Dynamo Lighting - fit and forget?

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robc02
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Re: Dynamo Lighting - fit and forget?

Post by robc02 »

... but your "original" thought is correct I think (as far as I understand), front a rear lights are definitely in parallel, in parallel downstram the overvoltage protection that is built-in and becomes "active" only once you switch-on the front light.


That's interesting. Are you saying that there is a protective device or circuit clipping the AC prior to rectification etc.? The rear light circuitry must then rectify and regulate the dc to drive its LED and standlight capacitor. - This must be the case as you can connect a rear light straight to the dynamo and it will work (for a short time!).

It would be interesting to see examples of the circuits used commercially. As mentioned in my earlier post, the only one I have seen is the reverse engineered Supernova triple, which supplies regulated dc to the rear light from within the front. A benefit of this design is that it only requires one standlight circuit for both lights.
PH
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Re: Dynamo Lighting - fit and forget?

Post by PH »

Mick F wrote:I would ideally like a main beam and a dipped beam. Riding along the dark lanes that swoop up and down and round and round, you need a full beam like you would use one in a car.

I've pretty much achieved that by combining the Edlux with a powerful battery light that wouldn't be practical to use all the time (Both blinding to oncoming vehicles and battery life) the mount swivels, so to "dip" it simply knocks to point away from whatever's ahead, or sometimes just put a hand in front of it. I've never timed it, but I doubt the "High beam" is in use for more than 20% of any ride. And of course I'm not too bothered if I run the battery down as I'm not relying on it.
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ConRAD
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Re: Dynamo Lighting - fit and forget?

Post by ConRAD »

Mick F wrote:This is the way dynamos used to be wired ... why not now?

Because things changed.
Here below ... with some simplification ...

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Mick F
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Re: Dynamo Lighting - fit and forget?

Post by Mick F »

My BB dynamo had an overvoltage device, and I hid it inside the rear lamp.
The dynamo fed its pair of wires to the rear, and was connected to the OVP device. The output of it was fed to the rear lamp and was taken off in parallel to the front light.

There's no reason that a modern hub dynamo system couldn't work like that.
Dynamo feeds up to front lamp with a OVP device within it. Output of it is fed to the front LED and in parallel to the rear LED.
That way, both lamps are protected.

Why have an OVP device between the front and rear?
Mick F. Cornwall
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ConRAD
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Re: Dynamo Lighting - fit and forget?

Post by ConRAD »

Mick F wrote:... dynamo feeds up to front lamp with a OVP device within it. Output of it is fed to the front LED and in parallel to the rear LED.
That way, both lamps are protected. Why have an OVP device between the front and rear?

Maybe the drawing wasn't clear enough, sorry.
Yes the OVP is inside the front light so when you switch it on the OVP comes on as well and in this way it protects both the lights.
The lights yes are in parallel but the wires of the rear must go to the front and not straightforward to the dynamo, in other words the rear light must come on only when you switch on the front.

ps: modern hub dynamos don't have OVP inside
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andrew_s
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Re: Dynamo Lighting - fit and forget?

Post by andrew_s »

In addition, there's the convenience aspect, in that the old method of wiring both lights in parallel to the dynamo relies on the generator being turned off to turn the lights off.
No rear lights have switches, so with a dynohub the only way of turning the rear light off is to either unplug it, or to connect it to the front light and use the front light switch. One of the SP dynamo hubs does have a switchable generator, but relying on that would be restrictive and comparatively costly.
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ConRAD
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Re: Dynamo Lighting - fit and forget?

Post by ConRAD »

robc02 wrote:... are you saying that there is a protective device or circuit clipping the AC prior to rectification etc.? ...

Yes, in the front light there's a built-in AC "clipping" device acting as overvoltage protection (OVP), most of the times nothing more than a double zener, that's it. In this way to the rear light goes exactly the same front light "clipped" AC wave, no rectification at all, this latter one is done "locally" ... at the rear!!!

ps: btw do you know that you can power a dynamo light (front or rear) also with a DC supply regardlessly of the polarity ?
.... but but but, never attempt though to power a battery light from a dynamo !!!
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PH
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Re: Dynamo Lighting - fit and forget?

