Ignition Live under Passenger Seat
- Thread starter t0mb0
- Start date
No there’s not mate.
as @Deaky says . . . . . but
While not an ignition feed as such,
you can use the BCM feed as a switched 12v feed which is live when the "engine is running".(just be sensible and dont try a draw 50 amps from it) (we used the BCM feed to switch our REDARC but also KEPT the AUX relay and used that as a switch to shunt the load from the AUX battery for any circuits that needed ignition or engine running only feeds, via a new fuse box)
But if you want a separate 12v live when the key is on the accessory position your need a new feed from the center line of the under dash center fuse box.....
looking at @Captain Backfire s pic above it looks like the AUX battery feed 100A fuse and relay at the top left.
then all the mid loom connectors at the bottom, which will be the rear PDC loom, passenger seat loom, and some other bits from the rear that i dont have on my PV.
While not an ignition feed as such,
you can use the BCM feed as a switched 12v feed which is live when the "engine is running".(just be sensible and dont try a draw 50 amps from it) (we used the BCM feed to switch our REDARC but also KEPT the AUX relay and used that as a switch to shunt the load from the AUX battery for any circuits that needed ignition or engine running only feeds, via a new fuse box)
But if you want a separate 12v live when the key is on the accessory position your need a new feed from the center line of the under dash center fuse box.....
looking at @Captain Backfire s pic above it looks like the AUX battery feed 100A fuse and relay at the top left.
then all the mid loom connectors at the bottom, which will be the rear PDC loom, passenger seat loom, and some other bits from the rear that i dont have on my PV.
But I thought the bcm feed wasn’t high all the time the engine was running? I thought it was only high when the ecu decided the leisure battery needed charging so it could flip the relay and join the two batteries to jointly take charge from the alternator?
Nope, the BCM feed switches live when the engine has started..
Then cuts out when the engine has stopped.....same happens with stop/start/regen. the relay clicks on and off all the time.
so when the engine has started the factory AUX relay connects the 2 batteries together, then disconnects.
weve also found out that there is no feedback to the ECU for monitoring the AUX battery charge level....
its just a factor of how much current the AUX battery will draw when its charging when the egine is running.
The ECU & BCM monitor the current at the starter battery and also the Alternator output to keep the starter battery at about 80% SOC state of charge. so that regen braking can pulse charge the battery (about 15v under braking)
If a high load is switched on like the AC or heated seats etc the ECU will call for a higher output from the alternator and dissable the start/stop function for that duration....
even when all this is going on..... the AUX BCM switched relay will be ON as long as the engine is running.
see here for more details >>>>>>
Stop/start...regen...smart Alternator... Dc-dc Charger For Leisure Battery Or Not?
there is a graph about half way down that details the exact switching of the relay via the BCM feed.
Then cuts out when the engine has stopped.....same happens with stop/start/regen. the relay clicks on and off all the time.
so when the engine has started the factory AUX relay connects the 2 batteries together, then disconnects.
weve also found out that there is no feedback to the ECU for monitoring the AUX battery charge level....
its just a factor of how much current the AUX battery will draw when its charging when the egine is running.
The ECU & BCM monitor the current at the starter battery and also the Alternator output to keep the starter battery at about 80% SOC state of charge. so that regen braking can pulse charge the battery (about 15v under braking)
If a high load is switched on like the AC or heated seats etc the ECU will call for a higher output from the alternator and dissable the start/stop function for that duration....
even when all this is going on..... the AUX BCM switched relay will be ON as long as the engine is running.
see here for more details >>>>>>
Stop/start...regen...smart Alternator... Dc-dc Charger For Leisure Battery Or Not?
there is a graph about half way down that details the exact switching of the relay via the BCM feed.
If the relay is closed as long as the engine is running, I really don’t understand how the batteries can persist for so long with very different levels of charge. I also measure very different voltages on each battery whilst the engine is running - far more than would be accounted for by cable voltage drop etc.
Did you run your experiments under a scenario where the leisure battery is near full? Because, whilst sometimes I see up to around 15amps swing in/out of the leisure battery when the relay is closed, sometimes when the leisure battery is close to 100% it doesn’t equalise with the starter at all - even when starter is low. It was because of this that I assumed the bcm only closed the relay when the leisure battery was below a certain level.
Weve metered out (with a clamp meter) about 18A of charging current coming into the Aux battery via the relay when the Aux battery is a lower SOC.
as the AUX battery charges . . . say on a long drive the SOC of the AUX battery increases, in proportion the current reduces.
so when both batteries are fully charged there is no current flow.
Current will only flow when there is a difference in potential (voltage), so when the AUX battery is low it will draw current from the starter battery and alternator when the engine is running.
Now on the flip side if the AUX battery is MORE charged than the starter battery say from solar etc then it has been seen the the AUX battery will BACK FEED current into the starter battery when the OEM BCM relay is engaged.
This has been witnessed by others on here with the Cally setup and the fancy panel on the roof that shows leisure battery setups etc. (was shown as -18A)
So in a Nutshell the BCM will do its thing to see that the starter battery is always at 80% SOC.
due to the nature in how the split charge relay joins the starter and Aux batteries together you would expect the AUX battery to also reach a 80% SOC.
@mmi done some nice readouts in the other thread. proving that his setup worked fine and kept both batteries at about 80% SOC.
in my case i think the EFB+ battery was a bit duff and squewing my early results.
