312-8, Not Charging Battery

[Target 1]

I have a 312-8 with Kohler 12 HP engine.  When the engine is running at full throttle, the voltage meter reads only 11.5 volts.  This just started last week, before the voltage meter would read 14 volts when running.   The engine is a Kohler K301s, SPEC 47812.   Now that it is not charging the battery, I have to put my battery charger on to start engine.   What is wrong??  Any help ?

[peter lena 8,052]

@Target  try this first , have any alligator clip  test wires ?  go from the battery , ground bolt  start point , to the rectifier , top inside edge of air filter area , would also slightly move the oblong wire 3 wire connection going to that , then clip the other end of alligator clip  to the top rectifier bolt mounting point .very often corrosion , debris , is poor to engine grounding areas, also check fuses for corrosion . basic stuff  . just a quick check , had that a number of times on related tractors , easy to make a strong point , pete

[Target 1]

Thanks Peter Lena!  I'll give it a try.

[gwest_ca-(File Mod) 10,491]

Your tractor is likely a 1985 model 21-12K801

You should have a 3 amp charging system with a 2nd circuit that powers the lights. On these models the lights work only when the engine is running.

The 3 amp circuit has a small diode in the harness at the connector that joins the engine to the tractor. This diode rectifies the charge current for a DC output to charge the battery but there is no current regulation. The small output is not capable of overcharging the battery in most cases.

These 22 files are associated with your model.

https://www.wheelhorseforum.com/search/?q=21-12k801&quick=1&type=downloads_file

The Kohler service manual explains the test proceedure.

[Handy Don 10,594]

Agreeing with @peter lena and @gwest_ca

Far more likely that there is a weak connection somewhere in the charging circuit than something failing. Only after eliminating that possibility should more involved testing ensue. 😁

Edited May 16, 2023 by Handy Don

[peter lena 8,052]

@Handy Don  unit I recently sold was solid wire / corrosion neglect , top to bottom . the entire back of dash was packed with wet grass , and split /  rotted connections . , then it started blowing fuses as it started to work , once it started to run / work the dirt packed fuel bowl , had its say . as you know , its never a 1 and done . keep digging , pete  

[953 nut 51,646]

The fuse holder is the most likely problem. It is located near the battery and quite likely to be corroded. Here is a drawing of the charging system.