Milky Tester, a quick-n-dirty 123 cell checker

After living with and testing various versions of the Milky Candle for a while now, I got the crazy notion one day that I'd like to have a little tester to check the 123 cells coming OUT of a no-longer-running Milky Candle. The MC runs on 2x123 cells so it has the capability to deplete those cells more deeply than would be possible with a 1x123 setup, but with 2x123 cells, very often it's one of the cells that's become fully drained and stops the MC from running, while the other one could still be used for a while more. My crazy little concoction, the Milky Tester, now lets me check those cells in seconds to make this determination.

Some views of my cobbled-together Milky Tester...

Diagonally, showing most of the important stuff. /ubbthreads/images/graemlins/wink.gif


View from the top.


Using the tester is simple. Just plop a 123 cell into the holder, and see if the amber LED lights up. If it does, the cell will most likely power the Milky Candle just fine; if not, feel free to discard the cell without guilt about wasted electrons. /ubbthreads/images/graemlins/grinser2.gif

Milky Tester with a good cell.


Bad cell... he's dead, Jim! /ubbthreads/images/graemlins/wink.gif


So far I've found that this little tester is remarkably accurate as far as checking for suitability of cells for use in the 2x123 Milky Candle. Of course, it's specifically tuned for that usage, so a cell testing as good may not necessarily work in your other lights. But hey, all I wanted was a tester for my Milky Candle cells!

So what's inside this engineering marvel? Well... not much, really. /ubbthreads/images/graemlins/icon15.gif The concept involves putting an amber LED in parallel (NOT series!) with a specific amount of resistance. For the resistance, I chose three 390 ohm resistors in series (in other words, 1170 ohms in total). The amber LED has a Vf of roughly 2V, perhaps just a bit less. With the resistors in parallel, the same voltage drop must occur across them as well, and by Ohm's Law that guarantees a certain minimum current flow through the circuit... in this case, something along the lines of 1.7mA. If my math is wrong please forgive me, but rest assured that the gadget works, even if it does so for the wrong reason. Which in my case is very possible! /ubbthreads/images/graemlins/ohgeez.gif

Guts of the Milky Tester!


Some caveats are in order here. This is most definitely NOT a particularly elegant circuit, nor is it the best way to handle such a tester. I just put it all together in a boring moment with scrap parts on hand, and it seems to do the job... good enough for me! /ubbthreads/images/graemlins/smile.gif Also note that it's NOT suitable to run on its own as some sort of little "candle" or area light, mainly because the LED has no resistance whatsoever in series with it, meaning a fresh 123 cell would send ridiculous amounts of current through it and cook it pretty quickly. That also means the cell should only be tested for a moment, then REMOVED FROM THE HOLDER, lest it cause overheating problems. There are ways around these problems, but at the moment I'm happy that the little tester is doing its job.

For those wondering, the battery holder is available from Digikey, as are the little diffuser caps (hmm... or was it Jameco for the diffuser caps?). The teensy tiny project box is from Radio Shack, and the amber LED was purchased many months ago from Craig of The_LED_Museum. Thanks Craig! /ubbthreads/images/graemlins/bowdown.gif

Well, hope this helps someone... if it helps perhaps three other people, I'll be glad to have spent the time doing the writeup! Thanks for reading!
/ubbthreads/images/graemlins/thumbsup.gif

Be cool if you could give these away with the Milky candle so we could test our cells too.

Cheers

PeterW

Way cool, dude! My Milky Candle is still going strong at 8+ days.

How hard would it be to make it a variable resistance tester? If that could be done, would it accurately indicate what the state of the battery is in?

For example, you are going camping or something and want to make sure your packing "healthy" fully charged batteries. Would this type of device be of any use?

Mike

Peter, it's a bit tedious to make these little testers, and relies on things I'm not so good at... like drilling holes in precisely the right locations so the battery holder doesn't sit crooked! /ubbthreads/images/graemlins/icon15.gif More importantly, I've only got something like 20 of the amber LEDs used in the tester. Other colors could of course be used, and I'm sure there are more of these little amber guys out there SOMEWHERE in the world, but it means more legwork tracking them down, recalibrating the resistance, etc.

On the other hand, I'm thinking it might make sense to offer folks a Milky tester at some nominal extra charge. Without it you can still test your 123 cells by checking the flash amps on a DMM... just that I got tired of whipping out the DMM every time I wanted to check some cells, and wanted a quicker solution.

