Using fuel pump feed to trigger leisure battery charge relay

[MagicWagon]

For reasons too boring to go into, I'm thinking of changing the way charging of my leisure battery is initiated when driving.
Currently I have a Voltage Sensitive Relay which is activated when the main battery begins to charge.
I would like to change back to using a simple relay that activates when the engine is running, however, for some reason, the feed from my alternator which would usually be used does not work and my attempts to troubleshoot that have failed.
I have my fuel pump wired via a safety/delay/primer relay, (i.e the pump is primed for a second or so, then the relay only activates when the coil is live).
Would there be any issue with taking another feed from that relay to the leisure battery relay ? I think that should allow me to achieve charging of the leisure battery when the engine is running.
Thanks.

[Mocki]

Atfternoon
Yes that will be all you need to trigger the split charger relay , although it’s not ideal as in theory your batteries will be joined together during the engine cranking if you turn the key too soon after initial switch on

You say your alternator blue wire is not triggering the split charge relay ? Does the chRge light go out on the dash when the engine starts ?

[Oldiebut goodie]

You don't use the blue wire for a VSR. The exciter wire only needs 1 -3 volts to start an alternator ( you can get the alternator producing the goods with a 1.5v battery ) You only need to pick up voltage from the engine battery as that will have the volts required to switch the relay once the alternator is charging it.
The only problem with a VSR is it can drop out too early if it is a preset one, I prefer an adjustable one so as to have more control as to the setting.
Personally I wouldn't possibly hamper the fuel pump relay by draining current there, I would keep the two separate. You can do without the leisure battery but not the fuel pump!

[MagicWagon]

Thanks for the replies. A bit of further info and background might be in order....

... not ideal as in theory your batteries will be joined together during the engine cranking if you turn the key too soon after initial switch on

Hmm, yes I hadn't thought of that

You say your alternator blue wire is not triggering the split charge relay ? Does the chRge light go out on the dash when the engine starts ?

The charge light never even comes on. I assume that's some other fault which I'm not sure how to troubleshoot. However, I can't detect any voltage from the alternator blue wire with the engine running.

You only need to pick up voltage from the engine battery as that will have the volts required to switch the relay once the alternator is charging it.

Yes, the VSR is wired to pick up from the engine battery.

The reason I was thinking going to a standard relay instead of a VSR is that I now have a Victron battery charger with multiple outputs. This will charge the main and leisure batteries separately, however, the charging voltage increase this gives on the main battery activates the VSR, and therefore connects the two batteries together, defeating the object of having a multiple output charger. Another alternative I thought of was having a switchover relay in between the main battery and the VSR which is wired to break the connection by a mains 12v adapter, that way, when mains is on, the VSR cannot be activated. However, I don't really like the idea of having a 12v adapter permanently switched on when hooked up to mains, especially as I intend to be on mains hookup at home to keep the batteries topped up during the winter. Any other suggestions/solutions most welcome. Here's the relevant part of my wiring diagram if it helps. NB. The relay shown in between the main battery and VSR is not currently there. This is the relay I was thinking of installing and feeding it from the fuel pump live.

[adie89]

You say your alternator blue wire is not triggering the split charge relay ? Does the chRge light go out on the dash when the engine starts ?

The charge light never even comes on. I assume that's some other fault which I'm not sure how to troubleshoot. However, I can't detect any voltage from the alternator blue wire with the engine running.

Is your alternator actually working? Test for voltage at the alternator before and after starting the engine, should go from 12ish volts to at least 13. I ask because I had the same fault but a 1.9DG takes so little power it literally started and ran for weeks moving in and out a workshop everyday.
If the charge light isn’t coming on, it may not be sending the exciter charge to the alternator (LED on) and then also would not switch a split charge relay if you used that method. You should get voltage at the blue wire once the alternator generates power, it’s that action of charging current that turns off your alternator LED (via a Zener diode) and tells you the alternator is working.

[Mocki]

yes i understand why you want rid of the VSR, they are not compatible to mutli output systems and solar controllers , because they cannot tell where the charge is coming from , and frankly not very reliable .

you really need to establish why you have no charge light, because other than the obvious ( you dont know if you are charging) it also is warning of alternator belt failure which on a wbx is water pump failure which is the only early warning you get before the engine is cooked!

if its not getting a feed onto the blue wire connection at the alternator, it isnt "exiting the alternator and isnt charging

[MagicWagon]

Thanks all for the replies. I did some further investigating, and found that the blue wire from the alternator had been severed.
I reconnected it, and the dash indicator light now comes on, then goes off when the engine is running.
I connected another wire to the blue wire to feed my relay and that now works fine.
For now, I have also left the VSR in place, so I now have the conventional relay, triggered by the alternator, and also the VSR after the relay.
Regarding the comment about not knowing if I was charging (without the indicator light) I worked around that by having an LED/Changeover Relay combo so the LED went out when the VSR activated.
I guess I don't need any of that now the blue wire to relay is working, but I'll leave it as it is until I have reason to change it.

[Mocki]

you really should just remove that vsr, its only going to get confused now....

[MagicWagon]

Hmm. I don't think it will get confused. It will only ever be connected to either the main battery (engine running) or smart charger (on hookup).
I might get confused however (hence why I have diagrammed all the electrics I have replaced.
There are, however, more things to go wrong.