JD 820 - 6 volt alternator on a 12 volt tractor?

[glenhenshaw]

Hi all,

I have a John deere 820, serial number 065272L. I've owned it since 2005 and have used it sparingly. For several years now I've known it had a problem charging the battery. I'd put a new battery in it and it would start 5 or 6 times, and then I'd have to start jumping it; after ten or twelve more starts that wouldn't work either, since the car doesn't really provide enough current to turn the JD starter, so I'd put a new battery in it.. Since I only use it five or six times a year, this system worked okay.

But this week I couldn't start it for anything and so got serious about fixing it. At the suggestion of my local JD dealer (really small place in southern Maryland) I pulled the alternator and took it in to be tested. And... lo and behold, it looks for all the world like it's a six volt alternator; it even says "6V" on the service plate. Which explains why it won't charge a twelve volt battery, but leaves us with a couple of bigger mysteries. First, the alternator looks nothing like the alternators shown on the various OEM parts supplier websites for this tractor. Second, how and why did anyone get a six volt alternator that actually fits - there are no apparent modifications to the tractor to make the alternator fit - and install it in what is clearly a twelve volt electrical system?

The JD mechanic, who in my experience is very good, is scratching his head. He's afraid to order a replacement OEM alternator since they all look different from the one that came off the tractor, and can't figure out how you could even find a 6V alternator that would randomly fit the wrong tractor.

Any ideas?

[kuboman]

Is it a 6volt alternator or generator. I have never heard of 6 v alternators but most old tractors had generators.

[glenhenshaw]

Is it a 6volt alternator or generator. I have never heard of 6 v alternators but most old tractors had generators.

Errmm... dunno. How do you tell the difference? I'm pretty good with my hands but have no mechanics experience.

In looking at pictures the external appearance of the part I removed looks like a generator (it's fairly long with respect to its diameter, and it has a front mounting plate with two offset bolt holes and a rear mounting plate with one hole). However, the parts websites all list alternators, not generators, for this tractor.

When did JD switch from generators to alternators? I think my tractor was built in 1971. And did the older 6v generators have the same mounting points as the 12v generators did?

[jd110]

The 820 shows a generator for serial numbers up to 075344 and an alternator for above that number. They are both 12 volt and both are made buy Robert Bosch. I attached a parts diagram for both versions. Can you post a photo of your generator/alternator?

[glenhenshaw]

What I have is clearly the generator...

[glenhenshaw]

So would a six volt generator fit in the same spot? And do I need a new voltage regulator as well as a new generator?

[jenkinsph]

glenhenshaw,
Looks like somebody stuck that 6v generator on there before they sold you the tractor.

I would get the proper generator and check the voltage regulator to see what it is. I would be inclined to change both to eliminate damage to the new generator.

I would heed the advice you get from jd110 an experienced deere mechanic.

[tommu56]

unless you need the correct part i would put a 10-SI alternator in it looks like the one in the right in the pictures some one else posted

here is a link on how to install and wire one

Wiring up the GM 10SI Alternator

and another

Catalog

and one more

The Delco 10-SI and 12-SI Alternators

[Tx Jim]

unless you need the correct part i would put a 10-SI alternator in it looks like the one in the right in the pictures some one else posted

I'll second installing a Delco alt. as long as there's enough clearance under the hood.

[glenhenshaw]

I'll second installing a Delco alt. as long as there's enough clearance under the hood.

This is great, guys, thanks. That sounds like the best idea. I have a fair amount of electrical experience so I'm pretty sure I could wire it in. But I'm worried about physically mounting it. Does anybody know whether a Delco alternator will fit on the same mounting holes as the original generator? Otherwise, does anybody know how involved the required modifications are?