Wow, THAT was weird

[Cleaverkid 11]

Doing a little late winter maintenance on the 854 today and had something happen that really surprised me. But this could be one of those things that will just show my complete ignorance with things electrical!

I had the cover off the old regulator to blow out the dirt/dust/cobwebs, and in the process I touched the top of one of the other of the two coil towers inside. All of a sudden the engine starts turning over! By itself! Double-checked the key and confirmed it was off...and even pulled the key OUT! Engine kept turning over. Pulled the plug wire to make sure it didn't start, and finally disconnected the negative cable on the battery to stop it.

So from what I've said, can someone tell me if this is expected, or do I have a short somewhere in the old regulator? BTW, once the engine stopped, I hooked up the negative cable to the battery and everything was back to normal. Even tried the key and it started just fine!

Am I going crazy???

[Save Old Iron 1,563]

You have just learned a lesson about working with SG based tractors.

The relay that you engaged is called the CUTOUT relay.

It is normally open (contacts open) until the tractor engine is started and the SG is generating over 11 volts. At that point in the start up of the tractor, the SG Reg senses the tractor is running and pulls in the CUTOUT relay to allow the rest of the SG Reg to become operational.

By closing this relay with the tractor off, you basically complete the starter circuit of the SG unit BUT YOU PULL ALL THE STARTER CURRENT THRU THE SG REGULATOR - NOT A GOOD THING.

There are some delicate, small gauge wires and connections inside the SG Reg unit - I would not advise using compressed air to clean out the unit.

[Save Old Iron 1,563]

Check this out

Let's start by pushing the Cut-Out Relay contacts together

1 - current flows out of the battery

2 - current enters the heavy duty windings of the current / voltage regulator relay

3 - current flows thru the (now closed) cut out relay

4 - current enters the high current windings of the cut out relay. This is where things get dangerous.

The cut out contacts that you closed MECHANICALLY now get closed ELECTRICALLY by the current flow thru the relay windings, AND THE CONTACTS THEN STAY CLOSED AS LONG AS CURRENT FLOWS THRU THE RELAY. If the tractor is in gear at this time, the tractor starts to travel regardless if you are in the drivers seat or not !

5 - current leaves the now electrically engaged cut out relay and travels to the

6 - the armature terminal of the SG gen unit.

7 - current flows thru the SG unit to ground - the SG Gen is now in the starter mode.

Hope that explains what happen to you.

[Cleaverkid 11]

Hey Chuck! I was hoping I'd get your attention on this one. I knew you'd have the answer without even thinking about it probably.

Well, unfortunately, I can tell it's too late now for the advise about the compressed air but hopefully, a few 80psi blasts didn't do too much damage to the old thing. I'll keep that in mind down the road, though. I can tell you that in the process, I did discover that that braided ground strap had come loose from the rivet on the side of the bottom plate, so hopefully I've got that soldered back down good. If not, I'll have to figure out how or where I can attach a good ground wire more permanently.

This is why I ALWAY make doubly sure the transmission is in neutral before I start monkeying with anything on my tractors.

Thanks again!

[wheelhorse656 20]

There are some delicate, small gauge wires and connections inside the SG Reg unit - I would not advise using compressed air to clean out the unit.

I have used caned air is that ok?

[Kelly 1,028]

90% of the ones I have messed with the insides look like new with no dirt, even ones the outside is ruff at best.

[Save Old Iron 1,563]

I have used caned air is that ok?

canned air / compressed air should not be needed but is not a problem unless you direct the stream at a fine wire, flex and break the wire. You will inactivate the VOLTAGE sensing part of the SG reg. But you have to physically damage the wire or beak the wire from a solder joint to cause a problem.

90% of the ones I have messed with the insides look like new with no dirt, even ones the outside is ruff at best.

the ones I have repaired had a complete surround of rubberized gasketing under the top cover. If this gasket was intact and functional, no dirt should be inside the SG reg assembly. If dirt or hydrocarbon fumes get into the SG reg inners, the relay contacts become corroded and coated. Once this happens, the relay ceases to function reliably.