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dynamo?

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Post by braderzzz788e Sun Oct 14 2012, 16:15

hi recently joined the club and forum, i have a 67 ragtop bug called lola, and have owned it for a few months now, im now old enough to drive her, but now worried because the dynamo warning light is lighting up and i have tested the dynamo and no voltage from the unit to the regulator, i also took out the 2 brushes, but all looks ok with them. does this mean ill have to buy a new dynamo?

brad
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Post by Grizzly Sun Oct 14 2012, 23:26

possably or it might just need polarizing.
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Post by Grizzly Mon Oct 15 2012, 16:32

Polarising your dynamo try this . . .

http://www.vw-resource.com/alternator_generator.html#polar

Questions are often asked regarding the need to polarize a generator.
If the generator is charging (the battery stays charged) then
you don't have to polarize it. When a generator has been left
unused for a long time (months or years), the metal core looses
it's magnetism, and it NEEDS a little residual magnetism to
start the charging process. Polarizing just gives it enough
"boost" in magnetism to start it charging properly. When it's
being used, it keeps its core polarized core so no need to do
it again.


Note: Why do generators need to be "polarized"? Automobile generators
need some magnetism to get started. This "residual" magnetism
remains in the field pole pieces even after the engine has stopped.
The next time the generator starts up, the residual magnetism
creates a small voltage in the armature windings. Not enough
to charge the battery, but enough to allow the field windings
to draw current. As the field current increases, the pole pieces
create even more magnetism. That makes even more voltage in
the armature, and the cycle continues until the generator is
capable of producing maximum output.


What happens though to a generator which has been stored a long time
or is freshly rebuilt? The residual magnetism may have decreased
to the point where it can no longer get the generator started
producing voltage. In the case of a new generator or one which
has been mis-treated, the residual may even be of the wrong
direction (North and South poles reversed). Polarization is
a simple process used to restore the field pole residual magnetism
and ensure the magnetic direction is correct.


To polarize a generator, connect a jumper wire from the (DF) terminal
on the generator to the generator frame. Remove the fan belt,
then connect a wire from the positive terminal on the battery
to the (D+) terminal on the generator. The generator shaft should
start to spin.


Note: Don't run the generator this way for more than a few seconds
to avoid overheating.


The generator will now be properly polarized. If the generator did
not spin during this process, the generator is most likely
defective.


Put the fan belt back on and re-test the generator voltage with
the (DF) terminal grounded. If the output voltage is still low,
the generator is defective.


Note:
Voltage regulators do not need to be polarized -- they are not
polarity sensitive. Even if voltage regulator came with instructions
to polarize it -- these instructions actually polarize the generator,
not the regulator. The regulator manufacturer simply wants to
make sure that your generator will work properly so you don't
blame the voltage regulator.


Neither to alternators need to be polarized. Alternators use a trigger
current to start the process of charging - electromagnetism,
so don't need any internal magnetism to begin with, like a generator
does.


That trigger current is supplied via the alternator dash light (it's
a tiny current and won't make the light glow when the engine
is running) so if that bulb blows - the battery won't get charged
and it will go flat. Curious circuitry VW used, but it works
just fine. So that means that with an alternator equipped VW,
you should always glance at the dash as you turn the key and
make sure the Alt light does glow with just the key on, just
to make sure that that circuit is intact.
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Post by owen Mon Oct 15 2012, 20:34

useful info Daz , i was thinking the same thing but couldn't find the right info . Guess if it runs like an electric motor it should be okay.
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Post by braderzzz788e Tue Oct 16 2012, 10:03

ok, thanks guys, ill try that and let ya know how it goes, hopefully make it to the meet on friday if i can. do many of you go to the meets?
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Post by Grizzly Wed Oct 17 2012, 14:31

braderzzz788e wrote:ok, thanks guys, ill try that and let ya know how it goes, hopefully make it to the meet on friday if i can. do many of you go to the meets?

Yep usually the meets have a fair amount of us turning up, you can never tell though depends what else is going on but the winter meets are on now and these were quite well attended last year even if not in peoples dubs.

liking the avatar btw Very Happy
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