Advice/help wanted about 24 vs 12 volt

Hey guys I'm hopefully about to buy my first m715 (http://www.m715zone.com/vb/showthread.php?t=25492)

I have always wanted a m715 I am a firefighter and our forestry truck I believe is a 69. I just got approved from the bank today for this purchase and I'm excited. I am trying to start my own off road shop and recovery business. I currently have a 2011 jeep JK and 3 76-81 jeep CJ7. I want to have this m715 as a tow rig, recovery vehicle and show piece.
My dream is to keep this looking original. I want to add exterior work lights and emergency lights and sirens. I also want to add winches to it for recoveries.

My dilemma is keep it the original 24 volt system or convert it to 12 volt. Mostly everything I want to add to it are all 12 volt appliances. Is there a easy way to add like a 12v fuse panel that I can wire everything into or just make everything 12v and wore it all like I would on a normal jeep?

Are there any good write ups on how to convert it to 12v I looked but didn't have the best luck. I know a lot of people say if there is nothing wrong with the 24 why change it? I agree I like the 24v it's more reliable and original. But what's the best way to wire up all the other stuff I want to add!??? Any advice would be great! Thanks I look forward to owning my first m715!!

Hello and welcome to the M715 Zone. Hope that you get your truck and show us some pictures.

Since the 24 volt system is two 12 volt batteries in series, you could just get your 12 volts from the connection that goes from one battery to the other one. Then, it would 12 volts to ground. I don't think that it would cause much problem as long as you are not doing something like running a high consumption item off of that battery. Theoretically, the charging system would sense the low battery and charge it through the battery that has more charge.

Some of our members have converted to 12 volts. That would necessitate new gauges and a new sender in the fuel tank, new horn, new starter (12 volt from a Jeep Gladiator truck), new coil, new distributor new lights etc. Not sure if the turn signal stuff will work on 12 volt.

Others will have more info for you if you just wait around for a few.

Good luck with the truck.

More information. Looks as though they also used the single battery for the 12 volt application. Look down in the document to page 17 or so.

http://www.m715zone.com/vb/pages/man...st_convert.pdf

We should call this the "Great Debate".

Problem being, everything out there is 12 volts, and Our Trucks are 24 V. Mil.

The "best answer" pulling that much of a load, seems to be add an additional alternator, an additional 12 volt battery or bank of batteries, Isolated and dedicated to 12 volt appliances. If this is something you can do, the time and effort up front will pay out for decades in ease and convenience of a isolated 12 volt system.
IF you decide to go this route, I suggest using 12 volt Deep Cycle Gel Cels, instead of "Starting batteries"... because You will be pulling load off of them , and not just starting the vehicle.

Don is correct in that you can "Tap Off" the 24 volt system to get 12 volts.
You can actually do that on each battery, being careful, and running a dedicated , isolated ground wire for the 2nd battery in the 24 volt system.

The problem with this "Tap off" option is that you may be pulling too much off one battery in the bank, and not any or enough off the second battery.

I "personally" believe that the alternator will accommodate for this imbalance, to a point, depending on how far down you pull the single 12 volt battery.

They also make electronic Battery Balancers for 24 volt systems, that will monitor the depth of charge on each 12 volt battery in the 24 volt bank, and charge each one individually depending on their hunger at the time.

I personally, run a stock 24 volt Truck ( with a Chevy 292 Engine and 12 volt dist. )
When I got the truck, there was a 24 volt to 12 volt converter box on the fender well to ONLY power the 12 volt post on the coil. That's It. Nothing else.

Since I bought the truck, I have added 10 circuits, 12 volts fused and Isolated to run Driving lights, flood lights, alley lights, washer fluid squirters, dome lights, cigarette lighter adapters for Q beams, a backup light, a SPARE 12 volt line for a future electric fuel pump,
a spare wire to run a 12 volt cooling fan... and a few other goodies.

Its possible to "Tap Off".. but its a little dangerous because everything needs to be kept isolated, fused... even on the NEG side, and honestly its pretty complicated BUT someone who has worked with low voltage wiring can figure it out pretty straight forward.

If I could make anything happen instantly...
I would like a 12 volt alternator, a 12 volt battery bank of Gel cells, all isolated.
What I have works, but I have a few Years experience dealing with both low and high voltage systems.

