Date: Sun, 15 Jul 2001 15:31:35 +0200
From: "Robbert J. van Herksen" <[EMAIL PROTECTED]>
Subject: RE: batteries
Hey Steven (your surname sounds "a bit" of Dutch...)
The best way to check Nicad batt's is to charge it to the full (following
the specs),
and then discharge it with a CONSTANT current.
Just connecing a passive load (a led wouldn't do too much, as the drain is
approx. 10 Milliamps, will take a month or so to discarge your battery.
Also a resistor will not give you a constant discarge current, as the batt.
gets emptier, the voltage drops slowly, hence the with a constant load
(resistor) the current drops proportionally with the voltage.
Best thing to do is connecting a "stabilized current-sucker" as I call it.
It's a simple device that you can make yourself (parts are available at any
good electronics hobby store, i.e Radio Shack), consisting of a
voltage-regulator and a resistor.
If you (and others in this list) are interested in building this simple but
surprisingly sophisticated device
, let me know and I'll give you a URL (on my server) from where you can
download all details, including schematic.
Now, just connect this test-load on a fully charged cell/battery, and start
measuring the time.
At a certain point the current drops really fast (because it tries to keep
up the dischargecurrent value, and it has to increase the load (the voltage
regulator does this automatically), and stop timing when the battery is
empty.
(contrairy to a lead-acid battery that should not be discarged all the way,
a Nicad cell doesn't mind being squeezed out completely, as long as you
don't reverse polarity...)
The measured time [decimal Hours), multiplied by the current [mAmps] (your
should measure it) gives your the approx capacity (mAmpHour) of that
particular battery.
Rule of thumb is that if you charge a cell with 100%, it will return approx
80%.
I even did it more fancier then this:
I have a small (computer) card, fits in any good old ISA slot,
and it contains a simple Analog to Digital converter.
It measures a DC voltage on it's input conector (the battery...), and
outputs a (scalable) digital value to the computer, which is recorded to a
file at (adjustable) time intervals, hence: food for graphs.
A special application makes a graph of these data, giving me a neat graph
picture.
That's my way of looking at the capacity of any rechargable cell.
>From these data you can calulate the capacity (or what's left of it) of the
battery.
Neat stuff, and this PCB is already 15 years old....... (jikes, I'm getting
old...)
Let me know if this info was usefull, or if you need more help.
Cheers
Robbert
Soesterberg, The Netherland
(and it's raining all day...)
> -----Original Message-----
> From: Steven Lagerweij [mailto:[EMAIL PROTECTED]]
> Sent: Sunday, July 15, 2001 14:01
> To: Libretto
> Subject: RE: batteries
>
>
> Date: Sun, 15 Jul 2001 13:53:27 +0200
> From: "Steven Lagerweij" <[EMAIL PROTECTED]>
> Subject: RE: batteries
>
>
>
> >>
> >>Does this mean the batterypack is broken or is there something
> wrong with
> >>the charging process?
>
> >Without another battery, it's almost impossible to say.
>
> Yes, that's true. But since I don't have another battery I was
> hoping someone
> here recognizes the problem from experience.
>
> BTW, I've checked the battery with a multimeter and it read only
> 5 Volts, so
> I am now trying to get it completely discharged with a LED
> connected to it....
> Could this help?
>
> Thanks again,
>
> Steve
>
>
>
>
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