12 volt IH 140 Generator.

Just had this generator rebuilt. Since I live about 20 miles from where I keep the tractor I took a drill and spun the generator with a digital volt meter hooked to the F and the A terminals, only ones it has. F should be the positive since it is a 12 volt negative ground?

Anyway the volt meter would take care of things if it was hooked up backwards. Using both a 18 volt cordless and a 1/2" Dewalt corded drill I never got the meter to read anything.

Is there something else the generator needs to work? I also thought a generator would work as a DC motor but it would not turn when hooked to 12 volts.

I guy who rebuilt it put in a new armature, brushes and bearings. I know he tested it before my wife picked it up.

Am I missing something or has it quiet work? I think it is measuring 14 ohms or so across the terminals.

Also is it necessary to put oil in the front oil cup? I don't know if this is a sealed bearing. I know the back has a brass bushing that needs oil from time to time.

Thanks for any help.

To test that way, provided you could get enough rpm, you need to ground the f terminal to gen frame, then hook you meter from Arm terminal to gen frame. When you put it on your tractor, be sure to polarize it by flashing from battery to armature terminal after all hooked up and before starting engine.

Need a 12 volt battery in curcuit for proper test. Field post needs positive exciting charge I think. Been awhile since worked with generators. RN

YES A generator will work as a DC Motor, BOTH are basically the same thing.

However, a genny produces its output between its ARM post and its case/frame. Assuming theres some residual magnetism in its iron field poles if you spin it the output voltage is measured from ARM post to case NOT from ARM to FLD post as you tried. The faster it turns and the more magnetic field strength present in its field poles THE GREATER THE OUTPUT.

If youre going to use it at Pos ground (or either ground for that matter), having no idea what was done at the shop, I STRONGLY SUGGEST YOU POLARIZE IT BEFORE START UP.

Heres how to peform the Motor Test

MOTOR TEST. You can Motor test the Gen. If its grounded and you remove the belt and apply hot battery voltage direct to its ARM Post and have the Field Post dead grounded to frame, it should motor n run well (Armature n Brushes and Commutator likely okay). Then, if you next remove the Fields ground and it speeds up some, the Fields probably good. If it passes both those tests, it should charge, and if not, it may be a wiring or battery or grounding problem. The hot battery voltage may be taken off the VR's BAT terminal or the starter post or the battery itself for this test.


John T

To the comtent below I will ad that it needs to turn CW looking at the pulley end. (I knew you knew that) Jim

Yo Jim, Thanks, actually I never even thought about it, good info for the poster. While on the topic, correct me if Im wrong, but in "theory" a genny will charge regardless of rotational direction as theres still an armature rotating inside a magnetic field BUTTTTTTTTTT as you point out they do have a correct rotation AND THE REASON IS THE BRUSHES ARE SET AT AN ANGLE VERUS STRAIGHT DOWN PERPENDICULAR WITH THE COMMUTATOR RIGHT???

Once the soft carbon brushes take on that circular shape they would catch n bounce badly if you reversed rotation right???

Lay some knowledge on me my friend

John T

A couple more thoughts to add to the previous posts:

A good 12 volt generator will show between about 6 and 12 ohms between the F and the generator case. And it will show a maximum of about a tenth of an ohm between the A and the case.

Before doing a spin test you should first polarize the generator. Ground the genny F terminal to the case then apply 12 volts to the A terminal for an instant. (If the tractor is negative ground connect the battery + to the A. If it's positive ground, connect the battery - to the A.)

Now when you ground the F terminal the spin the armature you should see voltage between the A and the case. Actual voltage will vary with RPM - could go as high as 30 volts or more at noremal operating speed (3,000 RPM). At lower RPMs the voltage will be proportionally less.

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If the rebuilder put in a new bearing on the drive end can almost guarantee it is sealed - the old open bearing is obsolete. Consequently I'd not recommend putting oil into the front oil cup. (The oil will eventually work it's way into the generator innards where it will do no good!)

The commutator end will still have a bushing. A couple drops of oil every so often is still required.

Thanks,

I have been turning it CW. This is a 12 volt negative ground generator. The A terminal is grounded to the housing and when I wired it to my truck batter all I got was a little arcing when I made the connections.

I know I have been spinning it at 1000 rmp's which is low but a digital meter should have read something other than 0.0 volts.

This does have a new armature and brushed. The field windings check out.

Davida, In response to your statement: "The A terminal is grounded to the housing"

As Bob M pointed out below THATS NOT EXACTLY SO its indeed very low ohms because those big copper armature windings and carbon brushes have very low resistance, therefore, many meters especially a non precision at low ohms unit, may read near zero ohms. The current actually flows from the ARM post,,,,,,, to the ungrounded brush,,,,,,through the armature,,,,,,,,,,,out the grounded brush,,,,,,,,,to case/frame.

ALSO to read the gennys output voltage you need to put the meter on the ARM post and case/frame NOT on the ARM and FLD posts.

Being Pos or Neg ground has nothing to do with FLD and ARM posts connections, the genny can charge at EITHER polarity. Once polarized to where the iron field poles have a certain North/South MAGNETIC POLARITY, when spun the genny will charge at the correct corresponding ELECTRIC POLARITY Pos ORRRRRR Neg.

So polarize it n spin it and put a meter on the ARM and case/frame and thennnnnnnnnnnnn see what voltage is produced ??? and/or run the Motor test I described below.

Hope this helps

John T

The phase relationship of the brushes to the armature windings account for current lag and the dynamics of the magnetic field in one direction over the other. Not much but enough to show output differences if the brushes are rotated manually to the sweet spot , then reversed in rotation. And you are correct on the brush curve dynamic, but the point of contact is found with less science, and more design trial reality. Great discussion, JimN

(quoted from post at 19:21:19 11/23/09) The phase relationship of the brushes to the armature windings account for current lag and the dynamics of the magnetic field in one direction over the other. Not much but enough to show output differences if the brushes are rotated manually to the sweet spot , then reversed in rotation. And you are correct on the brush curve dynamic, but the point of contact is found with less science, and more design trial reality. Great discussion, JimN

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Jim, if I may, I would also add that the minimum brush arcing is at your 'sweet spot' or flux-neutral axis, which is at a different polar position if rotated in the opposite direction. If rotated in opposite direction without relocating brushes to the 'new neutral axis there will be greater brush arcing & shortened brush life.

You are absolutely correct.
Jim