Thoughts on a hand crank powered LED flashlight?

There are a few hand powered flashlights out there, but they basically all suck. There are two commonly available shaking powered lights, but since shaking is a pretty miserable way to make power they don't last long. There are a few crank powered lights, but they are predominantly incandecent which boggles the mind. So I want to make my own. /ubbthreads/images/graemlins/cool.gif

So here are my initial thoughts.
Generator: Got to be crank power. Possible sources for this would be the classic Dynamo Light or the recently evolved cell phone emergency power cranks. Others?

Energy storage: I do NOT plan on cranking some light for the rest of eternity so it must store its power. Can't exactly change a tire in the dark and crank your light at the same time. Anyway, there are two schools of thought here. 1) Big honking capacitor or 2) NiMH batteries. They each have advantages and disadvantages. Caps can charge at any rate you crank, but don't do a great job of delivering the power. Batteries put out a good power curve, but have some very specific charge requirements that might not be well suited to a hand crank. Because of these I'm torn between the two. /ubbthreads/images/graemlins/confused.gif Thoughts?

To me, a flashlight that never ever runs out of juice is the ultimate. What do you think?

Hand cranked light should generate enough light to let you find the box of batteries and load the flashlight.

/ubbthreads/images/graemlins/yellowlaugh.gif

Seriously Marklein, I've always liked the idea of hand cranked flashlights, as long as they were efficient. I think ideally it would be an optional hand crank. In other words you could plug the flashlight directly into AC or DC and charge the batteries that way, or you could hand crank it. Of course what looks good on paper and what can be done in actuality are usually different.

Quickbeam modded a Coleman Sentinel a while ago. You can read about it here . /ubbthreads/images/graemlins/wink.gif

Wow -- sounds promising from the looks of that mod. I'd love to make one that had perhaps 2 or 3 Nichia's for low and a regulated, low powered 1w LS for high. I might just do one of these modifications pretty soon. Thanks for the link B@rt.

Yeah, I saw that. Decent mod. Call me crazy, but I don't want to pay Coleman $30 for that light though. My current train of thought is as follows. Nobody wants to crank a light for 30 minutes. Therefor no light will ever reach its maximum charge from cranking. Ideally you'd crank the light for a few seconds (say 30) and get a good length of light from it. Because of that I don't see NiMH as being the proper storage medium for such a light. The Coleman light suffers from this I think. Capacitors have a much easier and quicker charge time. A large capacitor (I'm talking 20 times the capacity of the ShakeLight) should hold quite a bit of power but since you're not shaking the generator should charge up a lot faster than the Shake or the Sentinal.

Just thinking out loud...

How much power does one of those dynamo lights produce? It can't possibly be more than a NiMh can take, and you wouldn't have to worry much about charging because most of the problems come from charge termination, I would guess that you would never fully charge the NiMh by hand.

Since you won't be cranking for 30+ minutes, you won't overcharge the NiMHs. As long as your design allows for a higher end-of-life impedance, batteries may be your best bet. A benefit of this is charging batteries and swapping out with a radio or something.

Tell me briefly about charging NiMH. Any problems with a too low voltage/current? How much charge current/voltage would be too much for a AA NiMH?

I've put a lot of thought into this breed of light for several years now and I always come back to the conclusion that super capacitors are the way to go given todays current technology limitations.

1. They don't go bad in a hot car like batteries do (you mentioned that you wanted to keep it in the car).

2. They can take a charge as fast as you can possible throw it at it. A battery can not come close to matching this ability.

3. They are rated to last 20-25 years and up! (This thing will probably outlast your car if not overvoltaged).

4. They will not go bad and leak out in your car and ruin your carpet like batteries eventually will.

The only real downside being (besides cost, of course) that they don't have nearly the same capacity that a NiMh/NiCad does per the same amount of area (power density, I believe is the term) so you will have to have a more bulky package to get the same amount of storage out of them as you would have with batteries. In this particular application, however, this is not such a major factor because who would want to hand crank for an hour or more to fully charge a couple of fully depleted NiMh cells anyway? You just don't need that kind of capacity for this sort of application.

