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What's the best way to add a battery like device to a dynamo light (self.askelectronics)

submitted 3 months ago by coke38 to c/[email protected]

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Hello everyone, I bought a bottle dynamo for my bicycle with a rear and front light. Though I have one little tweak that I would like to add and that's a way to keep it light up for about 1 minute (at least 30 sec) without pedaling. I thought of putting a capacitor in the circuit to store some energy but I would like what do you all think of it ?

Thank you for your time and have a nice day you all !

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[–] [email protected] 3 points 3 months ago (7 children)

I think the largest issue you'll run into is figuring out how to wire it. It definitely sounds like a fun project and possibly an opportunity to try out some of the inexpensive super caps that you can get on eBay for like 3 bucks a piece.

The only caveat I can think of is that you might need to find out how much voltage the generator puts out, as you definitely don't want to pump more voltage into them than they are rated for.

To do that I would open the device and hook up a multimeter to the Dynamo and then spin it as hard as I can and figure out what it's peak voltage is and then purchase and or design your super capacitor bank to handle its peak maximum.

You should also check and see if the device has some sort of rectifier, as Dynamo output is typically AC and LED lights are typically DC, so there is likely some sort of rectification. If you do have a rectifier I would measure it after the rectifier.

It may already also have a capacitor in it, in which case you could simply desolder that capacitor and then set up some breakout cables and run those outside of the case into your bank.

[–] coke38 4 points 3 months ago (6 children)

I should have put the stuff I have, so here you are : Dynamo : https://www.axasecurity.com/bike-security/en-gb/products/lights/7/93903195SC/axa-hr-traction-right Rear light : https://www.axasecurity.com/bike-security/en-gb/products/lights/7/93929195SC/axa-juno-e-bike-6-12v-80-mm Front light : https://www.axasecurity.com/bike-security/en-gb/products/lights/7/92520095SB/axa-nxt-60-steady

Indeed it seems like a great project I think the output is DC though I'm not sure. To be honest I tried to put a capacitor (50V) put it seemed to had no effect (maybe to little capacitance or more probably the coil of the motor should have eaten the storage. Is probably should add a diode to the circuit, am I right ?

[–] [email protected] 3 points 3 months ago (1 children)

If I'm understanding it correctly this generator has like wires out that then connect to the lights or something right?

If that's the case you'll need to see what kind of voltage it's putting out to those wires and then you would want to splice those wires into diodes to prevent the current from leaking backwards out of the capacitors. Then attach as many capacitors as you need for the voltage that it is providing, remembering that it is okay to have higher voltage ratings but not lower voltage ratings.

Chances are this will cause the light to be less bright as the capacitors are charging, so for the first few moments when you are riding it probably will be less bright but after the capacitors reach a steady charge you should see the light take a much longer time to dim down.

[–] coke38 2 points 3 months ago

Indeed, 2 pair of 2 wires so 4 wires can be connected to the dynamo.

I will try that, I need to find some proper diode then find the capacitor or buy it and I should be good. I'll keep you in touch if I manage to find the parts. Thank you

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