Diy dynamo flashlight

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devryd
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Diy dynamo flashlight

Hi guys,
I was thinking of building an emergency dynamo flashlight. It should have a few hundred lumens (at least 300lm) in a high mode and a pretty long runtime in a lower mode. Any ideas, how I should go about it? LiPo batteries should be a bad idea as far as I know, since they loose their charge relatively quickly and are not allowed to drop below a certain voltage, even in storage, as far as I know. I was thinking of using super capacitors for the job, but I dont know, whether thats a good idea. I also need a dynamo and suggestions for a driver.
Any help would be highly welcome, also if this is a completly stupid idea, please tell me

gravelmonkey
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Why not solar, suitable charger, and 2 or 3 spare cells? Much less work than cranking.

devryd
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I would like to have the light ready in any emergency. If I have a power outage in the night, a solar light wont do me much good. I do own a solar panel, which I could use to charge batteries for my flashlights, but I am looking for a solution that doesnt need any preparation.

Lightbringer
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Wellp, I got a set of these

https://www.amazon.com/dp/B08NPYHHPG/

but can’t really use them for their intended purpose (mounting plate + shade), so I have them as motion-detecting cat-lights by their litterbox.

One’s on “active duty” near the box while the other sits on the windowsill charging up. Low battery on A, swap for B and put A on the windowsill, and v/v.

Point being, lots of those doodads have solar cells, a battery, and the associated charging circuit. You wanna go crazy and put bunches of batteries in parallel for long runtime, it’s pretty simple, and always ready.

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devryd
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Not really what I am looking for, but that would be an option to have a light “always ready”. How long would a LiPo battery survive in such an “always charged” state. It would be bad, if I bought it for an emergency and the battery doesnt have any capacity left.
Thats the main reason, why I was thinking of using super caps

Lightbringer
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Supercaps can be limited as far as discharge current unless specially designed for it. Maybe a 5mm LED but not more.

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zoulas
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Am I the only one that does not know what a dynamo flashlight is?

devryd
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I dont know if it is the correct name. It’s a flashlight with a crank and a very dim led

zoulas
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Oh

Bort
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This is unrealistic, a hand crank won’t power a 300 lumen flashlight for long.
My emergency kit has two packs of NiMH AAs and two AA powered flashlights.
And a NiMH charger.

One can add some solar and a powerbank if they want but its not necessary.

A super capacitor won’t run the light long unless you only want moonlight mode. They just can’t hold much juice.

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devryd
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I know, it cant produce so much light for long
I was hoping for something like a Minute or so

zoulas
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What if you powered the crank by a cordless dewalt drill?

I can only wonder how many lumens would you get if you spun the crank at say 10,000 RPM. Would it ever equal an FT02S?

Muto
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zoulas wrote:
What if you powered the crank by a cordless dewalt drill?

I can only wonder how many lumens would you get if you spun the crank at say 10,000 RPM. Would it ever equal an FT02S?

Why use the loss of conversion of Dynamo when you could just tap the Dewalt battery straight up, with step down buck of course.?

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gravelmonkey
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devryd wrote:
I would like to have the light ready in any emergency. If I have a power outage in the night, a solar light wont do me much good. I do own a solar panel, which I could use to charge batteries for my flashlights, but I am looking for a solution that doesnt need any preparation.

I’m not saying don’t build one, I love the creative builds people show here on BLF, but for your intended use, the last thing you want to be doing during an emergency, is messing around trying to crank charge a light. An ‘off the shelf’ light is likely to be more waterproof, and potentially more reliable than a self-built crank light.

CR123 or AA lithium cells used to be the go-to ‘fit and forget’ power source for emergency lights if you’re worried about cell discharge.

Li-ion cells generally hold charge quite well, I’d say that a Convoy S2+ with Sst-20, 3×7135 option and a decent 18650 or two would be suitable.

devryd
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Ok I see, that the flashlight doesnt make sense for this use case, but I would really like to build it anyway. As far as I know, Super caps can provide really large currents, thats why they are used to store breaking energy in f1 cars. I was thinking of using something like a 3.8V 100F cap. This should be able to power a cree xpl at 500mA for more than a minute. or did I make a mistake here somewhere?

dthrckt
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You could start with an existing product and add the capacitor.

https://www.amazon.com/Kaito-Powered-Emergency-Flashlight-Cellphone/dp/B...

alpg88
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good idea, someone on fonarevka .ru build one, using cordless drill motor and gearbox as a generator, it was making enough power to light up xml at max current. without much effort
http://forum.fonarevka.ru/showthread.php?t=5336

devryd
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That is really helpful, Thanks
I have an old cordless Drill lying around, I will try it

devryd
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It actually worked
I now have a “generator” that can provide up to an amp to a cree xp-l. Its the only LED i currently have at home. Is there a disadvantage of using this LED also for the really low power mode?
Is a 5mm LED more efficient at currents of about 10 mA?
I was thinking of using 2 different cirquits, one for low and one for high. For low, just a 50-150 Ohm resistor in series with the LED, I know its inefficient, but i think its fine, for high 1 7135 without a microcontroller. If I am not mistaken, this should deliver 350mA to the LED, which should be bright enough I think. So I now only need the super cap and a way to charge it

alpg88
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you’ll be better off with single led and 2 modes

devryd
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Thats the plan so far, I was just planning to use 2 different cirquits connected to the same LED.

maniakman
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devryd wrote:
I dont know if it is the correct name. It’s a flashlight with a crank and a very dim led

Here is a nice restoration video of an old one….
1920’s dynamo lamp restoration

devryd
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I just finished the electrical design. I use 2 capacitors in series for up to 5V 100F
This gives me somewhat decent runtime on high, and a really long runtime on low. High is 350mA (amc7135), low is between 10 and 20mA(150Ohm resistor in series (I know its not really efficient, but i think its ok for the low power)) depending on the voltage.
I now just need a case, and I dont really have an idea, what I could use for it.

alpg88
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use plywood, you can make it into any shape, just read my thread about plywood lights i build, very tough, and easy to work with material.