Outer Limits 4x4 Board

Hey Guys,

Hoping someone with a bit more knowledge can shead some light on this problem for me! ive got a 24v SD33 Shorty Patrol running 2 x 12v batteries in series to make up the 24 volts.
The other day i think i left my cd player on standby and flattened one battery, whoops but no biggie charged it up and started the car fine a few times..

Then was up at gembrook on the weekend and had noticed the voltage was down on the usual 28v (at about 23-24) but was already on the road so ignored it.. Anyway stalled it on top
of a mud hill and damn thing wouldnt start! suspected the battery so went down the hill backwards without any power.. that was scary lol but my mate jump started me no problems..

The question is.. how does having one low battery and one strong battery affect the alternators ability to charge? how does a 24v alternator charge 2 x 12v batteries evenly?
is there a simple test i can do on my alternator to check if its alright without pulling the whole damn thing out!

Sorry for the essay, but thought more info the better!

Thanks Craig.

If you run your 12v from one battery you will kill that battery in supper quick time. The alternator will put the same amount of charge into each battery. The link between the batteries effectively makes it one 24v battery so the it would be like trying to charge half a battery more than the other half.
So you have a choice.
Run equal amountof 12v off each battery which will require above ground earthing and some very acurate measuring of amps to get acurate. Possible but not very realistic.
Or you need a 12v system. Either a 3rd battery charged by another alternator or a voltage reducer
Or a voltage reducer to power 12v.
Or something called an even charger that will equalise the charge between the batteries.
Or just replace the battery on a regular basis.

redarc make a voltage equaliser for centre taped 24v systems, it connects inline between your 24v and 12v supplies and tops up the lower battery to equalise charge.
without using that or a 24/12v power supply you will kill the lower battery which will eventually destroy the top battery.

Excellent! I was thinking it was something like that but havnt had any 24v experience.. thanks to both of you for your help!

Hopefully ill sort it out this week and be back on the tracks next weekend!

Thanks Craig

Your CD player should have run both batteries flat, I would say the battery was on its way out hence the lesser charge. Its not like a dual battery system whare you cano run off either battery, as mensioned above the two batteries are hooked up to make one big battery.

mkpatrol wrote:Your CD player should have run both batteries flat, I would say the battery was on its way out hence the lesser charge. Its not like a dual battery system whare you cano run off either battery, as mensioned above the two batteries are hooked up to make one big battery.

When the batteries are hooked up in series to make 24v they do not equalise the charge between them if you draw 12v off one battery. If you have a 24v to 12v reducer then you are drawing from both battereies but from what he said the assumption was made that he is taking power direct from one battery. Which is the problem.

the cheapest method is to use a 24-12 inverter, truckies have been using them for years to run stereos RT's etc. nzdarin is correct in only the last battery in the series will be run flat as its the only bat with 0V leg.
you can run off the other bat but caution is needed as the 12V to the stereo unit will in effect be floating above ground with the +ve at 24V and the -ve at 12V. touch either one to ground/chassis and you'll "let the smoke out"

so in short load the bats equally ie use a inverter that draws from both bats.

good luck

Sorry guys yeah i forgot to mention the cd player is hard wired onto one of the batteries,
its the way it came from the previous owner. So only one battery was flattened.

Found the charge equaliser on the redarc website.. giving them a call today to get one..
Hope they don't cost too much!

Ill let everyone know how it goes and how easy it is to install.


Cheers Craig

i think a 24/12v reducer is cheaper. i got mine (a 20A unit) for $150, i run my cd player, uhf, rear light and 100W spotlight of it. also have changed my front ciggie lighter to 12v and installed one in the rear. i also run my ERPS and central locking/immobiliser off my reducer.

ausoops wrote: also have changed my front ciggie lighter to 12v and installed one in the rear

the ciggie lighter in an MQ is already 12v...

the radio, ciggie lighter and in some models the dash lights run off 12v from factory...