Farm Equipment - D17 Generator loses polarity

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D17 Generator loses polarity

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=160953
Printed Date: 07 Jun 2025 at 4:59pm
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Topic: D17 Generator loses polarity

Posted By: KoryKreisler
Subject: D17 Generator loses polarity
Date Posted: 13 May 2019 at 8:50am

Good morning,

I've been reading this page a lot since purchasing a 1966 D17 last December. What a great web page! Anyway, I've got a charging problem on my D17.

I replaced the generator vs switching to an alternator because I read on this forum, the generator worked for the last 50+ years, why futz with it? Back on track, I installed it, polarized it and bingo, charging like it should. I shut it down and went to some other tasks, shortly after started smelling hot paint and there was a bit of smoke coming out of the generator. When I (as quickly as possible) disconnected the wiring there was arcing on the wire closest to the engine. I went did some research (here) and found that the regulator might be sticking, so I rapped it with a screwdriver a couple times and no more arcing. Started it up, repolarized it and back to charging.

Now that you all have all the background here comes the problem, EVERYTIME I start the tractor I have to polarize the generator. I don't know if it's related to the issue described above or if I'm doing something incorrectly but when I shut the tractor down and restart it will not charge until I polarize the generator again.

Any help or suggestions would be greatly appreciated!

Replies:

Posted By: DrAllis
Date Posted: 13 May 2019 at 8:54am

You have the battery installed as a POSITIVE ground, right ???

Posted By: KoryKreisler
Date Posted: 13 May 2019 at 9:14am

Yes, forgot to add that. The battery is currently wired positive ground. Before I bought a new generator I checked the battery. It WAS a new battery and was wired negitive ground. I switched it back so the gauge read correctly and the red hydro light works on the dash now too.

Posted By: Sugarmaker
Date Posted: 13 May 2019 at 1:34pm

Kory,

Welcome to the Allis Forum. I need to work on my 17 in this area too. Good luck. Lots of good folks on here to help. Oh almost forgot we need pictures!

Regards,

Chris

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D17 1958 (NFE), WD45 1954 (NFE), WD 1952 (NFE), WD 1950 (WFE), Allis F-40 forklift, Allis CA, Allis D14, Ford Jubilee, Many IH Cub Cadets, 32 Ford Dump, 65 Comet.

Posted By: Strokendiesel002
Date Posted: 13 May 2019 at 2:14pm

howdy!

When you say you "switched it back" - are you saying that you just switched the battery cables so it's a positive ground?

Or did you switch the leads on the coil to be positive ground, along with attempting to polarize the generator back to a positive ground?

edit - I see you posted that you started it and then polarized it - If I recall, you need to polarize it (the regulator, specifically) just prior to starting, as the generator itself will charge either way. I wonder if the regulator may be the cause of your issues

Posted By: Steve in NJ
Date Posted: 13 May 2019 at 8:19pm

Sounds like you have a VR that's not working correctly. Whenever you install a new or rebuilt Generator, rule of thumb is change the VR at the same time just in case the old VR may have an internal problem because of the way the Gennie was charging prior. What I always do is when one of our customer's needs a VR, I always ask them for the number off the Generator. (if its still there) Once you know the P/N of the Gennie, then you can mate the correct VR to it. Now, once you have things wired up again, before you start the Tractor, Polarize the Gennie first as Strokendiesel mentioned. Then start the Tractor. If things are charging, you should be good to go! Welcome to the forum!

Steve@B&B

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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife

Posted By: KoryKreisler
Date Posted: 15 May 2019 at 9:15am

Thanks for the replies. I didn't do anything with the coil, I assumed that the previous owner simply installed the battery incorrectly. How should the wiring look when its wired correctly?

I will get a new regulator ordered. Plan on playing with it this weekend so first task will be to install new parts, check the coil, polarize and see what happens. I'll take some pictures too!

Posted By: DrAllis
Date Posted: 15 May 2019 at 9:56am

If the battery is a positive ground, then the + terminal on the coil connects to the distributor (which is a ground).

