Crazy8 55 #1 Posted May 22, 2023 I have a C-121 with K301 Kohler engine. I noticed that I am reading just over 17 volts at the battery shortly after starting the engine and running at 3/4 throttle. The battery is nearly brand new and was just fully trickle charged before installing it. Is 17 volts excessively high? I didn't wait and watch it for very long to see if it tapered off any. Thanks Share this post Link to post Share on other sites
WHX?? 46,710 #2 Posted May 22, 2023 Way too high. You'll trash the battery. Replace the voltage regulator. 1 Share this post Link to post Share on other sites
squonk 38,850 #3 Posted May 22, 2023 Test it with a multimeter first. Factory gauges are not the most accurate things on the planet. 2 2 Share this post Link to post Share on other sites
Crazy8 55 #4 Posted May 22, 2023 Yes I was using my Klein digital multimeter. What should I expect to see at the battery? 14 volts or so? This tractor has the 3 terminal rectifier in it. Share this post Link to post Share on other sites
Crazy8 55 #5 Posted May 22, 2023 The service manual calls for 13.5 volts charging voltage at the battery. Share this post Link to post Share on other sites
kpinnc 10,686 #6 Posted May 23, 2023 Let me add this: 16 or so volts is not too high after something like a longer cranking session, but it should dribble back down to 13 or so within a few minutes. Your rectifier should respond to the load placed on it, and the overall condition of the charging circuit will definitely affect it. Even a brand new battery can have high resistance or a bad cell. Of course if it does I would return it. 2 Share this post Link to post Share on other sites
oldlineman 1,450 #7 Posted May 23, 2023 Make sure your rectifier is grounded very well. 1 1 Share this post Link to post Share on other sites
953 nut 51,542 #8 Posted May 23, 2023 If there is high resistance between the regulator/rectifier body and the battery "-" terminal it will try to overcome it by producing a higher voltage. Here is an explanation of the problems that can be caused by corrosion on electrical connections that was provided by @Save Old Iron The connectors used in this tractor series are in a harsh, corrosive environment caused by vapors from the battery being charged over a few decades.. Vibration causes the connections to loosen - corrosion starts within the metal terminals and a voltage drop develops across the corrosion. If you have a 10 amp current flowing across a 1 ohm resistance (contact corrosion) the electrical formula to calculate power is current squared times resistance so 10 amps x 10amps x 1 ohm resistance = 100 watts !! 100 watts of connector heating is the same as laying a 100 watt soldering iron on the connector 1 1 Share this post Link to post Share on other sites
oldlineman 1,450 #9 Posted May 23, 2023 Very good Richard, I thought those diagrams looked like Save Old Irons, he was a very knowledgeable member such as you and many others. Thank you all for sharing your great and variable knowledge, has helped me many times. Bob Share this post Link to post Share on other sites
pacer 3,159 #10 Posted May 23, 2023 13 hours ago, kpinnc said: 16 or so volts is not too high after something like a longer cranking session, but it should dribble back down to 13 or so within a few minutes. Your rectifier should respond to the load placed on it, and the overall condition of the charging circuit will definitely affect it. Even a brand new battery can have high resistance or a bad cell. Of course if it does I would return it. I've had a few tractors do this -- on start up show 15-16-17 volts and as I run it, will slowly taper off to the more common 13-14 volts. 1 Share this post Link to post Share on other sites
