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From: Joseph Legris
X-Mailer: Mozilla 4.77 [en]C-SYMPA (Win95; U)
Subject: Re: battery charger nightmare!
Date: Tue, 03 Sep 2002 17:28:59 -0400
NNTP-Posting-Date: Tue, 03 Sep 2002 17:23:24 EDT
Organization: Bell Sympatico
Boris Nogoodnik wrote:
> 12 packs no different then a single pack. Just replicate the charging circuit
> 12 times with a single power supply. All depends upon the complexity of charger
> you want. Simple case is just a resistor to provide more or less constant
> current. Do you need an automatic shut off at the end of charge? If you do,
> it's more complex.
> "Wonko The Sane" wrote in message
> > I need serious help. When I was being hired for my current job my boss
> > found out that I had had some experience in electronics and circuit
> > design (from my resume, naturally). Now he wants me to design a
> > battery charger (not my regular job). The problem is... I haven't
> > looked at a circuit in like 12 years. I can't remember a mosfet from a
> > nand gate. If this were a simple circuit, no problem, but it has quite
> > a unique design.
> > The battrery charger will be charging around 12 battery packs (1300
> > mAh - 1.2V x 3 batteries per pack). I'm kinda lost from there. I know
> > what all of the parts are and what they do, I just can't remember how
> > to figure out the different variables for the parts.
> > I have found some schematics for single batteries and/or packs, but
> > none that really help me with a charger that charges so many packs at
> > once.
> > If anyone knows of a similar schematic I could look at (or could draw
> > me a simple one), or any help with the basics, I would be most
> > sincerely appreciative.
> > Wonko The Sane
> > email@example.com
If you don't mind waiting 16 hours or so to charge the batteries all you
need is a source of 6 to 10 Volts, DC, and a bunch of resistors. Connect
a resistor (and perhaps a diode for safety's sake) in series with each
battery pack and come back tomorrow.
If you want rapid charging then you should go to your boss and ask to
resubmit your resume :-)
Seriously, it is not a trivial project. For rapid charging you must
accurately and independently determine the end of charge point for each
set of batteries. One way to do this is to sense the voltage dip that
occurs when a NiCd battery reaches it's full charge, and then to cut the
current off. Another technique is to measure the temperature of the
batteries, which will increase when charging is complete. You must also
detect fault conditions such as defective batteries or shorts across the
Here are a couple of samples. I cannot vouch for their quality or
reliability, but it will give you an idea of what's involved. I found
them by searching google on "NiCd battery charger circuit".
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