Where's The Fuse For Leisure Battery Relay Feed

T

t0mb0

Senior Member
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T6 Legend
Hi,

I've installed a DC-DC converter with the signal wire which was controlling the factory split charge relay into the D+ input to tell the DC-DC when to run. When I first fitted and tested it last weekend, it was running fine.

However, now the D+ signal isn't going high when the engine is running and hence the DC-DC convertor isn't turning on.

Where is the fuse for the relay/D+ signal wire?

(I've just bought forum membership to look at the fuse layouts but I don't think it's activated yet)

Thanks very much,

Tom
 
Welcome to the VIP Club @t0mb0

The D+ comes from the BCM, so im assuming that the fuse will be one of the numerous BCM supply fuses . . . . .

Have to tried disconnecting your DC-DC kit from the D+ line to see if it recovers after a key cycle?

heres a layout . . . . .

split charge.JPG

.

The BCM supply fuses are labled "On Board Control Unit"

Fuse Card


VW T6 Fuse Boxes - Overview Of Fuse Holder Vehicle Locations


VW T6 Fusebox - Fusebox/Fuse Chart SB - Engine Fusebox

VW T6 Fusebox - Fusebox/Fuse Chart SF - Lower Dash Fusebox Listings

VW T6 Fusebox - Fusebox/Fuse Chart SD - Lower Dash Fusebox Listings

VW T6 Fusebox - Fusebox/Fuse Chart SA - Primary Battery Fusebox

VW T6 Fusebox - Fusebox/Fuse Chart SC - Lower Dash Fusebox Listings

.
 
t0mb0 said:
However, now the D+ signal isn't going high when the engine is running and hence the DC-DC convertor isn't turning on.
Click to expand...
Hmmm... the battery management might have a its own mind. Did you check that the alternator is really charging. As the alternator sometimes just idles after starting the engine the possibility I'm thinking is that the signal to split charge relay is not yet activated. A definite sign of alternator idle is that engine battery voltage is (way) less than 12.6 Volts when engine is running. Unfortunately haven't actually thought/checked the status of split charge relay signal then.
 
Thanks Dellmassive. That split charge diagram doesn't appear to show a fuse on the control feed and I haven't yet found anything that sounds like it in the multitude of fuse locations - I'll keeping looking.

I'm pretty sure that the D+ isn't activating at all (rather than the DC-DC not registering it) as I'm also using it to switch a separate relay which definitely isn't activating either. I'll poke around with a meter later this morning and confirm.

We're off camping next week so, worst case, I'll just have to wire the D+ input up to a manual switch if I can't work out why the D+ isn't going high when the engine is on.
 
mmi said:
Hmmm... the battery management might have a its own mind. Did you check that the alternator is really charging. As the alternator sometimes just idles after starting the engine the possibility I'm thinking is that the signal to split charge relay is not yet activated. A definite sign of alternator idle is that engine battery voltage is (way) less than 12.6 Volts when engine is running. Unfortunately haven't actually thought/checked the status of split charge relay signal then.
Click to expand...

Yes, I think this is a possibility and it's consistent with some earlier tests I did trying to work out what was going on with the factory split charge. However, everyone else on the forum seem adamant that the relay was closed without fail when the engine was running so I'm still hoping they're right because I'm relying on it for my DC-DC converter to turn on!
 
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Previous testing showed that the D+ goes live when the engine was started, possibly triggered from the RPM signal, and shuts off when the engine is off during stop/start events.


So you need to check with a meter what the D+ line is doing.

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aux ss test 1105189.JPG .

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Last edited:
I've had a closer look at it - it turns out the D+ signal is fine after all. Unfortunately, the DC-DC unit isn't - it seems to have blown an internal fuse so I need to hassle the manufacturer. Installation looks fine and none of the external fuses on either the input or output have blown so it's a bit of a mystery why it's self-destructed. :(
 
It's a Votronic 3324 (model number: VCC 1212-30). I bought it because it's very compact (I have very little space under the passenger seat) and I have the equivalent solar MPPT controller which has worked very well.
 
Ok.. I wonder if your unit didn't like the 15v dc you get on the D+ line during regen braking...... or the constant on/off switching you get with stop/start.?

We've got the Redarc 1240LV and has been great.

The Victron MPPT is also highly rated..
As is the DS.
 
The Votronic unit is specifically designed for Euro 6 start/stop engines and the specification for the D+ line is 8-17v so it really shouldn't have had an issue there.

Which Victron unit are you referring to? I couldn't see a vehicle DC-DC unit in the Victron range.
 
Sorry... ment the Victron MPPT as a stand alone solar controller. Not sure if they do a DC-DC with out looking.

The Redarc can be used with solar (need to fit a change over relay)...

But I use a separate MPPT & DC-DC
 
Oh I see. I'm using a separate MPPT and DC-DC too because my solar panel voltage is too high for most combined units.
 
What about if you set your solar panels in parallel to drop the voltage? (But will increase current)
 
I can't - it's only one panel! It's a 250w unit with a maximum open circuit voltage of 36v.
 
Just be aware those aren't true battery-to-battery chargers, they are simply DC-DC converters intended for 12v appliances on a 24v system or vice versa.
They are more akin to a PSU, of course any excess voltage will charge a battery but these dont have the bulk/absorbtion/float phases that you might be expecting.
Cheers
Phil
 
Yeah, Victron really need to pull their finger out and do a proper DC-DC unit with decent combined MPPT solar input with their snazzy bluetooth functionality.

As far as I know, it’s only the Ring unit that can take larger solar panels and that thing is huge (and seems to have had some reliability issues).
 
Its a convoluted option, but you could use a DC-DC to drop the panel to half voltage at double current, to feed a LV solar input... you'd lose mppt but you could manually set the DC-DC to near the mpp. Its a daft idea ;)
 
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