Weak NiMH battery test?
 

I need to toss out NiMH batteries that won't hold enough charge (the
Pogo RipFlash destroys itself if the battery dies while recording).

Is there a quick way to test battery capacity?

At the moment I am resorting to a slow process

1. Put battery pair in RipFlash

2. Start recording, note the time when the first battery bar goes out.

3. Test the voltage of the batteries; label the weakest one with the
time and put the strongest one, recharged, back in the pool.

4. Take a new charged pair from the pool and repeat.

Eventually you get a set of batteries that last long enough for the
purpose, and a batteries labelled with time according to their weakness
that won't.

It's a little slow though.

Something that simply discharged the batteries and measured the
total energy or something would do better.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

On Sat, 10 Apr 2004 9:00:27 -0500, Ron Hardin wrote
(in message ):

I need to toss out NiMH batteries that won't hold enough charge (the
Pogo RipFlash destroys itself if the battery dies while recording).

Is there a quick way to test battery capacity?


I have yet to write up a mini-review on the CCrane QuickCharger Battery
Charger" but I think that's it's "interesting" to note that I have never had
a NiMH battery that failed to charge (out of mebbe 50 that I use).

Now - a /lot/ of them are in lowdrain devices, small clocks (about 2 or 3 of
these with one AAA), over 300 remotes that are under the sofa cushions as
well as the three that are on the coffee table as well as the three SW's (on
standby battery power) as well as various gee-gaws and gadgets. (Also note
that I, originally, bought a couple of 9v "transistor" [grin] batteries but
gave them away and went to alkalines on those devices (nearly all AC=powered
with 9v backup (weather radios and such).

The CCrane charger has a selectable "low drain" that can be automatic or
user-selected.

And you can check out a single battery by just inserting one battery in the
charger and leaving the translucent cover in place (I gort the older boy one
for Christmas and he caught this as I had missed it [sigh].)

You might be interested in downloading the instruction manual.


The reason I bought this - and it is not clear in their ads for some stupid
reason, I had to call - is that it charges "up to four" cells.


Does that mean that it can charge 1 cell, 2 cells, 3 cells or 4 cells?

[sound of trumpets sounding a clarion call]

Yes, that's exactly what that means. I figgered forty bucks ($30 return price
most times) was just a nifty price to pay to charge one of the 37 clocks that
use one cell or the shortwave radio that uses three cells.

And I was right; looks good - lasts a long time.


Gray Shockley
--------------------------
Entropy Maintenance Technician
Tao Chemical Company
--------------------------

http://www.compcomm.com/
Vicksburg, Mississippi US






At the moment I am resorting to a slow process

1. Put battery pair in RipFlash

2. Start recording, note the time when the first battery bar goes out.

3. Test the voltage of the batteries; label the weakest one with the
time and put the strongest one, recharged, back in the pool.

4. Take a new charged pair from the pool and repeat.

Eventually you get a set of batteries that last long enough for the
purpose, and a batteries labelled with time according to their weakness
that won't.

It's a little slow though.

Something that simply discharged the batteries and measured the
total energy or something would do better.

Ron Hardin crawled to the nearest keyboard
and summoned the courage to write:

I need to toss out NiMH batteries that won't hold enough charge (the
Pogo RipFlash destroys itself if the battery dies while recording).

Is there a quick way to test battery capacity?

Inelegant but works: charge the battery, insert it in a
single-battery holder, put a resistor across the leads, then measure
the time and voltage as it runs down.

Ohm's law: E = IR rearranges to I = E/R. For a single NiMH under
load, E is 1.2 volts or thereabouts. You might specify I so as to
drain the battery in an hour. I think the RipFlash uses AAA
batteries, so if the battery capacity is (just guessing) 900 mAh then
to flatten the battery in about 1 hour you'd have a drain of 0.9 amps
(=0.9 Ah / 1 h). Then R = 1.2/0.9 or a little over 1 ohm.

Note the power is I^2 R or about (0.9*0.9)(1) = 0.8 watts, so you'll
need a fairly high-wattage resistor, or achieve the desired R by
putting several resistors in parallel so they share the load.

I would guess that a weak battery might show a lower-than-usual
voltage under heavy load but don't know for certain. This would spare
you having to completely drain the battery.

HTH.



--
"The Great Satan put electricity in my toothpaste."

Gray Shockley wrote:
I have yet to write up a mini-review on the CCrane QuickCharger Battery
Charger" but I think that's it's "interesting" to note that I have never had
a NiMH battery that failed to charge (out of mebbe 50 that I use).

I have one but use it only as a voltmeter. I use the Maha C401FS for actual charging,
which does AA or AAA cells individually (any mixture up to 4), slow or fast charge
(I always use slow).

The not-charging problem isn't a failure to charge, but a failure to hold much charge.
That is, the battery runs down quicker and quicker. At some point it's a loser
and you toss it. The trick is finding those batteries easily, when you always use
them in pairs.

The Crane charger suffers mostly from being a parallel charger, so you can wind
up not having charged some of the cells at all, usually owing to a bad contact
with the charger. There's no way to test this, unfortunately; though you can test
that it happened when you finish. Then it's too late. The voltmeter is nice though.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

"Ron Hardin" wrote in message
...
I need to toss out NiMH batteries that won't hold enough charge (the
Pogo RipFlash destroys itself if the battery dies while recording).

Is there a quick way to test battery capacity?


Have you asked on sci.chem.electrochem.battery?

Frank Dresser

!doctype html public "-//w3c//dtd html 4.0 transitional//en"
html
 
pGray Shockley wrote:
blockquote TYPE=CITEOn Sat, 10 Apr 2004 9:00:27 -0500, Ron Hardin wrote
br(in message ):
pActually, CCrane has them on their Orphans age for $29.95. Ordered one
for my brother, who's little girl is almost one and already using up batteries
almost as fast as Pampers, one one for myself./blockquote

pbrPete Davis
blockquote TYPE=CITE 
pYes, that's exactly what that means. I figgered forty bucks ($30 return
price
brmost times) was just a nifty price to pay to charge one of the 37 clocks
that
bruse one cell or the shortwave radio that uses three cells.
pAnd I was right; looks good - lasts a long time.
pGray Shockley
br--------------------------
brEntropy Maintenance Technician
brTao Chemical Company
br--------------------------

bra href="http://www.compcomm.com/"http://www.compcomm.com//a
brVicksburg, Mississippi US
p At the moment I am resorting to a slow process
br
br 1.  Put battery pair in RipFlash
br
br 2.  Start recording, note the time when the first battery bar
goes out.
br
br 3.  Test the voltage of the batteries; label the weakest one
with the
br time and put the strongest one, recharged, back in the pool.
br
br 4.  Take a new charged pair from the pool and repeat.
br
br Eventually you get a set of batteries that last long enough for the
br purpose, and a batteries labelled with time according to their weakness
br that won't.
br
br It's a little slow though.
br
br Something that simply discharged the batteries and measured the
br total energy or something would do better.
br/blockquote
/html