24v question (1 Viewer)

[woytovich]

I have a friend out on a grand expedition across Africa.

His truck:
AfricaMinded | Overland | Vehicle

He is not a technical cruiser-guy and he sent me the following question. Since I'm not a 24v guy I was hoping someone here could help me help him...

He wrote:

"The toyota we have is 24V (2x 12V batteries in series used for starting the car) and we have an auxiliary battery that is 12V (105Ah) to power all the accessories in the car.

The car used to charge the auxiliary battery via a Mastervolt 6A converter which died somewhere in the bush and drained our starter batteries. This led me to redo the electrics in the car while being in Nairobi (create central fuse box, install a battery trickle charger powered via 230V and get as many wires and relays as possible out of the engine bay). We are now faced with the problem of replacing the Mastervolt converter that is dead and I am told that we need a 24V to 12V battery charger instead of a 24V to 12V converter. People give different opinions: the converter will not be able to charge the battery properly as it does not output the required 14.4V but 12V. A battery charger gives the appropriate voltage. I have no idea which is correct and and was hoping you can ask somebody for decent advise.

Another option, maybe expensive, is installing a 12V alternator but I have no idea what will be the implications."



Thanks,
Mark

 

[gotoy]

Here are few options for you:

1. Connect your axulliary battery in parrallel with one of the 12V starting batteries. This is a quick fix.

2. Take a 12v feed from one of the 12V starting batteries, removing the aux battery. This is a quick fix.

3. If you can find a 24v to 12v charger, that would be the best solution.

4. If you are not happy with 1 or 2 and cannot do 3, then go for an additional 12v alternator. If the alternator will fit in your engine bay I have no idea.

 

[woytovich]

"If you can find a 24v to 12v charger, that would be the best solution."




Can you point me to a source (online) that he could use?

 

[bj70_guy]

This one is very nice:
E940 30A 24v-12v Battery Charger

 

[Radd Cruisers]

Here are few options for you:

1. Connect your axulliary battery in parrallel with one of the 12V starting batteries. This is a quick fix.

2. Take a 12v feed from one of the 12V starting batteries, removing the aux battery. This is a quick fix.

3. If you can find a 24v to 12v charger, that would be the best solution.

4. If you are not happy with 1 or 2 and cannot do 3, then go for an additional 12v alternator. If the alternator will fit in your engine bay I have no idea.

Do not do 1 or 2 above and expect that to work for more than a few hours. You cannot draw 12V from a 24V system without using a proper solution, and it seems that you realize this.

go to: BCDC1220 DC Battery Charger | Redarc Electronics

and your life will be just fine.

Go to Roodogs to place your order for the Redarc parts -

neil <at> roodogs4wd.com.au

Neil will take care of everything for you.


~John

 

[gotoy]

Do not do 1 or 2 above and expect that to work for more than a few hours. You cannot draw 12V from a 24V system without using a proper solution, and it seems that you realize this.


~John

The system is not exactly 24V, there are 2 x 12v batteries in series. So my solution for a 12V source is to take from a connectionfrom one of 12v batteries only, not both of them. This will work. However, the 24 to 12 charger is a far better option.

I have not stated connect the 12v to the 24v!!!Bang!!

 

[cicak]

Do not do 1 or 2 above and expect that to work for more than a few hours. You cannot draw 12V from a 24V system without using a proper solution, and it seems that you realize this.

go to: BCDC1220 DC Battery Charger | Redarc Electronics

and your life will be just fine.

Go to Roodogs to place your order for the Redarc parts -

neil <at> roodogs4wd.com.au

Neil will take care of everything for you.


~John

I agree with John no 2 causes chaos with batteris and your wallet. Been there done that

 

[gotoy]

I agree with John no 2 causes chaos with batteris and your wallet. Been there done that

The life of the batteries will be shortened, but as a short term solution, will be ok.

 

[crushers]

no, it will not "be okay" for the short term. you are wrong in your assumption.

 

[cicak]

The life of the batteries will be shortened, but as a short term solution, will be ok.

I found the batteries - until we corrected the problem pulled the one with 12v down very quickly - i.e. every 2 months I had to replace the battery as it gets destroyed by having the voltage lowered to the point where the vehicle will not start one battery is 12.n volts and the other (the 12v slave) will be less than 10v and destroyed it will not charge backup and has to be tossed away. Its definatekly not wallet friendly and this took us 2 years to find and fix this problem and we wired in a 24/12v transformer and someone in the workshop left it runnign after the shut the truck down result 2 very dead batteries. So I am now putting a REDARC 24v-12V charger (ordering tomorrow) in to run a little 12v battery to run the stereo and the 12v windows - I guess one day I should convert the window motors to 24v (if possible) and then I will be fine.

