Vsr wiring with overide.

[Steptoesbongo]

Hi all
This is my first post and forgive me I have not given the correct terminology or all the info needed but here goes.

I have a CarGo vsr setup with an old sb acid110amp and a new AGM 140amp lb.
After charging by driving or mains, the Red light stays on as if the lb as it now is holding a higher charge is trickle charging the sb
Can I isolate the lb from the sb and if so rather than using the positive lead with heavy duty switches and wiring,
can I put a switch on the vsr earth trigger wire which is much smaller to isolate the lb then I can use a much smaller switch on the dashboard.

I am just trying to keep as much charge in the lb for the fridge with as little cost as possible.

[Bob]

I'm not sure the system will cope with a mix of lead acid and AGM batteries.

[g8dhe]

The VSR's in last few years have switched from sensing only one battery to sensing both batteries and if either battery is over the trigger voltage then it will operate and parallel the two batteries. After charging the voltage on a battery won't fall below the trigger voltage of the relay for some time, it can be from a few seconds to several 10's of minutes if the battery has no load on it at all.
So make sure that your not expecting instantaneous operation, once the alternator has stopped spinning and EHU has been disconnected then measure the voltages of each battery, you should see them slowly dropping from the charging level (13.6 to 14.4 volts) down to the resting voltage of 12.6volts, the relay should have its drop-out voltage marked on it it can be as low as 12.8 volts.

A different approach, that I prefer, is not to use a VSR at all but I use the IG2 circuit to operate the relay, this operates only when the Ignition switch is in the ON position, it is not powered during OFF, ANCILLARIES or START, this ensures that the LB can be controlled by the ignition key, but won't be used during starting or just leaving Ancillaries turned on (assuming your not using a swap loom, as normally ancillaries are moved across to the LB by the swap loom).

As to using AGM batteries, its not a good choice! AGM needs a reduced charging voltage once it has reached full charge, neither the Alternator or the standard 12 volt charges will handel this. Solar panel controllers do understand the batteries but don't understand that there may be other charging sources, the alternator never understands AGM batteries and will happily damage a AGM battery on a long run.

[Steptoesbongo]

Hi
I was expecting some degradation of the AGM battery because of the mix, but do you think the bongo charging system might get overloaded with the different batteries.
I do fully charge the AGM every now and again separately with an AGM charger to minimise the damage.

[Steptoesbongo]

Thanks Geoff for the in-depth reply, I will have read it carefully again, I have seen it before about wiring into the ignition but it might be a bit much for me, but I will look it up again and maybe it will make more sense now.

[nth]

In my experience AGM & EFB batteries don't have anywhere near the same lifespan as regular flooded batteries, even when fitted in a car that's designed to have one fitted. I don't rate them at all & would never fit one to a car that isn't required to have one.

[g8dhe]

Yes there are a lot of marketing words involved in selling AGM batteries They do initially seem to work well, but given the additional cost, they last no longer than standard flooded batteries due to the overcharging. Used in the right situation, wheelchairs, scooters etc where they can use the full discharge and then have a dedicated charger which is the only device charging them they work well and worth the money! But in our situation with adhoc charging and no limit on charging then there life is poor.

Using the IG2 circuit is not difficult just use a piggyback fuse available from eBay to plug into and replace the Front Wiper 20 Amp fuse, and add a low 5 Amp fuse to run the relay direct.

This then also gives you some control over the relay and should you ever flatten the starter battery then by switching to ON and letting the two batteries equalise for 20 minutes or so you can safely put some charge back into a starter battery to assist!