If he changed the circuit to “make end multiplication unnecessary”, he’d likely be losing accuracy, as all of the sudden a change in the amount of amp/hours would correspond to much smaller amount of change…

Posted at 8:04 am on May 15th, 2009 by Chris Lockfort

yeah. just use a calculator. he’s either have to change the crystal oscillator, or re-gear the watch, depending on its movement. not easy.

Posted at 8:38 am on May 15th, 2009 by Man On Fire

Or he could just change the numbers on the face of the clock…

Posted at 9:05 am on May 15th, 2009 by atrain

@atrain – bingo

Posted at 9:52 am on May 15th, 2009 by raged

a deep discharge protection should be implemented or it might be the last cycle of the battery ;)

Posted at 10:11 am on May 15th, 2009 by Till

i saw something like this on Sam Goldwasser’s RepairFAQ, he was using NiCd’s though. Yet another use for those cheap Pound World/etc clocks :)

Also, another approach would be a “step” timer with the input hooked up to a 555 timer set to pulse once every n seconds, so you can read the capacity in Ah directly off the clock’s dial.

Posted at 10:44 am on May 15th, 2009 by andre

I would use an arduino to do the math and then have it twitter the test results from each battery. c’mon hackaday, get on the ball!

Posted at 2:35 pm on May 15th, 2009 by greg

Can’t you just go through a resistor? Or am I being dumb… (it’s that second thing isn’t it).

Posted at 3:52 pm on May 15th, 2009 by pdx

@pdx: A little of both. Yes, you can go through a resistor, but this way you can reliably time the discharge with a given current draw. Otherwise, you’d have to sit there and watch your meter the whole time, noting down when the battery died.

;)

Posted at 4:49 pm on May 15th, 2009 by Skyler Orlando

@greg

Hack-a-day seems to be dyin’ a horrible death.

Posted at 7:20 pm on May 15th, 2009 by Micheal Smith

Wtf….. I just use a capacitor and a poteniohmer to calculate the end of the universe for my lipo’s

Posted at 7:36 pm on May 15th, 2009 by billhates

@ mike smith… what the hell is your problem. You dont want to find out how to check a battery!

Posted at 7:39 pm on May 15th, 2009 by billhates

Hmmm.. I have a watch EXCCTLY like that one and it is all analogue, no batteries inside, only an old school proper wind-up mechanism.

Posted at 6:38 am on May 16th, 2009 by Wazzup

Hmmm.. I have a watch EXACTLY like that one and it is all analogue, no batteries inside, only an old school proper wind-up mechanism.

Posted at 6:38 am on May 16th, 2009 by Wazzup

It would be simple to measure the time with any other device, but the circuit itself is simplicity at it’s best. Though if the “true” mAh rating is what you are after I don’t think you are going to get it with this since the “true” rating is usually done at a 1/5 C discharge rate. By “true” I mean what the factory puts on the label… you know, marketing crap.

@till: a pseudo deep-discharge is already in place: the white led. Of course you will still have leakage current through the PNP transistor, but that should be negligible unless you leave this thing hooked up for weeks.

As for making the calculation unnecessary, make it draw 1mA (yes, impossible with this circuit). Then see the number of hours it runs. :D You could make it easier though: change the total resistance (including parallel relay coil) to about 37.5ohms (drawing 100mA) or 3.7ohms (drawing 1A). A 1A draw should be well within the 1C discharge limit of most LiION laptop cells and give more of a “real world” capacity, just make sure your resistor(s) can dissipate that kind of power.

Posted at 7:19 am on May 16th, 2009 by Tetrafluoroethane

Just glad to see that it doesn’t use an arduino in a switch simulating role. This is a pretty clever way to find the amp hour rating. Might be a bit nicer to change the current draw to simplify the calculation, but the principle is sound and the use of the pocket watch is clever.

K.

Posted at 4:55 pm on May 16th, 2009 by khordas