Since I love electrical work and making Frankenstein , I've decided to convert my truck to a 12/24V system. The hub of the entire system is going to be the 200 amp 12/24V alternator from a HMMWV.

I want to put the starter and grid heaters on the 24V circuit along with a few choice accessories......

I know I can rebuild the starter with 24V parts, so that's no problem. My question is, if I use 24V relays, can I run 24V to the grid heaters? My instinct is telling me yes since they will be pulling almost 1/2 the amps they did on 12V, but I know there is a possibility something in the system (like the PCM) can keep them on for too long and possibly damage them. If that is the case, I'd just take the PCM out of it and run a separate switch to trigger the relays.

So, anyone a grid heater expert?

They used these engines in a lot of off-road equipment. A lot of machines are 24 volt, so you might be able to find one. Maybe the grids will cross reference? I'm sure you could find one out of a different engine and make it work.

When I converted my Willy's pick up to 12v I left a lot of the 6V stuff in. It all seemed to take the higher voltage fine.

I have no idea how a big draw like a grid heater will take it.

Because a grid heater is simply a large resistor/heating element, putting 24v into a 12v grid heater would probably result in disaster. Theoretically TWICE the normal amperage would flow and considering on 12v they glow red hot, it would also probably melt or catch fire. I'm sure you can find 24v grid heaters for a 6BT though. Other electrical loads like starters, etc once upgraded to 24v compatibility will draw roughly half as much amperage for the same wattage/power. Good luck!

Probably no need to worry about the starter. Switching from 6 to 12 volts in early model cars doesn't require a different starter.

http://lib.store.yahoo.net/lib/yhst-...2vreportv3.pdf

I disagree on the amperage as well. A device will only draw as much amperage as it needs. The key word there is draw. The battery doesn't push amperage, the device pulls amperage. For instance the radio only needs about 5 amps to operate. Even though the battery is rated for many times that it works just fine.

Voltage drives current and using simple ohms law (V/R = I) one may easily deduct that doubling the voltage over a resistor will double the current. I would strongly suggest not running a 12v motor/starter on 24v. Sure it will work, but its simple enough to upgrade them and you have the potential to again run double the rated power through it, greatly decreasing its life expectancy. Going from 6v to 12v (while still doubling) is only half the jump from 12v-24v. As you increase voltage, the tendency for excessive arcing to occur on the brushes/contacts increases. If you fed a 12v radio 24v I would be highly surprised if it didn't break.

Try plugging a 120V heater into 240V and see how that works out. Try a 12v light bulb on 24v. Incandescent lights generate about 5% light and 95% heat! The heating grid is the right resistance for 12v. 24v will burn it in two in seconds (It might be really bright inside your intake manifold for a moment). 6v starters will survive 12v, as GAmes said, but they spin over really fast and won't survive long if you crank more than 5 seconds. I've seen contractors fry skill saws in seconds because they were too cheap to put the proper voltage ends on their extension cords.
Overall, it sounds like a really expensive way to ruin a perfectly good truck.

Spot on mate!

gents . we have a winner .

IF the OP knows electrical wiring as he indicated , he would have known this .

We have a excavator with a 5.9 cummins. It has a 24v system with grid heaters. It is a kobelco sk200 mark 4. You might be able to look up the part number and see if they are the same. If different you might find the part number of the gaskets to see if the bolt patteren size is the same. A good cummins dealer should know.

Why? It works fine as it is. DON"T screw with what ain't broke.

As I understand it the grid heater is made up of two 12 volt elements. You may be able to modify the elements to work in series instead of parallel.

Hey, that could create one more bolt that could drop into the engine.

While I fully understand the reasoning behind using 24 Volts, I don't think it's worth the effort.