Phaserburn, sounds good! /ubbthreads/images/graemlins/smile.gif Especially since I gave you one with not-so-fresh cells installed. /ubbthreads/images/graemlins/ohgeez.gif

Hey Mike, I don't think it would be all that difficult to make the thing variable resistance. It would need a bigger housing to hold the larger components, and would need the variable resistor to be able to handle the amount of current that might potentially pass through it.

Quite honestly, I'm not sure I'll get to that for a while, but it wouldn't be very tough for you to whip something together yourself. Just build it the same way I did mine, but in place of the fixed resistors (they're in that piece of heatshrink tubing in the photo), wire in the variable resistor. That's it! /ubbthreads/images/graemlins/thumbsup.gif

BTW, regarding your signature line... Wonka rules! /ubbthreads/images/graemlins/cool.gif

DMM?

Keep in mind that there are newbies out here and abbreviations are very confusing.

DMM=Digital multimeter. Go here for a list of acronyms put together by LED Museum. /ubbthreads/images/graemlins/smile.gif


Mike

DMM = Digital MultiMeter. It's basically a little box that allows electrical testing of all sorts of things... voltage, current flow (Amperes [A] or milliamps [mA]), resistance (ohms), and often other things, too.

Here's a photo of some DMMs...


To measure the flash amps of a 123 cell with a DMM, you're basically seeing how much current flow the cell can deliver into the tester itself, with nothing else hooked to it... basically a short circuit except for the small amount of resistance inside the tester itself. You only do this for a second or so, as it's generally not a good idea to short a 123 cell! /ubbthreads/images/graemlins/icon15.gif For the purposes of checking flash amps, though, it's pretty safe. Take a look over here to read about testing flash amps in greater detail.

IMHO every flashaholic should own a DMM -- they're really useful! -- but unless you have special needs or plan on becoming a hardcore modder, you probably should set a price limit of $30 or so. Even Craftsman (Sears) has at least one nice DMM within that price range. I've seen the generic made-in-China DMMs sell as cheaply as $2.99... they work fine, but as one might expect, the build quality leaves a little to be desired.

Man, you can become a DMM-aholic if you aren't careful! /ubbthreads/images/graemlins/ohgeez.gif

Any way the internal parts of the checker could be modified with say 3 or 4 leds? I dont know if this would work, but you would have different resistances on each LED and depending on how many lit up would tell you how much is left in the cell? Would something like that work?

Hmm... possibly, but it would take a LOT of additional fiddling and/or end up a much more sophisticated circuit... and if you end up going down that road, there are already some pretty slick 123 cell testers out there, but they're also fairly expensive. /ubbthreads/images/graemlins/broke.gif You'd be better off going with the variable resistor and a single LED; then you could basically dial the resistor to a value that corresponds with whatever light you intend to use (you'd have to experiment a little at first to figure out what worked best for your particular lights).

With the Milky Tester, my goals were simple...
1. Keep it inexpensive
2. Make it accurate for testing 123 cells destined for the 2x123 Milky Candle
/ubbthreads/images/graemlins/smile.gif

[ QUOTE ]
milkyspit said:
Hmm... possibly, but it would take a LOT of additional fiddling and/or end up a much more sophisticated circuit... and if you end up going down that road, there are already some pretty slick 123 cell testers out there, but they're also fairly expensive. /ubbthreads/images/graemlins/broke.gif You'd be better off going with the variable resistor and a single LED; then you could basically dial the resistor to a value that corresponds with whatever light you intend to use (you'd have to experiment a little at first to figure out what worked best for your particular lights).

With the Milky Tester, my goals were simple...
1. Keep it inexpensive
2. Make it accurate for testing 123 cells destined for the 2x123 Milky Candle
/ubbthreads/images/graemlins/smile.gif

[/ QUOTE ]

What about #3? Send one to Mike. /ubbthreads/images/graemlins/wink.gif

Mike

Well, I just tried to skim through the whole "flash amps" measurement thread and unfortunately missed the explanation of the exact method. It took me long enough that I can't force myself to read back through the whole thing again.

So, will someone please (for the "flash amp impaired") just spell-out the procedure again in plain English over here?? I'm looking forward to the day when I can run my Milky Candle with all those little flash amps still hiding down inside my batteries.

When is that Milky Candle coming out anyways??

