Not really a question of power but more of voltage.

Will any damage occur if I connect my +12v system to a +24v diesel motor to jump start it? Do I need to worry about overloading my system with an extra +12v?

Not sure of the alternator comes into play but if it makes a difference I don't use the stock alternator, I have a 250A, 3G alternator.

 

Some context is needed here.

All diesel pickups, and many commercial trucks use a 12v electrical system. If they have two batteries, they're in parallel, so the total system voltage is still 12v.

Larger trucks (like Class 8+ tractor/trailer) and many buses, construction equipment, etc... use a true 24v system. If they have two 12v in series, you can connect your truck across ONE of the batteries, and help give it a little boost.

If you connect your truck across both batteries (or a single 24v battery) you will almost certainly destroy almost everything electronic in your truck.

 

lead head hit nicely. OP if you are talking about something like an F series super duty truck, they generally have two 12v batteries wired in parallel, which means there is a primary and a secondary battery. the primary battery is on the passenger side as normal, and is the one you connect the jumper cables to.

 

as long as you only connect to a single 12 volt battery you will be fine. with a series battery connection,
what i do is connect to a single 12 volt battery and let that charge for 10 minutes or so.
then switch to the next 12 volt battery and let that charge for 10 minutes.
then i try to start with the jumpers connected to the single 12 volt battery.
for a parallel battery setup, i connect to the first 12 volt bank and charge the bank for 20 minutes, then switch to the second bank and charge that one for 20 minutes.

the big thing is to make sure you only have the jump truck connected to 12 volts at all times, never let it see 24 volts.

 

These vehicle systems are 12 volts just like previous posters said. When a vehicle has two batteries wired in parallel, you retain the voltage of one battery but the amperage is stacked.

Now if they were wired in series, you'd keep the same amperage as one battery, but double the voltage.

I learned that while working on vintage guitar amplifiers. Got my *** shocked more than a few times with 500 + volts coming out of the power capacitors.

 

I've boost started Many class 8 tractors in my time, with my 150 5.0. Dead of winter, 3 out of 6 batteries dead or failing, etc. (I worked at a truck stop...) All were 12v, neg systems. Have also come across 12v Positive systems, and a 6v, double decker bus from the streets of London on it's way to the ports. 12v total, just more CCA. I always checked the leads to the frame from the batts to make sure. I am old, and prone to contradiction, so I always welcome fresh input to keep my 'cells' charged.
Regards,
Dan

 

Most of this I didn't know...thx

 

This /\/\/\ !

It's really not about diesel vs. gas. It's all about battery and voltage. In addition to what Tom posted, be careful about polarity. One thing that can get you into trouble when boosting multiple batteries, or positive ground systems would be to have the bumpers of the vehicles touching. Keep them apart!

 

In regards of the last post, had a pair of 'cheapie' cables. Wouldn't do Nothing as far as jumping. Shoved the starter vehicle against the dead vehicle, bumper to bumper, put both cables on the 'hot' terminal, and it started right up.

 

That't actually a funny solution.

I originally asked the question here because I did have to jump start a diesel a while back. After about a minute with the cables connected, the diesel motor barely turned over...after another minute or two it started. So this was really just my alternator charging the batt and storing amps. In my ignorance I thought this had something to do with a 24v vs 12v systems but I know that to not be the case now.

 

no, alot of them as 12 volt electrical systems with 24 volt starter. they use a series/parallel switch in the battery leads to make the 24 volts for the starter

 

I had two completely dead batteries in my '02 F-350 diesel once. Tried jumping it just by hooking cables to a running vehicle. Nothing. So I disconnected the ground cable from one battery and jumped to the other. That was quite a bit better, but still too much was going into the battery. So I pulled one battery completely out of the diesel (leaving the other unhooked) and stuck a good battery in it. It cranked over strong on the one battery and started right up. Then I hooked up the ground cable to the one battery, then removed the good battery and put the other dead one in (all while it was still running, being very careful not to let the batter cable touch ground).

 

Yup, if you are boosting 12V neg ground to another 12V neg ground, this can and has been done, but we're talking about multiple batteries, 12V vs. 24V systems and possibly positive ground. Not something you want to make any assumptions about.

 

In my experience, 2-gauge jumper cables are the minimum you should use if you actually want to use a vehicle to crank over a completely dead vehicle.

Anything smaller than that will likely require several minutes of the running vehicle charging the dead vehicle before you even can think about starting it.

 

i use 600 amp welding lead with 500 amp cable ends for my jumper cables.