D+ Signal

[jakemcc97]

Hi guys, looking for an alternative to the D+ wire from the alternator on my 2017 Highline. As it has a smart alternator it doesn't have a D+ (alternator excite, +12V when engine is running, 0v otherwise)

I guess something like this might be available on the comfort control module or similar.

Basically I need a wire to trigger my battery to battery charger, and I don't want to use an ignition feed as it'll drain the battery when sat with ignition on and engine off. I don't want to use a switch as I'll forget to turn it on.

I can hack something up to pull the info from CAN but I'd rather not if there's something easier available.

Cheers!

[maxx007at]

Hi mate,

There are smart battery couplers that switch on above a certain voltage and switch off underneath.

I believe Victron makes them, pretty sure there are also cheaper alternatives

[jakemcc97]

Not sure they work with a smart alternator though - that's basically a voltage sensing relay right?

I've also seen the D+ simulators (basically a vibration sensor) which seem like a janky way to do it so not planning on using one of those...

Basically just need a signal that goes high when the engine is running regardless of voltage. Cheers though

[STP]

If you plan on sitting with the ignition on but not running, then you are probably out of luck mate. Ignition is the on signal, the smart alternator uses LIN bus data to control it, so you don't have a DC 12V signal afaik that is only live when the engine is running, unless someone knows better.

[The_Evil]

I've been using a DIY'd voltmeter to control a relay to charge the leisure battery.
When the tension goes under 13V, it breaks the circuit and stops to charge the battery.
It works quite well.

[STP]

That's a good idea. I'm sure there are charge controllers which can do the same out there for folk who couldn't build their own.

[The_Evil]

I think the DC-DC battery chargers for RVs (the ones which also allow to charge from solar panels) can do this trick to as well as managing the charging correctly.
If leisure battery and wires are big enough, they can also allow to start the car using the leisure in case of emergency.

[VeeDub]

You'll need a Smart Charger like the Victron Orion DC-DC charger.

This is from the Victron manual on Engine Shutdown Detection:

"The engine shutdown detection mechanism simplifies your ORION-Tr DC-DC Charger system by detecting if the engine is
running without wiring additional switches or sensors. The factory default setting will work with most regular and smart alternators
but can be re-configured with the VictronConnect App.
Configuring the engine shutdown detection depends on the voltage the alternator generates when the engine is running. Regular
alternators generate a fixed voltage (e.g. 14V), whereas smart alternators generate a variable output voltage ranging from 12.5V
to 15V. Especially smart alternators in a regenerative braking system show significant alternator voltage variations."

https://www.victronenergy.com/upload/do ... pdf-en.pdf

[gibbedyCaddy]

I went with a relay switched with accessories combined with a dual battery isolator with programmed cut in and cut out voltages. The relay enables the battery isolator.

By selecting appropriate values for the cut in and cut out on the battery isolator I can have:
- aux battery always on when ignition is on.
- if I leave ignition on, limited discharge of main battery to 12.3v.

[jakemcc97]

Thanks for all that guys, think my original question has been a bit misunderstood though haha. I already have a DC-DC charger, I have a Sterling BB1225:

Link

I chose this one over the Victron one because it can reverse charge the starter battery with the "jump start assistance" function whereas the Orion DC-DCs are one way only.

As you can see it requires an ignition signal when using it with a smart alternator (a split charge relay doesn't work on Euro 6 cars as they changed away from a dumb alternator to LIN/CAN controlled smart alternators) - hence this thread.

Basically was just looking for a 12V signal that goes high when the engine is running like the D+ you'd find on an older alternator. The manual recommends using a 12V switched live, which is fine but will drain the starter battery when the engine is off.

A voltage sensing relay won't work as a smart alternator won't run at a constant voltage. It would work pre Euro 6.

Looks like to get what I want I'll need to build a little microcontroller circuit to pull RPM from CAN and trigger an output based on that. Would be a little bit of work but definitely doable with not much hassle as RPM is available on OBD2 which I should be able to get a DBC for.

Either that or trigger it based off the fuel pump relay? I guess that would come on when the engine is running or immediately post ignition on when the pumps fire.