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PeppyDan

electric pto clutch for Sunstar

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PeppyDan
The front electric clutch for my pto on my 1987 Sunstar has been starting to work intermitantly over the summer. Then a couple weeks ago it got much worse. It will work when the tractor/clutch is cold but once it has been engaged, it will only work about five minutes. If I try it the next day it will work the same again. I have cleaned the unit, checked and replaced the switch, adjusted the air gap, & checked the wiring, all good! I pulled the assembly off this evening and the only noticable defects are cracks in the coating over the field. Is this a sure sign of a defective field. I did notice the bearing inside the pulley assembly is very stiff but working smoothly, it doesn't feel like the bearing is shot just stiff. If I replace the assembly would it be a good idea to buy the new style electric clutch or just replace my older style. I have also considered buying just the field but with my stiff bearing I am not sure. Thanks for any help. Dan

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D-17_Dave
It could be a coil problem. But if so it could be grounding out yet still working some. This could do severe damge to the engine. Al talked about problems with some of the electric clutchs awhile back. Not sure if this covers all the diagnostic info but this article and the part 2 article cover tons of stuff on electric clutchs. I'd say start there. http://simpletractors.com/club2/topic.asp?ARCHIVE=true&TOPIC_ID=44263&SearchTerms=clutch

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PeppyDan
From what I'm reading in the link, the "old" clutch like I now have on it is better. How would I test my coil? I am assuming you are refering to what the parts manual lists as the field is what you're calling the coil. My main seal is not leaking so I'm hoping there has been no engine damage. If the coil is defective I will replace it. Is the stiff bearing also going to be a problem? I recall talking to Al a year or two ago about my other Sunstar which I was considering a 25hp Command engine for and he mention the "old" clutch wouldn't handle the extra power. This is why I mentioned the "new" style clutch. I could use it if I repower with the 25hp. Dan

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D-17_Dave
Dan. I think the long and short of it is if you plan on upgradeing the engine, now would be a good time. That way you can pic up an engine with the power you want and size the clutch to whatever size shaft the new engine has. More HP engine normally = a bigger crankshaft. I think I remember Al descibeing a failing coil as when it heats up it changes ohm resistance. He described more exact readings and the mounted coil clutches were better THEN. The newer clutches are supposed to be made to compensate for this and not be a problem. If I remeber right. I talked to an engineer at Warner clutchs and that's what I remember to the best of my knowlegde. Anyway, the newer clutches are made with the tourqe rateing's in mind of the new engines. If your gonna halve to buy a clutch, get the style that will fit the application, don't settle for something less. As for the bearing, a little stiff isn't much issue. When the grease heats up it should be easier to turn. Roughness in a bearing is a bad thing. Anything rough in any bearing causes friction and it'll self destruct if it's forced to operate under much load.

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sandyhillbill
I also have a 1987 Sunstar and had the same problem with the clutch. My problem turned out to be in the "interlock module". ended up disconnecting the wire on the right side as viewed from the drivers seat and ran it straight to ground of tractor and everything has worked fine for a couple of years now. Even the saftey interlock still works. You do need to take some ohm readings per Al Edens post on this subject to be on the safe side. As I recall I had problems with both front and rear clutch at this time.

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PeppyDan
Mine does not have the rear pto. I will do some checking this morning and strongly suspect that it is bad. I also found that my bearing is froze up and it was the bushing inside the bearing that was turning. I got the bearing pressed out of the pulley and will order a new one along with a new field if it's defect. This will be about $125 for the bearing & field as compared to over $300 for a new clutch complete. Dan

