It mostly depends on what is normal for the market they machine is used in.
Some markets may be tilted toward one or the other, making it more difficult to get parts and other support for the non-preferred option. Kind of like being left-handed in a right hand world. From a clean sheet of paper, 24 volt is generally better, as everything can be downsized except the insulation, which is not a significant factor.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

For industrial applications, 24 volt is often preferred as it coincides with a standard controls voltage. For marine and high reliability applications, 24v is preferred due to isolated ground.

Thank you much for responding. Lou Scannon and TugboatEng.
I understand it now.
In the beginning, I thought it was more about application side rather than downsizing components.

And can depend on the size of engine used. Larger engines would generally need 24 volts for the starting system.

We use air for that.

"How can we decide"?

You don't. The engine supplier does or if he's being generous then he offers you the choice.

Or just take the 24V and use two 12V batteries in series and run all your 12V stuff off one battery or share the load between two batteries.

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@LitteleInch
That is what I want to understand. Why there is 12v and 24v system. what makes engine manufacturer to decide whether to 12v or 24v?

Size of the starter motor and cables for one, plus all the other cables for power nowadays can be reduced in size.

apparently military trucks all use 24V so its easier to have one system.

Also before LED lights headlights could be 70W for 24V versus 60W for 12V.

Why do you want to know?

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Also: If you get a response it's polite to respond to it.

It is for my understanding. Sometimes, I configure engine and it comes to me as 24 v and sometimes 12 v. I was curious to know, why?

please, let me know if you have more literature or resources that I can go through.

Quote:

Or just take the 24V and use two 12V batteries in series and run all your 12V stuff off one battery

It's not as simple as that. Assuming the charging device is 24v (nominal), across both batteries obviously, if the two batteries are not delivering the same amount of current (which is what will happen if the "bottom" battery is delivering current to the 12V devices as well as to the 24v circuit), it will gradually become discharged while the top battery becomes overcharged. Over time, both batteries will be ruined. To do this properly, a battery equalizer is needed. These are commonly available, for exactly this situation.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

I did think it was a bit more complicated than I made out...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Mixing voltages also creates a ton of maintenance and logistical issues - miswired circuits that are over/under voltage, correct part/wrong voltage on the shelf, etc. Its bad practice that causes a lot of heartburn for both customers and the regulatory folks.

Wait until 48V becomes more common! Both car and commercial vehicle sectors are applying it particularly to hybrid powertrains and WHR [waste heat recovery] systems in CV's.

An interesting note, one of the reasons 24 volt never gained popularity for automotive applications is that the filaments for the light bulbs are much thinner and couldn't tolerate bumpy roads.

Diesel mechanic/generator tech here. Modern On road trucks (in North America anyway) are all 12 volt, presumably to maintain parts interchangeability with lighter on road vehicles.
Most of the smaller off road equipment and generators that only require one battery are 12V. Since batteries do not come in 24V, it wouldn’t make sense to add an extra battery just to make a higher voltage. Larger equipment and generators are usually 24V for reasons already mentioned including smaller conductors and less voltage drop.
I know some of the older gensets were 36 volt (just as Some older cars were 6V)

Heavy trucks in US start on 24 volts.

Batteries mostly come in 2.1v flavors.

Irbcan - Define "Truck".

I think the 24V mark starts at 5 tonnes plus.

Truck in Europe means large commercial transport capable of carrying 5tonnes plus.

In the US it seems to be used for pick ups/ domestic vehicles.

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Quote (Tugboateng)
 Batteries mostly come in 2.1v flavors 
 

Per cell, yes. For the vast majority of Diesel engine starting applications, 12V batteries are used and connected in series for 24V (when the system is 24V).

Quote (Enginesrus)

Heavy trucks in US start on 24 volts.

Many years ago, yes. Anything built in the last 30 years will be 12V start.

Quote (Littleinch)

Irbcan - Define "Truck".

For the purpose of this discussion I meant class 7 and 8 truck. Most Everything on the road these days is 12 volt anyway.

Fair enough. There does seem to be a bit of US Europe divide on this subject.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Quote:

Wait until 48V becomes more common! Both car and commercial vehicle sectors are applying it particularly to hybrid powertrains and WHR [waste heat recovery] systems in CV's.

I believe you are thinking of 480v hi voltage systems, which are commonly still controlled with 12v lo. College professors and the media have been predicting a lo voltage change for 20+ years, still haven't seen it tho for the obvious reason - no benefit and plenty of cost.

No, I did mean 48 volts not 480 V. Take a look at the DOE Supertruck program and you will see them using 48V for the electric PAS, air compressor, and WHR.

Not on top of this topic myself, but I note that the North American auto industry switched from 6v to 12v during the 1950s.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

Quote (TugboatEng)

An interesting note, one of the reasons 24 volt never gained popularity for automotive applications is that the filaments for the light bulbs are much thinner and couldn't tolerate bumpy roads.

All solved by LEDs these days.

je suis charlie