What's the advantage of 24volt system?

[realm]

What is the advantage of having a 24-volt starter? Was this done just to be compatible with other military vehicles, or is there an increased reliability in having 2 batteries?

I'm not an electrical guru, but seems like having a 12-volt starter with 2 batteries in parrallel would be better reliability. If one batt failed you have a 2nd to fall back on.

With the 24-volt system you gotta have 2 just to be par.

 

[68impalass]

a 24 volt starter will use half the amps a 12 volt will.

 

[Blood_of_Tyrants]

Yes, it was to make it compatible with the other military vehicles. And realm is right, you use half the amps while cranking on a 24v system.

 

[ida34]

Also makes it compatible with military radio systems and other 24 volt accessories.

 

[Dabba]

im not much of an electrical guy either. whats the significance of using half the amps?

 

[maybefixit]

24v was/is a popular standard for piston driven aircraft since it allowed all the wiring in the airplane to be smaller diameter. This allows a smaller size and weight of the generator/alternator and the starter.

It's my understanding that one of the reasons for a 24v MIL-spec voltage was so that you could jump-start a piston-driven US Army helicopter, observation aircraft, or DC-3 from the NATO receptacle on a Deuce (or genset, etc.). In very cold weather, it's easy to run down the small batteries in an airplane trying to get the thing started. Of course, as ida34 mentioned, then all the radios fit all the vehicles too.

I think all the modern jets have gone to the 400hz AC standard - which is what those generator sets are for.

Civi GM diesel pickups (from the 80's anyway) do use 2 batteries in parallel as you described- 12 volts but twice the amps available. I assume the single battery was not enough on those to crank the diesel without severely stressing the battery, especially if you're also cycling the glow plugs.

 

[reloader64]

Maybefixit, you assume correctly. Most gasoline engines have around 9:1 compression ratio. The old diesels, GM, Ford, and Dodge, all had a compression ratio of about 22:1. With the higher compression, relatively large cubic inch motors, and glow plugs or manifold heaters, one battery was really stressed trying to start them. I know the GMs still use two batteries, and I believe the Fords do, too. I don't know about the Dodge. Speaking of that, my '03 DuraMax is cranking slow, I need to check the batteries, before they leave me stuck somewhere.

Scott

 

[steelandcanvas]

I know the GMs still use two batteries, and I believe the Fords do, too. I don't know about the Dodge. Speaking of that, my '03 DuraMax is cranking slow, I need to check the batteries, before they leave me stuck somewhere.
Scott

My '97 Dodge Cummins has two batteries.

 

[m16ty]

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.

 

[bigflew]

I know up here in north mich. my 24v 1009 starts a lot eisier in extreme cold than a GM duramax 12v

 

[neb4x4]

What do you mean a Duramax 12V...? A duramax is a 32 VALVE Engine!!! 12 Valve Cummins maybe???? LOL

 

[littlebob]

24v was/is a popular standard for piston driven aircraft since it allowed all the wiring in the airplane to be smaller diameter. This allows a smaller size and weight of the generator/alternator and the starter.

It's my understanding that one of the reasons for a 24v MIL-spec voltage was so that you could jump-start a piston-driven US Army helicopter, observation aircraft, or DC-3 from the NATO receptacle on a Deuce (or genset, etc.). In very cold weather, it's easy to run down the small batteries in an airplane trying to get the thing started. Of course, as ida34 mentioned, then all the radios fit all the vehicles too.

I think all the modern jets have gone to the 400hz AC standard - which is what those generator sets are for.

Civi GM diesel pickups (from the 80's anyway) do use 2 batteries in parallel as you described- 12 volts but twice the amps available. I assume the single battery was not enough on those to crank the diesel without severely stressing the battery, especially if you're also cycling the glow plugs.

I think that maybefixit got it. If the vehicle is 24v and draws half the amps it is more reliable than a 12v system with the same size wiring and connectors.
In the airplanes they do it for weight in a MV they do it for reliability.

 

[neb4x4]

Oops... I had a brain fart!!!! I was just looking at a link talking about cummins motors 12Valve, and 24Valve... Then I came across this one and saw 12V not thinking or reading to much.... Sorry, I've been up too long....!!!

 

[Avn-Tech]

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

 

[ida34]

The car companies are looking at kicking the batteries up to 36 or 48 volts because of the extreme electrical loads in new cars. I can't remember the exact volt value but the whole idea is so the electrical wires can be smaller and hence lightening the car.

To help people with understanding the relationship of amps to volts I will pass along Ohm's law. Basically, amps determine the size of the wire. To lower amps you need to raise volts. The end result is Watts. A given electrical device will need a certain amount of watts to operate. This value stays the same no matter how many volts the circuit is. The lower the voltage the greater the amps. The basic formula is below.

amps X volts = watts.

This a website with calculators for all this. There is also a formula for resistance with explains how the big resister on the firewall takes 24 volts and transforms it to 12 volts for the glow plugs. It also explains why the voltage rises when a glow plug burns out.


Ohms law calculators.

 

[ida34]

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

I hate to differ but the power to turn over a high compression engine does not change. If a 24 volt starter is used for the engine then it will draw half the amps of a 12 volt starter. A 12 volt starter will still turn the same engine over and will require the same watts as the 24 volt starter but it will take twice the amps. 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. This does not apply to big rigs and big trucks as I have not worked on them much but I used to be and work as a certified mechanic in Michigan before I joined the Army.

 

[JohnFire]

I know alot of older fire trucks started with 24V. Up to at least the mid to late 70's. Later on most of the ones still in service were converted to 12V.

 

[AceHigh]

To me the most obvious reason was to keep GI and civi mechanics from stealing components. Just sayin...

 

[gsomersjr]

48 volt technology was going to be the future of automotive electrical systems. It is designed to use electric motors to drive the peripheral systems (ac,ps,alt,etc) instead of belt drive. This would allow the various systems to be placed throughout the engine compartment and not have to be aligned in a belt drive system. With the mess the car companies are in it's hard to say now when, or if, this will happen.

 

[mangus580]

I can tell you, the 24v direct drive starter in my 1009 spins considerably faster than the 12v Gear Reduction starter in my wifes 99 Suburban 6.5