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SwissT 20 Apr 2007 14:17

Split Charge Problem
I'm a bit useless with electrics and I'm in need of some advice.
I'm currently in The Gambia and have a 24V Landcruiser and use a third battery for camping equipment. I had a 24 to 12v converter with charge control but the part has failed due to a short and I can't find a replacement here or the parts to repair it.
I also have a 24 to 12v converter with charge control from a solar panel system but when I connect this and start charging the third battery, the electrics of the car such as the headlights start "pulsating" very quickly and the indicators (when in use) start clicking a bit irregularly.
The question is I am travelling back to Spain and the trip will take around 20 days. Do you think that I can use the solar panel converter without encountering problems?
Otherwise, can I connect the third battery to one of the batteries in the engine compartment and charge it that way when running the car (I do have a switch to disconnect the third battery from the others when camping)?
Is there anything else that you would recommend?
Thank you very much for any help on this.
Regards to all.

Roman 20 Apr 2007 16:33


When you say "24V Landcruiser" do you mean the alternator output is 24V, or it's just the starter motor that is 24V?

Quintin 20 Apr 2007 17:40

I'm a bit confused
When you say you have a 24:12 converter with a charge controller with solar panel system what exactly do you mean? Do you have 2 solar panels wired in series to give a 24V output which is then 'converted' down to 12 to charge the third battery or do you mean you have one (12V) panel which is converted up to 24V or indeed some other combination? I can't work out why you would need a 24:12 converter to charge you leisure side. I'm also confused as to whether your lights etc are pulsing when the the vehicle is running i.e. the engine is charging or does it happen when it's not?

That said, what must be happening is that somehow this solar charge side must be connected in some way to the car electrics side. It shouldn't be. I suspect that you must have a split-charge relay which is allowing 12V back into a system which is charging at 24V. Of course I may be talking rubbish! Basically what I would do is not attempt to try and charge the 3rd battery whilst the engine is running. If this is happening when the engine isn't charging I suspect the split charge relay is shot i.e. jammed on even when the engine isn't charging.

If you try and clarify your set up I may be able to come up with a better diagnosis. Bottom line is that something's wrong and I'd stop doing whatever you are doing to cause these symptoms.


SwissT 20 Apr 2007 18:19

Sorry, looks like I´m as bad at explaining problems as I am at solving electrical ones.
The Landcruiser is a HZJ75 24v everything: alternator, starter motor etc... and two 12v batteries. I take the 24v for the 3rd leisure battery from an auxiliary equipment box in the engine compartment.
Sorry about the solar converter confusion. There are no solar panels installed on the car, I just happen to have a house solar system and thought that I could use the solar converter to replace the broken converter that I was using before. It is when I use that solar converter that the lights start "pulsating".
I understand that charging the third battery from one of those in the engine compartment is not a very good option. Would it damage the system even if I use it this way over a period of 20 days?
Thank you very much for your replies so far and sorry again for the bad explanation.

Quintin 20 Apr 2007 19:07

I think the problem lies in the 'converter' you're using. Are you sure it's a 24 volt:12volt voltage dropper rather than a 12Volt solar charge controller? If it's the latter it will be operating at the wrong voltage (24 rather than 12) and the diodes fitted inside (to stop the charge flowing back to the solar panel) will have been knackered.

Look, to get you home what I'd do is simply charge the 3rd battery off one of the car batteries but do disconnect it when you stop the engine otherwise you run the risk of flattening one of your starter batteries. It's very bad practice but at least you'll get home safely.

In the long term what I'd suggest is that you get a Sterling 24:12 'smart' battery charger. This will charge your leisure battery far better than using the car's alternator. At best these achieve 70-80% capacity whereas a smart chager will charge to 100% and keep in fully charged all the time. Dead simple to wire up as well.

SwissT 25 Apr 2007 22:59

Thanks everyone for your help...
I've found someone at the last minute who is going to bring me a Mobitronic 24-12 converter with charge control. Should do the trick.
Thanks again, see you on the road.

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