Small Engines (Lawn Mowers, etc.)/charging system problems


QUESTION: I have a koehler 27 horse engine on a dixon mower.  5 years old.
Late last summer, charging system failed.  I had a new battery put on that would hold a charge(charged by AC battery charger) for enough time for me to mow twice (about 3 hours of mowing)  During this time i checked voltage at battery with engine running wide open and found that it was 12. 5 volts.  I checked every thing out early this year and determined that I would change the voltage rectifier/regulator.   This seemed to fix problem. Voltage would show 13.5 to 13.9 volts and engine would crank without problems.  This was good until late July.  Same thing only 12 volts while running engine.  I changed the regulator again, and again was fine, but only stayed good until Today.  Is there something that is causing these rectifier/regulators to go bad, or am I missing another problem??

ANSWER: What is the rectifier part number?

Some rectifiers/rectifiers don't seem to hold up as well as others.  A couple of things can cause regulators to operate hotter than normal which can cause them to fail.

Some items include:
1) Too small of wire
2) Poor connections
3) Poor grounds...related to #2
4) Old wire
5) Too much load on the regulator

Since the mower is not that old I'd rule out #4.  #'s 1-3 are pretty common on many mowers.

Are you familiar with measuring voltage drop?  Voltage drop is not a direct resistance measurement but gives you a better idea of the electrical system condition when the system is in use.  Voltage drop is a better test IMO as I have found poor grounds that when measuring resistance the ground connection passed.

Do you have an electric PTO clutch on the mower?

Google voltage drop and read the procedures for measuring/testing.


---------- FOLLOW-UP ----------

QUESTION: Rectifier part # is 4140310-s from Koehler.  I have been getting  part # 435081 from Jacks Small Engines online.

I do have an electric clutch that runs the cutting deck.

I will try to learn and measure the voltage drop and recheck all the connections and the grounds.


You can use another brand or style of regulator.  

The reg you have has 2 AC inputs, 1 DC output and must ground through the mounting screws.

Many replacement reg will have 4 wires:  2 AC input, 1 DC output, and 1 ground.

You can wire in another one just connect the AC alternator output from the engine alternator to the 2 AC inputs, connect the DC output and the ground.

I use Yamaha regulators on my Honda motorcycles as they are cheaper to buy and last much longer than Honda regulators.  I just solder the connections and then heat shrink followed by tape.  I have not had to replace the Yamaha regulator.


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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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