JD 318 1986 18 onan

jimshuff

New User
I am having issues with the charging system on this tractor. I bought a new rectifier, one of the cheapo's but seems to be the most common, and still have the same issues. The system discharges through the rectifier causing the circuit breaker to cut in and out, initially caused the battery to go flat until I heard the clicking noise and unplugged B+. I have tested the resistance through the stator which ran .1 to .2 and zero from each stator wire to ground. Should the 12 v from the battery be passing through the rectifier to the ac terminals and ground? Which is what seems to be happening. Or, did I get another bad rectifier? Everything is fine until I plug the wire onto the B+ (middle terminal) and the problems starts. I charge the battery with the B+ disconnected and I can run the tractor until the battery goes flat. I just bought a new multimeter thinking that my old faithful may have gone to that meter home in the sky but same readings!
Thank you for any input! I hate being stumped on something like this!
 
As I told you before in answer to your post on another Forum, NO the battery voltage is not supposed to "backfeed" through the rectifier/regulator.

If you care to email me I will forward a link to a factory service manual for the 318 and for the Onan engine that MAY be of some help to you.
 
I would check the AC Voltage at the outside terminals. Think it is supposed to be around 34-42 volts ac(The Onan Manual Bob suggests gives the exact range). Seems like you might have a short in the stator and it is making the rectifier act like a dead short. The multimeter is not picking up the short. Obviously check AC with the engine running. The system has been pretty trouble free over the years.
 
If this is a P218 eng with the exception of a grounded stator or shorted turns in stator windings the problem may be you have wrong pn regulator and it doesn't match alt stator.According to service manual I have for 16-24hp P series eng there are probably 2-3 different pn regulators used depending on spec letter of eng & alt output.

According to service manual I have stator outputs are rated as follows:
Spec A-20A,41VAC @ 3600 rpm,resistance .06-.10 ohms

Spec B-20A,57VAC @ 3600 rpm,resistance .10-.19 ohms

35A stator 47VAC @ 3600 rpm,resistance .06-.10 ohms

Do a google search for onan P218 service manual,click on link to wheelhorseforum.com & download service manual for eng(55 pgs)in same will tell you how to troubleshoot chargeing system,if nothing wrong with stator then you'll need parts list for eng/tractor to get correct pn for regulator.
 
Thank you for sending the link I got some resistance amounts from a response and they were what I had gotten with the new multimeter, .2 through stator and 0.0 from each lead to ground. I am leaning to another bad rectifier as things are all fine until I attach the B+ to the key switch where newer units go directly to the battery. I did see a couple of comments online from other guys having issues with the cheapo depot rectifiers, not sure if they were the same manufacturer or not but appeared the same. Do you think I should try a different one. NAPA has one with my cost being around $50.00 when it is $70.00 from our JD dealer?
Thanks again!
 
The other guys are correct about an original type repair.

Does your charging system work-charge the battery at over 13 volts up to about 14.5 volts-when the engine is running?

If so,

I have a different solution that has worked in the past: Install a relay powered by the ingition circuit that will only connect the DC wire from the regulator to the chassis wiring when the switch is on. That way, when you switch the mower off, the contacts in the relay open and isolate the regulator from the system.
 
Only two possibilities come to mind:
1. bad regulator, should be easy to test, there should be no continuity through the B+ to ground.. B+ to the AC wires shouldn't matter as they are not grounded, unless bad.
2. Battery polarity wrong. That is unlikely but would sure cause your issue. Battery installed with the + grounded or one that has be discharged and charged with the leads reversed.
 
BNob:
I really hate to get stumped on something and this is driving me crazy. I have the correct resistance on both the ac leads to ground, 00.0, and through the stator, 0.1-0.2 with 35.8 volts ac at full rpm but only 2.6 -3.0 volts dc. I went to our NAPA store and got the rectifier/regulator that they crossed referenced and it does the same thing as the others when as I connect the B+ terminal, the circuit breaker cuts out and the engine dies. I disconnect the B+ and the tractor starts up and runs until the battery would go flat if I let it? PTO turns on without an issue. I am grasping at straws and wondering if it could be the ignition switch? I have seen some comments that they can do some funky things! The current rectifier is larger than the two I got off of the internet for the cheap money, both were the same in appearance but no name so I do not know if they were the same company or not. I paid more for the second one thinking that it would be a better unit but it actually did burn up.
I have the JD wiring diagram and mine has the B+ Lt. Grn lead going to the switch where newer units go directly to the battery with the circuit breaker between.
In my mind, if there was a short in the electrical system, it would be shorting out with out the B+ connected and has to be in the rectifier and stator wiring which all seems to be checking out???? Like you said, there should not be a feed back through the rectifier!
Thanks again, I do appreciate it!
Jim
 
If you downloaded service manual for eng you would have seen on pg 8-5 of manual regulator has an auto shutdown mode to protect regulator if you have an open or short in tractor wiring,this might explain the low dc output voltage,your problem probably lies further back in wiring between ign sw/regulator or possibly in ign sw itself,this may have been a recuring issue on older model tractors & why ign sw was bypassed & alt output connected directly to battery,run a jumper wire from B+ of regulator to battery & see if battery being charged.
 

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