Skid steer alternator question

antfarmer2 said:

Looks like 1 and 4 hold the alt togther and would just be used as a ground

Click to expand...

gte said:

Thanks for the reply. Strangely enough, it triggered the battery light in the gauge cluster when it was switched, but the loader ran anyway and he was able to finish plowing, so we left it then but now are trying to fix it. I'm going to tell him to buy another alternator, but I would like to know why it would trigger the light? Looking at the wiring manual, there is a spot on the alternator where the lights get power directly from the alternator, but through a 47ohm resistor. It has a terminal called B+, which goes to the starter motor and eventually to the battery, and D+, which has a diode in it, and it feeds to the instrument cluster and to the headlights. Here is the link to a picture of the manual. http://s27.postimg.org/evj2pt6r7/john_Deere240_Alternator_Schematic1.jpg

Click to expand...

antfarmer2 said:

Let's wait for someone else ele is not my best

Click to expand...

gte said:

Ok, and for reference, here is the schematic portion of the alternator http://s4.postimg.org/lduehwspp/john_Deere240_Alternator_Schematic2.jpg

Click to expand...

discountufoparts said:

Did you check it to see if the battery is actually charging with a meter?? If its not it is not fixed. If its a ground that it needs it may be it is unable to ground through that stud and I would try cleaning it up with a wire wheel and check again. Also that stud breaking may have broken something internally in the alternator.

Click to expand...

gte said:

I did. It puts out 13.9v consistently. There is also another wire that will output 7v, only when the alternator is rotating. The battery light is still on though? When I turn on the headlights, it will trip the emergency brake too. I've bypassed the main key switch, the headlight switch and the emergency brake switch, but the behavior will still continue, the headlight switch triggers the emergency brake. I also ran a ground directly from the battery to the instrument cluster, still the same behavior. I unplugged the headlights, pressed the headlight switch to the on position and the emergency brake did not trigger. I'm wondering if the alternator and the emergency brake problem are related and the lights being on create too much load and cause some safety situation that triggers the emergency brake to be on?

Click to expand...

[email protected] said:

isn't 13.9 a little low? i thought they usually output like 14.2 or something

Click to expand...

[email protected] said:

either way, alternators aren't that much money i'd just replace it. why mess around? last thing you need is to have it shit the bed during a snow storm.

Click to expand...

gte said:

Totally agree, I told him to buy another alternator, but I wanted to diagnose it and learn, rather than throw parts at it. I think they are related, I would just like to know/learn why. I've spent about 4 hours in this electrical manual, I'd like to come away with something to show for it

Click to expand...

discountufoparts said:

With all that weird extraneous stuff going on I would almost think your circuit is backfeeding somehow due to lack of ground. Try creating a ground directly from your alternator bracket to your battery and see if all that goes away and try touching it or attaching it to different groundable areas of the alternator. Maybe try just touching that line to the battery ground itself to

Click to expand...

gte said:

It is definitely related. I found something in the electrical manual that shows what that other circuit is for, it's for the "Exciter Circuit" for the dash and also to power the lights and accessories. I had never heard of an exciter before, but I'm guessing it uses the diode so that if voltage from the alternator is not higher than a reference voltage (probably around 12v) and overcome the .7v difference the diode needs to turn on, it triggers that light indicating the alternator is not charging anymore? I'll be testing that and the ground theory tonight. http://s22.postimg.org/q98qbf3kh/john_Deere240_Alternator_Schematic3.jpg

Click to expand...

donald73d said:

A normal alternator has 3 wires plus ground. Output, sense and excite. The excite needs to be switched via key. The sense can see the battery voltage all the time and not discharge the battery. If you swap the sense and excite it will run and charge but will discharge when the engine is off (alternator may be warm). Some have a singe wire alternator which is self exciting. Bobcat has used Mando (Korean) alternator (Mercruiser does also). They seem to be decent until they fail and then forget rebuilding them. I would consider having the alternator checked at a shop that rebuilds alternator/starters. The shops are becoming harder to find but they are still out there.

Click to expand...