Yes, trucks often use 24V. I expect tractors do as well, but I can't remember. Fork lifs use 48V. Soon some cars will be using 42V.

Cheers

Greg Locock

As Geg said, Trucks (Goods Vehicles) often use a 24V system but no cars that I can think of (with the possible exception of some of the big 'trucks' used in the USA).

42V systems are one of the big pushes for the future for efficiency and weight saving reasons, but there are a number of practical problems that have delayed the volume introduction into the market.

Arent Military vehicles in the US either 24 or 28 V?

Thanks for the answers.  A sub-question that I should have asked along with the first one:  in such vehicles with 24 volts, is the cigarette lighter socket still at 12 volts? My instrument would plug in there.  Is this socket a standard at 12 volts?

I recently had a chance to check a few tractor/trailer (trucks) rigs to see what voltage they were using (a result of a post in another forum).  What I found was an almost universal use of 24V with a couple of exceptions.  My youngest, now disability retired from the US Army says that all the vehicles he came in contact with were 24V.  That was my experience of many years ago, also.
As a kid on the ranch and, later on my father-in-law's farm the tractors were 12V but, they were rather old and small in comparison to some of todays units.

Rod

Felixc. The 24v systems in trucks are all 24v. Some use an inverter to supply 12v for radios etc.
Harvey.

felixc / patdaly:

Not only US Army trucks but almost all land-based military vehicles world-wide have 24V batteries.

There is some comfusion about 24 / 28V. 24V is the nominal battery voltage; with the engine running, you get 28V. Equipment is therefore specified to run successfully between 18 and 32V for military equipemt in UK.

Lots of larger pleasure boats use 24/28V systems also. It's partly due to the need to crank large diesel engines - lots of amps at 12V!

Cheers - John

There are some tow-trucks that uses 24V (two 12V) to jump start the vehicles in cold weather (very remote areas). So if the vehicle has a dead battery (low SOC or open battery), you could see a voltage higher than your protection circuit rated at 18V.

In a previous life, I worked on a offroad/mining vehicles that ran two 12 volt batteries (24 v) for the starting circuit, and then ran 12 volts for the accessories/communications radios. I suspected that these where a compromise/oversight design based on what was available for the right price. The system worked well, but you always needed to have your voltage meter at the ready.

What is the SAE standard number for cigertte lighters / power outlets in cars? It might say what voltage can come out of there.

Do not worry about it. All the things I have seen designed for cigertte lighters didn't worry about 24V.

Thank you guys!  It looks like 24 volts may be found at many places.  I will add a high-side switch to turn off the device if the voltage exceeds 18 volts.  In addition to a TVS for surges, and a polyswitch for short circuit protection.  So it won't work during overvoltages but it won't break, with hopes that the owner will figure out that something may be wrong.

All 24 volt systems I have seen, run 2 X 12 volt batteries in series. It's pretty easy to run a circuit from one of the batteries only.

Regards
pat

Pat

Yes you can do this and it works. Remember you're charging in series and therefore both batts will get the same charge energy. But you're depleting one that also provides the 12v supply. Eventually you end up with one good and one flat battery, unless you devise an off-line system for charging at 12v in parallel.

Better solution is to use a 24 to 12 voltage converter. These come in 2 types - the cheap ones are inefficient but it doesn't matter unless you're using something for long periods off charge. The better ones are switch mode units which are around 80 - 90% efficient. Get them from auto or marine stores.

Cheers - John

don't know about electric vehicules but what I know is that
for forklift trucks you have dc motor controllers that work
at different voltages : 24 Volts, 36 Volts, 48 Volts , 72
Volts , 80 Volts. depending of the importance of the truck
and the technology of the controller is different
(mosfet, thyristor, transistor)
MB.
--
http://matthieu.benoit.free.fr/

I agree with harrisj about taking 12V from one of the two 12V in series. The advice from vehicle manufacturers is never to do that. Always use a 24v/12v converter. The exception being that it is ok to connect the memory of the radio to one of the batteries due to the very small current used.
Incidently, in Europe, all heavy trucks and buses(7 tons and above) are all 24v, probably due to the large torque required to turn the engine in cold weather.

