Charging leisure battery also charges main van battery?

[Tinium]

I've just fitted a CTEK charger to my leisure battery, so I can keep it topped up when on hook-up.

It's connected directly to the leisure battery, which is still in situ and wired up via a Durite split charger to the main van battery.

However, when I turn the CTEK on, both batteries start charging! The split charger is also activating (indicated by it's LED & I can hear the relay click).

I'd expect that I should be able to just charge the relay battery on it's own, even though it's still wired to the rest of the system - is that correct?

In which case, anyone have any bright ideas as to why both batteries start charging, before I start having to pull fuses etc. to trace the culprit down? (10 o'clock last night was too late for that!) I'm thinking that something somewhere is taking the raised voltage of the leisure battery charging and causing the main van electrics to also raise, causing the split charger to activate, and then allow the main battery to start charging. But as to what... the joys of inheriting other peoples wiring!

[Tinium]

OK, 30 minutes more research on the interwebs and it looks like the Durite split charger I have is bi-directional, ie, any increase in voltage on either battery will activate it (not that this is mentioned anywhere on their documentation). So that probably explains it Will check and confirm later - looks like simply disconnecting the leisure battery from the split charger when hooked up will be the cheap way to go for now.

[bigherb]

Easiest is to put a switch in the earth wire to the split charger so you can switch it off.

[cassandra]

Hi, why not leave it as is ? Can't see why you wouldn't want the engine battery topped up as well? After all things like the cab interior lights and the radio are probably running off the engine battery. I have deliberately fitted a system to my van to charge both batteries when on hook up.

Just a thought.

[Tinium]

Hi, why not leave it as is ? Can't see why you wouldn't want the engine battery topped up as well? After all things like the cab interior lights and the radio are probably running off the engine battery. I have deliberately fitted a system to my van to charge both batteries when on hook up.

Just a thought.

I asked this very question a while back before I started adding the CTEK
https://club8090.co.uk/forum/viewtopic.php?f=39&t=159081

Opinion seemed to be that the CTEK is designed to recognise when a battery is full, and at that point it switches to maintenance mode. If you've got two batteries of different capacities, types, ages etc, then this will confuse the charger, potentially causing issues to which ever battery is fully charged first whilst it tries to charge the 2nd battery to full capacity. (Though I imagine there's probably minimal risk whilst both batteries are in good health and of similar capacity). Mark S on that thread also points out that you can add a Battery Master between the lesiure battery and the engine battery and charge both that way; it'll take care of any difference between the two batteries.

As it is I've moved the stereo and 12v sockets over to the leisure battery already, so there's little draw on the main battery now. Plus I'll keep the clamp connectors in the van for the CTEK, so if I do ever need to charge the main battery, I can just switch it over quickly enough as the charger has quick-release connectors.

Long term I'm looking at this, which is similar to the setup some other people on here have:
http://www.ctek.com/storage/ma/e76fc6df ... attery.pdf
But I'll save my £££ for now until I get round the to the solar install.

[Tinium]

Easiest is to put a switch in the earth wire to the split charger so you can switch it off.

Genius, that's sorted it nice and easily, thanks!

[chewbacca]

Rather than a switch, use a mains powered relay to break the earth wire connection to the relay. With the relay coil in parallel to the charger.
As soon as you give the charger power, the relay energises and the split charger turns off.