VR...working or not?

[DFB]

Long story not so short.

I have been having some battery/charging issues over the winter months. I had found a broken battery post clamp on my negative cable replaced that, then still had a weak battery after a few days sitting. Considering it was the original John Deere battery that came with the tractor (14 years old wow) I decided to get a new one. So now I got a volt meter hooked up to read the charge rate and I'm seeing constantly changing voltage readings from 12.2 to 14.5. Normally I would just write this off as bad regulator and get another one.
but ol' uncle johnny wants close to $150 for a new one. So I really want to be sure.

I have the shop manual so I've been checking the system against the book specs Its a pretty simple looking circuit. Rotating permanet magnet 20 AMP alternator to supply the AC. Spec says 32VAC @ slow idle (no rpm given) - 50VAC @ fast idle 2850 rpm. All checks seem ok right at the harness connecter with the regulator unplugged. I get 32VAC @1700 rpm and 20VAC at about a 900 rpm idle.

Checked and double checked grounds and all wire harness back to battery.

John Deere Voltage Regulator M807915 looks like its used on 4010 4100 4110 4115 2302 2320 and 2520 series tractors. 6 wire 2 blue/ac, blk/grd, red/battery+, green discharge indicator light, yellow/keyed F2 fuse power circuit .

Now specs also say... alternator regulated voltage 12.2- 14.8 VDC, VR no load voltage 14.5 +-.05,
Charging circuit operation to maintain battery voltage between 12.4 and 13.2 volts.

System Operation: Battery sensing circuit...current flows from battery to key switch to VR, VR converts alternator AC current to DC current.
The status of the charge rate is indicated by the discharge light if the alternator output is insufficent VR supplys current to discharge light.

If battery voltage is low rectifier/regulator allows current to flow to battery to charge. When battery is fully charged VR stops stops current flow to battery.

Huh?

So is this working right or not

 

[jd110]

It is unusual to see the voltage fluctuating so much. The regulator may be bad, but first I would recommend unhooking the glow plug circuit. I have seen some stuck relays cause the charging system to seem like it is malfunctioning. With glow plugs on constantly, the charging system can't keep up.

 

[DFB]

Yea thanks for the quick reply...I also had been thinking the glow plug circuit might have something to do with it too, so I took the glow plug relay out and bench tested it to spec both for continuity and switch contact under batt. power Seemed to be ok.

With volt meter hooked up at VR connecter I can see the voltage draw down when I turn the key to ignition, then it comes back up when the timer switches.

But I can certainly try that tomorrow glow plugs are activated in the start position too

The VG is stamped RS 51

I've been looking for a possible aftermarket alternative

 

[rshrimp]

If your reading went from 12.7 or so to 14.5 I would say your regulater is just doing it's job and turning the charge on and off, but at 12.2 the battery is only at around 25% if charge. What is your static battery voltage? (at rest before you start the tractor and after it has set for at least an hour) I would put a charger in the battery overnight and make sure you are starting with a fully charged battery. Then start testing.

 

[Tx Jim]

I would recommend having alternator checked.

 

[DFB]

Its a good battery charge just read 12.8 on the voltmeter Old one is still on the bench and its showing 12.5 static after being charged thats when I decided to replace it. Heres my notes from earlier yesterday...the 12.2 was the draw down with the lights on in road position running at mid throtttle after 10 min. Bumped it up and was only reading 12.4 at full throttle. Shut the back lights off and at that point it climbed to a no load volt reading of 13.0 but no more at full throttle. So it was no load charging to some extent.

For years I have had two xtra 55w work lights branched into the lights on postion circuit for nightime plowing never had any battery/starting problem. I have them disconnected right now

I'm used to seeing steady charge rate numbers like 14.0 on the motorcycles.


So right now today its running battery showing a 14.5 charge rate at any throttle setting above 1500 rpm slight decline with road lights on...after about 10 min after starting started hopping between 12.8 13.5 then climbed back to 14.5 no load. Lights on again..1700rpm 14.5v...bumped up full throttle dropped to 13.5 then climbed back to 14.5Right now its holding steady at 13.1v with full draw load with work lights on too @ 2000rpm GO FIGURE!

Guess for time being I'll just watch it some more...maybe its heat related

 

[Tx Jim]

Is alternator drive belt tight?

 

[DFB]

What would I be looking for on the alternator? I read ac volt within spec. I ohm checked across alternator pins and pin to ground like I would on my harley even though deere has no such test seem to match those specs. I also tightend the belt obviously its old thats original part too.

 

[Tx Jim]

Is back of alt belt above,even or below sheave on alternator?

 

[DFB]

TX Jim its a notched belt belt just looked and it rides deep in the larger alternator pully but sits slightly above water pump and engine pully