Alternators

HenryO) · Feb 27, 2013

My new old 1948 Farmall H has an alternator instead of generator. Never had one before. Would the alternator drain a battery ? (it happened or so I am told) Would it require that the ignition switch be on to do that . what are the differences . Does the alternator have a built in regulator?? Thanks in advance for the answers I will get.

cecil bearden · Feb 27, 2013

I assume you have a one wire delco alternator that is used on most conversions. It does have a parasitic drain in the range of 10 milliamps. It will take several months to drain down a fully charged battery. I would get a Battery disconnect switch and install it. I have installed them on most of my equipment and will eventually have one on all my tractors and trucks. You install them in the circuit between the battery and the main power wire. Don't run your starter wire through it, it will burn out the switch. My Belarus tractors came with them from the factory.. They can sit for weeks and then start right up...

Dave Sherburne NY · Feb 27, 2013

If it is the 10 SI 1 wire alternator it has a built in regulator. If it has a parasitic drain, it needs a diode in the circuit. The link has a very simple explanation of how to wire it. I think when I got my diode at radio shack it was 3 diodes for less than $5. I never had to Rev the tractor to "excite" the alternator and never had it drain the battery after wiring it according to the Link
A lot simpler than wiring up a 3 wire alt. and no problems.
alternator how to

Bob M · Feb 27, 2013

Quick answer to your questions: "It depends"

Would the alternator drain a battery? Yes.

All alternators have a very low (a few milliamps) drain thru the diode bridge when shut down. Normally this is less than the self-discharge rate of the battery and thus not a problem. However an internally-regulated alternator improperly wired will drain a battery quickly - like in less than a day. So also can an alternator with a bad diode bridge. Finally SOME (not all....) so-called "one wire" alternators exhibit high standby drain. These can flatten a battery over few days.

Does the alternator have a built in regulator?

Again it depends. Most alternators used in 12 volt conversions (Delco 10SI and the compact Hitachi models) are internally regulated. Older Motorola, Presolite, Bosch, etc. may have the regulator fastened onto the rear of the alternator. Yet others (early Delco, Ford, Chrysler, Motorola etc) use a separate regulator mounted someplace away from the alternator.

We can tell you more if back the make/model of alternator or post a photo.

Kajun · Feb 27, 2013

Dave:

I'm really electrically-challenged. What is the "switched side " and the "load side" of the ignition switch ? Sorry to be so dense .

Thanks

Bob M · Feb 27, 2013

Dave - The ignition switch "switched" or "load" side is the terminal that connects to the load.

The other switch terminal (the "hot" or "high" side) goes to the power source - typically the battery or ammeter.

Kajun · Feb 27, 2013

Thanks , Bob M:
Told you I was elec-challenged . I would have come to the precise opposite conclusion. Obliged for sure.

Dave Sherburne NY · Feb 27, 2013

Maybe this will help I never had a farmall but they worked for my Cockshutt
Bob Melvilles wiring Diagrams

Alternators

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