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 !
I could be wrong, but wouldn’t the capacitor keep it from turning on until charged?
Yes but it should not be like 30 seconde long I think, so it should be OK for a bicycle :)
It should be possible to wire it so that when the battery is on, the light turns on instantly while also charging the capacitor. Battery meaning paddling
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.
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 ?
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.
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
Excuse me if I’m wrong but the description of your front light says in the first sentence: "The AXA Nxt 60 is a dynamo front light […] with a Steady light function allowing you to have 4 minutes of light when standing still. " Is that not already what you want?
Really good point, though as a stupid human I didn’t understood what was the difference between the Nxt 60 steady and the Nxt 60 E bike… Now I know. I don’t have this marvelous option =\ explaining why the back doesn’t light up either… Thank you for pointing it out, I couldn’t get the article from the site itself so I took another seller and it was not available (it is now)
Your typical bike dynamo puts out 6V AC. I bet yours does as well, so that diode sounds like a good idea.
Seems bad so, I have to make a diode bridge rectifier so =\ need to scrap more diode ! Too bad as I wanted to make something small
I’ve actually done that with a simple single diode rectifier and a supercap with zener voltage limitation:
If your supercap has a too low series resistance for the LED to light immediately you need an additional resistor in series with it. It is simple and small enough to directly fit inside the original lamp casing and has been working without a problem for over 3 years.
What I wanted to do was something like that
Though you seem to have a better knowledge and better circuit. I bought 2 super cap 5.5v so I wanted to put them in series (though get half the capacitance). Your approach seems to be better and I may take it. Though mine should be working ? Keep in mind that I’m a nooby in electronics and I keep learning from the internet so not the best to have solid base…
Does your solution works with 5.5V, the 6V dynamo does not blow it ?
Thank you for your answer I really like it.
Your solution may very well also work, good thinking. A few things to consider though:
- Putting capacitors in series requires balancing them
- A silicon full bridge rectifier drops ~1.4V frm the input
- Incandecent bulbs require a lot of current to get going, this may result in a delay for them to turn on
Ok, I forgot the voltage drop =\ I got LED light so should be fine. What I should do is put your circuit to the test without the capacitor and check if the voltage is low enough for the capacitor to handle ? How should I balance the capacitors ? (Even if I will not take this path, I would like to know)
Thanks again for your help
