Is it fried?

[wpr]

When I picked up my 725 at a yard sale, it did would not charge the battery. I didn't think much of it till now that I have rebuilt the tractor(everything but the S/G) since it would start the engine. After trying the diagnostic tests I found in the forums and everthing looking like a problem with the S/G I pulled it apart and this is what I found. [img]http://www.simpletractors.com/club2//uploaded/wpr/s-g-1.JPG[/img] [img]http://www.simpletractors.com/club2//uploaded/wpr/s-g-3.jpg[/img] I am thinking that this does not look good. Can someone tell me base on a simple visual inspection if this thing looks fried? I've never seen the insides of a healthy S/G to compare. Thanks. Wade

[Paul_B]

It's hard to say for sure, but it looks like the windings have shorted and got very hot. The coating on the copper wire and epoxy looks to be burnt.

[Al]

Wade, You have a very common failure. The generate field is fried. This is usually caused by either a bad or the wrong voltage regulator. When the regulator ceases to regulate, the generate field coil is grounded continuously. This causes it to get hot and melt the insulation around the coil. Then the wires short to the case and the meltdown continues. There are 2 field coils in a SG, one parallel for charging and a heavy series coil for starting. We stock these field coils, and all of the parts to rebuild these units. From Delco you must buy the pair we sell them separately. The ones we sell are wrapped with cloth insulating tape. It doesn't melt like the dipped insulation that Delco uses. Al Eden

[Al]

Wade, I just looked at your picture again. I think the cause of your failure is the bushing in the commutator end end plate. I believe heating from the armature rubbing on the pole shoe caused the problem. I missed the rub marks on my first look. When the bushing gets worn, it lets the armature rub the pole shoe. Al Eden

[wpr]

Al, You mentioned bushings in the endcap. I may just me confused about terminology but this starter generator has sealed ball bearings on either end of the armature. Is that normal? Here is a pic [img]http://www.simpletractors.com/club2/uploaded/wpr/s-g-4.jpg[/img] Wade

[Al]

Hi, You have the best of the SG units, the ones with two ball bearings last a lot longer than the ones with bushings, although the bushing ones across the board were more common. Two things I would check. Are the ball bearings showing any wear, Is there any looseness in them? Next I would remove the front bearing retainer and see if the hole the bearing sets in is worn. Sometimes these get egg-shaped from many hours of vibration and when the bearing is installed there is a gap on the side opposite the pull line of the belt. I have seen the front end frames that you can slip a .020 guage between the bearing and the boss in the frame. The bearing should be a push fit in the front frame, not just fall in. The rear frame almost never show any wear, because there is an O-ring in it that damps the vibration. The clearance between the pole shoe which holds the field coil in is very small (just a few thousandths) and it doesn't take much wear in the bearing system to allow the armature to rub on the pole piece. Another thing that can happen is if someone has replaced the field coil and not gotten the got the pole piece back in properly seated against the outside frame. Those rub marks should not be there and it may still be a regulator caused problem, but the cause of this contact between the armature and pole piece needs to be corrected. Al Eden

[Mick14]

Mine has the same problem--except its not burned,it starts the tractor but doesn't generate.the voltage regulator looks like an auto type,could yhat cause the problem . thanks

[JJ MARSHALL]

this can also happen to a mower that has a battery that will not take a charge, and is jumped off all the time.the the charging part of the S/G is over worked trying to charge up a battery that will not take a charge. BUT THIS WILL NOT MAKE THE ARMATURE DRAG. JJ

[Al]

JJ, I agree with you mostly. What you say is very often correct. This most often happens when the wrong voltage regulator is used. Example an automotive number regulator that has a 20 or 25 amp current section. The SG then runs full bore until the voltage section limits the output. This will not happen until the battery is charged. If the correct regulator is used it will limit the output to not more than 10 amps which reduces the field current when the voltage section is telling the SG more, more, more. Many people think that they can use a regulator that "looks" like the origninal. This is partially true. It will regulate the voltage the same as the correct regulator. The problem is not very many part numbers have a 10 amp current limit. With a high current rating, or a regulator that the current section is not set correctly, or the voltage section is set TOO high and the situation you just described will happen. After you fix it if you don't have the regulator checked on a test bench, a good chance for more "toast" for breakfast. You are absolutely correct about this. I want to congratulate you for bringing this important point up. One other thing. Many high amp automotive alternators are ruined when they are installed on a dead battery. A 50 amp alternator is only rated at 25 amps nominal duty. Throwing on a vehicle with at dead battery and using it for a battery charger, with out first charging the battery has trashed a lot of rebuilt alternators. This is a subject of many articles in the trade journals and one that most of the major rebuilders are upset about, because they get a lot of warranty claims that they shouldn't because of this. Al Eden If you go to our website edensltd.com and to the tech notes there are articles I have written on how and why the starter generater and voltage regulators work.