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Al
Hi, The Sun Star has a complicated electrical system. The Legacy's have been significantly simplified. They have several grounds on the firewall etc. that can get in the picture. The interlock module CAN cause the problem you see on this tractor. I see you have done all of the things I would have checked first. I would connect the coil to a battery for half an hour and put a charger on the battery for this time. I would monitor the current with an ammeter connected in series. You can use one from an old Landlord or Broadmoor, or one with a maximum range of 10 to 15 amps. Higher amp meters don't read accurate enough to read 4 amps with any accuracy. The clutch should draw not more than about 4 amps cold and may come down a little as it heats up. If it gets up to 5 or 6 I would check it with a quality Digital ammeter. If it up there with a good meter, the clutch is bad. Then when it is hot, disconnect both wires and measure the resistance to ground. Should be infinity. Any resistance is bad. If this all checks out, and the grounds all ck OK I would bite the bullet and replace the module. This module takes information from several sources and when all conditions are correct will engage the PTO. Think of it as a computer that takes several inputs and when the matrix of information is correct turns on the clutch. As I remember the early ones even sensed the engine rpm. The early modules are NLA, but have been superceded. with a new #. When you get the new unit it will look like the plug is made upside down. DO NOT TRY TO BEND THE KEY SO THE PLUG CAN PLUG IN LIKE THE OLD ONE. THESE ARE NOT CHEAP, AND NORMALLY THERE IS NO RETURN, ONCE INSTALLED or out of the bag. THE FACTORY HAS SEEN A LOT THAT HAVE BEEN DAMAGED BY TRYING TO MAKE THE PLUG WORK THE OTHER WAY. The plug on the cable needs to be rotated 180 degrees so it will plug right in. One other thing. The ground on this module is critical. Anyone that was a dealer in the 80s when these tractors came out should have a test module that you plug into the harness and you can start, kill, engage the PTO etc with the test box with the module disconnected. Good luck, Al Eden

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PeppyDan
Al, thanks for your detailed information to check the coil and the information about the grounds. Does the coil have a negitive and positive side that I need to hook up to the battery correctly or can they be hooked up either way. Here is a pic why I suspect the coil, looks pretty nasty to me!

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PeppyDan
I checked the clutch today. I attached it to a battery with a digital multimeter inline. It started out reading 3.84 amps and after about 25 minutes it was at 3.54. I then removed it from the battery and measured the ohms and it showed a 0.00 resistance just as it did prior to testing. This is the same reading I get if I attach the two test leads together. Al, is this what you refer to as infinity. This is known to me as a dead short. I just want to make sure we are on the same page as far as the readings. Where should I start as far as checking grounds? Thanks again for the help!!! Dan

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Al
Dan, If the meter reads 0.00 with the leads disconnected, and touching them to the leads and the case, it still reads that way it means there is no measureable resistance. I would expect a mumber like .1 if there was continuity. Does your meter go to 00.0 when you touch the leads together? Often they will show .1 or .01 ohms on the low ohms range which shows the resistance of the leads. If you are on like a 200 ohm range and it stays at 00.0 that should be what you want. If you have any doubts, go from one lead and ground and if it is 00.0 ground the other lead to the clutch and you should read abot 10 to 13 ohms if it does you are right on. That tells you the meter sees an open or no resistance and when you ground the other coil lead you will be measuring the resistance of the coil through the winding. Hope I am not confusing you with this. Hollar if I am and I will try to clarify it. Good luck, Al Eden

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D-17_Dave
quote:
Originally posted by Al
Hi, That does not look unusal for an old clutch. These coils do not have a diode accros them. Some of the new tractors have a diode in the plug to suppress the transients when the clutch is turned off. Al Eden
Al, can you please explain this part. I've never heard of this. thanks, Dave.

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PeppyDan
Ok, hear is what I've got.

This is what my meter shows with leads apart (selector is at 200ohms)

This is what my meter shows with leads cliped to each other

This is what my meter shows with leads attached to both wires of the coil at the same time. Thanks, Dan

