Why are there 2 batteries?

[koolex11]

I know it's a total noob question, but I'm trying to learn as much as I can before purchasing. I know 2 batt. = 24V. But what is the advantage to have that in a CUCV? If I understand correctly, if one battery dies then the truck dies, so one doesn't back up the other. So I guess what I'm wondering is why do MVs run 24V?

Not a mechanic, trying to learn something new and figured an MV might be a fun place to start!

Sorry if this answer is somewhere already. This site is huge! Thanks for your patience...

 

[Recovry4x4]

The military uses 24V on all ov there other tactical vehicles. It would make sense that this vehicle also have 24V so that it can slave or be slaved off of other trucks. Mil radios used in vehicles also are 24V, another need for it. 24V is actually a superiour voltage for starting circuits and the like.

 

[koolex11]

Can you temporarily rewire to bypass one dead battery and start the truck if needed? Or doesn't it work that way? I'm just thinking, what if I show up at GL on recovery day and 1 batt is dead from sitting? Want to avoid towing if possible.

 

[wreckerman893]

Diesels are high compression engines....in cold weather it takes a lot of Cold Cranking Amps (CCA) to start them.

Even my Ford Ranger Diesel has two batteries in it and it's a small 4 banger.

Lots of civy diesel trucks have dual batteries but they are set up for 12 rather than 24 volt.

If one battery is dead it is better to put two new ones in (or two used of the same voltage).

You do not have to use the big TL batteries that are in the truck....two high CCA batteies will work..you just have to make sure the terminals are on the correct side so you don't have to cross the cables to hook them up.

There are a lot of threads on batteries here.....search is your friend.

 

[jasonjc]

Can you temporarily rewire to bypass one dead battery and start the truck if needed? Or doesn't it work that way? I'm just thinking, what if I show up at GL on recovery day and 1 batt is dead from sitting? Want to avoid towing if possible.

You had better plan on BOTH batt being dead and the drive shaft bent and no keys.

 

[Recovry4x4]

Can you temporarily rewire to bypass one dead battery and start the truck if needed? Or doesn't it work that way? I'm just thinking, what if I show up at GL on recovery day and 1 batt is dead from sitting? Want to avoid towing if possible.

Nope, can't do that. You need to have a plan in place to drag it home on recovery day. You are more likely to find a driving deuce than a driving CUCV on a GL sale. Bring 2 batteries. Even if you jump it and get it running, can't take the chance that it will actually hold a charge. CUCVs are usually a pretty painless recovery but they are rarely driven off the lot.

 

[koolex11]

are cucv's still being used or are they all being demilled now?

 

[319]

are cucv's still being used or are they all being demilled now?

Still being used by at least the Guard.

 

[hwcurtice]

Interestingly, My 92 Dodge D250 Diesel, only had one battery. Big bugger, but just one. I asked about it too...

But then, because the guy worked at Kenworth, here in the PNW, I think he did some mods to it so he could stick a non-standard battery in there...

 

[USAFSS-ColdWarrior]

Side Note:
This thread is an excellent example of the mentorship available through the SteelSoldiers website.
My SALUTE to the upstanding character )aka: troops) helping with these fundamental questions from a new MV Addict.

Carry on

 

[koolex11]

I am always grateful for the help I get. I love all the different perspectives from every walk-of-life out there. Whenever people say the Internet is bad for our society I think of things like this. A perfect example of "making not taking"

 

[papercu]

only had one battery. Big bugger, but just one. I asked about it too...

Still 12v either 1 large battery with more CCA or two smaller batteries with the same CCA.
I would think working at the Kenworth place he had access to used truck batteries. Wayne

 

[combatmech]

Hey Koolex, If you do change both batteries, please please please be careful and mark your wires prior to battery removal. I changed the batteries in my first truck, didnt mark them, hooked up the back battery backwards and ended up frying stuff. Took a long time to figure out what got burnt up. My haste to fix a problem, just made it worse.
Good luck with your new MV!!

 

[Matt1031]

Twice the volts means 1/2 the amps necessary for the same power - Ohms law. For something like a light bulb it doesn't really matter, but For high amp draw loads like starters 24v is a much better deal. Starters require a *lot* of amps.

Practical example:
A 24v winch will draw approximately half the amps of a 12v winch under the same load. This means everything stays a lot cooler and huge honkin' 4/0 cables are not necessary.
Here's a calculator if you want to check numbers
and a Wiring gauge chart

24v is a clear winner for high amp draw applications.
When shopping for batteries, don't get hung up on the CCA number. With 24volts and twin batteries you don't need high cold cranking amps - high *reserve capacity* is what you want.

 

[Barrman]

The best advice is what you have already seen on here many, many times. Download the TM's and read them. Read them over and over again until you understand just about everything.

However, here is a fast course on CUCV electricals. They are basically a civilian Chevy truck. All the normal Chevy truck stuff is 12V. Lights, heater fan, wipers and such. Only the starter, glow plug and slave systems use both batteries and 24V. The front battery which is charged by the drivers side alternator is what the truck runs off of. The rear battery is charged by alternator #2 on the passenger side.

Several people have this in their sig lines and it is worth knowing. If it is electrical, clean it. If it is rubber, replace it. Read the TM and carry a -20 with you make up the watch words any CUCV owner should follow.

 

[USAFSS-ColdWarrior]

Ya know... I haven't had, nor do I currently have or NEED a CUCV class vehicle, but I find this thread interesting and now I'm starting to want one just to TINKER with.

I guess I'm an OD Addict, huh?

 

[Doucheand1/2]

Ya know... I haven't had, nor do I currently have or NEED a CUCV class vehicle, but I find this thread interesting and now I'm starting to want one just to TINKER with.

I guess I'm an OD Addict, huh?

you should they are great vehicles. "I have yet to have a bad chevy"

 

[maynard83]

When I had my M1010, I always carried a spare battery with me. Once when I was far away from humanity, the battery closest to the front headlights died and I used the spare to start the vehicle. Boy was I glad I was a little paranoid. With these trucks now reaching the 30 year mark, it is always smart to have at least one spare battery (among other things).
If you are recovering one from a yard, prepare for a worse case scenario so carry with you at least 2 batteries, tow bar or trailer, an air compressor, etc...
Best of luck to you. These vehicles are pretty reliable if you put some tender loving care into them.

 

[Recovry4x4]

Hey Koolex, If you do change both batteries, please please please be careful and mark your wires prior to battery removal. I changed the batteries in my first truck, didnt mark them, hooked up the back battery backwards and ended up frying stuff. Took a long time to figure out what got burnt up. My haste to fix a problem, just made it worse.
Good luck with your new MV!!

This can't be overemphasisized enough. Draw a diagram, take a pic. Especially true if you take along your local mechanic. Countless CUCVs have been munged up because they are so different than their civilian counterparts (electrically).

 

[trukhead]

The civi part of the truck runs on 12 volts. The military adaptations on the truck are 24 volt for above stated reasons. You can not use one battery to back up the other battery because they are connected in series as well as their respective alternators. The alternators are Isolated ground as well so you can't just swipe one off a monte out back in the weeds.

However there are articles out their to change out the trucks to 12 volt operation. I am going to retain the 24 volt on the restoration but will go with a 12 volt self exciting one wire alternators on the beater that came with alternators missing.

Find the TM's and wiring diagrams and study them as these military adapted systems are cool as all get out and very simple and very clever.