Author Topic: dynamo Lucas E3H  (Read 1867 times)

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Offline AdminPete

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dynamo Lucas E3H
« on: November 26, 2008, 05:54:17 pm »
Dear all,
after a long period off stand-still i am aware that the dynamo off my c11 1946 doesn't produce any current no more . I can't messure any current going to the battery. The dynamo lost its magnetism, i wonder how it happend. Of course the battery doesn't reload now, and the bike fails to ride after some miles with the lights on. Can i recharge that dynamo myself? Any reply is very welcome. Best regards, Filip (Belgium)

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From: floydpiper Sent: 06/01/2007 15:29
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From: floydpiper Sent: 06/01/2007 15:33

I sent you a PDF file on Remagnetising. I sent it to your email address. I will also try to attach it here.

Good luck. Please let me know how you make out, as I need to do this too. (My restoration is nowhere complete enough to worry about it yet).

Ps... Obviously you will need the correct equipment to do this, or find someone who does, or build one yourself (not easy).


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From: C10_11_12 Sent: 06/01/2007 18:55
I think there is no magnet on a dynamo. E3L have none. Magnetism is generated by the field coil (ths static one inside the dynamo). Current is produced by the rotor (connection D).
May be the regulator which stays open so that no volt comes to the field coil (connection F). With a low battery, the regulator connects to the field coil so that current is produced by the rotor. When the battery is fully charged, the regulator opens and no current goes to the field coil, so no current comes from the rotor and prevents the battery to boil. If you turn the lights on, the battery needs current so the regulator allows currents from the battery to go to the field coil and make the rotor produce electricity to the battery.

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From: floydpiper Sent: 07/01/2007 13:57

I think you're right. The file I attached is about Magnetos, not Dynamos. The Magnetos were made with magnets that were known to lose their magnetism. Dynamos also have magnets (ALL motors and generators do), but they are not of the type which lose their magnetism.

The odds are that the dynamo stopped working due to either a "dead spot" on the armature, or the brushes need to be replaced. Since it happened after sitting for a while, I am more inclined to suspect it is a "dead spot" on the armature (where it meets the brushes).

If so, the solution would be to dismantle it and clean the armature, where it makes contact with the brushes. The use of fine emery paper would do nicely.


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From: C10_11_12 Sent: 07/01/2007 16:44
Found these instructions about los of magnetism
Flashing the field     (this can be performed with generator mounted on bike)
     Because the pole shoe is soft iron, it won't hold the magnetism for an indefinite amount of time.  This is especially important when using a solid state regulator because they require a generator output of 0.7 volts in order to initialize. <o:p></o:p>

Disconnect the voltage regulator from the generator. <o:p></o:p>
Connect a temp. jumper to the "hot" terminal of the battery. <o:p></o:p>
Touch the other end of this jumper to the "F" terminal on the generator.  Maybe touch it several times holding no more than a second.  This should be enough to re-establish the field magnetism.<o:p></o:p>

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From: tsuretie Sent: 07/01/2007 17:32
yes Gregg,

there are no magnets in it!

the problem occurred indeed after a long stand still, but as the bike was
restored recently (it was a bike in a box!) i don't think the generator did
work ounce as it should do.

I read minus 1,5 Volt (idle speed, and even at higher speed) at the yellow
wire (D) instead off + 6 volt (or even more) as it should be. I disconnected
the two wires comming out the generator.

I took the generator apart today, examinde all the parts, but i seemed to be
allright. I tried to interchange the field coil leads as they should be off
different color (service sheet 809) but mine are both black, so somebody
could be mistaken in the past, but it didn't make any difference.

i even tried to repolarised it, as it is describe in lucas workshop
instructions part two, slightly different as the method of c10c11c12, but it
didn't change anything.

what could be the problem?

(sorry for my english, but i do the best i can :-) )

best regards,


Wie heeft het hart van de Japanners gestolen en heeft altijd iets in zijn
handen? Live Search weet het! En jij?


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From: floydpiper Sent: 08/01/2007 15:19
Hi Filip,

Look very closely at the armature. The armature is the area where the brushes rub against the spinning shaft. The area where the brushes touch is what you want to look at. You will see that it is made of metal ''sections'' that are separated by (what looks like) black ''filler.'' That ''filler'' is a non conductive material, which means no electricity can pass through it. That material is what keeps those ''sections'' separate from each other.

Now look VERY closely. Does that ''filler'' seem to be equally as high as the metal sections? The ''filler'' should be BELOW the metal sections. What happens is that after some time, the metal wears, and then it wears to the point where the ''filler'' material is at the same height at the metal sections. When that happens, the brushes no longer make contact with the metal when the armature is spinning fast.

What you need to do (VERY CAREFULLY) is to use a tool such as a very thin file, or a hacksaw blade (or anything like that which is not THICKER than the ''filler'' material itself). Then file, cut or scrape (depending on what tool you are using) the ''filler'' material until it is slightly lower than the metal sections of the armature. Don't go too deep! Just cut it deep enough that you know the ''filler'' is BELOW the level of the metal sections.

Then, you *MUST* take some extra fine emery cloth (sandpaper) and gently sand the entire armature to make it smooth again, so that the brushes don't get ruined when they rub against it. This part of the job is VERY important because when you ''cut'' that ''filler'' you will leave some ''rough'' spots near the areas where you worked. The emery (sand paper) will make it smooth again. The armature MUST be smooth.

One last thing. If you find that the ''filler'' does not need to be cut, you should clean the armature with the emery paper (sandpaper) anyway because ''carbon buildup'' on the metal sections (which will make it look black), can also cause the brushes not to make contact with the armature.

Please let me know if you understand my instructions. DO NOT attempt what I have told you to do unless you are certain you understand these instructions. If you do it correctly, you will add years to your armature. If you do it incorrectly, you will ruin it.


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From: floydpiper Sent: 08/01/2007 15:33

You are correct about how the Voltage Regulator works. However, Filip has determined that the Generator itself is not producing voltage. The Generator will produce voltage at all times. That voltage goes from the Generator to the Voltage Regulator, and it is the Voltage Regulator that allows the voltage from the Generator to continue on to the battery. (That is of course an oversimplified statement).

The point being that if no voltage can be measured coming FROM the Generator, then the Generator is the problem, not the Voltage Regulator, which is (to once again oversimplify) basically just an automatic ''on/off'' switch.


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From: Shivacapricon1 Sent: 10/01/2007 10:24
Hi Filip
I have been a silent observer to all the posts on the Forum
By now you should have got some idea of checking the dynmo
I hope the dymano is not opened by anyone before it last worked
then try the following tests
Short F and D points on the dynamo with a piece of wire and connect a 6 volt bulb to it The other end should be grounded
Rev up slowly and see if the bulb lights up,If yes your dynamo is perfect
If NO  dont loose hope
With the engine running connect a battery (6volt) (- ve) to ground on the bike
take the (+ve) and Flash it one the short wires occationaly to remagnatise the soft core internally
After which try the bulb test again
Post your results and we can proceed further
I have restored a G3L matchless 1941Rigid and currently restoring  a BSA 2.5 C10L plunger 1951
The tests are the same for all lucas Dynamos