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Al
Dave, With a lot of the new electronic stuff transients are a problem. On the solenoids of cars, many now have diodes across the winding to suppress the transients. When you energize the clutch a very strong magnetic field is created. When it is switched off this field collapses instantly and induces a very high voltage in the coil. This is the same thing that happens with a battery ignition when the points open. I would expect that if you hooked an oscilloscope across the winding on the coil you might see a spike of 200 or 300 volts for a half a millisecond. In newer equipment and especially in cars with the computers, and tractors with transistor advanced timing and fuel injection engines the computers tend to be destroyed by voltages above 15 to 18 volts. into them. The solution is to put a diode across the coil so when the switch it opened the transients are shorted by the diode being forward biased by the collapsing voltage which limits it to .5 to .7 volts. On most of the new alternators on cars, the rectifiers have Zener diodes in them across the output. A zener diode is a diode that looks like an open circuit when it is reversed biased. When it reaches its rated voltage level it conducts. In alternators this is to protect the electrical system from transients that might be introduced by the alternator. When you are checking the diodes in the newer alternators you need to check them for forward current capacity and for reverse breakdown voltage. You can have an alternator that charges and the reverse breakdown (zener)effect is not good and the alternator can work but when the regulator switches the rotor voltage on and off it can put transients on the lines that damage the computer. I will try to illustrate zener diodes. A 20 volt zener would look like a regular diode when it is forward biased and conduct . When reverse biased it would look open to any voltage up to 20 volts. At 20 volts it would start to conduct and would look like a short at any reverse bias above 20 volts. Zeners are used for the reference voltage to bias the pass transistors in voltage regulators. Another application is in the voltmeters in cars. If you use a 0 to 10 volt meter and a 10 volt zener you can hook one lead of the zener to the negative meter post and to ground and the other end of the meter to 12 volts. Thus went the zener is maintaining the 10 volt reference, the voltmeter would measure the voltage above the offset or 2 volts. By doing this they can have meter have an expanded scale for accuracy and by putting a face on it from 10 to 20 volts, it is easier to read accurately. If you used a 12 v zener, and a 0 to 3 volt meter, the meter would have a range of 12 to 15 volts full scale. You could read this 3 volt portion with much more accuracy than trying to read 13 volts on a meter with a 0 to 15 scale. Zener diodes are rated by zener voltage and watts of power the can dissipate when reversed biased. One needs to be careful when using the little Bosch relays in auto applications. The ones that have no shunt can have the power connected to the relay coil in either polarity, as can the ones that have the shunt resistors across the coil for transient reduction. If you have an application like one of these and plug one with a transient suppression diode in it and it is wired backwards as one of the other type might be you will let out the smoke the factory packaged in them for this type of problem. If you use one without the transient diode where it is needed it will work, but may put transients on the lines that could cause problems. These relays look exactly on the outside and are only differentiated by the part number. Al Eden

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Al
Dan. The 2.7 is normal for the coil. 12v divided by 2.7 ohms = about 4 amps which is about where you are at. I would expect to see more than .1 to ground if the coil was shorted to ground because your leads have .1 to start with plus whatever portion of the winding was. One other way you can check this would be to connect the coil to 12 volts again. Next take your voltmeter and measure the voltage from minus terminal to the body of the clutch. Then reverse the 12 volts to the two leads. There should be NO voltage to the clutch body from the minus terminal of the battery. This will accomplish the same thing. What we aare trying to accomplish is verifying that there is no path from the winding to the body of the clutch. The windings are wound with enamal insulated wire and then "potted" in the housing with plastic. If they make contact with the case it is bad. Sometimes the wire will be against the housing and the insuation will wear through and when the coil gets hot, will make and when it cools off it contracts and checks good. Also a note to Dave some of the new Simplicitys have a diode across the plug to the clutch. Al Eden

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D-17_Dave
Al, I've seen the diodes on a lot of GM-AC clutches. I understand the zeener's too. Some electrinics background years ago. I didn't know of the transient or wondering voltage problems. I use a lot of the plug and go relay's also. Never noticed any with a built in diode. Wouldn't it be possible for this to help explain some open coils without an external short? If the voltage spike occures where a coil has lost insulation, couldn't it ark over to ground and eventually burn a coil. Long shot but??? Also, if a mechanical switch is being used wouldn't that stop the back flow of the spike? Or even with a fully mech. system, no computer, would there be any need for the application of the diode other than to protect the actual component?

