24 volt starer

The unimog guys just run 24v to the 12 v starter. It spins really fast that way. [emoji16]

They have issues because there are both 12 and 24v versions depending on intended use. You can bottom tap a battery but technically it’s not a good idea because it asymmetrically loads the batteries and can cause premature battery death. I’ve been struggling in the background with my buddies truck. It’s a 24v mog but he wants to run trailer plugs and such. There are converters that will handle plenty of juice for about everything on the truck (lights, gauges, power ports etc.) but I wouldn’t trust them for the trailer brakes. I will probably bottom tap the brake control circuit which won’t get used that often anyway to cause issues with battery life.

A 24v denso osgr for the correct jd or Isuzu engine application with a drive gear change may do what you want.

laserjock said:

The unimog guys just run 24v to the 12 v starter. It spins really fast that way. [emoji16]

They have issues because there are both 12 and 24v versions depending on intended use. You can bottom tap a battery but technically it’s not a good idea because it asymmetrically loads the batteries and can cause premature battery death. I’ve been struggling in the background with my buddies truck. It’s a 24v mog but he wants to run trailer plugs and such. There are converters that will handle plenty of juice for about everything on the truck (lights, gauges, power ports etc.) but I wouldn’t trust them for the trailer brakes. I will probably bottom tap the brake control circuit which won’t get used that often anyway to cause issues with battery life.

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I was reading through this whole thread, checking to to see if anyone had this suggestion, and finally got to yours near the end.

I have done it several times on old 6 volt vehicles, it works fine. People convert the whole vehicle over to 12v, change the bulbs, wiper motor, coil, etc. but leave the 6v starter and use 12v on it, and it works fine. I would just put 24v on your 12v starter, I bet it works great and really turns the engine over fast. Then just swap the alternator over to 24v and do what you have to do to run the rest of the truck. I needed 12v on a military 6x6 once, I bought a 24v to 12v convertor box from the surplus center in Nebraska.

franklin2 said:

I have done it several times on old 6 volt vehicles, it works fine. People convert the whole vehicle over to 12v, change the bulbs, wiper motor, coil, etc. but leave the 6v starter and use 12v on it, and it works fine. I would just put 24v on your 12v starter, I bet it works great and really turns the engine over fast. Then just swap the alternator over to 24v and do what you have to do to run the rest of the truck. I needed 12v on a military 6x6 once, I bought a 24v to 12v convertor box from the surplus center in Nebraska.

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I've done this with a ****y 12V direct-drive starter on a 4-cyl John Deere diesel. Just wasn't cranking fast enough because it was worn out. So... rig up two batteries, give it 24V.
It cranked much faster. Only problem was, it wouldn't /stop/ cranking - The darn solenoid didn't have enough spring tension to break the connection when the contacts were basically fused together from the extra current.

Remember, for a given resistance, if you double the voltage you double the amperage and quadruple the wattage going through it.
Now, the higher cranking speed should increase the effective resistance, but you've got to be careful and make sure you can disconnect power to the starter.

It appears the only difference is the solenoid. The rig mechanic pulled up a master catalog, the windings/armature are the same part number.Ohms law says amps=watts÷volts. 4.2kw÷24=175 amps or 4.2kw÷12=350amps
1 horsepower equals 746 Watts.So a 4.2kw starter produces 5.6 horsepower. if you look at the math you will see that even a small change in voltage has a dramatic effect on amperage.it is much easier for the batteries to supply voltage than amperage during initial start.Weak batteries that allow even a 2 volt drop during start..4.2kw..4200/10volts=420amps to deliver the rated 5.6hp.

That's not quite how it works...
Batteries have internal resistance. The more current you draw, the lower the output voltage. The less charged (or more worn out) they are, the higher the internal resistance.

The starter motor can be treated as a resistive load also, at least while it's cranking the engine. The 4.2 kw is maximum but the engine load does not necessarily demand all of it. But, let's assume for the moment that it does (cold day, thick oil, etc.)

That 4.2 kw is probably at 10 volts, maybe lower, since a "12 volt" battery does not put 12V out under cranking load! CCA, cold cranking amps, is rated at 0F and 7.2V or above for 30 seconds... So, 420 amps. That's an equivalent resistance of 10/420 or 0.0238 ohms. Now if your batteries are weak and drop 2 more volts, now you only have 8V across the same 0.0238 ohms = 336 amps, and your power is only 8 * 336 = 2.7 kw. THAT is why low voltage causes weak cranking... not because batteries can put out voltage better than current.

This is an oversimplification, too, since turning DC motors have "back EMF" (acting as generator to oppose the supply voltage), the load changes once the pistons start moving, etc. But Ohm's Law still applies

Also, the 12V starter I bought off ebay came with a testing sheet. It was rated for rated power at 8V I think - somewhere between 7.2 and 8.5.

to the original post:

i had to get an engine running out of a truck once, and did not have any way of setting up a glow plug system. still need to get it started so.. basically hooked the batteries in series to make 24 volts. this was a sock starter nothing done to it. the reason most manufactures only use 12 volt is your average joe does not know how to jump start or charge a 24 volt system. and could be dangerous. anyways the motor spun to life like a damn air starter no problem. no glow plugs and a quick shot of ether fired right up after sitting for over a year.

If you give your stock starter 36V it will turn over at like 1000 RPM's for a while.

FordGuy100 said:

for a while.

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These are the key words, right?

FordGuy100 said:

If you give your stock starter 36V it will turn over at like 1000 RPM's for a while.

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Or you could engage it on the dyno for an extra ten horsepower