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#581412 - 01/17/15 5:40 pm Dynamo Help  
Joined: Jan 2014
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Brian L Offline
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Brian L  Offline
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Louisiana
I have a 54' M21 that has been sitting for 15 years. I did get it up and running but I can not get any output from the dynamo. When it is running, I used a test light on both the D and F terminal and got nothing. I also hooked the F and D together with the test light and got nothing. I tried to flash the dynamo but it did not make a difference. Any ideas?

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#581413 - 01/17/15 5:55 pm Re: Dynamo Help [Re: Brian L]  
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zoe Offline
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I don't remember exactly what they say right now but if you follow the instructions in various BSA or Lucas publications you can successfully test it. I think you connect the D and F wires together and then run a separate wire to a test light from either the D or F terminal on the dynamo which you ground on the dynamo body. If you turn the dynamo with a drill motor as fast as you can, counter clockwise on my A10, the test light will come on and you will observe that a load builds up as the dynamo bogs down a little if your dynamo is working. The way they ask you to wire it makes no sense to me but it works.

#581426 - 01/17/15 8:00 pm Re: Dynamo Help [Re: Brian L]  
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Rich B Online happy
Rich B  Online Happy



Joined: Aug 2001
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Stone Creek OH USA
Check to see if your brushes are sticking or worn out. Commutator may be dirty as well.


Life is too short to drink cheap, bad beer.
#581427 - 01/17/15 8:05 pm Re: Dynamo Help [Re: Brian L]  
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B31 Ally Offline
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Brian L,

If you join the D and F together with a wire then get a voltage tester or multimeter and put one test probe into the D or F terminal, it wont matter which terminal you use as they are now joined and put the other probe to the dynamo body. Start the bike up and if the dynamo is working it will show voltage. Don't rev the engine much past a fast idle as the dynamo is running open circuit and can soon be producing a lot of voltage as there is no voltage regulator in the system. There is the possibility that if you accidently connect the battery the wrong way round i.e. positive or negative earth, this can also reverse polarise the field coil the wrong way round so the dynamo wont charge even if you now reconnect the battery the correct way. You need to flash the field coils again like you have already done. Ask me how I know!

If this doesn't work the next thing I would be looking at is the possibility that the dynamo has seized as it has been sitting the past 15 years. This means removing it but that is a simple job on a M21. I am assuming here it is a Lucas E3L dynamo. If your lucky the slip clutch on the MO1 magneto that drives the dynamo will be slipping, if your really unlucky the seized dynamo will now have grinded the 58 teeth of the fibre gear that drives the dynamo as the slip clutch didn't slip.

If the dynamo isn't seized the next thing I would look for is the brushes, make sure they are free in their slides and that the two tension springs are still holding them down onto the armature. If all that seems to be working then take it to an auto electrician that knows something about dynamos and get him to test if the field coil is still energising and that the armature is o.k. If all checks out you can do a motor test on the dynamo.

Join the D and F terminal again with the dynamo off the bike and on the bench. If the bike is positive earth then run the battery positive wire to the dynamo body and the battery minus wire to either the D or F terminal, the dynamo should turn slowly like an electric motor in the direction of the arrow on the case. This is a starting point but is no guarantee that because a dynamo motors it will generate power.


Another thing I have done is to flash the dynamo while the D and F terminal is joined with the engine running and suddenly the dynamo started charging. This might not be recommended practise but it kick started a dynamo I had on a 1950 B31 plunger two years ago and it hasn't gave any more trouble yet. If it worked for me it may work for you.

I haven't mentioned the voltage regulator or ammeter yet as you need to prove first if the dynamo is a fault or is in perfect working condition. As you can see there is more than one thing that can stop a dynamo from charging but I hope I have gave you a few pointers on what to look for.

#581543 - 01/18/15 3:32 pm Re: Dynamo Help [Re: B31 Ally]  
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Brian L Offline
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Brian L  Offline
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Louisiana
Thanks for the help. I inspected the brushed and removed the dynamo and it did run off my 6 volt battery. I cleaned up the communicator and reinstalled it. It is now producing power. Unfortunately, my regulator is not doing anything with it. It has an electronic regulator and I will start troubleshooting that part.

#581570 - 01/18/15 6:52 pm Re: Dynamo Help [Re: Brian L]  
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Rich B Online happy
Rich B  Online Happy



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Posts: 4,950
Stone Creek OH USA
May sound dumb, but check your Dynamo brush wiring. The logical way to connect the brushes is incorrect shocked The brush wires actually cross inside the dynamo


Life is too short to drink cheap, bad beer.
#581603 - 01/18/15 9:39 pm Re: Dynamo Help [Re: Rich B]  
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B31 Ally Offline
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Northern Ireland
Yes, Rich B is correct, they do have to like cross them selves inside the dynamo, they fit easier into the holders in the wrong positions, been there, done that and was slightly confused for a couple of minutes! It will still charge like this but only if you spin it in the opposite direction, this is a handy tip when you need a mag that spins in the opposite direction to the one you have for another make of bike..

