Charging system / riding mower

I have a Simplicity mower with a 12 HP Kohler engine. The battery mysteriously went dead last week. I charged the battery and the machine started fine, but I noticed the ammeter needle was showing a discharge. Next morning the battery was dead again. I bought a new battery and still noticed the discharge on the ammeter. After checking the troubleshooting guide I disconnected the voltage regulator and the battery held its charge. I had to move the machine the next day and so I reconnected everything to start it. It was charging, but it went to discharge after it warmed up a bit. I'm not a mechanic, but I do know a little about electronics, and I'm suspecting that the regulator has a heat-related short. Before I spend the money to replace the regulator, can anyone tell me if I'm on the right track or if they have something else I should look for?

Thanks loads.

 

Hello hockey_knight. Welcome to our Do-It-Yourself Web Site and our Small Engine forum.

Quick and dirty test. Not the professional test everything method but may prove if the problem is the regulator or alternator.

Remove the wires from the alternator. Allow the battery to remain connected overnight. If the battery remains charged, the alternator is draining the battery.

An internal ground or defective diode is the cause. Replacement is the only real option. If the battery goes dead once again, suspect the regulator.

Disconnect the regulator from the wiring system, connect the alternator and retest. If the battery remains charged, suspect the regulator. Replace it.

If neither test provides the solution, the ignition switch may be grounding.

I haven't covered all of the potential possibilities. The other resident small engine service and repair professionals may offer additional suggestions, advice & help.

Check back on your question several times over the next few days for additional replies.

If you need further assistance, use the REPLY button. Using the reply button moves the topic back up to the top of the daily topic list automatically & keeps all communications in this one thread.

Regards & Good Luck.
Web Site Host & Small Engine Forum Moderator. "Accurate Power Equipment." Small Engine Diagnostics Services & Repair.

 

Another way to find the short (if you have the tools) is to use an ohm meter(multi-meter). First, diconnect the alternator, then touch one lead to the alternator wire and the other lead to the battery. If there is a short, the meter will show some resistance. If there is no resistance, then there is nothing wrong with the alternator. Then check the voltage regulator the same way. If there is resistance then you found your problem, if there is no resistance, then the voltage regulator isn't the problem. You can also use a circuit tester. A circuit tester looks kind of like a screwdriver with a pointed end and a wire coming out the back that goes to a clamp and the hande of the circuit tester houses a light bulb. To use it, connect the wire to the battery and touch the pointed end to the alternator wire. If it lights up, then that is the short. Then check the voltage regulator the same way. Another way to find a bad diode on the alternator is to check it's output voltage while the engine is running. It sould put out at least 13 volts. Any less, than the diode is bad, which coud keep the alternator from charging up the battery.

 

The alternator (charging stator) does not have a diode on this engine. The rectifier/regulator contains the diode. If I recall correctly, you can unplug the alternator from the rest of the charging system, and connect an ohmmeter across both alternator leads. If you have an open circuit, your alternator is bad. If the circuit is closed, there is one more step: Connect the ohmmeter across one of the alternator wires and ground. If you have an open circuit, it is good, if you show continuity, it is bad. Another way to check it is to crank it up and unplug it from the regulator. Set a voltmeter for AC voltage and check the alternator leads. If it is showing good voltage...(Can't remember, but 20-27 volts ac seems to be right), your alternator should be fine. If the battery is discharging with the regulator plugged in, but not when it is unplugged, I would tend to believe your regulator is bad.

Let us know what you find!

 

I did some of the basic checks you all have suggested and everything continues to point to the regultor/rectifier. I pulled it off the machine and there is a part number on the back. When I enter that part number in the parts sales databases I find on line, it won't come up. The part number that is on the unit is as follows: KOHLER 41 403 05 A .
I'm following instructions and entering the number without the spaces.

Is this part obsolete or part of an assembly I need to order?

 

The part has probably been superceeded to a new number. Use the model and spec # of your engine to get a new regulator.