Comments on: Unique Li-Ion battery tester

By: khordas

khordas — Sat, 16 May 2009 23:55:23 +0000

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.

By: Tetrafluoroethane

Tetrafluoroethane — Sat, 16 May 2009 14:19:22 +0000

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.

By: Wazzup

Wazzup — Sat, 16 May 2009 13:38:59 +0000

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.

By: Wazzup

Wazzup — Sat, 16 May 2009 13:38:40 +0000

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.

By: billhates

billhates — Sat, 16 May 2009 02:39:10 +0000

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

By: billhates

billhates — Sat, 16 May 2009 02:36:56 +0000

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

By: Micheal Smith

Micheal Smith — Sat, 16 May 2009 02:20:10 +0000

@greg

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

By: Skyler Orlando

Skyler Orlando — Fri, 15 May 2009 23:49:27 +0000

@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.

;)

By: pdx

pdx — Fri, 15 May 2009 22:52:45 +0000

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

By: greg

greg — Fri, 15 May 2009 21:35:45 +0000

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!

By: andre

andre — Fri, 15 May 2009 17:44:07 +0000

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.

By: Till

Till — Fri, 15 May 2009 17:11:23 +0000

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

By: raged

raged — Fri, 15 May 2009 16:52:09 +0000

@atrain – bingo

By: atrain

atrain — Fri, 15 May 2009 16:05:07 +0000

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

By: Man On Fire

Man On Fire — Fri, 15 May 2009 15:38:55 +0000

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.