Where to locate my D+ signal

[ForeignShaws]

I've just purchased a Renogy Dcc charger to improve my leisure battery charging whilst on the move. The instructions indicate that, with a smart alternator, the D+ signal input on the charger should be connected to the alternator signal.
I have a 2021 Auto-Trail on a Ducato, so I'm assuming that this applies to my install, but is there a more convenient location to pick up this signal than going back to the alternator? Alternatively, can I just use the switched 12v supply to the fridge instead or is D+ something more than just an engine running switched 12v feed.

 

[Lenny HB]

There should be a D+ connection on the fridge you could tap into. Not sure how Sargent electrics do but there is probably a relay box the D+ gets distributed from.

 

[Two on Tour]

I've just purchased a Renogy Dcc charger to improve my leisure battery charging whilst on the move. The instructions indicate that, with a smart alternator, the D+ signal input on the charger should be connected to the alternator signal.
I have a 2021 Auto-Trail on a Ducato, so I'm assuming that this applies to my install, but is there a more convenient location to pick up this signal than going back to the alternator? Alternatively, can I just use the switched 12v supply to the fridge instead or is D+ something more than just an engine running switched 12v feed.

If you're struggling to find where you can tap into a D+ signal, then the easy option might be to use a D+ simulator which senses the vibration of the engine running.

Voltronic D+ simulator

 

[LithiumConvert]

or is D+ something more than just an engine running switched 12v feed.

No, it is nothing more than an engine running switched 12v feed.

 

[Carolyn and Kev]

Found this out from a very Knowledgeable gentleman on here who helped me with a similar issue. The D+ is actually for systems that do not have a Voltage Sensitive Relay. Apparently it is a low current 12 volt feed from the alternator switching on and off relays to suit. Therefore albeit 12v..its a low current feed only .

Kev

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[Lenny HB]

Found this out from a very Knowledgeable gentleman on here who helped me with a similar issue. The D+ is actually for systems that do not have a Voltage Sensitive Relay. Apparently it is a low current 12 volt feed from the alternator switching on and off relays to suit. Therefore albeit 12v..its a low current feed only .

Kev

Not quite as simple as that, it is a low current 12v feed direct from the alternator it is not designed to switch loads of relays. Motorhomes often have quite a few things switched by a D+ signal so they fit special relay boxes or simulators so as not to overload the D+ output from the alternator.

 

[jwells]

What model Autotrail do you have, it may have a split charge relay that will need to be isolated as well!

 

[RioRob]

There should be a D+ connection on the fridge you could tap into. Not sure how Sargent electrics do but there is probably a relay box the D+ gets distributed from.

There is a fused power distribution box i.e. the Sargent ec40 which is located behind the drivers seat. It provides a connection from the vehicle battery to the leisure battery system and has D+ switched circuits for the fridge as well as a D+ "booster".

 

[autorouter]

There will be an existing arrangement to charge your leisure battery. Either a split charge relay or a small DC-DC charger. Whatever it is, it is very likely turned on and off by a D+ signal. So the D+ signal will be present at the distribution box, or at the existing DC-DC charger if there is one. There should be no need to go all the way back to the alternator.

If the existing arrangement is a split charge relay then as jwells says it needs to be disabled, if not it will simply short the DC-DC charger input and output, so it does nothing. If the existing arrangement is another DC-DC charger, then that probably needs to be disabled too, but may be OK to leave it connected.

 

[Tombola]

I've just purchased a Renogy Dcc charger to improve my leisure battery charging whilst on the move. The instructions indicate that, with a smart alternator, the D+ signal input on the charger should be connected to the alternator signal.
I have a 2021 Auto-Trail on a Ducato, so I'm assuming that this applies to my install, but is there a more convenient location to pick up this signal than going back to the alternator? Alternatively, can I just use the switched 12v supply to the fridge instead or is D+ something more than just an engine running switched 12v feed.

make sure you do have a smart alternator, some autotrail requested non smart but none sure what date up to.
Mine was 2020 and was none smart, an autotrial imala

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[autorouter]

I've just purchased a Renogy Dcc charger to improve my leisure battery charging whilst on the move. The instructions indicate that, with a smart alternator, the D+ signal input on the charger should be connected to the alternator signal.

The D+ signal can be used to trigger the DC-DC charger, whether the alternator is smart or non-smart. It's the best and most reliable method of triggering. If it's a non-smart alternator you can get away with a voltage-sensitive trigger mechanism, but that doesn't work for a smart alternator because the voltage varies too much.

Since the D+ is already used in motorhomes to switch on the fridge while driving, and the existing DC-DC charger or split charge relay if there is one, then it shouldn't be a big deal to find a wire with the D+ signal on it.

 

[Barti Ddu]

I've got a 2021 Autotrail based on a Ducato. It has a standard (not smart) alternator and a Sargent split charge rather than a B2B.

