View Full Version : John Deere 318 Charging Problem

05-26-2007, 11:42 PM
Working on a John Deere 318 with a Onan engine. Does not charge properly. Battery light comes on if you start the mower deck or turn on any lights. Tried a new voltage regulator, didn't help. I checked to coil with a continuity tester and it check almost no resistance, so it's not open. Battery tests about 13 volts with the engine running and about 12.5 with it shut off. Any ideas?

05-27-2007, 08:52 AM
Check across the outer two terminals on the rectifier/regulator. Set your meter on A/C volts. There should be at least 28 A/C volts at full throttle. If not then change out the stator. If there is 28 volts then check the center terminal. There should be battery voltage there. If there is then it's the regulator. If not trace the wire and repair. Also have you lights on at full throttle when checking across the battery. You need more than 12.6 volts to get a charge in a battery. This will at least get you started. Post back with your readings for more help if needed.

05-28-2007, 12:12 AM
The stator checked almost 40 volts across the wires with the engine at full throttle. The center lead had battery voltage. Replaced the regulator with a new one, the battery light is still on. Will trace the wiring and look for other problems.

05-28-2007, 12:18 AM
What is the battery voltage at full throttle and the lights on? Sorry I made you change out the regulator again. Make sure all grounds are clean and tight. It's sometimes hard to repair mowers with words.

05-29-2007, 12:04 AM
Battery shows 14 volts. I found I could make the battery light go off and on by wiggling the wires going to the ignition switch. Will pick up a new switch in the next couple of days and try that. Problem may be the switch or the harness. The wires that connect to the terminal on the edge of the switch rather than the main harness appear to be the problem. They are hot with the switch in the run and start position.

05-29-2007, 12:13 AM
It's charging alright. Sounds like your on to the light issue. Let us know.....

06-04-2007, 11:55 PM
New ignition switch fixed the problem.

06-05-2007, 12:09 AM
Great job! The Onan is built as tough as they get!

06-09-2007, 03:37 AM
I have a similar problem. Same 318, using P218G engine. No power, and engine won't run unless connected to charged battery. Changed voltage regulator/rectifier, still same problem. Voltage at AC is 38-42 VAC. No voltage at the bat Term. Checked with both machine ground and to the aluminum plate/heat sink of the regulator. Could it be the new from JD dealer, voltage regulator is bad?

06-09-2007, 10:44 AM
With the key in the (on) position you must have battery voltage at the center connection on the regulator. If not trace the wire back and find the problem.

06-10-2007, 01:00 AM
yes I agree, but what I have done to test, and I am probably wrong here, cause I don't have a schematic, is to connect the 2 leads from the stator (AC volts) to the regulator, then with the engine running, test the output voltage DC comming out of the regulator, both with it connected to the wire terminal and without. Should I not get 13 volts dc comming out of the regulator (center terminal labeled bat) with the negative test lead to ground?

06-10-2007, 01:30 AM
The stator leads go to the outside terminals. Whith the engine at full throttle and running with all leads connected to the regulator. There should be 12.6 volts or more on the center lead. At least 28 volts A/C on the outside terminals.
With the engine NOT running and the key in the "on" position there should be battery voltage to the center lead.

06-11-2007, 12:20 PM
khouse, I re-read this entire post, and I have noticed that my problem may not be the same. I was getting an itermittent charge light if I had front pto, snowblower and lower rpms, which is probably understandable. But that is not the problem here. The motor dies without battery power, period. No lights or ptos running, no loads other than motor itself. That is what made me think it was stator or rectifier blown. I was using and eventually battery had no juice and therfore no more engine running. I read to test the regulator by checking votage at the regulator, and if key is off, and there is battery voltage at the center terminal, then its the regulator/rectifier. I replaced that. Still the motor cannot run on its own. I then started the engine, kept the battery connected to keep engine running, disconnected the stator leads, and checked their voltage, about 40 VAC at full throttle. I then connected all leads back to the regulator and tested battery lead, 13vdc. With the engine off, key on, I get battery voltage at the center lead (13vdc). With the key off, I still get battery voltage at the center lead as well. I have the P21G Onan with electronic ignition. I replaced the keyswitch about 3-4 years ago, just after I bought the machine 4 years ago. I have traced some of the wires, I get 13volts on both sides of the 20a circuit breaker mounted on the side wall. The center battery lead from the rectifier, becomes a light green wire, and goes thru the firewall, connecting to one side of the 20a Circuit breaker, on the same side, connected to red which goes to ignition switch. On the other side of the circuit breaker is a red wire directly to battery. So if my stator and regulator are making power, I think, why doesn't it keep it going? Does this machine need to have a battery connected in order to run? After about 5 seconds, the charge light goes out, so it seems that the battery is being recharged.

06-11-2007, 01:20 PM
I'm on the tail end of this thread and have only read the post above this one(no time to read all now). This engine MUST have battery voltage to the ignition coil at all times for the engine to stay running. It will not stay running without a battery hooked up.

Bill Kapaun
06-11-2007, 02:21 PM
"With the engine off, key on, I get battery voltage at the center lead (13vdc)."
You should get battery Voltage, 12.6VDC (try to measure a bit more accurately)

"With the key off, I still get battery voltage at the center lead as well."
You shouldn't have any.

"I get 13volts on both sides of the 20a circuit breaker mounted on the side wall."
You should get battery Voltage, 12.6VDC

"The center battery lead from the rectifier, becomes a light green wire, and goes thru the firewall, connecting to one side of the 20a Circuit breaker,"
That's why you have battery V at the center lead of the rectifier at all times.
The rectifier lead should be going to (probably) the "A" terminal of the switch, which is disconnected when the when the switch is in the OFF position.

"on the same side, connected to red which goes to ignition switch"
RED should be going to "B" terminal of the switch. B is basically the main 12V feed to the switch (to/from the battery). When the switch is ON, B & A are connected.

When the engine is running/charging, current flows from the regulator, to the A terminal, which is connected to B (in the run position) and on to charge the battery. IF the engine isn't running,(switch on), current flows the opposite direction to "energize" the regulator.
The A terminal, typically supplies other "Accessories", such as fuel shut off solenoid, possibly lights etc.

The GREEN wire should be connected to the A terminal!
Hopefully the other terminals are hooked up correctly?????

With all that said, I don't think that is the real problem.
Possibly you "cooked" the regulator since it had battery V on it ALL the time?

What reading do you get on the battery with the engine running full speed AND all electrical loads ON? (accuracy counts)

06-14-2007, 10:58 PM
Well had to fix my Digital volt meter to get better results. I have 12.45v at the battery, all off, bat disconnected. And with bat connected, one pto running, headlights on, I get 14v at the battery. So must be charging. I looked at the wiring, and they look factory in their places. So I guess I will leave things where they are. Thanks for all your help.

06-15-2007, 01:08 AM
Sounds like all is working fine!

Bill Kapaun
06-15-2007, 01:47 AM
Did you switch the wiring so that the regulator doesn't have battery voltage when the key is off?