D2 5j alternator

Do you mean 27amps output or 27volts while running? Either one will be enough to keep the batteries charged. Usually when you shut it down, the batteries should hold a little over 24, more like 25-26 volts for an hour or two at least.

Have you had trouble with the batteries going dead? The way the 24 volt electrical was installed on the JD tractor, one battery negative was connected to the starter winding all the time (stud on the end of the starter) while the positive of that battery was grounded to the frame. If the starter got "leaky" it would kill the right side battery while leaving the left side charged up. They used that arrangement so they could run all the electrical except the starter and generator on 12 volts. If you have it connected that way each 12 volt battery will be connected to the frame, one by the + and one by the -. A straight 24 volt system will only have a jumper between the two batteries (no connection to the frame there).

If the 1 wire alternator starts charging by itself or you jump it to excite it each time, it should be plenty to keep the batteries charged, that doesn't take much output. If you have lights etc, then you might not get enough out of one bacause of the rpm the engine turns (only ~1500). If you have belt drive, with a good pulley ratio, you can increase the rpm. If it's a direct gear drive conversion, then you get what the gear ratios give you and if you need more, then you have to find an alternator that will supply it at that rpm.. Sometimes the 1 wires won't excite and you can wire up a regulator plug and a switch to give them some juice when you start it up, but you have to remember to shut off the switch every time or use an oil pressure switch to so it.

There is 24 volts when the switch is on ,o when off. How do you exite it? Thanks, a lot of info!! I think I can use it.

Is it a Delco alternator?

If it is, look at the end with the output stud on it. You will see there is a regulator plug on the top edge and the output stud will be on the left side of the thing, about 9 o-clock. To make it excite you need to apply battery voltage + to the right hand terminal of the regulator connection on top. You can do this with a temporary jumper or a permanent install.

This wire must be switched off whenever the engine is stopped and really only needs to be connected momentarily each time the tractor is run. If you have a switch on it, just run a wire from the switch down to that terminal. If you want it to be automatic, connect it to an oil pressure operated switch that closes when pressure builds up and opens when the engine stops. This is the opposite of the typical oil pressure "idiot light" switch, but you should be able to get one most anywhere.

Once it excites, it will usually maintain voltage even when it's idled down, it's just that sometimes they won't excite when you start one up after it's sat up for a while. On a truck or something like that, you can usually rev the engine up and make one excite, but you just don't have the rpm to make a stubborn one go on an old CAT.

If you go to an autoparts store sometimes they have an extension harness for Delco alternators where someone has modified an engine and needs a few more inches. Cut off the female end and use the male end that plugs into the alternator. The heavier wire that plugs into the left regulator terminal nearest the output stud can simply be connected to the output stud full time, no switch needed on that one.

If this doesn't do it, we'll figure something out😊