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Discussion Starter #1
Anyone here have any ideas why a 318 would be showing battery overcharge symptoms besides a faulty regulator/rectifier?
The regulator tests ok with my tester and voltage output is just under 14.5 VDC.
Yet the battery continues to bubble out acid after 20-30 minutes of full speed running.
I am familiar with the typical charging system on lawn tractors. As I understand it: the alternator puts out a certain amount of unregulated AC voltage. That voltage is converted to DC by the rectifier and limited to approximately 14.5 volts DC by the regulator and directed to the battery. As the battery charges, the voltage exiting the reg/rec should reduce to whatever amount is being pulled from the battery by the ignition system, electric PTO clutch, headlights, and any other electrically driven loads that might be applied to the system to simply maintain full charge in the battery.
So, if the reg/rec is testing ok, how can it still be overcharging the battery?
The alternator can't grow coils and the flywheel can't grow magnets to increase the raw electrical output over that originally engineered into the system. The worst that can happen to the charging system is a short in the stator coil which would reduce the amount of voltage produced in the first place.
There is nothing (I believe) between the reg/rec and the battery. The worse that could happen there is maybe a short that directs the recharging voltage back to ground instead of into the battery.

What am I missing here?
Any of your well-considered thoughts are greatly appreciated!
 

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What engine?

14.5 @ idle or full throttle? How old is the battery? 13.8-14.1 is a normal range for most systems. Anything North of 14.1 for very long will start to cook a good battery. Bad cell in the battery will cause problems too.

TJ
I disagree with the voltage opinion. 14.5 should be within the limits of charging voltage, depending on temperature, etc.

I'd say you have a bad battery
 

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It's not your charging system, it's your battery. Deere used to offer a battery cap with a tube fitting, to divert bubling acid away from the painted areas of the tractor. So even new batteries can be a problem. Check the specs for your tractor and match the battery to the spec required.
 

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The Magnificent
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The temptation might be there to get an AGM battery, but I don't know if the JD's charging system will properly charge one. GM discovered this with Corvettes years ago.
 

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Off the top of my head I don’t remember the electrical specs. Of the 318. I don’t believe it has a regulating circuit in it? But I could be wrong.

In a nutshell, among other things, the single component that is monitoring the output voltage in a small engine regulator / rectifying circuit is the Zener diode, which is what should be tapering of the charge as the battery reaches its max charge (pre determined max).

I would use a Clamp type ammeter or a DC shunt and see what type of current draw you are getting when its running.

I also agree, if you haven’t already, I would test the battery as well.

What device do you have that tests the regulator?


Good luck.
 

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Discussion Starter #7
The 14.5 V statement was ballpark from memory. The voltage from the charging system peaked solidly in the green area of the tester range somewhere in the vicinity of 13.5-14.5 VDC. I did not put a DMM on it at the time for a precise reading.
The regulator/rectifier tester is a Kohler product with idiot lights on it. Plug wires onto appropriate spades on the r/r and push a button. Red light=no good, yellow=marginal, green=OK.
I have JD service manuals for the tractor and the Onan P218G engine. Neither list any AC output specs for the stator. But again, unless that stator has been overproducing too high a voltage since the day it was wound, there is no way I can concieve of it gradually increasing its output over time to overwhelm the rectifier/regulator.
I will test again and possibly replace the battery and see what happens.
The bottom line is there are only 3 components that I am aware of that could fail:
Stator - fail syptom typically too low an output
Rectifier Regulator - fail symptoms=not longer rectifies or no longer tapers output
Battery - fail syptom-no longer holds a charge. But I have learned from you folks that a bad cell can cause acid leakage, too, as a fail sypmtom.
We'll try that and see how it goes.
Thanks!
 

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Stator output at idle is around 25-30 Volts AC & about 50 Volts AC at 3600RPM. Stators are either good or bad, one with an open in the windings would give no output at all.

Connect a known good battery that is fully charged and then check the battery voltage after starting, with a voltmeter. 13.8-14.2 is normal, if after 5-10 minutes of running it is at 14.5 or more the regulator is bad and will start to cook the battery. A battery that is in a low state of charge but otherwise in good condition will show around 14.5 at first and then taper down to 13.8 or so once it reaches a full state of charge.

TJ
 
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