Don't know which commercial trucks in the U.S. use 24V, but the largest US-owned manufacturer of Class 8 trucks - the largest trucks - do NOT use 24 volt systems.  We use 12V exclusively.
Lots of 12V batteries,  but only 12V total.

Felixc:
If your design works with 9 to 18 V , it must take a fairly
low current; could you please tell us how much it is?

<nbucska@pcperipherals.com>

     All Military-series (or M-Series) vehicles used by the United States Military run on a 24V system.  This is so our troops can get a jump start and can just start other colilition vehicles because many foreign countries have start 24/ run 24 vehicles.  Now although the HMMWV is 24 volt, the Hummer (civilian version) is a normal start 12, run 12 system.  But vehicles like the M113 Armored Personnel Carrier, M1A1 Tank, M1078 LMTV, and M35 "Deuce" transport truck are all start 24, run 24.

SSgt J. Lerner
Vehicle Maintenance, USAF

www.sae.org has a hotlink to info on 42v battery.  Looks like the coming thing.  Should you design for this higher voltage now so the instrument works in the future applications?

why not just use a voltage regulator, like L7805 or L7812?

Felixc: Add a cheap switching regulator !!

<nbucska@pcperipherals.com>

Class 8 trucks mainly use 24vdc for accessories and some 12vdc for low amp apps like communication or signaling devices.

Thanks guys for all the comments.  The design has been done using a LM1572 from National Semi. It is a 500KHz switcher.  With a switch to turn off whenever the voltage was exceeding 18 volts.  I needed 1.5 amps at 5 volts.  The product has a sealed casing, plastic, and is quite small.  Power efficiency and real estate were important constraints in this design, as this was a retrofit of features that were external to the device. A couple of thousands of boxes have been produced with no troubles so far.  Cross fingers.
With the emerging 42-volt standard, new switchers chips have appeared during 2003, that can handle higher input voltages.  More will come in the future, I'm sure.

In the US Air Force, our
systems were all 28V.

Current over the road trucks (Class 8) pretty much all use 12V systems - there are a lot of batteries but they are wired in parallel.

Truck

UK military uses 24v apparently so that we can jump start HMMWV's that have a flat battery (Lerner 1 please note) Land Rovers for military use have 24v systems but the civvy versions run 12v.

I have a feeling that a lot of civilian heavy commercial trucks also use 24v but you'd need to check that out.

Most light aircraft went from 12to 24 volts in the 1970s as electrical systems were getting too heavy due to adding more features (radios, lights, heaters, sensors, etc.).  The higher voltage allowed smaller, lighter wires and electrical equipment.

24volt
European and Japanese heavy trucks.
Many Japanese small trucks and 4X4s.
Most earthmoving machines, cranes etc.
Most military vehicles.
Most large marine engines.
Rail engines.
Some large self contained agriculture equiment,eg combines.

12volt
Cars.
Most agriculture equipment, tractors etc.
Onroad USA trucks (I believe this is to allow the use of cheap readily available accessories, eg TV's, fridges etc)

Some vehicles used to have a 24v start 12v run system. This system used a series parallel switch to link the two 12v batteries in series for 24v starting, and in parallel to give 12v for normal running.

Working on both 12v and 24v systems I see the advantage of using 24v.
Starting is easier due to the higher cranking speeds that 24v systems usually have.
Tail lights are also brighter in truck/trailer units due to the reduced voltage drop in the wiring looms.

Gentlemen,
I have some equipment that uses cat 3512b engines that are 24 volt systems. The mechanic that works on these units wants to hookup 6 12 volt 55 watt work lights and pull the 12 volt off the center post on the 24 volt batteries(2 12 volt in series) I need some reference materials on unbalanced charging.

Gentlemen,
I have some equipment that uses cat 3512b engines that are 24 volt systems. The mechanic that works on these units wants to hookup 6 12 volt 55 watt work lights and pull the 12 volt off the center post on the 24 volt batteries(2 12 volt in series) I need some reference materials on unbalanced charging.

