YM 2000 Electrical Problems

[normde2001]

I would be checking the diodes in that alternator about now.

 

[Mahindra35]

If you received a noticeble shock when shutting down you have received
a secondary voltage from some kind of coil or solenoid or relay when the magnetic field collapses
when the power is shut down to the devices coil.

Maybe check the fuel shut off solenoid and circuit on your injection pump or any solenoids that operate any hydraulics that are normally activated with the key ON.

I am not not familiar with your particular tractors entire wiring or hydraulics but your tractor may also have a battery load solenoid that cuts power to your electrical bus when the key is turned off.

Look for what is called blocking diodes that connect to the relay or solenoid and are wired from the positive terminal of the solenoid or relay and then connect to ground.

These diodes are designed to direct the collapsing secondary voltage from the windings of the coils to ground to prevent what you have described.

If one of these diodes has failed there is no path to ground for the solenoid or relay coil and
a momentary high voltage is directed back to circuits of the electrical system.

Blocking diodes are normally installed across the field windings of solenoids and relays,some are internal to the solenoid and wont be found in your circuit.

The diodes look like small resistors.


Denny
//Mahindra35
PC-SYSTEMS

 

[California]

There aren't any solenoids, coils, etc on the YM2000 in stock configuration so far as I know. It's a very simple tractor.

Does this tractor have some option controlled by a solenoid? Front pto clutch, for example?

 

[Mahindra35]

There should be a fuel cutoff solonoid in your diesel injection pump

A Pto Clutch could be a source of high voltage reverse current as you have said.

Essentially "ANY" electrical device on the tractor that uses a coil
even a horn relay.

Any DC coil will "Induce" a much larger secondary voltage when the primary voltage to the coil
is shut off. This is how your lawn mower coil works when a magnetic field passes
over it

It induces a secondary High Voltage when the primary field collapses.

This is why it felt the same to you when you shut the key off as your lawn mower felt.

The horn relay if it even has one would not be suspect in this case because it would only be activated when the horn button was activated.

Do a thorough search for any possible source. A load relay for your battery bus will look almost identical to the starter relay you use to find on Ford Motor vehicles.

I am sorry I am not familiar withn your particular tractor but all vehicles use
these type of devices in some capacity and can be a source for your described problem.

You could disconnect the alternator from the circuit temporarally and
see if you can duplicate the condition.

Denny

 

[Fredex]

Fredex:

I checked the voltage at the alternator F terminal with the engine running and it was between 5 and 8 V. The running voltage across the battery was 15. Disconnecting F the voltage at the battery went down to 12 to 13 V and did not seem to be charging. Also, with everything connected and running, I turned the ignition switch off and on and the engine seemed to be laboring more than you would expect from a charging alternator with the switch on.

FL_Jerry:

The following conditions were tested with the engine not running.

1. The F terminal (white/black wire) has 12 V with the ignition switch on. There is continuity to ground with the ignition switch off.
2. The N terminal is grounded.
3. The new fuse block is wired the same as the original with the IG line (yellow wire) taken off a 10A fuse. There is 12 V at the back of the regulator with the ignition switch on. There is continuity to ground with the ignition switch off. In just checking this line I was shocked when I turned off the ignition switch.
4. The white/red wire has 12 V at the A terminal of the alternator, the starter solenoid, the B terminal of the ignition switch and the regulator.

Fredex and FL_Jerry, I am not the sharpest when comes to dealing with electricity; I hope I have checked what you were looking for, if not I can easily check something else. Any idea what is going on?

Could the alternator shop have missed a bad diode? After they checked it the first time I checked the A terminal at the alternator and found it had continuity to the housing so I took it back and they said that was ok.

California, thanks for the wiring diagram.

Well, 5-8 volts at the F terminal is probably a bit high. That voltage regulates the alt. output which, at 15 volts is high. Disconnecting the F terminal brings system voltage to 12-13. That is a good thing - should cause alternator to stop charging. The shock you received when turning of IGN Sw is probably from collapsing magnetic field in a coil somewhere - in the regulator or alternator field, maybe somewhere else. You didn't say what that regulator terminal connects to.
A puzzler. Shop sez alternator is OK. Regulator is new. One of them isn't right. Either there is a phhhht diode in the alternator or the regulator is doing something funky or the regulator is getting bad data about battery voltage. Checking/adjusting regulators can be done but you have to take the can off and sometimes they are riveted on. One easy check is the wirewound resistors. They are usually under the base. See if one or more is burnt. Also check that on the old reg you took off
On EDIT: Just re-read your original post with more care. You burned out indicator/idiot bulbs and were shocked while turning off IGN SW with egnine not running. I'm going to walk the plank here and put my money on a bad diode in the alternator. The alternator diodes should keep those inductive-kick transients out of the rest of the electrical system. I don't think there is anything else on the tractor that can develop a strong enough kick to burn out the bulbs.

