is no Earth point for the rear leisure battery.

 

[benArrayx]

If everything works as it should once you’ve earthed the leisure battery then just make that connection permanent to the nearest/easiest part of the chassis.

Problem is it doesn't work as it should, there's a massive drain on the battery for no apparent reason, goes between 4A and 20+A. This is when the extra earth cable is attached and ignition off, all accessories off, no plug in the 220V socket.

 

[sidepod]

Ok start by removing all of the load from that battery. In other words, pull all the fuses on the battery. Check the drain. It should be zero. Replace the fuses one by one and check the drain each time until you find the offending circuit.
Once/if you find it you then need to work on that till you find the fault, which could be a partially melted cable allowing drain to earth.

If the drain is still present with all fuses removed then the fault is between the battery and fuse box. See above for possible fault.

If this second scenario is the case then the next step is to locate the connection at the fuse box that comes from the battery. Disconnect it and install a temporary link. Recheck the drain. If it’s gone then make this temp link permanent.

 

[benArrayx]

This might help. If you want to use the original Earth from front Leisure Battery then you need to follow the Earth under the carpet. Maybe the wire is burnt out.

NB, there is no Earth point for the rear leisure battery.

Thanks WG. we considered the wire being burnt out, which is why we tested the continuity all way along the wire from front to back (while not attached to either battery), and there was continuity. Doesn't this rule out a burnt wire?

From your original reply I think you are saying also check continuity from THAT earth point to another earth point. Will try to do that tomorrow... From the pdf you attached the earth point should be under the carpet and before the cupboard?

 

[benArrayx]

Ok start by removing all of the load from that battery. In other words, pull all the fuses on the battery. Check the drain. It should be zero. Replace the fuses one by one and check the drain each time until you find the offending circuit.
Once/if you find it you then need to work on that till you find the fault, which could be a partially melted cable allowing drain to earth.

If the drain is still present with all fuses removed then the fault is between the battery and fuse box. See above for possible fault.

If this second scenario is the case then the next step is to locate the connection at the fuse box that comes from the battery. Disconnect it and install a temporary link. Recheck the drain. If it’s gone then make this temp link permanent.

Ok thanks for this advice, will try to do this tmw

 

[sidepod]

check continuity from THAT earth point to another earth point.

Given that the van body is one big lump of steel this would seem to be a pointless exercise.

 

[yossarian]

We can't find the chassis earthing point for the front leisure battery, the cable just disappears off under the carpet, we can see the same cables in the inspection hatch at the bottom of the cupboard under the sink but no sight of any earthing point. Do you know where that should be?

My understanding that there is a single earth via the shunt for the leisure battery system. If you are getting bad current readings you should have a look at the shunt and check if it was damaged by your high current. The negative path is not fused (generally not a problem as the positive side is well fused.)

T6 owners will help you find it. It's somewhere in the vicinity of the bottom your fridge I think.

Look for a high resistance (above 0.x Ohms) on the shunt . The higher the resistance the more the control panel will overread the current.

 

[sidepod]

I was working on the basis that the camper control unit functions ok which suggests the shunt is functioning ok ?

 

[yossarian]

I was working on the basis that the camper control unit functions ok which suggests the shunt is functioning ok ?

Let me reread. I thought it was dead until another chassis ground path was connected...

 

[yossarian]

it's clear that the battery under the seat should be connected to earth (ie the van body if I understand correctly, I'm not an electrician!), but for some reason seems not to be, given that without making an extra connection the control unit is off, and making an extra connection turns it on.

This bit says "blown shunt" to me? The ADC may still need consideration...

 

[yossarian]

https://vwcaliforniaclub.com/resources/basic-schematic-of-leisure-electrics.198/download

Leisure electrics work on hookup and with split charge relay closed. The shunt looks like a likely culprit if I look at this schematic.

 

[sidepod]

Seems reasonable, although if the shunt is blown the control panel won’t show a voltage?
It should be simple enough to establish if these two connections and the shunt are in tact.


Worth remembering when checking continuity, this only proves an electrical path. It doesn’t tell you the cable isn’t shorted to earth or another core somewhere along it’s route. Always good to also test a disconnected cable to earth and prove parallel paths.

 

[yossarian]

Problem is it doesn't work as it should, there's a massive drain on the battery for no apparent reason, goes between 4A and 20+A. This is when the extra earth cable is attached and ignition off, all accessories off, no plug in the 220V socket.

Ammeter instability may be an indication problem. A 20A drain should be accompanied by a noticeable drop in the battery voltage. If the battery voltage is stable and your current (A) indications are up and down this is probably a false reading.

Does your control panel indicated voltage tie up with what you see on the battery with a multimeter?

 

[yossarian]

You could prove an indication problem by adding a low amp fuse in line with your ground connection.

 

[yossarian]

I think the paths indicated in green are suspect (wrong colour I'm sorry)

D1 and C1 to the control unit seem to be intact.

https://vwcaliforniaclub.com/resources/vw-t5-wiring-diagrams.7/download

 

[sidepod]

The shunt should visibly be good or bad. It’s essentially a coil of wire wrapped round a bar. If it’s burnt out it’ll be obvious.

 

[benArrayx]

Ammeter instability may be an indication problem. A 20A drain should be accompanied by a noticeable drop in the battery voltage. If the battery voltage is stable and your current (A) indications are up and down this is probably a false reading.

Does your control panel indicated voltage tie up with what you see on the battery with a multimeter?

Battery voltage does drop rapidly with time, they were at 10.5V after 2-3 hours the other day, starting fully charged. That's how I noticed the weird drain.

Yes battery voltage on control panel agrees with multimeter reading.

 

[yossarian]

Battery voltage does drop rapidly with time, they were at 10.5V after 2-3 hours the other day, starting fully charged. That's how I noticed the weird drain.

Yes battery voltage on control panel agrees with multimeter reading.

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

 

[benArrayx]

The shunt should visibly be good or bad. It’s essentially a coil of wire wrapped round a bar. If it’s burnt out it’ll be obvious.

Ok, so location of the shunt is probably under the fridge?! I have no idea how to access that...

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?