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PeppyDan
I attached the coil to a battery and let it heat up again today. I then checked from the body to the negative side of the battery, no voltage. So it's back on the tractor. I did find a couple of slightly loose motor mount bolts so they are now tightened. I won't be able to try it for a few days, I ordered a new bearing for the pulley and I'm waiting for that to come in. Id there anything else I can check before bringing the tractor to someone that can check the module? Thanks for your help! Dan

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Al
Dan, I don't know of anyone that can "check" the module. They can run the tractor without the module connected with the switches in "the box". As much as you have run down already, I would suspect the module is bad. If you take it to someone and have them run it on the box, you still may have a bad box. If they spend an hour on it at 50.00 or whatever (thats where we are) they get out there and you still have to buy the module. I don't remember what they are, as I remember 80.00 to 100.00 dollars. In discussing them in the past with the factory, they do some wierd things and their advice was: "just replace it" when we couldn't pin anything else down. You would be gambling the cost of the module against a dealer retracing your steps and you having an hour or 2 of labor on it and still replacing it. One thing when you get the new module it will look different from the original. The plug on the cable needs to be rotated 180 degrees. DO NOT BEND THE LOCK KEY FOR THE PLUG OUT SO THE PLUG WILL PLUG IN LIKE THE ORIGINAL DID. Do so and its $90 worth of non winning lottery tickets. I wanted to build a logic tester for these modules, but Simplicity can't get a circuit of what is in them. This is proprietary to the company that makes the module and they won't give to anyone. Good luck, Al Eden

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Al
Dave, The relays look the same on the outside. There might be a diode symbol between the coil pins with some mfrs. The diode stops the arcing of the switch contacts. It clips the transient to .7v. If you put a condensor across the coil it will colapse and the capacitor will charge and them it discharges back and you get what is refered to as ringing. This creats and alternating current diminishing voltage. The capacitive reactance and the inductive reactance determine the frequency this happens. In an ignition coil another winding is wound around the outside and by mutual inductance the secondary voltage is induced in the secondary winding. It is just a step up transformer. In these older tractors and older cars, transients aren't a big deal. Kohler had a probem in fuel injection engines about 3 years ago with the engines running really rich in the field at times, particularly in Walker mowers with the way the computers were mounted and located. Since the oxygen sensor in the muffler puts about 70 mv when hot and activated and this varies with the fuel mix. When the mixture changes the oxy sensor changes by a very few millivolts. (1000 of a volt)and sends this info to the computer. The computers then processes this info. Grounds and wiring connections from the sensor to the computer are very critical. The computer can't tell if the oxy sensor changed a couple of millivolts or its ground changed a couple of millivolts. It just sees the summ difference. I know of a couple of these mowers, that they fought and fought, finally replacing the computer module and then the engine. The culprit was the ground lug on the ground wire in the cable to the engine from the computer box. They had used a stainless steel lug, and it was letting the computer box move around ground wise by a few millivolts and the mixture was going crazy. The fix was to cut the stainless lug off and put a copper lug on and solder it after crimping. This provided a lower resistance ground. They issued a service kit like this to fix these. With fuel injection, the computer deals with analog signals varying by a few millivolts and changes them to digital pulses of varying duty cycles that hold the injectors a fraction of a millisecond longer to give more fuel or less for a leaner mixture. These situations don't like transients on the lines and so this why even these low current coils need transient suppression diodes across them. As to early relay failures, they could be getting transients from something else. At 12 volts at 100 ma. (.1 Amp) the coils would have a resistance of about 120 ohms. Power dissipated would be 1.2 watts. Now if you get a 48 volt spike from a defective alternator on the 12 volt line you would see .4 amps on this very thin wire in the coil and the coil would be dissipating P Power = E sq over R= 48 sq =2304 over R 120 =19.20 watts of power dissiapated in the coil during the transient. This is exceeding its rating by 15 times. Now if you have an alternator with a bad stator winding or a bad diode or an open output noise suppression capacitor and it is turning about 9000 rpm (3 times the crank speed) and since these are delta wound they would put out 3 spikes per revolution time 9000 rpm this is 27,000 times a min. or 450 times per second this little relay it getting beat up by a transient that is exceeding its design dissipation by 15 times. If these relays are demonstrating very short life cycles it can very well be from transients. Hope this makes sense. If it is confusing, I will try to explain it better. Just remember that power is a square law function and that if you took a 110 volt 1200 watt heater and plugged it into 220 it would radiate 4800 watts of energy and if you plugged it into 480 volts it would radiate 19,200 watts of enery. (for a very short time) Al Eden

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D-17_Dave
Beleave it or not Al I understand most of it. What concerns me is how to test for the irregularities, such as the alt. problems. Understanding where all they can come from, and what the results are to look for gives me a lot of ideas about how to apply this information. Kind of a cause and effect thing. You information and insight is really apprceiated. I'll try to keep this info in mind.

