Split Charge while charging from mains

I've had my 90 for about 5 years now, it came with a split charge system already in place, with the main, and and additional battery for the winch, relocated to a box in the rear. It's always worked a charm, I've never had any fault with it.

Over lockdown, the landy didn't go very far, and on a couple of occasions I ended up with not enough charge in the batteries to start the old girl up. I've got a lot of technology and electrical paraphernalia in the cab, so it doesn't surprise me that something is slowly draining the battery, and I've only now discovered this due to the lack of trips I've been making.

It's no big deal, but for the first time, I've had to try and charge the batteries from the mains - and this is where my lack of full understanding of the split charging system lets me down a bit. Which battery am I supposed to be connecting the mains charger to? For now I've gone with the main battery, and this has worked, overnight it got enough juice to start her up. But something I've noticed on both occasions now, is that after a while, the split charger relay starts clicking away. I can hear it in the night, turning on, and then 10 to 15 seconds later turning off, and then on, and then off, etc. I'm assuming the high voltage coming into the battery is tricking it into turning on to charge both batteries, but then something makes it turn back off again, and on again, and off again.

By the time I disconnect the charger in the morning, I'm still not seeing either of the batteries fully charged again, so I'm assuming that for the first hour or so, some charge gets in without this issue starting, then as the batteries start to ramp up in charge, this issue starts, and this prevents any more charge from getting in?

Either way, I get enough charge to start up, and after a journey, the batteries are back up to full charge again. But it would be nice to know how to get a full charge in from the mains without the split charge system from interfering?

I totally accept that I might be completely misunderstanding what's going on. So any advice or correction would be great, thanks!

Not sure on the split charge but would an isolator or just disconnect secondary battery work? Depends on what the second battery powers, then once started the split charge would charge it.

If in your worried disconnect the second battery and charge it up once the main one is ok

I mean, that does definitely seem like the most simple solution to this, and I'll definitely go down that route if no one can suggest what might be going on, and how to avoid it without disconnecting things.

It may be that the charger is putting just enough power into the main battery for the split charger to kick in which then drops the power in the main battery so charger split charger disconnects then the power builds up and cycle is repeated,

I charge of the mains with a split charge. The split charge relay behaves like it would with the alternator and switches between the batteries. In practice this means a short (ie 1 or 2 hours) charge doesn't work with both batteries connected as it could be spending half that time on the battery you don't need. This is a problem for me as I have a tracker that draws down the leisure battery so the split charge favours this which is fine on a long (12 hours) charge but a pain if I just want to boost the starter battery for an hour. I have a 50A fuse next to the starter battery and I flip that out if I need to boost charge the starter battery.
2 things have helped more than I expected -
a new 75a alternator and smaller pully, the old one was not pushing out enough volts and this seemed to make the spilt charge less effective. Now it boosts both batteries quickly.
a small solar panel permanently fixed to the roof, this keeps the leisure battery topped up and means more of the charge goes to the starting battery on short journeys as the leisure battery voltage is higher..

rob1miles said:

I charge of the mains with a split charge. The split charge relay behaves like it would with the alternator and switches between the batteries. In practice this means a short (ie 1 or 2 hours) charge doesn't work with both batteries connected as it could be spending half that time on the battery you don't need. This is a problem for me as I have a tracker that draws down the leisure battery so the split charge favours this which is fine on a long (12 hours) charge but a pain if I just want to boost the starter battery for an hour. I have a 50A fuse next to the starter battery and I flip that out if I need to boost charge the starter battery.
2 things have helped more than I expected -
a new 75a alternator and smaller pully, the old one was not pushing out enough volts and this seemed to make the spilt charge less effective. Now it boosts both batteries quickly.
a small solar panel permanently fixed to the roof, this keeps the leisure battery topped up and means more of the charge goes to the starting battery on short journeys as the leisure battery voltage is higher..

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This is great information - I've also purchased one of these solar battery chargers, but was reluctant to start using it until I get more of an understanding of the split charge system. The last thing I want to do is to leave that on for a few weeks and find that I've killed the split charge relay or something with it continuously flicking back and forth.

Solar goes to solar charge controller - a cheap one, it works fine. This is connected to the leisure battery. On a sunny day the relay does click back and forth but the solar is charging at about 1/2 to1amp and the relay is good to 50a.