AC 620 Onan-Voltage to stator?

I haven't worked on that particular model, but...  most would use 12V to flash the field, then it could ramp all the way up to as high as 90+V in operation.

I went through this about a month ago. All of the components looked good when I ohmed them out with my DMM. When I checked the AC voltage coming from the stator it was a little low on one side at idle and hit 117 vac at full throttle. I decided to replace the stator and rectifier but keep the old regulator. After changing the components and making sure the regulator and rectifier were well grounded it still was not charging. I added a jumper wire from the battery straight to the charging system and found I had 13.6 volts DC. Make sure to check the rest of the wiring.   The ignition switch has 1 terminal that goes to the charging system and was too rusty to pass any current. Sorry for the long reply.

Thanks for the warm welcome. I used a 12 ga. wire with alligator clips on each end. I went straight from the pos battery terminal to the white wire that hooks the regulator and rectifier to the charging system. This wire is the output from the rectifier and the regulator uses it to decide how much to charge the battery.

This may be huge overkill, but we have a Case 646 with a CCKA that is not charging. Stator is open. Everyone that I have talked to says the Onan charging system was a weakness. With no more stators available from Onan, the solution is mount a compact alternator to the  frame and drive it with a pulley from the  flywheel. 

I have the  alternator and am ready to work on bracketing it to the engine. When I get to the point that I have it installed, before I install the baffles, I will photograph it and post it. I have  a single wire alternator  and this mod will eliminate about 30% of the wiring. It will be simply a single wire to the ammeter. More to come.

Before you wire a 1 wire directly to the Ammeter on that machine, I would re-think that idea! If you don't use that machine all the time, everytime you get on it to use it, the Battery will be low or dead. If you want to be smart (and safe) about it, wire a compact 3 wire Alternator through the key switch. This way when the switch is off, everything is off, and there will be no parasitic draw on board the Tractor from the Alternator or anything else. Let the Ignition switch be the master switch. Another thing, if that machine develops a short somewhere while you're on it, and you have wired direct, you'll set that machine a blaze, or burn everything else up. THAT is an expensive venture to replace or repair that mess. Leave 1 wire Alternators to Automobiles...
Steve@B&B 

There are quite a few different mfr's and types of compact Alts out there in the Automotive and industrial world. Denso, Mitsubishi, Bosch, and Motorola to name a few. Each have there own type of mounting, so careful research needs to be done when retrofitting one of these pint size units to one of these Tractors. Most of the small compact size Alts vary in the amp department also. They range from 33- 45 amps, and go as high as 72 amps on some diesel applications. The small amp units would work quite well on a 620 or 720 when upgrading from an antiquated stator system that is getting tougher and tougher (not excluding expensive) to find parts for. I just purchased a 620. It needs its engine repaired first before I can run it and see if the stator charging system is working. If it doesn't, you can bet I'll design a retrofit kit that will upgrade the old stator system for the 620 and 720 machines if possible and be a safe, reliable, and effective kit. I already have plans to upgrade the Ignition switch in mine. Sheesh! Cheap junky Indak switches they used! Yuk!    Forgot to add, some of these units are expensive. Some around $95.-$150 bucks. But you could have more than that in a stator system pretty quickly, and still not have the reliability...
Steve@B&B


Edited by Steve in NJ - 20 Nov 2013 at 9:14pm

You heard right Brian. Had a few twin Kohler engine flywheel magnets come apart and take the stator right out along with some of the wiring. What a mess.  Not cheap, not cheap!

One magnet came loose in mine, and ripped off the stator wires, tore everything up.  This spring/early summer.  Pulled engine, bought a used stator and flywheel - expensive -didn't help.  Hired starter/alt. mechanic to use the Al Eden checklist to troubleshoot - varied results.  Bought new regulator, didn't help.  Bought new rectifier - didn't help.  Had already checked ign. with a loose 12 volt headlight bulb to reg/rectifier assy to make sure was getting 12 v. all the way thru when switch was on.  Bulb was bright.  Total outcome= VERY EXPENSIVE, and still not charging.  Spent money I really didn't have available to spend on this problem. Will be going the mini alternator route come spring, and selling the new Onan rectifier and new Onan regulator I purchased. (freezing my fingers in this cold will not happen for fixing this issue)  Expensive lesson.

There are some pictures on ebay of flywheels. Some don't look too pretty.
Seems like the flywheel on the Gravely version has some sort of alum retaining ring to perhaps prevent magnets from falling out.   Anyone know what the stator pole to magnet gap is on the 620?
So looking at a block wiring diagram of the charging system I say huh?

To be honest with you Jerry, I didn't look at the OEM switch yet to see what would be a good replacement that will fit in the original's spot. One of my good customer's that's very familiar with these machines mentioned today, the Indak switch is special to the 620 and 720's to energize the electric clutches. Looking at the wiring diagram that was posted in another thread, doesn't look anything special to me. I have a service manual coming to get familiar with the machine and its circuitry. But as I mentioned, looking at the wiring diagram, doesn't look anything special to me. I'm sure I can come up with a nice heavier Ignition switch to do the deed, but at the present time with 620 outside under a tarp, and it being 27 degree's out, I'll stay here in the shop and keep working! I'm a real "wee-wee" when it comes to the cold. The older I get, the worst I get!
Steve@B&B


Edited by Steve in NJ - 24 Nov 2013 at 4:25pm

I would also be interested in the ignition switch fix and alternator fix. Both are trouble points on these tractors. Thanks Tracy