#581703 - 01/19/15 4:31 pm Re: Dynamo Help [Re: Brian L]  
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trevinoz Online content
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trevinoz  Online Content
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newcastle australia
If your brush wires cross someone has connected the field wires in the wrong places.
Depending on the rotation, the field wires may cross but under the brush plate.

#581718 - 01/19/15 6:31 pm Re: Dynamo Help [Re: Brian L]  
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John Healy Online content
John Healy  Online Content


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Boston, Massachusetts
To wire a Triumph generator (anti-clock facing drive end) face the commutator end with the armature at the bottom:
The left brush goes to the "D" terminal. This can be located on the brush plate or the plastic cover.

The right brush lead crosses over to the middle and goes to the ground screw located on the face of the bearing housing.

The field wires cross each other (inside the generator behind the brush plate) in the direction the field coil is wound. The wire coming from the left, as the coil is wound, crosses over to the right and goes to the "F" terminal. The wire coming from the right crosses over to the left and joins with the right brush wire on the ground screw.

Note: If you are wiring a generator that turns the opposite direction (clockwise) than a Triumph you reverse the field coil wires.
On the M21 the wire (yellow band) coming from the left side of the field coil is connected to ground. The field wire coming from the right side would be connected to the "F" terminal. Verify this by motoring the generator!

Again, if it is an original Lucas field coil it has a small yellow band on the wire coming out from the left side of the field coil. Anti-clock generator rotation this wire is connected to the "F" terminal. Clockwise rotation this wire is connected to ground.

Because both the generator's output polarity, and the residual magnetism used to start the charging process, must be established you have to flash the field. Flash as described in other posts above. When you flash the field you re-magnetize the iron block that retains the field coil.It is this small magnet that starts the generator generating electricity. Without it you have just an expensive paper weight.

So for a Triumph it is:
Left brush "D" terminal.
Right brush ground
Left field wire (yellow band) "F" terminal (crosses in back of brush plate and comes out on the right side.
(For a clockwise ground this lead is grounded).

Right field wire ground(crosses in back of brush plate and comes out on the left side.
(For a clockwise generator connect this lead to the "F" terminal.)
* Then Flash field.
* Test for 1 1/2 volts at idle, 2-3 volts at charging rpm, output from just "D" terminal.
Test for full output by connecting "D" terminal to "F" terminal. Go easy to high an rpm can damage the armature!!
Check to see if you have the field coil wired correctly by motoring it.

After flashing the field you should get get around a 1 to 1 1/2 volts (2-3 at charging rpm) out of the "D" terminal when the generator is turning over just above idle. Flashing magnetizes the iron block that retains the field coil in the generator housing. This small amount of residual magnetism is enough to get you that few volts (1 1/2 approx.) you can measure off the "D" terminal.

When testing with the "D" and the "F" terminals connected together be careful at how fast you turn the generator. The 2-3 volt output from the "D" terminal is being fed back into the field coil. This creates a bigger and bigger magnetic field increasing the output from the "D" terminal. As rpm's increase, and the magnetic field with it, the voltage can increase to the point where the commutator can no longer handle the load and the solder begins to melt.

Thanks to trevinoz for straightening me out on the details!!!
Thank You trev


Last edited by John Healy; 01/21/15 6:38 pm.

#581868 - 01/20/15 4:31 pm Re: Dynamo Help [Re: Brian L]  
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trevinoz Online content
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newcastle australia
The field wires are either crossed or uncrossed under the brush plate, depending on the rotation of the generator.

#581900 - 01/20/15 9:20 pm Re: Dynamo Help [Re: Brian L]  
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John Healy Online content
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While Trev is right for the M21, if my memory serves me, rotates in the same direction as a Triumph (clockwise as viewed from the drive end). The wiring I described above is for this rotation. The correct connection of the field can be confirmed by motoring the generator.


#582048 - 01/21/15 5:01 pm Re: Dynamo Help [Re: Brian L]  
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trevinoz Online content
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newcastle australia
John,
Triumph is anti-clock and M21 is clock, as are the majority of magdyno equipped machines.

#582069 - 01/21/15 6:41 pm Re: Dynamo Help [Re: Brian L]  
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John Healy Online content
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Boston, Massachusetts
Trev - I modified the post above. Will you look at it and advise me of any corrections it needs...
John


#582239 - 01/22/15 5:18 pm Re: Dynamo Help [Re: Brian L]  
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trevinoz Online content
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trevinoz  Online Content
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newcastle australia
John,
Generally you are correct in stating that the field wires are crossed for clockwise rotation but if the armature has been rewound and the winder uses a different method to the factory, it's pot luck.
The motor test is the way to test and if the correct polarity is used, the field is magnetised correctly.
As to corrections, the Triumph rotation stated is incorrect. Sorry.


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