What's the advantage of 24volt system?

[StrykerPez]

I've had experience with 24v in two of my civvy vehicles. One was a VW race motor for a fiberglass sand buggy I built. It had something around 13:1 compression and I went through 2 starters in about a month before deciding to upgrade. Just so turns out, a second Optima battery and a 24v starter off e-Bay was cheaper than a gear-reduc starter. The second vehicle was my gigantic 97 GMC 3500. I set up a 24v system in it because I got a 20,000lb winch that was 24v.

 

[bigflew]

clarifacation duramax 12 volt

 

[pvtjorge]

Putting a 24 volt stater on a L134 engine (flat head 4 cylinder) didn't make much since for over coming torque. Must have been for other reasons.

 

[m16ty]

I am not sure what you mean by older diesel cars and trucks but all the ones I have worked on have been 12 volt with two batteries to provide the extra amps needed without running the batteries down. I have never seen a car that started on 24 volts in the civy truck or car world.

I have never seen a big rig that was 24v either. Some maunfacturers may have made some prototypes but to my knowledge they never produced any in large numbers. One of the main reasons I doubt they did is you couldn't run the lights on any trailer on the market unless you changed the bulbs.

I do think it's something the trucking industry needs to look into though.

Most constuction equipment is 24v. That is the only widely used civilain application of 24v that I know of.

 

[bigflew]

Putting a 24 volt stater on a L134 engine (flat head 4 cylinder) didn't make much since for over coming torque. Must have been for other reasons.

your right about that. must be so a jeep could slave start a tank.

 

[maybefixit]

Here's a puzzle for anyone who's in engineering:

Assuming a single vehicle (let's say with a GM Diesel engine so it makes sense):
Using a 12 volt starter should take 2x the amps of a 24 volt starter to rotate the engine.

But: Assuming that the armature length in both 12 and 24 volt starters are identical (let's just say for fun they are the same casting), will the 24 volt starter have more torque?
I'm thinking that the magnetic field strength will not matter (being derived from the wattage) but, do the thinner 24 volt wires allow more turns on the same size armature, allowing more field density?

 

[pvtjorge]

Maybe the 24 volt system on the jeeps was to help jump start small aircraft engines. I think someone said that already. My M38 has 24 volt system with slave cable outlet.

 

[GoHot229]

24v is better in many ways IMO. Smaller wiring, less voltage loss over long wires, cranks faster, and seems to have more reserve capacity than two batteries in parallel.

I offen wonder why more vehicles in the civilain world haven't went to 24v. Mainly big trucks and diesel pickups. I guess it has to do with people not liking change so they stay with 12v.

I'm somewhat confused here....I was working on my Duce here and there on the guages and the wireing used looked to be ten to twelve guage, relativly largr as wireing goes?

 

[hobie237]

Group,

The starter needs to be 24 V, for the cranking torqe to overcome compression. By running a 24V system, you drop one component of failure (24V - 12 volt system) and also helps save batteries. THe old desiel cars/small trucks started on 24 V, then went to 12V for normal ops.

As mentioned earlier, the military used 24V to help with compatability.

Laterrrr
Avn-Tech

So how, exactly, do you explain all the civilian trucks with the SAME MOTOR that starts JUST FINE on 12v?


The primary driving force, for the military, is standardization. Secondary benefits are derived in the fact that the wiring can be smaller to the starter, the starter may or may not be better (debatable), etc. Of course in daily usage these benefits are mitigated by the fact that you have a handful of harder to get/more expensive parts, not to mention the fact that jumping off a normal 12v car/truck is a royal pain (sorry, not all of us do all our driving in convenient little convoys).

 

[m16ty]

I'm somewhat confused here....I was working on my Duce here and there on the guages and the wireing used looked to be ten to twelve guage, relativly largr as wireing goes?

Well the military does tend to overbuild things. I don't know what the size of alot of the deuce wiring is but I do know that the insulation is thicker than on most vehicle wiring. That may be throwing you off.

12ga wire is good for 20amps no matter the voltage but a light or gauge will use roughly half the amps on 24v than it would on 12v.


hobie, It does seem like my brother's M1008 turns over faster than the civilain GM diesels of the same era (especially in cold weather). Don't know if it has to do with 24v or not but it does seem that way.

 

[hobie237]

Turning over faster may also have to do with the batteries that are in there. Remember that the stock configuration calls for a minimum of two 550CCA batteries. Most of the guys with military trucks tend to have much stronger batteries (many with civilian trucks do, too, but that's another story). The internals of the starter may result in faster cranking as well, I haven't torn into the starters to see what the differences are. The point is that the 12v system is more than enough for the truck.

 

[maybefixit]

I don't think the military uses the 24v so that they can use smaller wires in Deuces and tanks and tractors. On land & water vehicles you want to keep a larger wire for durability, vibration resistance, and corrosion survivability. Also the land vehicle design engineers will pick 12-14 gauge wire out of habit, and the mechanics are used to working with those size wires. I'd bet that the starter, ground, and charging wires on a M1009 are the same diameter as the civi version, even though they could (theoretically) be several sizes smaller.

The military doesn't care if a Deuce is 4 pounds heavier, but in a Cessna Bird Dog (L-19 /O-1 Observation aircraft) that 4 pounds is almost another gallon of fuel you could carry. They would use smaller wire in aircraft for weight savings, and those mechanics are used to the smaller wire size.

