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MG TD TF 1500 - Best Method For Polarizing Dynamo

Hi, have been down with a bad back for several months (long story) and just getting back to her TD.

I know some of this has been covered before and I have searched the archive for information. However, this is a slightly different question and I would appreciate recommendations (have visions of sitting on the garage floor surrounded by smoke).

Are there any benefits that make one of the following generator polarization methods better? Are they equally effective?

I kind of like the second (VW Owner) method simply because you see a response that seems more definite than just sparks).

Polarize Your Positive Ground Generator (MG TD/TF BBS):
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1. Remove both leads from the generator
2. The generator is case is still grounded (positive for a positive ground car)
3. Connect a jumper wire to the hot side of the battery (negative for a positive ground car)
4. Then, quickly wipe the free end of the jumper wire across the small field terminal on the back of the generator
5. Make sure that you wipe the wire quickly so that current flow through the field windings is kept to the shortest amount of time
6. Disconnect the jumper wire and reconnect the generator leads and you are done
7. The generator will now be properly polarized.

CAUTION Make sure that the free end of the jumper wire does not touch ground (the generator case or any metal area under the bonnet while connected to the battery. Or, the wire will instantly turn into an incandescent light for a short period of time and will cause severe burns to any hand holding it.



Polarize Your Positive Ground Generator (VW Owners):
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1. Remove the fan belt
2. Remove both leads from the generator
3. The generator is case is still grounded (positive for a positive ground car)
4. Connect a jumper wire from the DF (field) terminal to the grounded generator case.
5. Then, connect a hot jumper wire (-) from the battery to the D (armature) terminal on the generator.
6. The generator shaft should now begin to spin like a motor with the above connections
7. Only run/motor the generator this way for a few seconds to keep it from overheating
8. Disconnect the jumper wires and reconnect the generator leads and you are done
9. The generator will now be properly polarized

If the generator did not spin it is defective. If the generator did spin, install the fan belt and re-test for generator voltage with DF terminal grounded. If the output voltage is still low, the generator is probably defective.

Thanks for any help/recommendations
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WHTroyer

Not sure how momentarily connecting (flashing) field to wrong side of battery will correctly polarize a Lucas dynamo as your VW instructions say to do. Field should get flashed to hot side of battery, not ground.
D mckellar

D mckellar,might have (probably have) summarized it incorrectly, but that is how the VW group seems to do it.

DF -----> ground (through the case)

D -----> hot wire from battery

https://www.youtube.com/watch?v=i-WeDmZCogU
https://www.youtube.com/watch?v=wd9NqZ-H2wI
https://www.youtube.com/watch?v=EJQkQtg4QXQ
https://www.youtube.com/watch?v=FOxixsjuQzw
WHTroyer

Since I am looking for verification of the VW polarization method, thought it would be good to show the generator wiring. Similar with an added harness ground wire for the case.

WHTroyer

WH - The first procedure is how I was told to polarize the generator and the procedure I follow (and is reprinted on my Homepage at: http://homepages.donobi.net/sufuelpumps/ It is simple, works every time doesn't have yo jumping through numerous hoops as the other procedures do. The second procedure is a quick check to see if the generator is working at all. Cheers - Dave
DW DuBois

John Twist explains how to do it in a video:

https://www.youtube.com/watch?v=PPUfQtVEJGg

And even a faster method proposed by Moss:

https://www.youtube.com/watch?v=wH_yIeKsBSM

Jesús
J Benajes

A little over ten years ago Barney Gaylord (MGAGuru) and I looked into using a Bosch solid state VW regulator on T-cars or MGA's. It ended up not being feasible for a number of reasons. One is that the field coil of the VW generator is not connected directly to ground. Also, the Bosch regulator cover is connected directly to the 12 volt line (easy to let out smoke).
Another problem was in the translation of the Bosch instructions. Also, the Bosch diagram for polarizing the generator mislabeled the jumper wire. Barney and I agreed that the T-car polarization technique is much better (and safer) than the Bosch method. Bud
Bud Krueger

Wondering when polarization is necessary? John Twist's video seems to recommend doing it after major electrical work, replacing a battery etc. As my car hasn't seen an electron for 46 years perhaps this is something I should do prior to start up? Cheers
Peter TD 5801
P Hehir

Polarization should only be necessary when a generator is put into service. In simplified terms, what you are doing is the creation of a permanent magnet by passing current through the windings around the field coils. The direction of the current will determine the magnet's polarity. When the armature rotates through this magnetic field it generates current in the armature windings in the direction controlled by the magnet's polarity. The regulator regulates the current through the field coils when the armature is being rotated. This initial, residual, magnetism is necessary to create the initial current in the armature.

