alternator troubles

[851 roger]

I have a ford 851 with the 12volt system. I just replaced the amp guage because the old one was rusted out. Also the last several times I tried to start it, I had to put the charger on it for a while. I pulled the single wire from the alternator and with a 12V test light and the tractor running I got nothing from the alternator. My question is----does the RPMs need to be high for the alternator to put out amps ???. I've pulled it from the tractor so I could get it replaced, however maybe I'm missing something. Just after I replaced the amp guage I ran it up pretty good and the guage showed nothing. With it idleing, the amp guage would drop slinhtly when the lights were turned on. Any help would be great!!!

[Qapla]

You really need a volt meter to test an alternator to see just what it is doing. That said, running at idle should give something. If it is not to difficult to remove I would take the alternator to a parts store like Advance or AutoZone and let them test it since they will do it for free.

[the old grind]

Single wire alternators need excitation and get none of it if that wire is disconnected and can't get it from the battery. If your system was converted or had the alternator replaced only recently be sure an automotive alternator wasn't installed. There are different number sequences to tractor alts, partly to protect OEM suppliers from lo-buck automotive competition, but also for their unique differences. Car stuff operates at higher rpm and doesn't always get up to speed or generate full amperage on tractor installations.

My deere has a car alternator because the PO saw a big saving when recognizing it's drop-fit compatibility and omitting a pricey regulator, a poor way to cut costs. As a result I get little to no charging within the rpm ranges I usually operate at. You'd have to check a single wire type with the battery connected. There are cheap LED testers that show what's going on, and you could hook up a cig lighter socket with alligator clips if you don't plan to install one permanently.

If you park your Ford outside, corrosion can cause brushes to seize and lose contact after wearing down a bit, or they could be worn short enough to lose spring tension. Boggers sometimes splash muddy water onto/into theirs, and I've seen guys rap the housings, as has long been done with starters, to break 'em loose & get 'em home. It's not too difficult to replace brushes, even if left with an auto repair manual that at least instructs on your particular type.

I suggest you connect a voltmeter to your battery, run up to 1500 rpm or more, and see if the voltage increases when you connect the alternator's wire. It should jump to ~13.5 to ~14.5v if everything's ok. If the battery isn't fully charged & there's no increase you have a problem for sure. Starter/generator repair shops usually understand tractor-specific alts, so be sure to ask if you call around. They'd be better able than auto part suppliers to test yours properly, and may be able to replace diodes or other internals. btw: you might have them look up the number stamped into the housing to verify whether you have a car alt. If yours fails a voltage test you may have to spring for the real deal.

Don't go on my word alone, I'm sure others will jump in. If there's a repair shop nearby, call & get it in for a checkup. They'd probably appreciate the business, and might save 1/2 the cost of new by rebuilding what you have. If it's 'car stuff' that's on your 851 you might have to start over.

[joecdeere]

single wire alternators usually take about 800-900 rpm to excite and begin charging, if you do a slow advancing of the throttle watching the lights or the amp gauge, you will see when it trips. On my Massey it's about 800

[don45640]

Sometimes it's just stuck brushes or a broken wire into the brush, so check it out unless you aren't into that sort of thing. don-ohio

[851 roger]

Ok, I took the alternator in and it checked to be bad. I put a new one on and everything is hooked up just like it was before all this started.
My next (brain dead ) question is---does the amp guage only show a charge if the battery is low? I ran it about 10 minutes with the lights on and the guage never moved. I suppose I will find out later if the battery gets low. Any ideas from you tractor wizards????

[sam5570]

You really need a volt meter to test an alternator to see just what it is doing. That said, running at idle should give something. If it is not to difficult to remove I would take the alternator to a parts store like Advance or AutoZone and let them test it since they will do it for free.

yeah even though you have replaced the alternator you still need to put volt meter on it to see what it's doing you may have a bad guage or in some casses i have seen the guage it's self short out.

[Winmac]

My next (brain dead ) question is---does the amp guage only show a charge if the battery is low? I ran it about 10 minutes with the lights on and the guage never moved.

What the amp gauge shows is dependent on where it is installed in the system, that is why a volt gauge is generally a better indicator of charging state.

At my work we had a dozen or so single wire alternators installed on equipment, they were nothing but trouble, every day we were boosting equipment to get going. I suspect the build quality was the main issue, when i looked into it was completely random weather or not they would charge and would not kick in until 1700 rpm despite the fact that the alternators were low rpm start.
The only solution was to swap them all out and install three wire alternators and 95% of our battery issues were gone.

[mitch becton]

as i have stated before with the 10si which will produce about 60amps power or the 12si which will produce about 94amps of power either new or unit with multiple rebuilds if the air gap between the rotor and stator becomes to big it causes the unit to have to run at a higher rpm to turn regulator on .the simple truth to fixing this problem is to get local rebuilder or diy install a stator activated regulator which is still activated by a 1 wire hook up this will allow any unit to start charging at about 400 rpm's "YES" 400 you eliminate the diode trio which makes the 400 rmp process to work also their is no seperation with these set ups whether auto or farm application except that there were some 10si/12si units for farm use but were totally sealed to keep corn and cotton and other debris out of alternator. if you need some of these regulators just let me know and they come with instructions the kit is about 20.00 each

[don45640]

Just a thought.....my backhoe stopped charging the battery,and lo and behold.....the regulator was separate and up on top near the dashbord's top.Took it apart and it had fell apart inside. don-ohio (:^)