Kohler Generator starter relay failure

[HeavyHaulTrucker]

Sent: 8/13/2004

I couldn't find anything in the past discussions regarding this, and I just spent all day diagnosing a problem that was resolved with a $7.00 part --- I wanted to pass it along so no one else would waste this much time.

Yesterday afternoon, my generator output dropped to 72 volts -- for no apparent reason.  In fact, at first, I thought that the AC had crapped out -- but after pulling the cover and taking some voltage readings, I realized that it wasn't getting full voltage for some reason.  I checked the interior outlets on the other circuits, and found the same thing -- only 72 volts.  I shut down the generator, but it would not completely shut down; it would wind down to about 100 rpm, but then it would just continue running like that -- even after I pulled the plug wire and shut off the fuel!  This was getting eerey!

Finally, I opened the top of the controller and pulled the main battery cable -- it shut down.  So I opened up the end cap and started checking the brushes -- I expected to find one bad brush, since the output I was getting was exactly 2/3 or normal (and I knew there were 3 AC brushes.  No such luck -- the brushes were almost new, and just as they should be.  So I packed it up for the night, to continue this morning.

This morning, I started out by checking all of the hold-down screws for the brush & wire connections in the end-cap -- everything was tight, but at least I did get the dust & dirt cleaned out of it.  Next step was to check out the controller; I found that several wires in the 12 volt circuit had melted into the main ground wire (a big 8 gage white wire), so I replaced/ repaired all of them.  I started it up and checked my voltages -- no change.  And when I tried to shut down, I again had to remove the main battery cable.

Now I was scratching my head big time; I had gone over anything that I thought might remotely effect the voltage level, and gotten no results.  So I began retracing my steps and checking what I had done -- maybe I had wired something wrong?  After another couple of hours, I was agian right back where I started.  But something happened this time, when I pulled the battery cable to get the genset to shut down.

Without thinking, I removed the battery cable before I hit the "STOP" switch; of course, the engine kept running since its spark comes from a magneto & points.  I glanced down at my voltmeter, thinking that I would not have any voltage because there was no 12 volt input for the generator to work with -- the voltmeter read 125 volts!  And, all of a sudden, the whole cause and solution hit me like a ton of bricks!

The Kohler genset does not use a starter; the starter relay feeds 12 volts into the set of brushes that are normally used to generate the battery charge voltage -- this turns the generator into a motor until the engine catches and starts producing voltage above 13.6 vdc.  At this point, the relay is supposed to de-energize and the genset starts producing full AC power.  Well, as it turns out, the contacts on the starter relay were sticking closed at start -- even after voltage had risen.  The resulting "tug of war" between the two sections of the genset were dropping my voltage by exactly 1/3.

I had a friend of mine run me down to Auto Zone for a relay; they did not have the actual relay that I needed, so I decided to use a Ford starter switch.  They are virtually identical, except that for some reason the "STOP" switch would not have any effect on the engine.  So, after looking at the schematic in the manual, I found that the ground was being switched but I needed to switch positive to make the starter relay coil energize but I needed to simply break the Fuel Shutoff Solenoid circuet to make it shut off properly.  So I simply drilled a hold in the front of the controller cover and installed a kill switch to shut if off when I need to.  It is running fine now and, in fact, repairing those melted wires restored my battery charging that had not been working for the past couple of weeks -- so now my coach batteries are always charged when the genset is running.

John

[DanD2Soon]

Sent: 8/14/2004

John,

You know I wouldn't wish you any bad luck, but I sure am glad you have the same genset I do!

Matter-of-fact, I kinda wish you had more of the same equipment I have...(LoL) - My "HeavyHaulTrucker" folder is filling up with lots of really sweet pieces of info and troubleshooting tips about my Kohler...

I suppose it just emphasizes why this group is so important to all of us!

Thanks again,
DanD

[MSN Member]

From: HeavyHaulTrucker
Sent: 8/16/2004 

Glad to hear it, Dan.  I think that, aside from than the great cameraderie, this sort of thing is one of the best parts of this group -- we all get the benefit of the lessons learned by one of our members!

You know, it is funny, but for a $1700.00 coach, the genset is the ONLY thing that I have had more than one trouble incident with (aside from the starter, that is)... and with the rewiring of the controller and the new starter relay, I don't think I will have any further trouble with it either.  It is running great, and uses an average of .47 gallons per hour at 3/4 load -- I am very happy with it... especially on the 90 degree plus days we have here in south central Texas (I have been in the San Antonio area for about 3 weeks now).

John