Alternator experts

Will it harm the alternator or cause battery discharge if the exciter circuit is wired to be hot all the time? I'm working on a magneto tractor with a kill switch only. Not much of a place to put a oil pressure sensor on this tractor and I don't want to put the exciter circuit on a separate switch. I don't seem to have any discharge noticible (ark) when I take a battery cable off to check for discharge.
 
In the long run yes it will hurt bot hthe alternator and battery if wired like your thinking about doing. The alternator will not last as long due to heat build up in the excite circuit and it will discharge the battery over time. Easy way to wire it up would be with a double pole switch so one side was the excite circuit and the other the kill switch
 
Not a good idea. Here's what I've done for years.
In most circuits you need an isolation diode to keep the alt. from backfeeding the ign. In this case it won't , but put one in it ( with the band towards the plug in , and hook the other end to your headight circuit. Now , when you fire up the tractor , switch on the headlits momentarily ,the alt gets it's excitation , and turn off the lites ! The alt is turned off when you kill the engine. I've got an Oliver 70 , A JD"B" and a Farmall "A" all wired this way , just remember to flash the headlites when you start it !!
 
I don't know what you are doing with the tractor but unless it's daily use or you need lights I would not put a charging system on it. A battery will start a magneto tractor lots of times before it needs recharging.
 
there is always a place to put a oil pressure sensitive switch-- put a T in between what ever is there to measure the oil pressure -- done it on a H farmall with a mag -- works great good luck -- Roy
 
The current is sufficient to light a small lamp. not much arc to that, just milliamps but it will drain the battery. A STDP switch (single throw double pole) can be set up to ground the mag when stopping the engine, but completing the exciter circuit (with a 10 ohm resistor in series)when pulled out.

From the site shown below -- the switch is -up- on (mag not grounded) but exciter on or Switch is down Mag grounded, Exciter off.
DPST 2 Position On - On Cole Hersee 25 amp Toggle Switches
5590
Your Cost $12.75 Jim
a171235.jpg

Untitled URL Link
 
I have not found a Farmall engine that I was not able to put an oil pressure switch on to excite the alternator. What tractor/engine are you working with? The picture that I attached is what I have done with the Farmall CUB,
a171236.jpg
 
Another way is to use a push-button starter switch. After it starts, just push the switch for a few seconds to kick it in & it will keep charging until the engine stops.
 
either go with the OP switch, or toss a horn button on there and give it a blip after you get over 400 rpm, or hook it to the lamp switch and just turn the lamps on for a second to juice the exciter line.

leaving excite on all the time will kill the battery..
 
like Jim said, the arc was probably there, just so small you missed it.
lots of good solutions posted.
Pulling the neg battery cable when you park it (or a quick dis-connect) is always a good thing anyway and would solve the problem if you want it hooked up all the time.
I'm working on a JD that I haven't rewired yet. I just put a short 2" stub on the excite terminal. After starting, and doing my quick
'everything ok?' walkaround, I just touch the stub to the battery terminal for a few seconds and let it go. Then, I'm good til I shut it off.

ps if you be a hack or too lazy to walk to the toolbox for testing stuff...like me.., that tiny arc will let you determine which spade is which on a no schematic, unfamiliar alt.
(What the hey is a mitsubishi, and what is it doing on a JD anyway. :D )
 
Jim,
Wouldn't this need to be a Double Throw switch. Single throw would have both sides activated at same time.

5590 in your link would be ideal for this setup, wired as I have illustrated
a171255.jpg
 
Single Throw indicates it has only two positions, as up and down, no other stable toggle locations. A double throw has a middle position with OFF at that location. The switch I referenced was of the first type, and it is capable of doing the job. Jim
 
(quoted from post at 16:34:14 10/11/14) Or, use a self-exciting one-wire alternator?

Sounds like the easiest solution in this case.

I just converted one on a White 2-110. Wiring harness was open between the alternator and the connection at the cab plus there was no power coming from the cab. The customer decided that would be a better choice for him rather than pay me to locate and repair the actual problems. Alternator starts to charge at 1200 rpm now. Before it would not start to charge until the engine had been running at full throttle for a while.
 

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