what battery to run a voltage sensitive relay off

[Risingsun]

As above says ... just about to fit a VSR for a battery in the boot and was thinking the main battery was the drivers side so looking to run the VSR of the passenger side battery as it is a 24v starting vehicle ...
has anyone done this in the past or see any problems with it

thanks
Dave

 

[Chris]

I have a VSR in my set up and really I don't think in this application it really matters where you pick up the voltage to trip the relay. But if you ever had a fault with the second battery and for some reason it wasn't charging, then this might affect the VSR and you wouldn't charge the battery in the boot either.

However, I'd suggest that there are two options as to where you take your feed to the battery to be charged. My personal preference is to come from the battery being directly charged by the alternator. There seems little point in sending current to the second battery with the associated losses to then send it on to the 3rd battery.

Be sure to connect directly to the battery terminals so that you don't end up in the 24v start somehow. I would also advocate using a separate live and earth cable to the battery and not use the chassis as the negative. It's just better practice and reduces the chances of parasitic drain. Even better would be to run cables to a DC to DC charger and then onto the rear battery so that there is an effective break in the circuit and you don't end up draining your cranking battery if you leave something switched on. This can happen if the VSR goes wrong.

 

[Risingsun]

I have a VSR in my set up and really I don't think in this application it really matters where you pick up the voltage to trip the relay. But if you ever had a fault with the second battery and for some reason it wasn't charging, then this might affect the VSR and you wouldn't charge the battery in the boot either.

However, I'd suggest that there are two options as to where you take your feed to the battery to be charged. My personal preference is to come from the battery being directly charged by the alternator. There seems little point in sending current to the second battery with the associated losses to then send it on to the 3rd battery.

Be sure to connect directly to the battery terminals so that you don't end up in the 24v start somehow. I would also advocate using a separate live and earth cable to the battery and not use the chassis as the negative. It's just better practice and reduces the chances of parasitic drain. Even better would be to run cables to a DC to DC charger and then onto the rear battery so that there is an effective break in the circuit and you don't end up draining your cranking battery if you leave something switched on. This can happen if the VSR goes wrong.

Ok Chris thanks for that ... so what stops my 3rd battery getting a 24v surge when the vehicle is being started

thanks

 

[Chris]

The system doesn't work like that. At no point is there 24v across the battery terminals themselves. It's a ridiculously complicated system in in mine and some others' views utterly unnecessary. But that's the way Mr T designed it. Where you can end up with 24v is if you start messing around with earths and so on. If you stick to using the main terminals and only connect to one battery you should be fine. The 'clever' system takes the parallel batteries, momentarily disconnects them and reconnects them in series through a different circuit if you like combining them at the starter motor.

Yes you could get it wrong for example by connecting a winch in the wrong way, but it would only matter if you were winching and cranking the engine at the same time. If you search in the 80 forum there is much more posted about this. From memory, Rich gives a pretty good explanation. But that all boils down to - connect to the battery terminals.

 

[Risingsun]

The system doesn't work like that. At no point is there 24v across the battery terminals themselves. It's a ridiculously complicated system in in mine and some others' views utterly unnecessary. But that's the way Mr T designed it. Where you can end up with 24v is if you start messing around with earths and so on. If you stick to using the main terminals and only connect to one battery you should be fine. The 'clever' system takes the parallel batteries, momentarily disconnects them and reconnects them in series through a different circuit if you like combining them at the starter motor.

Yes you could get it wrong for example by connecting a winch in the wrong way, but it would only matter if you were winching and cranking the engine at the same time. If you search in the 80 forum there is much more posted about this. From memory, Rich gives a pretty good explanation. But that all boils down to - connect to the battery terminals.

Thanks for the help I will try and get it done this weekend

cheers

 

[Chris]

Excellent.

Btw as a relatively new member, you know, you don't have to click 'quote' each time you post. Just click 'reply' It makes the threads that bit shorter.

 

[uHu]

If this is a 100-series, there is no 24 volt. The 2 batteries are all the time in parallel, connected with a thick cable, acting as one. You can take power from either one, doesn't matter which. There is no version of the 100 with 24 V starter.