 

[California]

Checking/adjusting regulators can be done but you have to take the can off and sometimes they are riveted on. One easy check is the wirewound resistors. They are usually under the base. See if one or more is burnt.

I think he did as I did, and replaced the original mechanical regulator with a modern potted one. If so, there's nothing to adjust and no resistors visible. Since the problem continued unchanged after replacing the regulator, I would turn my attention to the alternator.

On EDIT: Just re-read your original post with more care. You burned out indicator/idiot bulbs and were shocked while turning off IGN SW with egnine not running. I'm going to walk the plank here and put my money on a bad diode in the alternator. The alternator diodes should keep those inductive-kick transients out of the rest of the electrical system. I don't think there is anything else on the tractor that can develop a strong enough kick to burn out the bulbs.

If he doesn't have any optional equipment then it has to be the alternator, no matter how improbable. There's nowhere else to look. I think at this point I would swap in a rebuilt alternator. I think I paid $29 (72 Datsun no A/C) and that's cheaper than tearing your hair out chasing mysteries.


Gary, can you clarify - no optional front pto, no electric remote hydraulics control, no electric anything aside from headlights and horn?

There should be a fuel cutoff solonoid in your diesel injection pump
...You could disconnect the alternator from the circuit temporarally and see if you can duplicate the condition.

These early Yanmars are about as simple as a shovel. You want to stop the engine, you close the throttle all the way to the end. It stops. There's no electric fuel cutoff, it's apparently mechanical within the injection pump. See the wiring diagram I referenced above. I like your idea to unplug the alternator and see if the problem continues. There isn't a bus relay or horn relay, and the starter solenoid is the only other coil on the machine so far as I know.

 

[normde2001]

"I like your idea to unplug the alternator and see if the problem continues."

He said he did that, and the problem goes away. I agree, buy a $29 alternator. I would still check those diodes.

 

[Soundguy]

Could a key-off solenoid have been added by a prev owner..?? or a low psi charge-fuel pump? Either would benefit from a reverse shunting diode setup that was mentioned earlier..

Soundguy

These early Yanmars are about as simple as a shovel. You want to stop the engine, you close the throttle all the way to the end. It stops. There's no electric fuel cutoff, it's apparently mechanical within the injection pump. See the wiring diagram I referenced above. I like your idea to unplug the alternator and see if the problem continues. There isn't a bus relay or horn relay, and the starter solenoid is the only other coil on the machine so far as I know.

 

[Mahindra35]

I think everybody has a pretty good handle on this one.

If the alternator is out of the circuit and the problem goes away,and it sounds
like everyone that is familiar with these tractors on this thread are pretty sure there are no other "Coils" of any kind then that is your source.

If I understand that you took the alternator to be tested and they simply
put it on a test stand to verify output they would not detect a "leaky diode"
in that manner. A leaky diode could still produce rated output.

Dissassembly and physical testing of the diodes would be the better way
of knowing the condition of the componets.

If he is using a mechanical Voltage regulator remember it uses a coil to
vibrate the contacts and might be a source but that is probably unlikely.

Normally these transiate reverse voltages dont burn out filiments in light bulbs. We are usually more worried about protecting electronic componets
from these spikes such as Ignition modules and Onboard computer componets.

good Luck

 

[Gary2]

Thanks for all the replies:

Measuring the AC voltage out of the alternator is around 90 volts running with the ignition switch on and around 75 volts with the switch off.

To my knowledge there are no other solenoids on the tractor other than the starter. The electrical equipment consists of factory head lights, rear turn signals, NAPA horn wired into the existing horn circuit and a rear halogen work light that I just installed on the pre-wired red/black wire circuit that terminated at the rear axel.

If I disconnect the two prong plug going to the alternator terminals F & N the voltage spike / bulb blowing condition goes away when turning off the ignition switch.

The new regulator is similar to the original with points but the new version does not have adjustment screws like the original Hitachi.

I believe the ignition switch is original because I replaced the key with the JD part number CH12206.

I will return the alternator to the shop and ask them if they will disassemble and check the individual diodes. Thanks for all the responses; this is truly a great forum because of you. Will keep you posted, Gary