dynamo rear light help

[sebdickson]

Hello,

Does anyone know what the output is to a rear light on a dynamo setup (more specifically edelux?)

Would I be right in thinking it is a 6V AC waveform just with a lower current pushed to it? Or is it already rectified by the front light?

I don't have an oscilloscope so don't know.

Motivation is I have a battery powered rear light with a dead battery, and I was wondering what wizardry I have to do to get it to connect - it is well within 0.6W

Cheers!

[Brucey]

not sure about an edelux but most headlights just feed unrectified AC to the rear light. There is no current limit per se.

To make this work with a lower voltage DC lamp you need to at least have a rectifier and regulator of some kind. If the front lamp pushes 6v DC out then you still need something to regulate the current/voltage. This can be as simple as some resistors and diodes, but if the rear light has a 'soft' switch it could do all kinds of weird things.

The reality is that it is usually a lot more straightforward to get a 'proper dynamo light'. They are not all a lot of money, e.g. you can get a Spanninga Arcus (rack mount) light with standlight from SJS for less than a fiver.

cheers

[Carlton green]

Hello,

Does anyone know what the output is to a rear light on a dynamo setup (more specifically edelux?)

Would I be right in thinking it is a 6V AC waveform just with a lower current pushed to it? Or is it already rectified by the front light?

I don't have an oscilloscope so don't know.

Motivation is I have a battery powered rear light with a dead battery, and I was wondering what wizardry I have to do to get it to connect - it is well within 0.6W

Cheers!

As far as I know traditional Dynamo rear lights take a 0.6 W (or maybe marked as 0.1A) 6 Volt MES bulb. Dynamo’s push AC and it’s nominally rated at 6v. Whether an equivalent bulb to fit your light is available I don’t know but I’ve always wondered whether if armed with drill and soldering iron one couldn’t make a battery light into a Dynamo one. It would probably be better to buy a set of batteries or a proper Dynamo light, I bought an inexpensive LED rear Dynamo light and am delighted with it.

[rjb]

I've had good success in doing this using cheap poundshop rear 3v battery lights. Only works if you rectify the AC output and I fitted a 120 ohm resistor in series with the light to drop the voltage. I didn't fit any batteries to the lights.

Link here to one I made from a GU10 led. viewtopic.php?f=5&t=116628&hilit=Gu10+Free

I ran this with a 6v rear light and a 120 ohm resistor.

Dynamos don't push power out. They respond to meeting the load requested by your lights. More lights means the dynamo power output increases.

More info on this excellent site for soldering iron wielding tinkerers.

http://pilom.com/BicycleElectronics/DynamoCircuits.htm

[Jdsk]

not sure about an edelux but most headlights just feed unrectified AC to the rear light.

And that means that you can test what's happening with a cheap multimeter on its AC voltage range, you don't need an oscilloscope.

Jonathan

[sebdickson]

Cheers guys, that's what I wanted to know.
Im only doing it for a little bit of fun for a project, ive got a perfectly fine setup already!

[ConRAD]

... more specifically edelux? ... would I be right in thinking it is a 6V AC waveform..

Roughly right: from edelux to the rear light you get an approx 6.7 Vrms chopped AC waveform, not necessarily synusoidal though.

... motivation is I have a battery powered rear light with a dead battery ...

I'm afraid your battery powered rear light won't work with your edelux output.

ps: conversely a dynamo powered light will work fine with a battery ... in this case polarity doesn't matter.

[cycle tramp]

Good evening...
Just been into the shed and counted 3 failed cat eye led lamps. The l.e.ds are fine, but in each case the micro switch has failed...
...if I want to convert the lamps so that they're powered by a dynamo, should the wiring go large dynamo capacitor, recifier, smaller capacitor then battery tag, and then from other battery tag back to dynamo or have I over complicated it, and if I go that way, what do I do about the failed mircoswitch?
Any suggestions would be gratefully received.

[Jdsk]

Which diagram are you working from?

Jonathan

[Brucey]

Good evening...
Just been into the shed and counted 3 failed cat eye led lamps. The l.e.ds are fine, but in each case the micro switch has failed...
...if I want to convert the lamps so that they're powered by a dynamo, should the wiring go large dynamo capacitor, recifier, smaller capacitor then battery tag, and then from other battery tag back to dynamo or have I over complicated it, and if I go that way, what do I do about the failed mircoswitch?
Any suggestions would be gratefully received.

If the switch has failed then you need to bypass it. You say 'microswitch has failed' but actually in most modern lights it isn't a normal physical switch, it'll be a switch like the ones in TV remote controls, where a miniscule current is drawn in the 'switch' on a momentary contact and that then latches a circuit, and the actual switching of the power is done by a semiconductor. The biggest difference between a switch in a modern LED bike light and a TV remote switch is that the former often goes 'click'. If the switch is 'working' and you try and use it in the circuit, every time you set off the switch may have to be toggled again which would have to be a PITA. If the switch is not working it will have to be bypassed.

Bypassing switches like that is rather problematic. The easiest way of doing it reliably is possibly to send power directly to the LEDs via another route instead, and that would involve soldering tiny wires to tiny solder pads on the circuit board, and possibly breaking the connections to the original circuitry. If you do this the feed should have a current limit built into it so that the LEDs are kept happy. You would need a rectifier, a capacitor on the output (if you don't want the rear light to flicker at low speeds) and something to regulate the current through the LEDs. The last of these could be as simple as a series resistor, provided you are happy that the input voltage to the circuit doesn't exceed its nominal value.

But if you do all that you have basically built a new light, apart from the housing and the LEDs themselves. And saved yourself very little.

FWIW the failed switches in the lights probably just need cleaning, so if you want to do something useful with your failed lights, I would try that.

cheers