I'm sure you can figure it out easily. Just fuse everything. Isolate everything. Grommet any thru firewall or thru metal wire holes, and cover all the wires with wirw wrap when you are done.

The waterproofness of said coversion.......
Will NOT be MIL SPEC watertight.... as the M 715 is from the factory.

The Winch will be Your big power draw, then the lgihts.
Go deep cycle on your 12 volt isolated system, should you choose that route.

Hope that give you some ideas.

Fuse everything. Double check everything. Isolate everything, even the ground wires.

Good luck... just throwing some stuff out here.

I just want to clarify,

all of the 12 volt circuits i installed were directly off the batteries themselves, and NOT off the 24 volt to 12 volt converter.
Its still there and still only running the single 12 volt post on the coil, and everything else is direct wired and fused.

I DID make a short jumper wire that will reach from the 1st 12 volt battery ( the one grounded to the chassis), so should the 24 volt to 12 volt converter box ( electronic ) ever fail, I can reach this wire pre fabricated from above the windshield wiper area, and connect it directly to the battery, then to the coil...

Effectively bypassing all of the lectronics on the truck, and allowing me to start and run with no electronics involved ( I have points and a condenser as well )

BTW, I like Your Truck.
That radiator/ grill guard is nice and the entire truck looks sound and solid.

I'm sure I left out some important details on the 12 volt system.

Just giving some ideas and getting the though process going.

If you have a stock engine, not sure how to install a second alternator, but it should just be a bracket, longer belt and Isolated connections to the engine ( like a fiber washer isolating the alternator bracket from the metal of the engine )

There is one more option.

A 12 volt bank of batteries in the bed ( gel cell ) that are solar charged, AND shore power charged , just like an Ambulance or Fire truck, with a removable shore power plug that disconnects if you drive off.

Also a small 12 volt 2 cycle generator, like a Coleman Lightening, will charge the batteries out in the field... and will also do 24 volts with the flip of a switch and 1000 watts of 115 volt with another flip of a switch.

Happy Hunting.

If You , errr when You have more questions... just ask.

Welcome to the zone. The advise above is correct. Good luck and post some pictures.

Thank you all for you responses. Most of the lights I want to add will be led so they won't draw much. I'll look into everything you guys mentioned. If I keep it all 24v I'll probably spend the extra money and get a 24v winch.

I think it is a bad idea to just tap off one battery to get 12 volts from a 24 volt series set up.. What can happen is one battery will get low and the other will not but the stock alternator cannot "sense" that only one battery is low and charges both batteries. You will end up under charging one battery and over charging the other.


I'd suggest doing a full 12 volt conversion or using a separate 12 volt system with a separate 12 volt alternator and battery.

Or just leave everything 24 volts.

About 6 years too late im afraid but for any one else that finds this forum my local sheriff's office search and rescue had this dilemma. They added a 100 amp chevy one wire alternator mounted above the original 24v, the original 24v alternator had the three belt so we used the empty forth. All the accessorie lights and radios were ran off a power fuse block distributor. I do not know yet of any problems. Ive personally think it works fine ive had to replace the 12v alternator twice cause im cheap and buy the carquest remanufactored ones.

Not being an electrical expert. If you choose to use the stock harness and convert to 12V there will be no fuses. If you were to add fuses do you need to add a whole block of them? lights, starter, horn, etc, etc or can you just put one big fuse inline from the battery.

A lot of Big rig trucks running 24V are already doing this (tapping for 12V power). All you need is a "battery equalizer" to evenly pull a charge from each 12V battery and keep them balanced ("equalized").

Here's a great article on how to do just that!
Guide to Successful Dual-volt systems


On the flip side side... Some light duty trucks/tractors with a 24V starting system only use 24V for the starter, and they basically use the center tap method to get 12V to run everything else.
They run a 12V alternator to charge both batteries by using a charging isolator to charge 12V batteries in series rather than charging both batteries at 24V wired in parallel.
Essentially running 24V only at startup, and 12V the rest of the time. Running a dual 24V/12V system this way favors 12V power with only intermittent 24V draw.
If you have a heavy continuous 24V draw on a regular basis, You'll want both batteries to be equal (equalizer) to ensure consistent balanced power for both your 12V/24V devices.