Double Dynohub: 2 Sturmey Archer generators in one - to be steam driven

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Richard Hed

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FWIW I also use leather belts for one of my lathes. I join them with a scarf joint about 30mm long and standard PVA glue , clamped between two pieces of metal while setting. No stitching or other reinforcement of any kind. The first belt was already on the lathe when I got it but had to be shortened to fit my re-arranged drive set-up. It must have been at least 30 years old but still pliable. It eventually came apart but not at the join I made. The current belt was also made using leather belting that came with the lathe and would also be the same age as the previous one. It has been on the lathe for 3 years now and shows no sign of coming apart. I don't use a lot of tension on the belts (belt slip is my safety fuse) and always remove the tension when not in use.
This will be a belt that removing the tension every time I'm done using it, will be a real pain. But so what? There is lots of leather around. The only real prob is that it might set in one position for 8 months unless I can remember to take the tension off in that interval.
 

Steamchick

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Hmmmm... 10 year old Sturmey Archer advice hasn't really aged much, so maybe I should risk running without the controller? But at the risk of blowing the LEDs I think I'll leave it as it is.
 

BaronJ

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Hi K,

I wouldn't count on it ! LED's have come on rapidly over the past few years. Phosphors have changed and improved. The amount of light produced has dramatically increased and the power requirements for a given amount of light has fallen.

This also means that the V, I, requirements of any particular LED need to be more tightly controlled.

Modern LED lighting systems, particularly those that are dimable use a technique known as PWM (pulse width modulation). This allows high value current pulses to be fed into the LED, currents that if constant would greatly overload them and burn them out.

But because the frequency rate at which these pulses of current are applied to the LED chip, it has time to cool between them. So you can get more light for a given power input.

With the system that you are using you have a varying voltage that is going to alter the light output. What you actually need is a constant current, irrespective of the voltage to drive your LED's.
 

Steamchick

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Possibly that is why I have a very short lifetime for a pair of 7W LEDs as daytime running lamps on my Moto Guzzi V50? They are supposed to be OK between 6V and 18V but I do have to replace them much more frequently than bulbs. The voltage control is a modern electronic box as the original solenoid contactor for the Bosch alternator stops working over 3000 rpm crank speed. And I use use all 7000 rpm sometimes... (It's so smooth I just don't notice until that slight tingling in th toes....).
Back t the Double-Dynohub. As far as I understand.... The rms voltage from the PWM controller across its internal capacitor, will give a smooth enough voltage so the current drawn by the LED array will be similarly smoothed? Or will it be likely to go fut?
Ta,
K
 

bluejets

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Hi Bluejets,

This is a link to a ten year old post that is way out of date !
Last time I looked, electrical theory remains fairly constant.
Unless of course you intend to rewrite all the theory books as well.
 

BaronJ

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Hi K,

Have a check on the battery voltage at high revs. In theory the battery behaves like an enormous capacitor. But as the battery ages its capacity falls and it starts to become unable to supply the load ! the net result is that the system voltage can rise higher than normal.

As far as the dynohub is concerned, there will be a minimum amount of current that it can produce. Normally the current is measured at the nominal voltage output, this gives you the wattage rating of the dynohub.

Your LED's have maximum and minimum current and voltage ratings. Too little current and they will be very dim, too much and they will burn out.

Attached is a data sheet for a typical LED used for lighting.

There is far far more data than you need, but the important parts are I, V, and T. Have a read and see what you think.
 

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awake

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Watt?

(Groan).
Of course, you realize that even a groan - much less a counter-pun - is received as nothing other than a volt in favor of more! :)

For those of you who are suffering through this ... resistance is futile. You may as well prepare yourselves for induction into the circuit of puns that are likely to follow - I judge the potential to be high. Like Dorothy on the yellow brick road, be ready to say, "Transistors, transformers, capacitors, ohm my!"

Okay, I'm done now.

:):):)
 

Richard Hed

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Of course, you realize that even a groan - much less a counter-pun - is received as nothing other than a volt in favor of more! :)

For those of you who are suffering through this ... resistance is futile. You may as well prepare yourselves for induction into the circuit of puns that are likely to follow - I judge the potential to be high. Like Dorothy on the yellow brick road, be ready to say, "Transistors, transformers, capacitors, ohm my!"

Okay, I'm done now.

:):):)
Well? Potential well, gravity well, oil, water?
 

Steamchick

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Well, here's the latest pics:
Situation: I have fitted an engine - that needs piston rings and bearings replacing, as it is fundamentally "US" at the moment. Maybe a winter job to make a new crank, plus bearings, con-rods and pistons? I have made a lamp-post - it lights when the genset is driven by my hand-drill at over 200rpm. I have to do a bit of fitting on the base to mount the lamp-post, and finish fitting the genset wiring. I think it will need a screen between the engine and generator, otherwise the generator will get rather manky with wet oil and stuff from the engine... I have deliberately left the sides of the generator open, so people can see the magnet rings whizzing around the stators when in operation... - Rotors may get painted in "warning" colours (Black and Yellow? Red and White? Red and Black pole pieces? - TBA...) - but that is another winter bench job. But it's back to the boiler and burner for now...
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