As John said it does not work very well at all running 12v of one battery on a 24v vehicle

Gotoy unless you have run this for a long period I would luve to know and how short is short? large 12V current draw (e.g. a fridge) will definately not be "ok short" term.

regards

 

[gotoy]

I found the batteries - until we corrected the problem pulled the one with 12v down very quickly - i.e. every 2 months I had to replace the battery as it gets destroyed by having the voltage lowered to the point where the vehicle will not start one battery is 12.n volts and the other (the 12v slave) will be less than 10v and destroyed it will not charge backup and has to be tossed away. Its definatekly not wallet friendly and this took us 2 years to find and fix this problem and we wired in a 24/12v transformer and someone in the workshop left it runnign after the shut the truck down result 2 very dead batteries. So I am now putting a REDARC 24v-12V charger (ordering tomorrow) in to run a little 12v battery to run the stereo and the 12v windows - I guess one day I should convert the window motors to 24v (if possible) and then I will be fine.

As John said it does not work very well at all running 12v of one battery on a 24v vehicle

Gotoy unless you have run this for a long period I would luve to know and how short is short? large 12V current draw (e.g. a fridge) will definately not be "ok short" term.

regards

Perhaps I should have used, 'temporary fix', or 'field fix' as opposed to 'short', something to last until a visit to the workshop.
Running appliances such as fridges like this...no.

 

[Radd Cruisers]

The system is not exactly 24V, there are 2 x 12v batteries in series.

Oh, boy....

The new math: 2 x 12 = 12 ? (answer should be 24V).

It is a very common misconception that you can draw of one battery and that the charging system will be okay. The reality is that this is not true, and the system goes quite rapidly out of balance.

Been working on 24V systems for over 20 years and I've seen some interesting things in my time.... I can't even start to explain what one guy wanted me to do to balance his 24V system by using light bulbs and diodes and all kinds of switches and wires.


~John

 

[lowenbrau]

Mark and anybody else faced with this situation...

Speaking as an electrician who has owned many 24Volt Land Cruisers and associated farkle I'd recommend putting gotoy on your ignore list and then going back and re-reading this thread. There is some very good advice here.

Additional options...

I use a 24-12V Surefire converter which puts out 13.8V to charge my aux battery. It works OK but would be better with a higher volt output.

There are two ways to use an auxillary 12V alternator. One is as a standalone to charge your aux battery they other is to use a one wire alternator connected to your low starting battery and lose the aux battery altogether. Connect all your 12V accessories to the low battery. Believe it or not the batteries will remain balanced and the 12v alternator will supply only the unbalanced load.

 

[gotoy]

Mark and anybody else faced with this situation...

Speaking as an electrician who has owned many 24Volt Land Cruisers and associated farkle I'd recommend putting gotoy on your ignore list and then going back and re-reading this thread. There is some very good advice here.

Additional options...

I use a 24-12V Surefire converter which puts out 13.8V to charge my aux battery. It works OK but would be better with a higher volt output.

There are two ways to use an auxillary 12V alternator. One is as a standalone to charge your aux battery they other is to use a one wire alternator connected to your low starting battery and lose the aux battery altogether. Connect all your 12V accessories to the low battery. Believe it or not the batteries will remain balanced and the 12v alternator will supply only the unbalanced load.

The only solution for an auxiliary atternator would be to charge an auxiliary battery independently of the main batteries, (2x12vdc batteries in series giving 24vdc) and alternator.

Your 2nd option will still cause unbalance in the system and lead to short battery life.

I agree with your 24-12 converter however the 24 to 12vdc charger, as from Redarc, would provide the permanent solution. Don't forget to use fuses in the wiring!!


as for the 'ignore'...well no issue with me!!!

Enough from me on this topic. Will only read.

 

[Whistler74]

An idea I've been kicking around lately: Rather than one larger aux battery and having to use a 24-12v charger, how about two smaller batteries in series (but parallel to the main batteries) so they would charge from the alternator. Then run the 24-12v converter from the aux. batteries.

Pros: 2 spare batteries could start the vehicle in a pinch
I suspect a converter is easier to find than a charger
Less voltage drop if batteries are at the rear of the vehicle.

Cons: cost of an additional battery
A bit more space needed

Any other thoughts? Crazy idea?

cheers

 

[lowenbrau]

An idea I've been kicking around lately: Rather than one larger aux battery and having to use a 24-12v charger, how about two smaller batteries in series (but parallel to the main batteries) so they would charge from the alternator. Then run the 24-12v converter from the aux. batteries.

Pros: 2 spare batteries could start the vehicle in a pinch
I suspect a converter is easier to find than a charger
Less voltage drop if batteries are at the rear of the vehicle.

Cons: cost of an additional battery
A bit more space needed

Any other thoughts? Crazy idea?

cheers

It is not a bad idea. I did the same thing in an HJ60 I used to own. The biggest down fall is that most of your accessories are 12V and the converters are at best 85% efficient. It seems better to waste that energy while the engine is running.