Forever Flasher (& flashlight)

I built the flasher circuit from Dave Johnson's website, See URL

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But it just went full on, wouldn't flash. So I had to put a 2.2k from Q2 base to emitter to get it to flash. I also used two 0.1 uf ceramic caps instead of rhe 0.68 uF, and the flash rate is right around 1 Hz. The peak current is 17 mA, and average current is about 100 micromps at 3V.

I then connected it to a 3V photovoltaic cell and a 1N4148 to prevent the current from going back into the photocell, and a 6800 uF capacitor to store the current generated by the light. I put the photocell directly under a light bulb, and it works fine, and it keeps working for less than a minute when the light is turned off. So now I need a lot bigger capacitor, something that will run it for a coupla hours.

I'm thinking that it would work good using a pair of 1 F, 2.0V supercaps in series, charged by the photocell.

I bought a Forever Flashlight, the one that has a single white LED, with a magnet and coil in the barrel that charges up a supercap when it is shaken. It works, but I'm disappointed in the light output. The instructions say to shake it for 90 seconds, but even longer than that gives the LED only a few mA, not a really decent amount. It has a lens to concentrate the LED's light, so it's better than just the bare LED alone. Obviously it's meant to be used for situations where a regular flashlight might not be working, like in an emergency/earthquake preparedness kit. The body of the flashlight is clear plastic so I can see the parts inside, and there's a supercap in there, but the plastic is too thick to see the value, which is blurred.

So I'm wondering if I should order a couple of these supercaps. The solar cell is rated for 3V at 40 mA, see the SPL-60 on All Electronics website,

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It puts out an honest 4V in bright sunlight, so I would think that it will charge two 1 F supercaps in series in a few minutes. 3 TCs at 40 mA would be 38 seconds, roughly. Maybe I should try for a couple farads to keep it running all night long. Has anyone done this before? Do these supercaps have low enough leakage to stay charged up for a half a day? After seeing their performance in the 'Forever' Flashlight, I'm not so sure.

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Watson A.Name - 'Watt Sun'
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it looks like you could use a peak at Elna's catalog,

Their 100F capacitor (I'm picking the biggest one because I can) rated at 2.5V charts out to run for about 200 seconds at 50mA (I'm taking this at a

1.5V cutoff, use a switching (buckboost) led controller and get more. especially if you are useing more than one with a supply of 4V. I dont know what elna's 100F capacitor costs. I imagine its not cheap.

CATALOGS! I must have more catalogs! HA, HAHAHAHAHA!

Dan

"Wats>

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dan williams

See if you can find one of those "wind up" flashlights. Similar to the Freeplay radios. That seems to be better technology in terms of time spent winding vs illumination time. I've seen one with a selectable xenon mode (runs charge down fast) or 3 white LEDs (less light for much more time).

If a while LED uses 20 mA, then a 40 mA PV cell will give you 2 minutes of run time for each minute of charge time (ignoring losses and lots of other things). If you fully charge the supercaps in 38 seconds, you'll only get about twice that running time. Add super caps (and $$) to get more time.

You might be better off looking for some DC-DC converters, NiMH charging controllers, etc. and using as many mAh of battery capacity as you need for your design illumination time requirements dictate.

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Paul Hovnanian P.E.

Er, the flasher takes about 100 microamps. That means that it should run maybe 400 times longer than the charging time, something less than

4 hours. I guess I could parallel a second pair of 1 Fs to give a total of 1 F at 5VDC. That should give a flash time of several more hours. I can't say because I don't know what the cutoff voltage is for the flasher.

Batteries go bad, I want to have a forever flasher, not a 5 year flasher. That's why the 1 F supercaps.

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Watson A.Name - 'Watt Sun'

As a coincidence, you should take a look at the DutchForce forum...

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The specific thread is:
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=452

Tim (Sc3mat1c)

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Tim Williams

Lithium D cells are $20 (US) or so, and have a capacity of around 20Ah. This would run the flasher for around 200000 hours, or around 22 years. Add a light sensitive switch, and you can probably extend this a bit. And you can leave off the solar cell too.

A couple of NiCd AA cells would probably run it for around 6 months, after a full charge.

(this is probably around the right draw, they'll self-discharge in around a year in most climates anyway)

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Ian Stirling

In article , snipped-for-privacy@charter.net mentioned...

Here's the URL for one of the schematics of the inverter. This one says it works down to .4V, there are others on his website.

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I was thinking of putting the circuit and solar cell in a clear epoxy block. I've done it before by pouring a thin layer, and arranging the working circuit, then pouring another thicker layer over that. Trick is to get rid of the bubbles. So using a 5 year rechargeable battery is not an option. I would consider using rechargeable cells if it was in a package with a battery holder. But I've already got one of those. ;-)

I checked out the eBay URL, but it's not clear to me how many LEDs are in the package. It says 100 pcs but in the pic looks like it's a lot less. And the 'buy it now' price is a bit on the low side for that quantity. So I'm not sure if I'd buy them. Another factor that bothers me is that any time one buys LEDs at cut-rate prices, there is a very high likelihood that they're seconds or rejects. I've purchased low priced LEDs that have flaws in the lens, or that are not centered properly in the epoxy package, etc. I've done very well by buying from Nichia or from Wilcoxson's

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Also, you can buy Yoldal LEDs that are similar from
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but I haven't bought any from there, so I can't vouch for the quality.