Posted By: KoryKreisler
Date Posted: 17 May 2019 at 9:01pm

I'm seeing many different ways to polarize the genne, battery to gen with a jumper wire correct?? If so, I may still have problems with new Gen and New regulator. Going to get my meter on it in the morning.

Posted By: DrAllis
Date Posted: 17 May 2019 at 9:44pm

Just ground the field and fire it up to more than 1200 RPM. Grounding the field terminal on the gen will make it put out 100% and I've never had to polarize one doing it that way.

Posted By: DaveKamp
Date Posted: 17 May 2019 at 9:46pm

Down Steve's path, what's important to realize, is that generators and mechanical voltage regs 'adopt' a given polarity. The day they're made, they have NO polarity. Once they're connected and started, they start a development time where operation magnetises the ferrous components. Electric fields create magnetic fields, and the cores 'become' weak permanent magnets.

Electromechanical devices that use DC current 'identify' themselves to whatever polarity they've been 'raised' under.

Yes, you have to 'force' polarity upon a generator... but you also must understand that an existing magnetic field doesn't 'like' to be changed... and until the polarity change occurs, it will be VERY troublesome and fickle.

The mechanical voltage regulator operates on concept of magnetic field strength... when you apply higher voltage to a relay's solenoid coil, that coil develops a stronger magnetic field, which will tend to help 'pull in' the contacts.

Example: when you apply voltage to a coil, and raise that voltage gradually, eventually you get enough magnetic pull to cause the contacts to close. As voltage falls, the magnetic field eventually gets low enough for the contacts to open.

Imagine however, that years of current flowing through the solenoid winding, that the framework around the solenoid has turned into a weak electromagnet. NOW... when voltage comes into the coil, it takes LESS voltage to pull in the contacts, 'cause there's ALREADY some pull there.

IF the solenoid coil's magnetic polarity is one way, but the CURRENT FLOWING THROUGH is opposite, ti will take substantially MORE current flow through the coil, to cause the relay's contact armature to pull in.

So... if your coil was operated in a + ground application, and you've changed to a -GND application, that regulator coil is probably NOT going to work 'nicely''' at least... not 'till you've run that machine long enough for the coils to shape their 'new magnetic identity'.

To accellerate the correction, the use of a degaussing coil (pushing AC current through a coil nearby) might 'erase' the coil's magnetic disposition, and return the coil to a 'magneto-physical' neutral state, then adopt a reliable operation character.

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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.

Posted By: KoryKreisler
Date Posted: 18 May 2019 at 9:35am

Field grounded, still no charge. I've tried all the polarization tricks in the book and still no go.

Both the generator and regulator are new pieces, starting to think I should have went the alternator route. Not giving up.

Posted By: KoryKreisler
Date Posted: 18 May 2019 at 10:01am

Just tried the trick to get the generator to motor off the battery and it doesn't move. Well it moves about 1/4 turn and needs help the rest of the way. I think I found my problem. Assuming the VR fried the old generator, and the new one.

Posted By: Gerald J.
Date Posted: 18 May 2019 at 3:36pm

There are two ways to assemble and wire a generator field and it takes a different regulator circuit for each one. One way is to connect one end of the field winding inside the generator to the output post, then the regulator grounds the other end of the field winding to get maximum output voltage. The other way is to ground one end of the field winding to the generator shell and connect the floating end of the field winding to the field post. Then the regulator supplies battery voltage to the field to get maximum generator output voltage. The wrong regulator will keep the generator from working.

Gerald J.

Posted By: KoryKreisler
Date Posted: 19 May 2019 at 1:40pm

Got it! Took the generator off, one of the brushes was sticking, put it back in and went through all the install "stuff". She works like a charm! Thanks fellas.

Posted By: chaskaduo
Date Posted: 19 May 2019 at 3:00pm

We all learn something.

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1938 B, 79 Dynamark 11/36 6spd, 95 Weed-Eater 16hp, 2010 Bolens 14hp