Trailer/Caravan Charging from a T6 (Help requested – Voltage Measurements When Towing)

[mmi]

Help – voltage measurements when towing a trailer/caravan requested.

When towing, what’s the voltage at your cigarette lighter socket (in the lower one in the dash)?

No fancy instruments are needed, just any gadget will do.

The following background data is appreciated:
1) Factory/aftermarket tow bar electrics?
2) Trailer with/without a battery and charged via T6 tow bar socket?

Thanks.

Background: I did a few measurements but as I don’t tow very often or long I’m a bit curious if the voltage is always above 14 Volts when towing a trailer - or has it been just a coincidence .

 

[n10n]

Looks like 14.2 - 14.4, unaffected by regenerative charging or DPF regeneration. I think conventional charging scheme might be used with trailer attached.

 

[jayc001]

I have the same cigarette lighter with voltmeter and I purchased it because ai was concerned my fridge wasn't working on the caravan and also charging leisure battery.

I found by Caravelle doesn't automatically start the alternator when tin tent is hooked up. Just sits around 12ish volts. Alternator only kicks in is high load through Bcm detected (headlights, blower etc). For that reason I tow with headlights on.

 

[jayc001]

I have the same cigarette lighter with voltmeter and I purchased it because ai was concerned my fridge wasn't working on the caravan and also charging leisure battery.

I found by Caravelle doesn't automatically start the alternator when tin tent is hooked up. Just sits around 12ish volts. Alternator only kicks in is high load through Bcm detected (headlights, blower etc). For that reason I tow with headlights on.

For reference it's a ECS 13pin electrics. I did have issues getting fridge pin working and despite help from ECS and coding changes was not able to get it to work so used a Tec3m box. Was handy as gives engine switched live under passenger seat for my inverter.

 

[n10n]

I found by Caravelle doesn't automatically start the alternator when tin tent is hooked up. Just sits around 12ish volts. Alternator only kicks in is high load through Bcm detected (headlights, blower etc). For that reason I tow with headlights on.

For reference it's a ECS 13pin electrics. I did have issues getting fridge pin working and despite help from ECS and coding changes was not able to get it to work so used a Tec3m box. Was handy as gives engine switched live under passenger seat for my inverter.

That’s interesting!

I don’t tow often, in fact just today first time with T6, just a trailer for about 100 miles and the voltage sat at 14.2-14.4 throughout. The trailer had old school 7 pin plug so used a 13-7 adapter - maybe that makes a difference?

 

[jayc001]

Mine sits at 14.9 when towing and alternator on (high load or overrun).

I was a little bit concerned the higher voltage may be an issue for caravan electrics but voltage drop means it's not over 14.4 anyhow.

 

[n10n]

Mine sits at 14.9 when towing and alternator on (high load or overrun).

I was a little bit concerned the higher voltage may be an issue for caravan electrics but voltage drop means it's not over 14.4 anyhow.

Is your towbar or prep OEM from factory? Definitely sounds like there’s some differences, maybe coding. Mine never went above 14.4 today like it usually does without a trailer.

 

[jayc001]

I fitted myself and it's 3rd party. No trailer prep so installed under passenger seat and connection to Bcm. It's recognised in VCDS as original part number though and accepts coding changes.

Parking sensors disable and screen shows trailer connected so I'd have though it would trigger charging OK but doesn't.

 

[n10n]

I fitted myself and it's 3rd party. No trailer prep so installed under passenger seat and connection to Bcm. It's recognised in VCDS as original part number though and accepts coding changes.

Parking sensors disable and screen shows trailer connected so I'd have though it would trigger charging OK but doesn't.

For comparison, here’s my trailer module coding. Not sure if there’s something in central electrics or ABS for towing… afair at least PDC has, but you have that working.

Address 69: Trailer (J345)       Labels:. 1K0-907-383-V2.clb
   Part No SW: 1K0 907 383 H    HW: 1K0 907 383 G
   Component: Anhaenger     H12 0130 
   Revision: 3B001001    Serial number: 00000452142320
   Coding: 410D000103000000
   Shop #: WSC 02739 790 00000
   VCID: 323672A2E42DDB1AC9F-8067

No fault code found.

 

[n10n]

Here's some CAN internals from a moment of connecting a trailer while engine is running and PDC active

• PDC left inner sensor (red) sees the trailer at under 1m distance first
• Both the left outer and inner (red, green) see me coming to connect the trailer, distance goes near 0
• Trailer connected (blue)
• Rear PDC is deactivated automatically when the trailer is connected (brown). Interestingly, the sensor distances are reset also at that point - I would have thought they keep reporting the distance but are just ignored.
• Voltage at main battery jumps to 14.7V (cyan)
• Alternator power production jumps from 500W to >2kW first but stabilises to around 1700W (grey)
• Strangely, today the voltage was little bit higher first but later in the drive it went again to 14.4V
• There's absolutely no way my simple trailer with just couple of lights and no battery would eat over 1kW so the van does this as a part of charging program when trailer is connected
  

 

[n10n]

Here's some CAN internals from a moment of connecting a trailer while engine is running and PDC active

• PDC left inner sensor (red) sees the trailer at under 1m distance first
• Both the left outer and inner (red, green) see me coming to connect the trailer, distance goes near 0
• Trailer connected (blue)
• Rear PDC is deactivated automatically when the trailer is connected (brown). Interestingly, the sensor distances are reset also at that point - I would have thought they keep reporting the distance but are just ignored.
• Voltage at main battery jumps to 14.7V (cyan)
• Alternator power production jumps from 500W to >2kW first but stabilises to around 1700W (grey)
• Strangely, today the voltage was little bit higher first but later in the drive it went again to 14.4V
• There's absolutely no way my simple trailer with just couple of lights and no battery would eat over 1kW so the van does this as a part of charging program when trailer is connected

View attachment 207374

One more interesting tidbit: alternator DFM signal reacts to the power increase but returns to (almost) it's levels before power production increase. Not quite sure about this one but as the DFM is the "load signal", I think this might be an indication of the power production increase to be commanded rather than load based.