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Can a bad alternator

Depending on what is wrong with alternator, yes. With tractor not running, disconnect the power lead coming from alternator to ammeter/battery. Touch lead back to terminal. Sparking indicates alternator is draining battery.
 
It can, but so can any thing else that's not turned off, and a bad battery can discharge itself with no external draw.

If this is an old school tractor, pre electronics, you can do the "spark test".

Warning! Only do this in a well ventilated area and not with the battery on a charger!

With everything off, and some charge in the battery, remove one cable, touch the cable to the battery post and watch carefully for a spark. There should not be a spark.

Or connect an incandescent test light between the post and disconnected cable. The light may glow very dimly, preferably not at all.

If there is a spark, or the light glows bright, start by disconnecting the alternator wiring. If the draw stops, the alternator is bad.

If it still has a draw, start disconnecting other accessories, wire harnesses, keep testing between each disconnect until you narrow down the drain.
 
I had a battery explode on my Chevy 4x4, as I went to start it, and I thought somebody had unloaded a 12 gage at me. BLAMMM!!! I bailed out the drive's door. The truck rocked side to side, smoked and fumed. I would NEVER NEVER get a spark anywhere near a battery.
 
I agree with Steve mostly except for that spark test. Not a good idea!!! Even a cheep HF digital meter set on DC voltage will do the trick. With the ground cable unhooked, one meter lead to the cable clamp and touch the other to the battery post. You might read a tiny amount of voltage because those meters are very sensitive. Hopefully you should read nothing.
 
Many thing can cause that. Yes an alternator will but so can something as simple as a light bulb that does not go out due to a bad switch etc. On my Wives 1997 van I found a simple door light which did not go out due to a bad switch would drain the battery over night. Removed the bulb and the problem went bye, bye
 
Safer way would be to use an ammeter in series between battery and cable and watch for increase or decrease in amperage draw as different things are tried.
 
Even a good one can. I get a small milli amp draw, I forget the figure ? on mine and the alt. all tested fine. Sort of the nature of the design of most alt. You won't see a spark but it will drain it down in time.
If something is bad in yours it can even drain super fast.
 

I was told by some people that an alternator can't draw down a battery if it's hooked up correctly. I asked why there were diodes made to prevent the draw down if it can't happen and was told it was for people who couldn't hook the alt up correctly. On another site I got talking with some people who really knew these alternators and was told that a battery being drawn down by the alt was entirely possible, that it was the classic sign of a "leaky" regulator IIRC, and that the cure was the diode. As it was explained to me, it's not that the regulator was really "bad", it just carried a little voltage in the wrong direction. I dunno, it's all magic smoke to me, but these guys have that "PE" after their names.
 
It did on my 4440. And not consistently, either. Sometimes it could sit for a month and be fine and then out of the blue it would drain it. It never felt warm and it would take about four days to draw down, but it was that alternator. I had it rebuilt within the year prior so I didn?t even consider it. This time I got a brand new one. Problem solved.
 
(quoted from post at 09:11:00 03/13/19)
I was told by some people that an alternator can't draw down a battery if it's hooked up correctly. I asked why there were diodes made to prevent the draw down if it can't happen and was told it was for people who couldn't hook the alt up correctly. On another site I got talking with some people who really knew these alternators and was told that a battery being drawn down by the alt was entirely possible, that it was the classic sign of a "leaky" regulator IIRC, and that the cure was the diode. As it was explained to me, it's not that the regulator was really "bad", it just carried a little voltage in the wrong direction. I dunno, it's all magic smoke to me, but these guys have that "PE" after their names.
Click to expand...
f the GM 10SI and connected with 3 wires, it's parasitic drain is measured in micro-amperes (millionths of an amp), your battery will likely self discharge sitting on a shelf not connected to anything before this tiny drain will kill it. Call it a smallish 60 amp-hour battery & draw say, 500 micro amps from it: 60/(500/1000000)= 120,000 hours or 5,000 days or 14 years. No diode that you can add will change that drain in the Sense wire. If a "one wire" version, the draw is a little more, but you can see that even if double the above, it will still be insignificant. Some "one-wire" units drain more than others. If alternator is killing your good battery in days, then the alternator is bad.
 

JMOR, I'm sure you have a far better understanding of this stuff than I do. I'm just passing on what guys who seem to speak the same language you do told me. I don't think either of you is lying or anything, I just think that some things happen that we either aren't explaining right or otherwise don't understand the cause for it. It's kind of like the ethanol issue in small engines and 2 strokes- some people (like me) know for a fact it's and an issue and how to avoid the problems, others have never seen a hint of the issue and swear we're all either idiots or crazy. Both sides are going to butt heads till the cows come home!
 
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