Many thanks. /ubbthreads/images/graemlins/thumbsup.gif

Uh, Scott, If this makes it to semi production like your red Milky Candles could you put me down for one. /ubbthreads/images/graemlins/blush.gif I told you I couldn't resist; my list just keeps growing. Too many cool toys.

Thanks,
LT

Just a quick note on DMMs, if you don't have one and also happen to be in the market for a light meter, you can get a free DMM when you buy a light meter from these guys. Actually it's for anything over $50 but I'm thinking Flashaholic needs here. http://store.yahoo.com/webtronics/freedmmoffer.html
http://www.web-tronics.com/digligmetlm.html

Oh, I see, the "flash amps" test is simply stated right under the pic of the DMM's above.... /ubbthreads/images/graemlins/ohgeez.gif

I purchased an Inductance meter from here and got a free DMM included. Good deal.
http://store.yahoo.com/webtronics/freedmmoffer.html
http://www.web-tronics.com/digligmetlm.html

Rdshores, the DMM that's second from the left in the photo I included several posts above was my freebie from those guys! /ubbthreads/images/graemlins/grin.gif

Sotto, it's pretty simple, and yes, it was kinda written in summary form as you noticed. /ubbthreads/images/graemlins/wink.gif But since I was in the middle of typing up an unnecessarily verbose explanation and don't feel like having it go to waste, I'll paste it here... /ubbthreads/images/graemlins/ooo.gif

(snip snip)

1. You need a digital multimeter (DMM) with AT LEAST a 10A range. If you don't have one, stop here. /ubbthreads/images/graemlins/frown.gif

2. Set your DMM to its highest range (usually 10A or 20A). You often need to plug the positive probe into a different socket (labelled "10A" or "20A") in addition to pointing the knob to the appropriate setting.

3. Touch the negative probe to the bottom of the 123 cell and the positive probe to the top of the 123 cell. AS SOON AS YOU DO THIS, WATCH YOUR DMM'S SCREEN! You'll see the numbers shoot upward rapidly, then start going down again. Remember what the highest value was, and STOP THE TEST. This should only take a second or two to accomplish. It's not important to remember the entire maximum value; only the first couple digits are necessary. In other words, you want to know whether your 123 cell is giving you 4A vs. 9A flash amps, not 4.5768A vs. 9.3847A. /ubbthreads/images/graemlins/smile.gif

4. The number you remembered (the max) is the "flash amps" for that 123 cell at that particular point in time. You'll need to test a bunch of cells to get accustomed to what normal readings are for fresh cells and not-so-fresh cells on your equipment. For example, using Fluke 77 III digital multimeter (DMM), which incidentally is a fairly common item up for sale on ebay, and a really nice DMM, most fresh 123 cells register flash amps of at least 9A. SureFires actually tend to register a little less than the Battery Station brand. That doesn't necessarily mean the Battery Station 123 cells are any better... each brand will have its own characteristics. Again, in my own case, I've learned that once a SureFire cell registers 6A or less flash amps, I should expect it to conk out sometime in the not-so-distant future. But remember, YMMV! Use the same DMM for all your tests and get used to the types of readings you're seeing for fresh cells and otherwise.

5. That's it! /ubbthreads/images/graemlins/grin.gif

(snip snip)

So how long will the Milky Tester run on a single 123 cell? /ubbthreads/images/graemlins/grin.gif

-Mike

/ubbthreads/images/graemlins/ohgeez.gif

[ QUOTE ]
So how long will the Milky Tester run on a single 123 cell?

[/ QUOTE ]

Okay, I'll spare Milkyspit the heartburn of having to give an elaborate answer to your silly posting...From the first post in this thread (which is the absolute minimum anyone should read before asking a question such as this /ubbthreads/images/graemlins/twakfl.gif /ubbthreads/images/graemlins/banghead.gif /ubbthreads/images/graemlins/jpshakehead.gif):

[ QUOTE ]
Also note that it's NOT suitable to run on its own as some sort of little "candle" or area light, mainly because the LED has no resistance whatsoever in series with it, meaning a fresh 123 cell would send ridiculous amounts of current through it and cook it pretty quickly. That also means the cell should only be tested for a moment, then REMOVED FROM THE HOLDER, lest it cause overheating problems. There are ways around these problems, but at the moment I'm happy that the little tester is doing its job.

[/ QUOTE ]