24V to 12V split charger?

[Arfur's World]

Hi All,

I need to install a split charger to keep my leisure battery topped up, does anyone have any experience of this from a 24V to 12V system? Is it something that can be done?

Any help appreciated.

Martin

 

[rockwood]

You need a 24v to 12v converter. They are indeed out there. What kind of power demands do you have?

 

[Arfur's World]

I have absolutely no idea. I've purchased a caravan and will be installing all of the systems and wiring etc from that, so I just need to keep the leisure battery topped up when driving. I'm not planning on powering from the 24V in any other manner.

 

[ianc]

I'm assuming you have a fridge. Is it absorption (runs on gas and also 12v when you're driving) or compressor (similar to home fridge except 12v)? One way or the other - it's likely to be your biggest 12v power consumer.

Sterling do some very good 24V->12V chargers but they're expensive. See http://www.shop.sterling-power.com/acatalog/Non---Waterproof-Battery-to-Battery-Chargers.html

I

 

[dwh]

You can't do a split-charge relay from 24v->12v.

You could use a solar charge controller - many that will charge a 12v battery can accept up to around 30v on the input side. Most MPPT units can since the input->output voltage differential is where an MPPT gets its magic from.

The problem is that the solar charge controller would be trying to charge the 12v battery from the 24v bus even when the engine is off. So for that you could rig a normal dumb solenoid controlled via ignition switch to tie the solar charge controller's input to the 24v bus only when the engine is running.

That would be okay, since most solar charge controllers get the power to run themselves from the battery side (in your case, the 12v side) and require hooking up the battery before hooking up the solar panel. That's essentially what you'd be doing - leaving the charge controller hooked up to the 12v (battery side) of the charge controller, and then making/breaking the connection to the 24v side via the split-charge relay.


The problem is not charging a 12v battery from a 24v supply. The problem is allowing it to stay connected too long, and thus pushing the 12v battery to too high a voltage. That's why you need the charge controller (a.k.a. charge regulator in places like Oz (or where they speak the Queen's English)), to make sure the 12v battery voltage doesn't rise too high. Many "12v nominal" solar panels have voltages up over 20v and most are in the 16v-21v range so a "24v nominal" (i.e. up to 28.8v real world) input to the controller does not represent some sort of outrageous overload.

 

[rockwood]

I suppose running a dedicated 12v line from one battery only to the caravan would be much easier.

 

[ianc]

I understand running from one of the batteries in the 24V circuit is a No No. I read lots of warnings against it when I was considering similar.

 

[Arfur's World]

In my simple brain (and it is really, really, simple!) I had thought that may work too. What were the warnings?

 

[grizzlyj]

I think the imbalance screws up one of your vehicle batteries quite quickly.

What about http://www.red-bhw.com/voltage-redu...et-1505.html?zenid=el1o4b8sclb38a1lshf30m2vp2

No idea if it is actually suitable though, but you could ask them?



Edit, sorry, I read that you had a caravan and wanted to charge that. Nugget.

 

[Anton2k3]

Hi Arfur's World,

I have one of the sterling battery to battery 24-12v chargers on my mercedes vario camper, and I must say i'm very happy with it. It charges at 30amps consistently, and doesn't run my 24v battery bank down, as there is an auto cut off when the voltage dips too low. Similarly, it will not over charge the 12v system as it is also a 4 stage charger, allowing float mode when the batteries are full.

Worth the money? Definitely! It would cost at least the same to have a 12v alternator custom mounted.

 

[dwh]

Guess which battery will fail first?

 

[andylod]

Hi Arfur

I to have the Sterling 24-12v charger on my Vario, and its a very easy install and charges the leisure batteries easily..... its the kind of thing you spend a bit more money on, fit, then forget it.
Good Luck

Andy

 

[michaelh712]

Martin, I'm not clear what you are trying to do. I'm assuming that your mog is 24 volts, from two 12 volt batteries. Absolutely do NOT pull 12 volts from one batter alone, as one will die a premature death and leave you stranded and not able to start the truck. If using a third battery that you want to run 12 volt accessories, get a good 24-12 volt converter and run 12 volts from your third battery. Install a battery cutoff switch between the converter and 12 v third battery, so that the 12 volt won't drain your main batteries. Depending on your 12 volt needs, buy a quality converter. I use a Vanner high end, used often in marine environments, available cheap on ebay often.

 

[canals1164]

Martin
Just agree with Andy, we fitted a 24-12v battery charger and it works realy well. I have one 110ah battery which I was going to sue for only a back up and charging 12v phones etc. As usual the list got longer and it now has quite a few items that are not powered by main 24v batteries. It seems to sort itself out and keeps the battery charged well. It also charges when our main 24v charger is charging from 240v.
I have found out you get what you pay for, we used several cheaper or 2nd hand items on our truck and apart from one they have all caused grief and been replaced!!
Good luck and I hope you have a lot of fun converting your truck, the caravan option looks a good plan.
all the best
Ian

 

[docka]

Another vote for the Sterling charger/dropper. Easy installation, intelligent unit.