Notice that the shake lights don't use batteries. If they did, you would have to shake them for hours to ever fully charge them. Anyway, this is my perspective on the situation and I've yet to see anyone suggest a better way of doing this, but like previously stated, this is surely not the cheapest solution because super capacitors are still relatively new technology and are still quite expensive because of it. Hope this helps. /ubbthreads/images/graemlins/smile.gif

One horsepower = 745 watts. One watt of cranking input requires 1/745 of a horsepower cranking input. To generate one amp at say 6V (6 watts) would require 6/745 horsepower/human physical input. And that's at 100% efficiency. Human-powered battery chargers are a reality in some "survival" radios/flashlights, but not typically of "Surefire-class" performance. If I could find one of that caliber, I might consider it for the exercise factor /ubbthreads/images/graemlins/grin.gif .

Larry

I've often wondered about the feasibility of a wind-up spring type of energy storage generator for an emergency light - like a wind up clock uses (ribbon coil). It would be interesting to compare energy density of a wound spring assembly to that of super caps and NiMH, etc... (Horsepower in - Watts out)

(edit) Oops - I see that's what the Freeplay incorporates /ubbthreads/images/graemlins/twak.gif

Bob

Various ideas in this area were discussed previously in this thread. There might have been another one, but I'm not sure.

Graham

Good link Graham. Mostly talk about magnets and coil windings, though still useful. The cap info at the end is very nice...

Still looking for info on "trickle" charging NiMH. Anyone?

[ QUOTE ]
marklein said:
Good link Graham. Mostly talk about magnets and coil windings, though still useful. The cap info at the end is very nice...

Still looking for info on "trickle" charging NiMH. Anyone?

[/ QUOTE ]

Charging information is easily available on this here internet. You might start at one of my favs, Eveready, I kinda like the cat:

Energizer Batteries

Tech info it top right, go to 'rechargable', 'application manuals', then 'NiMH'. Charging rates between timed charges at C/10 and 'trickle' at C/40 should work just fine. So if you're using say 1800 mAH AAs you can 'safely charge until you drop dead' at 180 mA. Does that suit your needs? Crank a minute (at 200 mA), run for ten (at 20 mA)?

From a practical standpoint you can also safely charge a discharged battery at C (1.8 Amps in our example) for a full hour (no doubt far longer than you could crank, even as part of a 'tag team'). (If you can), crank a minute, run an hour and a half?

FWIW, I wouldn't worry about it. You probably can't hand crank enough energy to get into trouble.

As I said back then, 'supercaps' aren't really suitable unless they're supported by serious electronics as the voltage drops rapidly with discharge. Chemical storage ('batteries') solves this issue.

Doug Owen

I like the idea of a hand crank, and plug-in charging. Doesn't the Coleman Sentinel do this?

And as for thinking out loud, what about caps & battery?

Re: Thoughts on a hand crank powered LED flashligh

Mark, I've tried the current Nightstar and it doesn't suck. It's bulky and expensive for a 1-LED flashlight, but it works fine, you shake it for 10 seconds or so and you have a useful light for several minutes. There are some other models including the original Nightstar that don't work nearly as well.

Re: Thoughts on a hand crank powered LED flashligh

"As I said back then, 'supercaps' aren't really suitable unless they're supported by serious electronics as the voltage drops rapidly with discharge."
My friend Caitlin Williams has a really small(a little larger than a 9v battery) model car that charges in 45 seconds, and it can run for quite a while on one charge.
I have no idea what cap is in that car.

Re: Thoughts on a hand crank powered LED flashligh

[ QUOTE ]
star882 said:
"As I said back then, 'supercaps' aren't really suitable unless they're supported by serious electronics as the voltage drops rapidly with discharge."
My friend Caitlin Williams has a really small(a little larger than a 9v battery) model car that charges in 45 seconds, and it can run for quite a while on one charge.
I have no idea what cap is in that car.

[/ QUOTE ]

If it was a cap. , it would charge in about .001 seconds.
It is likly a small NICd cell.

Re: Thoughts on a hand crank powered LED flashligh

Everyone seems to think that supercaps are expensive. I have to disagree in my case. I once bought a batch of 20 supercaps (1F 5V) from a local electronics supplier. Came to about $6 a piece at $120 for the lot. Yesterday I bought a pack of 4 Energizer NiMH. At $21 a pack, that's $5.25 per piece.

While that is a huge price difference if you're comparing charge capacity per dollar, in an application like this (hand-cranked light) that really doesn't matter. What you're looking for is a power-storage device that accepts fast charge (500mA or more) without blowing up, doesn't breakdown under heat and can be recharged till almost eternity. So supercaps are probably better than chemical storage (rechargeable cells) in this application.