I have a john deere 310c. The other day while digging the alternator light came on and my tachometer stopped working. I have a manual and did some checking.I found out the 12v at the exciter terminal is present but the output of the alternator remains at 12.6v whether the motor is low or high rpm.I have two questions. first if the alternator stopped charging would that also effect the ac pulse that drives the tach and second if the alternator belt is a bit loose (the belt tension should be set so it has about 1/2" of deflection when pushing on it mine has about 1" but seems to turn the alternator fine) could that also cause my problem.Is there any other thing that might cause this other than a faulty alternator.
First question, it depends, the diodes could be burned out/leaking and that would keep it from putting out charging voltage, but it might still produce a signal for the tachometer. Yes, the loose belt could cause your problem, especially since if it's loose, then the belt and the pulley are probably worn round and smooth, and because the fan draws more power than the alternator, so the alternator could run fine with the loose belt, but the fan slows it down enough to not produce the voltage. I'd expect the tachometer to be "fishy" for a while before it stopped completely if the belt was slipping, just a hunch though, I've never seen a fishy tachometer from a slipping belt. Deere seemed to use whatever brand of alternator was sitting on the shelf sometimes, what brand is yours? Some of the Delco's you can stick a small piece of metal into the back to ground/bypass the voltage regulator, that would give you full output and tell you the regulator is not working, easy and cheap to replace.
Deere used either a Delco or a Motorola (black plastic cover over the back) on the 310C, depending on serial number. Replacement alternators for that machine I believe are all Motorola's.
It appears they used different alternators on it. Here is a link to the parts book. ---------> https://partscatalog.deere.com/jdrc...xPRyw2OTExMjpFUVVJUE1FTlQsMzE3ODA6Q0hBUFRFUl0
This alternator is a rebuilt one.The only info. I can find on it is a sticker that reads re-manufactured for john deere by prestolite.I believe it's the 65 amp. motorola type, at least that's what the manual refers to it as and the pictures in the serv. manual match my unit.I agree with you Delmer,that you would expect the problem to come on more slowly with a slipping belt.I run a small electronic repair shop (38 yrs) so I've pulled the alternator and will put it on the bench and check what I can.I am still curious as to the missing ac pulse but both issues have to be related.The service manual is lacking vital information when it comes to actually trouble shooting the alternator itself.
Maybe these will help.
mg,thanks for the response.I took a look at those downloads and didn't find too much detailed info regarding theory of operation as to how the ac tach. pulse is generated in relation to the regulated B+ output.I did disassemble the alternator and checked internal windings/connections there was some corrosion and rust at some terminals everything else checked good.I cleaned it up,put it back in the hoe and tightened the belt,but no luck.I suspect the regulator portion of the alternator.I've got a new rebuilt on order.
The alternator produces three phase AC that's then rectified to DC. The tachometer pulse is just connected to one of those phases before the rectifier, so that the tachometer gets a frequency that is proportional to engine speed.
On mine the alternator does not wake up until you reach a certain RPM. It may be 1000 or so. My battery light will turn on and my hour meter not working, but as soon as I press the accelerator it wakes up and starts working.
DC is not linear, it has frequency also, just don’t cross the zero mark, you can run tachometer from DC signal, I’m not saying that’s how it work on this particular machine. There’s actually a tachometer kit sold that connects to regular alternator B+, all you have to do is calibrate using machanical or optical tachometer. Just FYI.
Is this alternator brushed or brushless?
Pretty sure either of the alternators are brush type, and the tachometer is hooked to a "W" terminal that is wild three phase, or one phase of three phase.
I might be mistaken, but if you don’t get current to the rotor you will not be getting phases and frequencies.
Agreed.
May be checking the brushes first will be good idea?
I agree with TVA. The ac tap comes directly off one leg of the 3 phase windings and if there is no ac then there is most likely no excitation voltage. Since GEM checked excitation voltage then there is a problem internal to the alt like the brushes or the regulator.
Just got back in the saddle this am,was out in western MN. at my nephews place trying to shoot a duck.JL my alternator used to act as you described at first start up the charge lamp stayed on for a short time at idle until rpm was sufficient then it would go out and remain out.TVA it does look like they use the positive going portion of the ac sine wave to drive the tach. and yes this alternator has brushes that checked good at least from a continuity and visual stand point when I had the alternator apart.Mg as I stated in an earlier post I too suspect the regulator to be my problem but ordered the whole unit jic also may I ask where you found the pdf in post 16 it's more complete than my deere service manual.Thanks all.
It is from John Deere's Tech manual TM1419, page 9015-00-54.
Installed my rebuilt alternator and I'm back to digging.....for now.
geminijo, I hope that has you going. My battery light did not go out this morning when I pressed the accelerator and I noticed the lights did not work also. That has me thinking Relay faulty. Always something it seems.
JL, It sure seems to be that way,maybe you'll be lucky and find a blown fuse or something simple.A guy learns more than he wants to when owning an older piece of equipment.Until next time......