12V Charging - discussion

Hi All,

So as some may know, I completed the wiring for the 12v conversion on the M last week.

Well, been thinking about both the sense wire and the ammeter over the weekend.

As an initial note - I know there are tons of drawings out there, but in all of them I have seen the sense wire is shown jumping straight to the battery terminal on the alternator.

I did not do it this way.

I ran the sense wire up to the battery by the starter push button.

Logic being I wanted to account for voltage drop, load conditions, resistance in connections etc and not have the alternator locked down into internal sensing which would could ignore the above - plus will prolly add lights in future 😀.

(As you can see, I went away from the "stock" idea and now am like, look, my butt is gonna be in it, might as well make it mine. &#128518

I believe someome else mentioned also doing it this way?

Y'all think that location (by the foot push button) is the best location? Better one?

Logic here make sense or no?

Next - I think I am going to remove the Ammeter and put in a voltage gauge.

Lot of y'all do that? Recommendations?

Thanks 😊

Good discussion Champagne, most (especially sparkies) are already aware that jumping the voltage sense wire to the alternators big main output stud is an imperfect but simple and easy wiring method that works. The actual battery voltage (on its terminal) is a more accurate method due to possible inline voltage drops HOWEVER the cheat method works pretty decent as unless the connections are bad and resistive (drop a lot of voltage) the voltage at the alternators output stud is pretty close to that on the battery.

As a used tractor dealer past farmer and a sparky Ive seen MOST wired to the alternator which never caused a problem even if as an engineer its my opinion actual battery voltage is preferred.

People should do it however they well please, as mentioned above by starter push button or starter switches or solenoids or other locations. At the starter switch is almost the exact same thing as on the battery itself subject to resistance and is better engineering wise then the alternator GOOD CHOICE CHAMPAGNE even if it makes little difference as if on the alternator in reality subject to resistance

On autos as I recall and have observed THEY SENSE BATTERY VOLTAGE AT LOCATIONS OTHER THEN THE ALTERNATOR !!!!!!

Hey its an electrical question expect many opinions

John T

Hi John,

Cool, good to hear.

Thank you for the input, read losts of your past posts yesterday regarding 12V coils, 6V coils etc - good stuff.

Btw, what's a sparky?

Sparky ?? Those of us who are a bit nerdy and into electrical stuff lol Im a longgggggggg retired Electrical Engineer but still love sparky chat and try to help best I can

Pleasure chatting with you

John T

I would sense the voltage at the foot push button or if not a Farmall M at the first connection the Battery + cable connects to for 12 volt negative ground system.

I agree with John T - as always(!) - how you connected the sense wire is theoretically the best. However as a practical matter, jumpering the sense terminal to the alternator output stud works fine, especially on a tractor with small electrical loads and short battery cables.

Re using both a voltmeter and an ammeter: Having both provides the best view into health of your charging system/battery. It is my preference when space allows. (FWIW my 70's-era Kenworth 10-wheeler came from the factory with both ammeter and voltmeter....)

That is the ticket. Jim