Question re running 12v accessories with 24v truck?

[DonFromCanada]

Just a quick question regarding the easiest way to add some 12v accessory plugs (cigarette plugs) to my 24v truck.

I would like to add at least three plugs (two in the front, one in the back) to provide 12v power to my accessories (GPS, cell charger, etc) as well I would like to put a normal 12v radio in the truck in the center cubby.

Is there an easy way to do this providing enough amperage? Also, how do I know if my truck is a positive or negative earth ground?


Thanks!

Don

[J!m]

A 24 to 12 volt step-down transformer should not be too hard to find. A 240 to 120 step-down will work as well, but it will be very heavy and large. You just need half the windings on the secondary side as on the primary side. You can also use A step-up transformer (if this is all you can find) and wire is backward to step down. Since it's D/C to D/C it's fairly straight-forward.

What may be easier/better is to get an inverter for 110 volt power. These can typically take 24 volt input with no issues and give 12 volt output (optional on some models, so check first) as well as 110 volt A/C power for running your margarita blender.

To check polarity of the vehicle, see which cable from the battery is attached to the frame. Negative ground attached the (-) battery terminal to the frame, while positive ground attached the (+) battery terminal to the frame.

I may be wrong, but I'm fairly sure ALL 24 volt trucks are negative ground.

Also, an expert on the big military generators may be able to provide a pin-out to get 12 volts out of that generator by halving the windings. I imagine it is not easy, or impossible, or more people would do this...

[greenmeanie]

Trying to turn a 24V gen into a 12V for the same power loading is a bad idea. Because P = IV for the same power loading the current in the winding will double. This means more heat in the windings and, if it doesn't just melt down off the bat, a far greater likelyhood of a short and reduced life. Removing windings can also affect power quality although this is more of an issue with AC gens and modern electronics. 24V gens are too expensive to play games like this with when a step down transformer can be done cheaper and is the tried and accepted method.

Cheers
Gregor

[DonFromCanada]

Trying to turn a 24V gen into a 12V for the same power loading is a bad idea. Because P = IV for the same power loading the current in the winding will double. This means more heat in the windings and, if it doesn't just melt down off the bat, a far greater likelyhood of a short and reduced life. Removing windings can also affect power quality although this is more of an issue with AC gens and modern electronics. 24V gens are too expensive to play games like this with when a step down transformer can be done cheaper and is the tried and accepted method.

Cheers
Gregor

I appreciate the replies.. I think the step-down transformer is the way to go for me - any ideas on where I could get one?
My only idea is possibly a shop that stocks parts for tractor-trailer big-rigs. Truckers have to have 12v accessories, right?

/Don

[JimCT]

Transformers work it AC current, not DC, you want a 24V to 12V convertor. Do a Gogle search or on Ebay, there are always a few in ebay for sale. Using the same in our '63 Unimog radiobox. Jim

[Erin]

Try a 24V DC to 12 V DC converter. 24 to 12 VDVC is a simple coversion resulting in a reduction in potential and a loss of heat. Try Googling "12 24 DC converter" and see what comes up. I recently researched a 24 to 12 VDC converter and was pleasantly suprised that a black box converter was available to use in that purpose. Keep on Keep'in on and you'll find it.
Slangavar,
Erin

[RollingBrick]

Hey Don,

Not sure if anyone on the board here has had any dealings with these guys but they sell 24-12v step down converters.

Cold War Remarketing, Inc.
8571 N. US Highway 85
Littleton, Colorado 80125
Phone: (303)346-8462
Fax:(303)346-8463


http://coldwarremarketing.com/images/24-12ReducerSM.jpg

24-12 Volt Converter!

Sheldon

[a109]

If you are able to split the load fairly evenly you can tap 12 V off each of the batteries. The down side of this very simple method is the need to ballance the load. An unballanced load will result in un even charging of the batteries and an early battery death.

John

[TeriAnn]

Just a quick question regarding the easiest way to add some 12v accessory plugs (cigarette plugs) to my 24v truck.
Don

Silly question. Do you have a 24V battery or two 12V batteries in Series? If you have two 12V batteries in series you can add a 12V subharness by running a wire off the connection between the two batteries.

[JimCT]

tappingoff one 12v of a 24v system will ensure premature death to both batteries, the voltage regulator will never see the true load and conditon of the batteries. A convertor is the way to go. Jim

[Pleco]

We once had to get the same volt drop for a military application. Because of the high wattage needed, and the inherent nature of the troops to be a little rough, we put 9 high wattage diodes in series on a heatsink to get the volt drop. It is very robust and quite cheap. You can also use a variable dc power supply, and take the transformer out, and connect your 24 volt to the input. It all depends on the amperage needed. Remember that you will burn 12V (drop from 24V to 12V) x the amperage in Watts. 1 amp will give you 12watts of heat. If you want to pull 5 amps, it will become 60 watts. This is quite a bit of heat to dissipate. In the higher case, diodes on a heatsink will work better. If it is properly assembled, it should last almost for ever.

[Willard]

tappingoff one 12v of a 24v system will ensure premature death to both batteries, the voltage regulator will never see the true load and conditon of the batteries. A convertor is the way to go. Jim


That is guaranteed, in my Diesel LC it was 24 volt, someone put a 12 volt winch on it and a few other accessories and it killed the battery every 6 months. replaced with a 24-12v converter and a 24V winch motor and never a problem again.
I have a 24-12V converter in my Rover and so far so good.

[a109]

tappingoff one 12v of a 24v system will ensure premature death to both batteries, the voltage regulator will never see the true load and conditon of the batteries. A convertor is the way to go. Jim

If you can balance the load on the batteries, which will mean two wiring systems, the charge will be ok BUT this is hard to do.

John