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PeppyDan
I believe I found the culprit. I started removing the module from the tractor to switch with my other Sunstar, and noticed the green wire in the plug appeared to be partially pushed out of the plug. I removed the terminal from the plug and adjusted the tab which holds the terminal into the plug. Also noticed the terminal on the module was bent as if the wire terminal was not properly inserted. I straighted it out and plugged the plug back into the module making certain the green wire terminal made a good connection. I started the tractor and ran the deck for about 25 minutes with no problems at all. I will get to give it the real test this winter as this is the tractor I us for snow blowing. Thanks again for all who helped. Dan P.S. I got the bearing for the pulleys and installed them today!

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Al
Hi, Great Dan. Dave, I would use an oscilloscope, and look at the 12 volt line at various places. You can connect the ground lead to the alternator case and the probe to the out terminal. Always use a shielded probe and the ground clip on the probe. These units have such a high input impedence that they will pick induced items from the air. When you use the probe it is shielded and grounded at the probe. All you then have exposed is a little point about 1/4" long. If you try to use conventional test leads you will have so much on the screen and just moving the leads around will give you so much garbage you can't even discern what any of it is. You can look at the 12v near the igniton supply also you could look at the AC compressor plug and you could watch what it does when it comes on and off. We have a pretty good Tektronix oscilloscope that we look at every alternator we fix. You can also look at the output of a starter generator and look at the output of each segment of the armature as it is running. I have taken the scope off the test bench and looked at the pulse signals on each fuel injector nozzle, and observed the duty cycle when the engine is reved up etc. When looking for transients we use the AC input setting. That we can look at what is on top of the 12v. If you are looking at the output of an alternator when it is chargine at 14.6 volts, using this method, the zero reference is when the voltage goes up from the 12v level. So we see 6 peaks of a sine wave about 3 to 4 volts peak side by side. If there is an open diode, one of the peaks will be missing. This way you can see exactly what each leg of the stator and each diode is putting out. Another way you can look at this is to use a high impedance high frequency AC voltmeter. These meters will only measure the AC component sitting on the 12v as the scope does on AC input. The scope will let you see graphically exactly what is happening in the circuit. Digital voltmeters won't work well for looking at transients as they operate on a sampling process and just one spike it won't respond to I certainly hope that I didn't come across as talking down to you. I know that many people don't really understand some of this stuff, and I try to illustrate it as best I can. I have written some Tech articles on basic electical theory on my web site. edensltd.com. I just got to the point that I was going to write and add some basic troubleshooting techniques to apply the theory to a practical application. I still want to do it, I just haven't had time to get back to it. I learned my basic electroincs from a borrowed used correspondence course when I was 12 years old and fixed radios and tvs (black and white) in the 50s when I was in high school. Graduated in 1955 at 16 and went to work for Collins Radio, Later a Rockwell Intl. Company. I was the youngest technician they ever had. My first test job was testing 600v dynamotor aircraft power supplies. Ironically due to 50s labor laws I could test them, but was too young to run a freight elevator, so I had to push a cart load on the elevator and walk down staris and push the button and remove them when they got down their. My high school (40 students in the whole high school) superintendent helped me and encouraged me. He was very good at explaining things and I know how important this was to me. I try to write as clearly as I can and am always happy if anything is confusing when people ask me to clarify it. In no intended question you rknowledge. Sorry if I came across that way. I DID NOT take it that you felt that way, but I just wanted to make my intents clear. Thanks Al Eden

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D-17_Dave
Not a problem at all and I certainly didn't want to sound as if I alone understand what your refering to. I've never heard of testing the circutry like this. This type of insite, breaking the components down to thier base component, allows my to understand what all I missed in a real education. Something I missed out on. I for one thoroughly enjoy your technical replies. Keep em' comeing. Dan, sorry, I didn't mean to hijack your post. But this was to good to let go by without learning something else.

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