12v is a fine standard, so is 24v, and the client base is totally different for each. I'd say neither is inherently better, and both are really driven by their market's inertia. Come to think of it, I guess I'm saying that's true for the wire size issue, too.

 

[Bklyn Phil]

In WW2 the Army vehicles used 6 volt electrical systems. This changed over to 24 volt during the Korean War. I was in uniform from 56 to 62 and all the "stuff" we had then including 400 cycle generators for the radar vans and 60 cycle gens for the AA guns had a 24 volt system. It was labor intensive to pull the four batteries from the generators to check them for water.

Here are two articles that mention the WW2 6 volt systems

6 volt electrical WW2

http://med-dept.com/amb.php (35 pp of text and pix)

http://home.att.net/~dodgewc54/ (2 pp w/ links to WC 54 and WC 64)


Phil, Bklyn

 

[m16ty]

Around the time of WWII almost all vehicles were 6 volt. I know I've changed many old tractors that were 6v over to 12v. Makes all the difference in the world. I just figure going to 24v is just that much better.

 

[hobie237]

Yeah, pretty much everything prewar (and for a bit of time post war) was 6v. Then the industry standard went to 12v, and the military, for a variety of reasons, went to 24v.

 

[Bklyn Phil]

I recently got 105 WW2 TMs on CD. Lots on ordnance and a few on motor vehicles. It seems the smaller vehicles had 6 volt systems (up to the deuce); bigger trucks had double batteries for 12 volt starting, tank engines that were 9 cylinder radial (aircraft) engines ran on 24 volts.

Some fun reading dealing with freezing batteries, engine pre-heatring, cranking without ignition to distribute lubricating oil, old shade-tree-mechanic diagnostic lists.

Phil Bklyn

 

[Speddmon]

hobie, It does seem like my brother's M1008 turns over faster than the civilain GM diesels of the same era (especially in cold weather). Don't know if it has to do with 24v or not but it does seem that way.

The 24 volt M1008 ( and any 24 volt starter) does turn over faster than any other 12 volt starter due to the configuration of the starter motor itself. Starter motors are what we call series wound motors. Meaning the field windings and the armature windings are electrically in series with each other. This is done to provide higher torque than if it was a shunt wound motor.

a lot of my experience is with 250 volt DC cranes. Shunt and compound wound motors allow for more precise speed control when lowering a load so you don't smash things. However when lifting, the compound would motors are reconfigured to series to give more torque to lift the load, especially if the load is stopped in mid-air.

Therefore since you don't need speed control to start a motor but you do need a boat-load of torque, starters are series motors.

Here's a puzzle for anyone who's in engineering:

Assuming a single vehicle (let's say with a GM Diesel engine so it makes sense):
Using a 12 volt starter should take 2x the amps of a 24 volt starter to rotate the engine.

But: Assuming that the armature length in both 12 and 24 volt starters are identical (let's just say for fun they are the same casting), will the 24 volt starter have more torque?
I'm thinking that the magnetic field strength will not matter (being derived from the wattage) but, do the thinner 24 volt wires allow more turns on the same size armature, allowing more field density?

Yes the 24 volt starter does have more torque, and the magnetic field strength plays a great part in this. Without going into great depths of the theory of DC motors, as a DC motor starts to turn the amperage needed to turn the motor drops significantly. The reason for this is a phenomenon known as counter EMF. As the motor turns the windings actually generate voltage (counter EMF) going the opposite direction the the voltage applied. In a compound wound motor this counter EMF if used to help with the speed controlling properties, but in a series wound motor (Starters) the counter EMF just feeds into the circuit and creates more speed. That is why you can never run a series motor without a load applied to it. The faster it turns, the more counter EMF, creating more speed and more counter EMF and so on until the motor literally spins itself fast enough it disintegrate. But with a load applied that counter EMF is magically turned into torque.

 

[Coal Cracker]

24v is better in many ways IMO. Smaller wiring, less voltage loss over long wires, cranks faster, and seems to have more reserve capacity than two batteries in parallel.

I offen wonder why more vehicles in the civilain world haven't went to 24v. Mainly big trucks and diesel pickups. I guess it has to do with people not liking change so they stay with 12v.

From what I hear in the automotive world, 24v is being looked at and researched. They are looking for ways to lighten up the vehicle bodies and switching to all aluminum wire. also chrysler was supposed to have been develpoing a starterless engine, my understanding is that they are/were trying to inject fuel into the combustion chamber and ignite it, thereby throwing the piston down, and starting the combustion process

Also heard of possible cevelopement of air start, dont know how much of a developement that is though, since the 40's-50's some diesel locomotives used that process, ALCO for one.

 

[m16ty]

Also heard of possible cevelopement of air start, dont know how much of a developement that is though, since the 40's-50's some diesel locomotives used that process, ALCO for one.

I've seen big rigs with air start for years. Advantage is it turns the engine over faster in cold weather. Disadvantage is that once the system gets some age on it and develops small leaks you can find youself with no air to turn the starter after the truck has sat awhile.

 

[Verkstad]

I've seen big rigs with air start for years. Advantage is it turns the engine over faster in cold weather. Disadvantage is that once the system gets some age on it and develops small leaks you can find youself with no air to turn the starter after the truck has sat awhile.

My experience is air starters are mainly on delivery trucks. They may restart dozens of times in a day. Airstarter is much simpler and longer lasting over electric
Also the battery demand, maintenance etc. is less.

Also dual starters are an option on many motors, one could be electric, the other air.

Rgds, Jakob