If the generator has sat idle for 47 years it certainly should be polarized before expecting it do anything. Just follow Dave DuBois' instructions. Bud
Bud Krueger

Thanks Dave, Jesus, Bud and Peter. Your responses really are appreciated. Going to Dave's page now.

Bud, as usual, your knowledge of both the T-cars and Bosch generators help to put the different methods into perspective.

Regards,

Bill
WHTroyer

First reply told you quite precisely and without a bunch of nonsense why the VW method was bogus for a lucas generator. Some people can really cut through the crud, can't they? Fairly simple, flash with live current and not ground current to field. The VW method is some half baked nonsense I would expect to find being worshipped on mgexp.

Other reason to polarize is if you change car from pos to neg ground or vice versa. It still the same technique (no need to try and translate verbage from pos ground English); it simply live current (not ground) to field for flash. If changing grounding polarity on car then you will need to swap the wires on back of the ammeter, or it is going to read backwards
S Cole

If you change do the horns suck instead of blowing?

The first method is more than adequate, done it more times than I want to remember.

I had connected the battery in the "new" polarity first.

Peter
P G Gilvarry

Thanks for this timely post. I am not so patiently awaiting a backordered generator for my positive ground '51 TD from Moss. I want to make sure I hook it up correctly if it ever arrives.

Bob
Bob McLeod TD 5618

S Cole, Idaho, USA - "The VW method is some half baked nonsense I would expect to find being worshipped on mgexp.

Other reason to polarize is if you change car from pos to neg ground or vice versa. It still the same technique (no need to try and translate verbage from pos ground English); it simply live current (not ground) to field for flash."
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Thanks S Cole. Appreciate your helpful and very supportive in-your-face response. At least you recognized my innate love for "half baked nonsense".

However, still working on "live current". Is "live current" better than plain ordinary current? I know it has to be better than dead or mostly dead current.
WHTroyer

Keep trying WHT and you may soon get it. Not sure what you are trying for with "plain ordinary current." AC or DC current will always be "dead" when ground connected to itself. Same when you connect the live to only itself. In DC there is only live and ground to deal with, aka- cathode and anode. In AC there is live and common to worry about, with ground added for safety. Both systems have live current, and if you really do not understand all this you should not even concern yourself with flashing a generator or wiring a house plug. Get it done by someone who understands electricity. The life you save may be yours.

If you use some car battery jumper cables to flash the field it will send sparks flying and burn up your generator real quick, don't do it. ALl you need is a 16 gauge wire to do it. Maybe a 14ga (14ga is a bit larger diameter than 16ga) A 16ga jumper wire carries MUCH less current than those jumper cables to start a dead battery. You can seriously injure yourself from the current from a car battery. Just look on youtube and you will find all kinds of people welding things using a car battery. Flashing a generator does not require welding current, but both welding and flashing do require LIVE current.
S Cole

S Cole, Idaho, USA - "Keep trying WHT and you may soon get it."

Its called sarcasm. Current is simply a rate quantity (a flow of charge). Never heard such interesting metaphysical explanations or descriptions before.

Kind of like damping and dampening. The difference between a decreasing amplitude and throwing water on something.
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WHTroyer

WHT I am overjoyed at your sudden departure from ignorance, into the land of know it all!
S Cole

On Dave DuBois' web site,on the Polarity Change technical article:

Instruction #2 says to “reverse the primary leads…..,” but my car had no leads installed to reverse.
Currently, my TF has a red wire coming from the distributer and a white wire coming from the harness. What would be the distributer connections for a negative-grounded car? (red to + or -/white to +/-?)

Instruction #3 says to “reverse the leads on the ammeter….”, but what were they to begin with? Brown or Brown/White on the left or right? I cannot tell if the ammeter wires have ever been switched. For a negative-grounded car, what terminal does the brown wire and brown/white wire connect to , left or right (as you look at the back upright side of the ammeter?

I'm doing simple, low-amp tests on wiring right now, trying to sort things before applying the full battery load to the car, and am running into some problems.

Stay tuned for more electrical questions. I appreciate all help in trying not to burn up my harness.

thanks,
Tyler

Tyler Irwin

Mr Cole's recent contributions on this & other threads are clearly contrary to the spirit of this forum. I'd like to see you moderate your tone sir, or better still, go elsewhere.. Cheers
Peter TD 5801
P Hehir

The need to re-polarize does come up. I removed my dynamo this summer to tighten the pulley bolt. After reconnecting, no charge. Once I re-polarized per John Twist's method, all was good. It is a bit nerve wracking.

Tom
'54 TF
T Norby

If you are going to spark the dynamo it is a good ides to fix a small strip of metal to the terminal and brush the jump lead from the battery against this. If you spark directly against the terminal you can b****r up the brass threads.

