🚀 go-pugleaf

In article <535@cbnewsc.ATT.COM> parnass@cbnewsc.ATT.COM writes:
+---------------
| hobbit@topaz.rutgers.edu (*Hobbit*) writes:
| > I just opened up what porports to be a battery charger for some unknown...
| The Alexander SM12000 Smart Charger is shown in the new Alexander catalog.
| It is supposed to rapid charge a battery at a 450 mAh rate.
| A 500 mAh battery will be fully charged in 1-1/2 hours.
+---------------

Note that that's not particularly at the top end of modern fast-charge
NiCads. The charger for my Radio-Shack [really Mobira] cellular phone fully
charges its 1 Ah (1000 mAh) battery in one hour, so the charge current is
somewhere well over an amp.

+---------------
| A red light indicates the battery is being charged, and
| a green light means the battery is ready to use...
| The crystal and ICs might be for timing the charge.
+---------------

Or the crystal may be the oscillator rock for a one-chip micro that just
happens to have an A-to-D converter in it somewhere. A lot of those "smart"
or "fast" NiCad chargers these days work by measuring the temperature [that's
right, you heard me!] inside the battery, and dropping to trickle charge
when it gets high enough. Seems that NiCads under heavy charge soak up the
juice until they are really full (which you can't tell by measuring the
voltage, which goes up as soon as you start charging), then start dissipating
the charging current as heat.  This heats up the battery pack, and thus a
thermistor built into the pack, which resistance is measured by the charger.
A lot of one-chip micros have a few channels of A/D built in, which can be
used for things like measuring resistance.

By the way... You can usually tell these batteries by noticing at least
one "extra" lead or contact on the battery/charger interface [minimum of
three, therefore]. 

+---------------
| Alexander sells charging sleeve inserts for various batteries,
| including Icom, so I wouldn't junk the charger.
+---------------

Note that a rapid-charger circuit is quite specific to the battery type, as I
know of no standard for the internal thermistor. Thus it doesn't suprise me
that the "Alexander" charger might have a micro in it. I suspect those sleeve
inserts have some programming resistor(s) in them somewhere that tells the
micro in the charger what the needed charging profile, ending temperature,
and thermistor resistance are for the particular battery type.

[My single-function Radio-Shack charger "gets by" with two voltage regulators,
four op-amps, and miscellaneous transistors & discretes. And that's starting
with a D.C. input...]


Rob Warnock
Systems Architecture Consultant

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