Post by PH »

It's all interesting stuff, but I like that it just all works, I turn the switch and the lights come on... hurray!!!
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Mick F
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Re: Dynamo Lighting - fit and forget?

Post by Mick F »

ConRAD wrote:
Mick F wrote:... dynamo feeds up to front lamp with a OVP device within it. Output of it is fed to the front LED and in parallel to the rear LED.
That way, both lamps are protected. Why have an OVP device between the front and rear?

Maybe the drawing wasn't clear enough, sorry.
Yes the OVP is inside the front light so when you switch it on the OVP comes on as well and in this way it protects both the lights.
The lights yes are in parallel but the wires of the rear must go to the front and not straightforward to the dynamo, in other words the rear light must come on only when you switch on the front.
Just the same then! :D

So ................. why is my rear light brighter than before?
Spanninga vs Edelux
Can only be that the Edelux is more efficient so there's more power available.
Mick F. Cornwall
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ConRAD
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Re: Dynamo Lighting - fit and forget?

Post by ConRAD »

Mick F wrote:... so ... why is my rear light brighter than before? ...

1. ... yes why not, it might be efficiency
2. ... or a different cut-off value of the OVP
3. ... or some other built-in electronic trick
4. ... or ...
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SA_SA_SA
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Re: Dynamo Lighting - fit and forget?

Post by SA_SA_SA »

ConRAD wrote:...ps: btw do you know that you can power a dynamo light (front or rear) also with a DC supply regardlessly of the polarity ?...

Unless its a Herrmans H One S (V2): I have one and it doesn't like DC at all (won't light) meaning I had to make a battery to square-wave AC circuit for aligning the beam when stationary :(

B&M specify a max DC voltage for Some Cyos (presumably to protect any zener clamps) and from memory, I think some of the Lyts circuitry are so minimal I am not sure they would withstand DC
------------You may not use this post in Cycle or other magazine ------ 8)
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ConRAD
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Re: Dynamo Lighting - fit and forget?

Post by ConRAD »

SA_SA_SA wrote:....

You are right, so far I tested only an Edelux and a Lumotec setting the voltage somewhere below the "assumed" cut-off value.
USB-5V is fine, polarity doesn't matter.
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robc02
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Re: Dynamo Lighting - fit and forget?

Post by robc02 »

ConRAD wrote:
robc02 wrote:... are you saying that there is a protective device or circuit clipping the AC prior to rectification etc.? ...

Yes, in the front light there's a built-in AC "clipping" device acting as overvoltage protection (OVP), most of the times nothing more than a double zener, that's it. In this way to the rear light goes exactly the same front light "clipped" AC wave, no rectification at all, this latter one is done "locally" ... at the rear!!!


That's interesting to know, and I can see why a designer might choose to do it that way. However, the only circuit diagram I have seen (the Supernova one) doesn't have AC overvoltage protection - either that or the reverse engineering of the circuit missed them. It rectifies and smooths the AC with the front LED connected across the output and the rear fed from the same supply via a linear regulator. Annoyingly, I did have on old one of these boards (sent back to me following a warranty replacement) but I think it got thrown away. I do, though, have a spare B&M front light. When I get time I will have a look at the circuit board.
edocaster
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Re: Dynamo Lighting - fit and forget?

Post by edocaster »

Having the overall switch in the front light control both lights is a requirement of German law.
RJC
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Re: Dynamo Lighting - fit and forget?

Post by RJC »

I think the Cyo circuitry has been described as a voltage halver/current doubler.
If a white LED needs say 3.5V at ~3Watts the input will rise to about 7V 0.5A which is converted to 3.5V 1A internally,
so the LED in the front light is effectively the voltage limiter, since the current is limited by the dynamo.
A voltage limiter set appropriately is not a bad idea in case something goes wrong in the front hub.

If driven from a battery which will deliver a fixed voltage rather than the approximately fixed current of a dynamo you will need to make sure the voltage isn't too high or risk something burning out. I think B&M said 7.5V max dc for the Cyo.
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