Jan T
J Targosz

Yes, these various methods will work to polarize the generator. Let me explain why I suggest Dave DuBois' method. All you're doing is momentarily causing current to flow through the wires wound around the field coils in the direction that will properly polarize the magnet poles.
John Twist's method of momentarily shorting between the A and F terminals of the regulator does what you want to do IF the ammeter is properly connected. That's where the A terminal wire is routed from the battery. The spark is safely away from the battery.
Jan's suggestion is fine, but isn't necessary.
Dave's technique is to connect the jumper to the field connector of the generator and to then brush the other end of the jumper to the starter switch terminal. There is no sparking at the generator field connector.

What's with this sparking? If you measure the resistance of the wires connected to the field terminal you'll find that, in normal conditions, they will read about 6 ohms. Our friend, Mr. Ohm, says that if we connect 12 volts across 6 ohms we'll get (12/6)= about 2 amperes of current. That's not much. What's with the sparking? That 6 ohms worth of wire is wrapped around these field poles to create magnetic fields. The spark occurs when you remove the jumper and the current abruptly changes from about 2 amps to zero. The magnetic field that was created by the current collapses around these wires and induces a very big voltage. That's where the spark comes from, just like the coil firing a spark plug.
Dave's technique may put a little wart on the starter switch terminal. That's a lot better than sparking at the battery terminal where explosive gases linger.
Sorry to be so verbose. Bud
Bud Krueger

I agree with Bud on "what's with the sparking?" SCole mentions NOT using jumper cables, like you would use to start another car's dead battery, for flashing. He suggests 16 gauge or maybe 14. I would go farther and suggest 18 gauge. I've done this numerous times including changing polarity with 18 gauge. I have thought before about Jan's concern of damaging the fine threads of the field terminal when flashing, and part of my routine is to put the nut back on prior to flashing, as cheap insurance. "Sparking" is not the best description of what is needed, it is more of a very DIM momentary "flash" at the point where the jumper wire is touched to the field terminal. I think sparking evokes images of something like arc welding, with sparks flying and landing on your (unprotected)shoe and leaving a burn mark.

I must say I found the OP's comment, and subsequent thanks to everybody but me to be rather unfriendly, and counter to the spirit of this forum.
"D mckellar,might have (probably have) summarized it incorrectly, but that is how the VW group seems to do it." "Thanks Dave, Jesus, Bud and Peter. Your responses really are appreciated. Going to Dave's page now.

Bud, as usual, your knowledge of both the T-cars and Bosch generators help to put the different methods into perspective.

Regards,

Bill "

My reply, the first reply to the OP's question,

"Not sure how momentarily connecting (flashing) field to wrong side of battery will correctly polarize a Lucas dynamo as your VW instructions say to do. Field should get flashed to hot side of battery, not ground."

(correctly) and quite succinctly addresses the flaw with trying to polarize a Lucas dynamo using that VW method. Sorry if OP somehow found some personal affront within those words.





D mckellar

Sorry D mckellar, it was not my intentional to offend you. Thank you for your response. There was no way I "found personal affront" with your post as you imply.

In my following post addressed directly to you, I only meant that I might have (probably have) summarized the VW method incorrectly and provided several links so you could see firsthand how they were polarizing their generators. I was admitting that I might have summarized it incorrectly. Was that really "rather unfriendly, and counter to the spirit of this forum"?

Just maybe, someone asking a foolish question is honestly looking for information to increase their understanding. They might benefit more from a friendly, supportive discussion than (i) an immutable declaration of fact without explanation or (ii) being told they posted "half baked nonsense". You don't learn much from either reply.

Very sorry this was an uneducated, "half baked nonsense" question. Since it is difficult for me to asses the ignorance level of my questions prior to asking, this will be the last question ever ask here.

Other MG forums seem to be friendlier.
WHTroyer

I want to leave this thread with the following information in case someone finds it in the future and is interested. Asked the same question on a VW Forum and they were very friendly and at least tried to answer (and explain) my question:

"Each method will work to polarize a generator depending on the internal structure of the generator. The correct post to flash with the hot post of the battery depends on whether the generator field is internally grounded or externally grounded. It is imperative to know how your generator is grounded because incorrectly polarizing can burn out the armature.

Externally grounded generator are polarized (key off) using a jumper wire to momentarily connect the battery and armature (gen.) post. This will produce a flash and not a severe spark.

Internally grounded generators are polarized (key off) by connecting all leads but the one to the generator field or F terminal. With a jumper wire, momentarily connect the insulated battery terminal to the F terminal. There will be a flash and the generator will be polarized. Then, re-connect the F terminal lead.

To check for External Ground, remove one brush (it doesn't matter which one). This will not show a break in continuity between the armature and field. For Internal Ground remove one brush. This will show a break in continuity between the armature and field."

Again, thanks Bud for your answer.

D mckellar and S Cole, how hard would that have been.



WHTroyer

This thread was discussed between 28/12/2016 and 31/12/2016

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