Why not runs the lights in series instead?

(in pairs, assuming each light wants 12V)

each light wants 12 volts
havent thought about running in series
my idea was to use 24 volt bulbs (less current, less drain)

Unbalanced loading of individual cells in a series battery is a recipe for disaster.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

A common setup on larger truck is
24 V start to keep startr motor size down
12 V run to take advantage of all the 12 V stuff on market

25 years ago I had professional reasons for being intimately familiar with electrical systems in tractor trailer type trucks as well as busses in the USA (as well as in Europe).  Back then, in the USA 12/24 systems which used a crossover relay called a 'series/parallel' switch to series 2 or 4 12V batteries to make 24V for starting (only) were quite common.

After the truck was started, the 'series/parallel' switch put all the batteries in parallel for 12V operation of the electrical system.

Battery technology improved, and not only do trucks no longer use four 12V batteries for 12 V start, they now commonly use only three.  The weight savings of even one battery is significant.

I haven't seen a 12/24 volt start system on a modern truck in years, but I still have quite a few 'series/parallel' switches in my possession if anyone still uses 12/24V start.

The only heavy duty vehicles that commonly use 24 volt systems in the USA are MCI busses, the brand manufactured for and by Greyhound.  Finding 24 volt bulbs and apurtenances for them is a pain in the neck for their owners, since they are not common to tractor trailers and not on truck stop shelves.

As an aside, I haven't seen any air starters in the last 20 years either in case anyone asks.  Officially it was 19 lb. lighter than an electric start, but few people had the brass to use them.  When their one battery went junk and it failed to start, there were two things to jump, electrics for the fuel cut off switch and an air line to recharge the starter air resorvoirs.

Now an opinion.  European trucks back then (I can't speak for now) used 24 Volt electrical systems while the USA used 12.  European fuel costs have been in the range of double that of the USA for about the same time period.  Across the fleet of tractor trailers in Europe, the reduced weight of the electrical systems due to the use of 24V systems represents real weight.  IF or when diesel fuel costs permanently stay above $3.00 USD/gal, look for 24V or 42V electrical systems in our rigs.  It represents real weight savings across the number of truck/trailers in our country.

rmw

There are still air starting systems around (one of the larger fleets still uses them), but they are not nearly as common as they used to be.

Truck

Well in MHO. You can bet on 42VDC systems on some, most then, on all cars and trucks.
42VDC driving all the auxillary equipment:
Fuel pumps
Lighting
Power breaks
Air Conditioning
Power stearing
Power seats
Power this
Power that
The only belt (aux) drive off the engine will be to the altenator.
I cannot say when but, it will come.

Regards
pennpoint

 

I concur with nzsparkz. In my 20 years of experience in the medium duty off road sector everything I have come in contact with was 12v.

The only exception was a military spec forklift, with 24v being a NATO spec. We even had to equip it with a NATO jumping receptical, which is one big round socket with both terminals, so young "jarheads" can't reverse the polarity and blow something up.

As for electric forklifts, there are several commonly used voltages. 24, 36, 48 and some 72

I know of at least one large fleet that still uses air start (or did as of my last contact with them.  But they also put aluminum wheels on every position except the steers.  They said that aluminum saved weight everywhere else, but wasn't strong enough for the steer axle.  Funny, most tractors come stock with all steel wheels except the steer axle which is aluminum wheels.  Go figure.

Our forklifts, for what it is worth, are 36 and 48 V. respectively.

rmw

I'll put even money on less than 50% of the US new vehicle fleet being on 12 V, not 42V, by 2012. takers?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

I wouldn't touch that bet.

rmw

Greg, I would bet on 1/3 of new models using 42v by '12

Félix,

1.5Amps? I guess you are using a DC/DC converter, or?. Which EMC directive do you have to fulfil? A DC/DC converter which such a high current probably gives you EMC troubles. Do you have any shielding?

Antonio