I've recently fitted a Victron B2B. I removed the cab battery fuse in the main Sargent control unit to disable the original split charger. I anticipated having to connect to the D+ signal, but tried it first without using the Victron auto-engine sensing and it works a dream.

As soon as the engine starts the alternator puts out a steady 14v, and the B2B fires up a few seconds later. The alternator puts out 14v irrespective of idling, braking, accelerating. The joys of a non-smart alternator!

I don't know if the Renology B2B has engine sensing, but if it does give it a try.

 

[Carolyn and Kev]

Not quite as simple as that, it is a low current 12v feed direct from the alternator it is not designed to switch loads of relays. Motorhomes often have quite a few things switched by a D+ signal so they fit special relay boxes or simulators so as not to overload the D+ output from the alternator.

Think you need to read it again Lenny? I stated it is a low current wire only. Did not state it will operate anything other than a low current appliance by that a relay or fuse board feed for a particular circuit. May just be the way you read it or it could be the way i may have put it possibly?

 

[HarryML7]

If it helps this articles describes the convertors socket and d signal.

Converter's socket - MisterG

The Peugeot Boxer, Citroen Relay and Fiat Ducato can be equipped with an option for a “Conversion Interface” or Converter’s socket. Fiat: “Electrical Interface Supply Socket (For Conversions)” option 081 Peugeot: “Electrical connections interface box / Includes reinforced alternator” option JI01...

misterg.org.uk

 

[ForeignShaws]

What model Autotrail do you have, it may have a split charge relay that will need to be isolated as well.

It's an Imala 625

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[ForeignShaws]

If you're struggling to find where you can tap into a D+ signal, then the easy option might be to use a D+ simulator which senses the vibration of the engine running.

Voltronic D+ simulator

Thanks Paul. There must be one I can get to but this is a useful backup.

 

[ForeignShaws]

If it helps this articles describes the convertors socket and d signal.

Converter's socket - MisterG

The Peugeot Boxer, Citroen Relay and Fiat Ducato can be equipped with an option for a “Conversion Interface” or Converter’s socket. Fiat: “Electrical Interface Supply Socket (For Conversions)” option 081 Peugeot: “Electrical connections interface box / Includes reinforced alternator” option JI01...

misterg.org.uk

Great information.
I need to access that panel. On my vehicle the supply fuse for the step and fridge are mounted just in front of it and I'm intending to mount the charger on the base of the drivers seat adjacent so it will be great if both D+ and the battery connection were so conveniently located.

 

[ForeignShaws]

I've got a 2021 Autotrail based on a Ducato. It has a standard (not smart) alternator and a Sargent split charge rather than a B2B.

I've recently fitted a Victron B2B. I removed the cab battery fuse in the main Sargent control unit to disable the original split charger. I anticipated having to connect to the D+ signal, but tried it first without using the Victron auto-engine sensing and it works a dream.

As soon as the engine starts the alternator puts out a steady 14v, and the B2B fires up a few seconds later. The alternator puts out 14v irrespective of idling, braking, accelerating. The joys of a non-smart alternator!

I don't know if the Renology B2B has engine sensing, but if it does give it a try.

Thanks.
Engine sensing isn't mentioned in the installation guide but Renogy seem to be pretty responsive so I can ask.
I must admit I assumed I've a smart alternator, but maybe I need to do more checking first. Keep forgetting it's really a commercial vehicle .

 

[ForeignShaws]

The D+ signal can be used to trigger the DC-DC charger, whether the alternator is smart or non-smart. It's the best and most reliable method of triggering. If it's a non-smart alternator you can get away with a voltage-sensitive trigger mechanism, but that doesn't work for a smart alternator because the voltage varies too much.

Since the D+ is already used in motorhomes to switch on the fridge while driving, and the existing DC-DC charger or split charge relay if there is one, then it shouldn't be a big deal to find a wire with the D+ signal on it.

Thanks.
I was hoping that maybe there was some standardisation and that a usable D+ signal would be in the same place in all similar aged Ducatos .
Looks as though I'll be having some fun with a multimeter over the weekend.

 

[ForeignShaws]

There should be a D+ connection on the fridge you could tap into. Not sure how Sargent electrics do but there is probably a relay box the D+ gets distributed from.

The fridge fuse on my vehicle is mounted immediately under the OS door post, right below the location of the converters socket as described by HarryML, so I'm hoping it might be an easy find.

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[ForeignShaws]

make sure you do have a smart alternator, some autotrail requested non smart but none sure what date up to.
Mine was 2020 and was none smart, an autotrial imala

Mines an Imala as well - 625. Need to check.

 

[Barti Ddu]

Thanks.
Engine sensing isn't mentioned in the installation guide but Renogy seem to be pretty responsive so I can ask.
I must admit I assumed I've a smart alternator, but maybe I need to do more checking first. Keep forgetting it's really a commercial vehicle .

