24VDC boost to 12VDC truck
24VDC boost to 12VDC truck
(OP)
We have built some military vehicles that operate on 12V but have 24V capabilities. We've done this by using a battery bank with some of the circuits coming off of one set of batteries wired in parallel (12V) and then the other circuits coming off both of the sets of batteries wired in series (24V). Under normal conditions this works great but when all the batteries in the battery bank are dead, the truck has to be boosted by a 24 V supply (written in the spec). The problem is that the vehicle electronics and the starter system are all 12V. If you have enough time, you can run the 24V through both battery sets and wait for them to charge but in a military environment, this is not feasible. We looked at the possibility of connecting a huge resistor to simply throw half of the heat away but because the starter has a variable current draw, the voltage drop across the resistor would also be variable.
My background is in mechanical so forgive me but I think that there may somehow be a solution in this thread using zener doides?
thread237-145132: Best way to get high current from dirtbike magneto?
Thanks in advance
Charlie Harland
My background is in mechanical so forgive me but I think that there may somehow be a solution in this thread using zener doides?
thread237-145132: Best way to get high current from dirtbike magneto?
Thanks in advance
Charlie Harland





RE: 24VDC boost to 12VDC truck
RE: 24VDC boost to 12VDC truck
An additional piece of info is that the starter draws from 100 to 800 amps while the rest of the vehicle system (glow plugs, dash lights, sensors) draw significanly less. Its my understanding that it all has to be energized in order for the boost to work.
RE: 24VDC boost to 12VDC truck
http://en.wikipedia.org/wiki/DC_to_DC_converter
800 A is a lot to ask of a converter system, however. (Unless you want to tow it behind your rig.)
RE: 24VDC boost to 12VDC truck
Steve Wagner
RE: 24VDC boost to 12VDC truck
RE: 24VDC boost to 12VDC truck
A reliable solution would be to replace your glow plugs with 24V ones. Or Rewire them putting pairs in series, then reconnect them across 24V.
Reconnect your starter across 24V.
Leave the rest of the stuff across the one series battery.
Now when normally starting you will have more starter power. The modified glow plug circuit will run them at the same power.
During jumps nothing will now be different. The instruments and lamps and other stuff will run as normal.
Yes, you can run the 12V starter on 24V. It's done all the time on millions of diesels.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 24VDC boost to 12VDC truck
RE: 24VDC boost to 12VDC truck
My suggestion is: These 24 volt vehicles that you will get the jump-start from, surely they will have two batteries in series, so just jumper from one of the batteries, voila - 12 volts!!
Alternatively, it may be possible to get a carbon pile regulator setup to do the dropping 12 volts under load. This would be an interesting retro piece of engineering.
Also the diode series string suggested earlier would work, you would get about 1.6 volt drop each, puck, or capsule diodes would easily carry the current, could be expensive.
Regards, Ray.
RE: 24VDC boost to 12VDC truck
1. A disconnect switch for the 24V stuff so you only have the 12V and then jump from one battery of the source.
2. Rearrange the electrical system so that you have both batteries in parallel and a boost converter for the 24V stuff.
Best is just to get 12V from the source vehicle; you don't really want power electronics in the starting circuit for a large Diesel engine.
RE: 24VDC boost to 12VDC truck
rtronics; Some of us actually read ALL of a Poster's posts NOT just the original one. He can't consider having 12V available from the jumping vehicle...
Keith Cress
kcress - http://www.flaminsystems.com
RE: 24VDC boost to 12VDC truck
A 24 volt jump would have to be directly to the starter. You could probably design a "Jumper" connection that would only apply 24 volts to the starter solenoid.
Bill
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"Why not the best?"
Jimmy Carter
RE: 24VDC boost to 12VDC truck
RE: 24VDC boost to 12VDC truck
Then, the boost will end up suppling the correct voltage to the necessary parts to start the engine. As for the starter motor, it really doesn't care if you supply 24V to it occasionally.
I do know that many 6V vehicles have been boosted from 12V vehicles and many 12V vehicles have been boosted from 24V vehicles. Happens in industrial settings a lot. When batteries go dead whatever other source is available is used. Pick-ups or small tractors running 12V are boosted off dump-trucks or loaders running 24V. Over voltaging the whole electrical system is not a very good solution though.
RE: 24VDC boost to 12VDC truck
RE: 24VDC boost to 12VDC truck
You should consider what I said about the glow plugs too, because on my measly 6.2L diesel they draw 120A.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 24VDC boost to 12VDC truck
They didn't like ether either. I once had to crank a bus left for a week at around freezing and at about 10,000 ft. (left in an airport parking lot without access to plug in's) and I didn't have any ether (Heck it was June). But I did have a small propane bottle (for deicing brake lines when they froze) and I took the air filter out and put the bottle in with the valve opened and ran up front and cranked it with the gas flowing and when it busted off then I had to run back to get the propane bottle valve shut and out of the intake before it got sucked into the engine. Closest call I ever had getting one of those dogs cranked. Thanks for the memories Keith.
rmw
RE: 24VDC boost to 12VDC truck
All equipment except the starter ran on 12 volts. The batteries charged on 12 volts. One batery was re-connected in series to supply 24 volts for starting. During starting all lights and accessories were supplied with 12 volts from one battery. At all other times both batteries were paralleled for 12 volt operation. The series parallel switches are available off the shelf.
The wiring diagrams for the switches should be available from the supplier selling the series parallel switch.
Why re-invent the wheel??
Bill
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"Why not the best?"
Jimmy Carter
RE: 24VDC boost to 12VDC truck
The big question is - What kind of load can you run off of a single 12V battery when it is one of two series connected 12V batteries that are dead and being boosted?
My first though was that if the batteries are just run down and need a charge that they would likely share enough to run a significant load. Probably not the starter motor but they should be able to run every thing else. So, using a 24V starter and 12V electrical system is possible.
However, if one of the batteries has a physical defect such as a dead or shorted cell then all bets are off. This is the case where boosting might not work because the 12V system would not get the correct voltage.
RE: 24VDC boost to 12VDC truck
They were developed years ago when 12 volt systems would not reliably start diesel truck engines and 24 volt lamps would not stand up in vehicle service.
There are not many 24 volt accessories available compared to the numbers of 12 volt accesories.
A 24 volt boost must be applied directly to the starter circuit. A simultaneous failure of both batteries is rare. Even if both batteries are low, a twelve volt boost across one of the barreries will often start the engine.
There are hundreds of thousands if not millions of 12/24 systems in use.
Bill
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"Why not the best?"
Jimmy Carter