So, has anyone purchased some of those eBay LEDs?

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Watson A.Name - 'Watt Sun'

In article , snipped-for-privacy@mauve.demon.co.uk mentioned...

Forever isn't 6 months, nor 5 years, nor 22 years. Thanks, but I'd really like to get the info I asked for on the 1 F supercaps.

BTW, I have a 1 LED flasher that runs off four AA 2000 mAh Ni-MHs, and it lasts for about a month, maybe a little more. I don't know what the peak current thru the blue LED is, but it's very bright. Maybe two flashes per second. I've noticed the Ni-MHs lose some of their capacity sitting around for a month or three. But that's just a guesstimate.

If I pot a clear epoxy case of the LED in clear eopxy, what does it do to the beam pattern? Suddenly the index of refraction is the same as the lens, so it isn't a lens any more. POOF! The beam goes wide angle, I would guess. Maybe I'll have to dunk a couple LEDs in a glass of water to see what happens!

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Watson A.Name - 'Watt Sun'

I would not be very certain that the supercap would still be working after 20 years.

Why do you want 'forever'?

Ni-MH have a very bad self-discharge rate, especailly in high temps. You may well find NiCd better.

Pretty much.

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http://inquisitor.i.am/    |  mailto:inquisitor@i.am |             Ian Stirling.
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Ian Stirling

Relevant circuits on my page at

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1) LED flasher 2) Solar Engine

...Stepan

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Stepan Novotill

Leave

Leave an air space in front of the LED lens to reduce that problem.

Reply to
Stepan Novotill

Good idea! Probably ought to try to keep the epoxy with co-planar surfaces also.

Or, better yet, pot with the LED lens sticking clear thru the encapsulation.

...Jim Thompson

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Jim Thompson

Sorry about that. I thought you were trying to apply the supercaps to the flashlightapplication, not the flasher.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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Paul Hovnanian P.E.

In article , snipped-for-privacy@hotmail.com mentioned...

Yeah, wacky is the right word. I checked the flickering LED circuit and it looks like the values for the caps and Rs in the oscs aren't right. But you _have_ to resave that gawdawfully huge delayed off switch .PNG to 1024 by 768 size. The 6600 pixels wide is ridiculous!

The solar engine doesn't seem to do anything other than store up and release the charge in the capacitor. I'm not sure how this would help my situation.

The LED flasher is a V boost circuit. We've already been thru a few of those here in ABSE and the other sci.electronics ngs. I checked that ferrite bead on both Digi-Key's and Mouser's website and it's just a tiny thing. I can't figure how you could pass that many turns of even fine wire thru the center hole. The only way I can see how you'd do it is to wind the wire around the outside like a regular bobbin. Even then the thing is going to be tiny, with really fine wires. And I don't believe this has 120 uH inductance (nor 120 mH, as it says in the text).

Anyhoo, this circuit is kewl for 1.5V stuf, but I've already got 3 or

4V from my solar cell, so no problem. It runs the flasher okay. It's just a matter of pulling in enough charge from a few minutes in direct sunlight, where the LED can't be seen, and then once the cap is charged, bring it inside where it can flash for hours. Or it could be set near a window to charge up and as the sun sets, it continues to flash for hours. That's why I need the 1F or so supercap and some info on how they work in this kind of circuit.

I bought some already wound inductors from Mouser, and they work good for the inverters I made. It would be easy to just wind a few turns of #28 or finer wire around the outside of the bobbin of this inductor to give a feedback tickler coil like the one you made. I like already assembled coils because of repeatability factors and just plain time savings.

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Watson A.Name - 'Watt Sun'

If you stick that solar cell in clear epoxy it will fail after short time because of different thermal expansion. (done that, that's why I say that) Rather take some silicon based potting and glue the cells on top only. Then use a frame with a plastic or glass inlet to protect the cheap cells from humidity.

ciao Ban

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Ban

Silicon is a hard substance that is used to make solar cells.

Silicone is a polymer that's used to make everything from flexible tubing to sex toys.

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http://inquisitor.i.am/    |  mailto:inquisitor@i.am |             Ian Stirling.
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Ian Stirling

In article , snipped-for-privacy@web.de mentioned...

Now you've _really_ ruined my day! Y'see, the solar cells _already_ come from the factory mounted in clear epoxy! Now what am I gonna do? Are they going to fail when I put them in the sunlight? :-(

But since they are already coated with epoxy, I can assume that potting them in an epoxy block will not do any more harm. Am I right?

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Watson A.Name - 'Watt Sun'

Are you another self appointed apostrophe inquisitor or what? There is already one in this group. But maybe in holydays.

thanks for the correction Ban

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Ban

Sorry, it's just a pet hate. :)

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http://inquisitor.i.am/    |  mailto:inquisitor@i.am |             Ian Stirling.
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Ian Stirling

Try this one:

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A well working forever flasher, I think.

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buck rojerz

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