I'd (incorrectly) assumed my 2021 Autotrail Ducato had a smart alternator too.

See this thread I started a couple of years ago -

Thread '2021 Autotrail PVC - smart alternator?' https://www.motorhomefun.co.uk/forum/threads/2021-autotrail-pvc-smart-alternator.257871/

Have a look at the negative terminal on the cab battery. If just a plain connector and no shunt as in my photo then it's going to be a standard alternator.

Alternatively, see if the cab battery voltage changes using a multimeter (or a plug in USB cig lighter voltage display) when the engine changes from idle to acceleration. If it remains fairly constant then again it's indicating a standard alternator. Mine is rock solid at 14v when the engine is running no matter what load is placed on the engine.

 

[ForeignShaws]

I'd (incorrectly) assumed my 2021 Autotrail Ducato had a smart alternator too.

See this thread I started a couple of years ago -

Thread '2021 Autotrail PVC - smart alternator?' https://www.motorhomefun.co.uk/forum/threads/2021-autotrail-pvc-smart-alternator.257871/

Have a look at the negative terminal on the cab battery. If just a plain connector and no shunt as in my photo then it's going to be a standard alternator.

Alternatively, see if the cab battery voltage changes using a multimeter (or a plug in USB cig lighter voltage display) when the engine changes from idle to acceleration. If it remains fairly constant then again it's indicating a standard alternator. Mine is rock solid at 14v when the engine is running no matter what load is placed on the engine.

That looks to be a simple check, and the install says I don't need to connect the D+ signal lead on a dumb alternator, so could be the original question is irrelevant. Thanks Barti Ddu

 

[ForeignShaws]

There is a fused power distribution box i.e. the Sargent ec40 which is located behind the drivers seat. It provides a connection from the vehicle battery to the leisure battery system and has D+ switched circuits for the fridge as well as a D+ "booster".

Thanks. I knew that box had the fuses for the fridge and step (took me ages to locate the step fuse when it failed). Didn't know it also had a D+ connection, but it now seems likely that I have a dumb alternator in which case I don't need to connect to D+.
Could be I've been seeking a solution to a problem that I don't have

 

[StillGoing]

Thanks. I knew that box had the fuses for the fridge and step (took me ages to locate the step fuse when it failed). Didn't know it also had a D+ connection, but it now seems likely that I have a dumb alternator in which case I don't need to connect to D+.
Could be I've been seeking a solution to a problem that I don't have

Personally, I’d still use the D+ on the B2B

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[ForeignShaws]

There will be an existing arrangement to charge your leisure battery. Either a split charge relay or a small DC-DC charger. Whatever it is, it is very likely turned on and off by a D+ signal. So the D+ signal will be present at the distribution box, or at the existing DC-DC charger if there is one. There should be no need to go all the way back to the alternator.

If the existing arrangement is a split charge relay then as jwells says it needs to be disabled, if not it will simply short the DC-DC charger input and output, so it does nothing. If the existing arrangement is another DC-DC charger, then that probably needs to be disabled too, but may be OK to leave it connected.

Thanks autorouter . The Sargent PSU has an illuminated 'Charging' switch, but I'm pretty sure that's just for EHU. Might be worth a call to Sargent technical to check. They're usually pretty helpful.

 

[Tombola]

That looks to be a simple check, and the install says I don't need to connect the D+ signal lead on a dumb alternator, so could be the original question is irrelevant. Thanks Barti Ddu

Yes thats what I did on my autotrail Imala 735.
It sensed the signal no probem without D+

 

[ForeignShaws]

I'd (incorrectly) assumed my 2021 Autotrail Ducato had a smart alternator too.

See this thread I started a couple of years ago -

Thread '2021 Autotrail PVC - smart alternator?' https://www.motorhomefun.co.uk/forum/threads/2021-autotrail-pvc-smart-alternator.257871/

Have a look at the negative terminal on the cab battery. If just a plain connector and no shunt as in my photo then it's going to be a standard alternator.

Alternatively, see if the cab battery voltage changes using a multimeter (or a plug in USB cig lighter voltage display) when the engine changes from idle to acceleration. If it remains fairly constant then again it's indicating a standard alternator. Mine is rock solid at 14v when the engine is running no matter what load is placed on the engine.

I guess the shunt is the little grey box on the - ve terminal then. Looks as though I do have a smart alternator

 

[Tombola]

I guess the shunt is the little grey box on the - ve terminal then. Looks as though I do have a smart alternator



View attachment 1001271

some folks do unplug them to disable the smart shunt

 

[Barti Ddu]

I guess the shunt is the little grey box on the - ve terminal then. Looks as though I do have a smart alternator



View attachment 1001271

Yes indeed. Looks like you need to find that D+ after all.

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