Charging Problems - SMTA

My SMTA wasn't charging for a while and now it will discharge when sitting for a few days. I am running it stock. Gen, VR, 12v + ground.
After is stopped charging I repolarized the VR. This then made it charge in proportion to the RPMs. When it is WOT the DMM says around 16v. When it is at idle the DMM goes crazy and all over the place as soon as a touch a lead on ONLY the - terminal.
Should I throw a new VR on it? Any recommendations on finding a good one?
Would a bad VR cause the battery to drain?
Let me know if you need any more info or tests performed.

Sounds like your voltage regulator has gone bad.

A properly working regulator will limit system voltage to 14.5 (give a take a few tenths) at all RPM's above about 900 RPM. Also if the VR's cutout relay is stuck closed it will drain the battery flat in less than a day.

Suggest doing this: After shutting down the tractor disconnect the ground cable at the battery. If the battery now stays up after a few days, the problem's definitely the VR. However if the battery still goes flat the battery has worn out and needs to be replaced.

There are an assortment of issues here:
It was not 12v from the factory, so it isn't "stock"
but that is OK.
One polarizes the generator by jumping Bat to Gen on the regulator. (the VR is not polarized by jumping it might have polarity if it has solid state parts in it, and some new VRs do, but it is usually able to charge either polarity.
The charge rate is a little high at 16v but two other things are important. The use of a DMM is frequently impossible on these unless you pay for a Fluke meter or equal. THe sample rate of the meter grabs information on a noisy (irregular to beat the band) voltage source, and will not average the spikes or valleys it encounters. An analog meter with a needle is usually the much more accurate answer.
A bad Vr would cause a bat to drain, but it would also heat up wires and heat the generator, if it did.
Thus the drain is either a light that is on, the ignition switch is not turning off all the way, or (most likely) the battery has a bad cell in it. I would check the battery first.
It is easy, charge it up with one terminal disconnected from the tractor, then let it sit for a few days and measure the voltage. The DMM will work here! If it is less than 12v, and will not start the tractor,, it is bad. I think the charging system may be OK. Good luck, Jim

(quoted from post at 19:22:29 07/08/10) There are an assortment of issues here:
It was not 12v from the factory, so it isn't "stock"
...

Click to expand...

I thoughts SMTA's were the start of the 12v tractors. My bad.

Thanks for the help guys. I will go throw the charger on it.

I threw the charger on the battery in the tractor and a known good battery. The tractor started with each. I will leave the "bad" battery out of the tractor and the known good battery in with the cables hooked up. This should double check the battery situation and ensure a VR problem.

Would any problem in the generator cause the battery to discharge?

BTW, the DMM read up to 16.9 at WOT when I tested it tonight. If I had to guess I think I would go with a bad VR.