View Full Version : polarizing Generator

20th May 2005, 18:40
I just put a new wiring harness on my 77 XLH. The manual says to polarize the Generator whenever the wiring is unhooked. The instruction tells how to do it at the regulator but mine has been converted to an electronic regulator so I can't do it like the book shows. Do I still need to polarize it since itís an electronic regulator?

20th May 2005, 18:49
Yes you do. You are polarizing the generator, not the regulator. Look in your manual, they show more than one method of polarization. Call an auto electric repair and they can give you other proceedures for doing it if your manual isn't like mine. I am at work and don't have access to my manual.

20th May 2005, 19:20
thanks you for the quick answer

20th May 2005, 19:53
You can flash it from the battery directly to the generator. :smoke

20th May 2005, 22:51
thats the positve side to the A post on the generator? Right?

21st May 2005, 02:56
thats the positve side to the A post on the generator? Right?

Yes...here's what it says in the H/D service manual under "Polarizing Generator".

"Generator on motorcycle and connected to regulator:
Connect one end of a jumper wire to the generator armature terminal.
Momentarily touch the other end of the jumper wire to the positive terminal of the battery.This restores the magnetism.Remove jumper"

So yes , battery + to A (A = armature) just touch it for a second and you may or may not see a spark.No spark doesn't mean it didn't work,it may already have the right polarity.Good luck! :D

21st May 2005, 03:14
I keep a 4 ft piece of insulated 16 gauge wire with an alligator clip on one end, specifically for this task. Clip it on the gen A terminal, touch the other end to the battery +ve, roll it up and hang it on the wall, ready for the next time.

21st May 2005, 04:28
Thanks Guys

20th July 2008, 22:33
I have a 74 Ironhead and have seen in my manual that you should jump the GEN and the BAT directly at the regulator for 59-77 models, and for 78-84 models jump BATT to A terminal. Is it not going to work if I jump from the battery to the generator on my 74? I ask because my regulator is a mother to get to. Thanks guys

72 Ironhead XLH
20th July 2008, 22:36
will work that way too,

20th July 2008, 22:46
Yes, and welcome to the forum!

15th January 2010, 07:13
Will not polarizing hurt anything? Besides draining the battery and leaving you stranded of course.

15th January 2010, 13:02
I believe I've read that when the generator is not properly polarized, the contacts on a mechanical regulator will prematurely burn and wear, due to excessive arcing.

15th January 2010, 13:54
Incorrect polarity may result in relay, battery or generator damage.

My own experience is that it may do not damage during a short ride, like 10 or 15 minutes. Other than that i do not know.

To really answer this question one would have to understand exactly what is happening electrically, which i do not.

15th January 2010, 14:23

A generator can deliver current for either a positive or a negative ground system?

A generator produces current by passing conductors (the armature windings) through a magnetic field. The magnetic field is produced by electromagnets that surround the armature. Basically, the field portion of your generator consists of copper windings around iron core, often referred to as the pole shoes.

The voltage and current delivered by your generator is determined by the strength of the magnetic field and the speed at which the generator is running. But, the polarity of the current is determined by the polarity of the pole shoes, or the direction of the magnetic flux or field, which is determined by the direction of current through the field windings.

When you start your engine, the generator will start delivering current. Since the generator is still isolated from the electrical system by the voltage regulator it will start producing current based on the polarity of the pole shoes. As soon as it begins producing current, some of that current will be directed to the field windings to strengthen the magnetic flux.

If the generator polarity is reversed, the generator will build up voltage and close the cutout relay points. This put the generator in series with the battery, and their voltages are added together. This high voltage across the points (about twice the battery voltage) can cause high current and enough heat to weld the points together.

This damage does not happen immediately. The instant the points close, the voltage is about the same on both sides of the relay coil, so very little current flows, and spring tension reopens the points. But, generator voltage will again close the points, and the cycle will repeat at a rapid rate. Heat and arcing will finally weld the points together.

When the points weld, the battery and generator are connected at all times. The low resistance of the generator allows the battery to continue to discharge through the generator. The high current can create enough heat to burn the armature.

How do you control the polarity of the pole shoes? The polarity is determined by the direction of the last current through the field windings. Since even a very small current can polarize the shoes, never assume the generator is properly polarized. You must polarize the generator every time it is disconnected or serviced.

To polarize the generator, simply make a short jumper wire to short between the battery (b or bat) and generator (g or gen) lugs on the cutout relay or voltage regulator. Only a split-second or a spark is required, so simply tap your jumper wire onto the lugs and pull them right back off.

Reference: John Deere Fundamentals of Service (FOS): Electrical Systems, Fifth Edition. 1984. Chapter 4, Charging Systems. John Deere Service Training, Dept F, John Deere Road, Moline, IL 61265

Fe Head
15th January 2010, 15:07
Incorrect polarity may result in relay, battery or generator damage.

My own experience is that it may do not damage during a short ride, like 10 or 15 minutes. Other than that i do not know.

To really answer this question one would have to understand exactly what is happening electrically, which i do not.

In addition to what others have said above it is important to understand what is going on inside the typical generator.

The soft iron shoes on either side of the armature are very very poor at retaining residual magnetism and will become "apolar" or magnetically neutral very quickly leaving virtually no magnetic field lines crossing between the internal shoes of the generator.

When this situation exists the startup initial rotations of the armature can easily set up the first flow of the electrons opposite to what is needed relative to the battery's polarity.

This is not a good thing to continue without grave cosequences

As all typical DC motorcycle generators are of the parallel shunt self excitator design once the reversed flow is established it will porduce and maintain the reversed North, South poles.

Moreover, it will never correct its self without active intervention.

If our Sportster's generators were of the series external excitator type this step would never be needed - however they are not therfore polarizing correctly guarantees a positive outcome everytime.


15th January 2010, 18:31
I wonder if it would fry a solid state regulator as well. My main concern is with the generator, as I just got this thing back and its not charging.

15th January 2010, 21:31
Same as you Mick, I keep a jumper on the wall in the garage. Doesn't matter which place you jump from be it the battery plus terminal or the B+ terminal on the regulator (mechanical).

12th February 2010, 18:45
If testing for polarity with a meter, at what point do you determine that it is correctly polarized. I need to eliminate possible faulty wiring, generator, and/or regulator. Due to not properly polarizing the generator, I was left stranded and had to push the bike about a mile to a friends house. Now that I have polarized and recharged the battery I am wondering what rate the meter should read at.

ryder rick
12th February 2010, 19:17
What you are doing when you "Polarize" a generator is to set up the residual magnetism in the field poles.

Since the generator is self exciting (self powered) it relies on the residual magnetism in the poles to get itself started.

It depends on residual magnetism to make voltage to provide power to the field windings at startup.

This allows the bike to be push started with a dead battery, and eliminates the need to provide external power to get the generator started.

When a generator sits for a LONG period of time without running it may loose that residual magnetism. Or when a generator is rebuilt the pole pieces may get swapped or be new and thus may not have residual magnetism or the polarity of the residual might not be correct.

A working Generator light with a fully charged battery will usually get a generator running that has been previously run and not disassembled. The back feed voltage through the gen light from a full battery is not as strong as a "polarization" but has the same effect.

NOTE: When polarizing do not strike the F terminal by accident, you will burn the field control relay contact in the regulator and ruin it. And probably smoke an electronic regulator. Just one touch is all it takes and instant junk...