So the general idea is to swap-out the factory relay for a DC-DC charger.
this will then allow the Aux battery to reach 100% SOC and NOT allow it to back-feed into the starter battery.
and the other preferred method is to fit solar charger to keep the leisure battery/ies topped up.
as for the voltage levels, i had multi meters connected up to the batteries similar to how @mmi did....
when the BCM relay was connected i saw very similar voltage levels across both batteries.... (maybe 0.4v difference lower on the Aux battery due to cable volt drop)
both batteries showed the 15v regen spikes.
BUT only the starter battery showed the 9.6V drop when the motor was cranking in start stop mode, this was due to the relay isolating the AUX battery.
as the AUX battery charges . . . say on a long drive the SOC of the AUX battery increases, in proportion the current reduces.
so when both batteries are fully charged there is no current flow.
Current will only flow when there is a difference in potential (voltage), so when the AUX battery is low it will draw current from the starter battery and alternator when the engine is running.
Now on the flip side if the AUX battery is MORE charged than the starter battery say from solar etc then it has been seen the the AUX battery will BACK FEED current into the starter battery when the OEM BCM relay is engaged.
This has been witnessed by others on here with the Cally setup and the fancy panel on the roof that shows leisure battery setups etc. (was shown as -18A)
So in a Nutshell the BCM will do its thing to see that the starter battery is always at 80% SOC.
due to the nature in how the split charge relay joins the starter and Aux batteries together you would expect the AUX battery to also reach a 80% SOC.
@mmi done some nice readouts in the other thread. proving that his setup worked fine and kept both batteries at about 80% SOC.
in my case i think the EFB+ battery was a bit duff and squewing my early results.
So the general idea is to swap-out the factory relay for a DC-DC charger.
this will then allow the Aux battery to reach 100% SOC and NOT allow it to back-feed into the starter battery.
and the other preferred method is to fit solar charger to keep the leisure battery/ies topped up.
as for the voltage levels, i had multi meters connected up to the batteries similar to how @mmi did....
when the BCM relay was connected i saw very similar voltage levels across both batteries.... (maybe 0.4v difference lower on the Aux battery due to cable volt drop)
both batteries showed the 15v regen spikes.
BUT only the starter battery showed the 9.6V drop when the motor was cranking in start stop mode, this was due to the relay isolating the AUX battery.
to test it yourself,
you your meter.
take out the AUX relay, the 2 larger terminal are the feed/load side(one side starter battery, other side AUX battery)
The 2 smaller terminals are the perm ground Ov (brown i think ) and the BCM 12v+ switched feed.
i inserted (carefully) 2 small wires into the 2 small terminals to meter out the BCM switch feed. You will the see the 12v switch on/off when the engine starts and stops.
Now you need 2 meters for the next bit.
move your jumper wires over to the big terminals and connect a meter to each.
with the engine not running you will see the voltage of both of the battery's on each meter.......
when the engine starts and the relay closes you will see the voltages should be the same.
I understand all of that, and have measured up to 15 amps swing out of the aux battery and into the starter when the relay is obviously closed and the two batteries have unequal potential differences.
However, I have also observed the leisure battery being at 100%, the starter being far lower and no equalisation occuring over a significant drive which lead me to my original assumption that the ecu opened the relay when the leisure battery was near full. Have you done your experiments in a scenario when the leisure battery is close to 100% which would allow you to confirm or disprove my assumption?
However, I have also observed the leisure battery being at 100%, the starter being far lower and no equalisation occuring over a significant drive which lead me to my original assumption that the ecu opened the relay when the leisure battery was near full. Have you done your experiments in a scenario when the leisure battery is close to 100% which would allow you to confirm or disprove my assumption?
yep done that.
relay stay closed 100% of the time engine running.
it only drop's out when engine switch off.
super easy to test yourself and see on a long drive to prove the point.
relay stay closed 100% of the time engine running.
it only drop's out when engine switch off.
super easy to test yourself and see on a long drive to prove the point.
Ok, I’ll try and do some more measurements. This time I’ll measure the bcm feed directly rather than just current flow on the aux and voltages on both batteries.
My results with significantly different voltages and no equalisation are a bit of a puzzle currently, and not consistent with your results.
My results with significantly different voltages and no equalisation are a bit of a puzzle currently, and not consistent with your results.
cool, do your tests and post them here, . . . . . . the more pic the better.
just take pics of your meter readouts and setup.
a picture says a 1000 works etc.
just take pics of your meter readouts and setup.
a picture says a 1000 works etc.
If the aux battery is 100% charged the voltage would be about 12.8 Volts. As long as alternator keeps the voltage at or above that level the aux battery would stay fully charged as there would be no current flow out of the aux battery.
The voltage would be below that only when alternator is idling but even then not much below. I think these are the moments when those 15 Amp currents out of the aux battery are seen.
Checked a few recordings but in those for some reason (low main battery?, other loads??) I rarely saw main battery voltage below 13 Volts, so would be a kind of expected to see aux battery stay fully charged in those cases. Anyways, obviously need to do some more experimenting…
Hi, i'm a newbie, I was looking for a Live + under Seat for turning on the dc-dc charger and I found a (I hink so) usable pin.
The #2 pin in the left of the yellow connector is 0 volt without the key And +10 with key pos1 (Contact) and ignition Live.
I use a delay relay to start the dc-dc within 8secs from key insert.
I got a T6 multivan outdoor 2018.
(Sorry for my english, I'm from Spain and the spell check is crazy when writting other languajes haha)
what color is the wire?
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T17F - brown plug (17 pin conector) (pin2__) what colour wire?
pin#2 is - T17f/2 brown wire - rear PDC sensor wire?
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T17F - brown plug (17 pin conector) (pin2__) what colour wire?
pin#2 is - T17f/2 brown wire - rear PDC sensor wire?
It looks grey with a black stripe on my screen, but I can’t be certain.
