Miller dynamo.

john998

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Hello, Can someone please tell me the voltage expected from the residual magnetization at startup.
This from a 6 volt Miller newly refurbished and polarised. Before the rebuild of the dynamo the engine had to be reved hard to start it changing. This with a Ken Bell regulator.
At the moment the dynamo is on the bench being driven with an electric drill, not sure of the RPM
being achieved as the drill is not getting up to full speed. It is outputting 1 volt from D terminal with
this set up, but the regulator won't kick in. If I put a lamp between positive and D it starts to change,
and continues to until you stop and restart without the lamp.
My question is do I blame the dynamo or the regulator. John
 

Magnetoman

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My question is do I blame the dynamo or the regulator.
You haven't provided enough information to assign blame. You wrote that the dynamo is "newly refurbished," but does that mean refurbished by Ken Bell and put on a shelf for the past decade before now using it, or refurbished by someone else in the past few months?

As I discovered to my dismay, Ken didn't understand electricity well enough to have made voltage regulators himself. Whether or not he had his name printed on a regulator, it would have been made by someone else. Does anyone know where he sourced the regulators he sold? Without testing your regulator it isn't possible to know if it is functioning correctly, but if it was made by someone with a good reputation it can help focus the initial troubleshooting.
 

john998

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Hello, thank you for your reply. The dynamo has a new armature and feld coil fitted by my self in the
last few years. Ken stated that his regulator where manufacturer by a well known automotive electrical manufacturer.
What I am looking for was a rough idea of what voltage will start the regulator, as I said it has been difficult to start the old dynamo charging for so time. John
 

Magnetoman

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The dynamo has a new armature and feld coil fitted by my self in the last few years.
I don't know how long the piece of iron in the center of your field coil will retain a small amount of magnetism, but the dynamo won't work without a sufficient field from it. Also, if it was polarized "backwards," i.e. for the incorrect output polarity, that's a problem as well. However, before making my next suggestion I need to know if your system is wired for positive or negative earth. Also, did the dynamo ever work with the Ken Bell regulator, or is it an "upgrade" that you have yet to get working properly for the first time?
 

john998

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Hello, negative earth, the regulator has worked for 25 years on the old dynamo but gradually
it needed more rpm to kick it off.
I get the impression that on the bike it would work but would have the same problem.
It has always been an excellent regulator except for this problem starting in the last few years.
The dynamo motors in the correct direction when connected in the test configuration.
John.
 

timetraveller

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Many years ago I fitted a 'Bell Conversion' to my twin. New armature, field coil and regulator. I remember that one of its characteristics was the need to take a great handful of throttle before it would start to charge, after which it did the job. However on many of the small country roads down here in rural Sussex at night I would see an eight amp discharge on the ammeter while trying to keep the revs down on corners to avoid waking the local. Even with a decent battery an eight amp discharge still means that the lights are not what one would want. It was that that lead Dick Sherwin and I to develop what has become known as the 'Walkernator'. With that on a twin one never sees a discharge on the ammeter once the engine is running at above tick over speed.
 

Simon Dinsdale

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John
I suspect the problem is the initial switch on voltage of the Bell regulator. You will need at least 0.7V to overcome the forward voltage drop across any semiconductors in the regulator and most probably a bit higher. You also need to rotate the dynamo enough to generate the current required for the field winding to increase the magnetic field.
I have used several types of solid state regulators over the years, JG, then my own, and now a DVR2 from Dynamoregulators.com. The DVR2 is the one that I have found starts charging at the lowest RPM and does not display the high initial switch on that you describe.
i have no connection to the DVR2 manufacturers, just a satified customer.
Simon
 

Magnetoman

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Given that your dynamo motors, and does so in the correct direction, it moves down on the list of suspects and the regulator moves to the top.

As a brief refresher, the residual magnetism in the iron is enough to create a magnetic field at the armature that is enough to generate a small voltage as the armature begins to spin. A regulator works by feeding that back as current to the field coil to increase the magnetic field experienced by the armature, thereby increasing its output. Once the field strength and rpm are high enough that the output voltage has reached the ~7 Volts the battery wants to see, the regulator feeds less of the generated current back to the field coil in order to maintain the output at the required 7 Volts.

Even without feedback to the field coil, as long as there is residual magnetism the dynamo will increase its output linearly with rpm. Short of absolute failure (no pun intended), a regulator can be built, or begin to malfunction, such that it doesn't start feeding current back to the field coil until the output voltage from the dynamo is higher than a too-high value. Timetraveller's experience with a Ken Bell regulator is consistent with this being the problem. Even if your regulator was sort of OK-ish when new, depending on its internal construction, it's possible that aging of its components over the past quarter-century has moved its too-high value to a much-too-high value.
 

john998

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VOC Member
Hello TT, yes could not agree more, having fitted a Walkenator to the late lament Mark Goodson's
big Comet it worked wonderfully.
My solo has a magneto that has been faultless for 50 years and as I now subscribe to
Joe Lucas's dictum that gentlemen do not ride after dark I feel that 6 volts is OK.
All I need is a headlight to act as a indicator of presence. John.
 

john998

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Hello, MM, yes I think you have it, until you asked me I had not considered how old the unit is.
Will buy a new regulator. Regards John.
 
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