>
>Much of what happens directly relates to the battery condition and
>the charging circuit. Old tired & dry batteries may not draw enough
>current to pop a fuse (or trip a breaker). Astron relies on a narly
>scr to crowbar the main fuse/breaker.
Sounds like a case for checking your batteries routinely.
After all, they have a very finite lifetime, and are expected to wear out.
Hospitals replace them routinely.
>Not if the battery impedance was high enough to simply boil the
>battery dry. (ie... tired or dry batteries).
See above
For that matter, we should be checking the electrolytics in these
power supplies every year or so, as they have finite lifetimes too.
Typically 2000 hours at 85C or thereabouts, with the lifetime
doubling for every 10C reduction in temperature.
Jim Williams of Linear Technology published a much more accurate
formula involving ripple current, ESR, and a few other factors, but
the first approximation works in most cases.
When I worked for Muzak, I was exposed to thousands of systems that
were out in the field.
Those that were cycled daily failed far more often than the ones that
were left on 24-7.
Most of our failures in power supplies and amps ended up being caused
by open or leaky electrolytics.
SOP was to replace the transistors and ship them back out, but I
noticed a fair number coming right back within a short time, with the
same failures.
I started replacing the large electrolytics routinely if they looked
to be more than a couple of years old, and our repairs went from five
guys busy, to one guy like the Maytag repairman (me). The other five
guys were then able to spend more time in the field doing profitable
things instead of repairs on leased gear.
>.... Replace the regulator board with an updated version and clean
>up some of the sloppy assembly.... you've
>got a pretty good low cost high current consumer grade DC power supply.
Yeah. Basically, it looks like they took a National app note for the
723, and called that a finished design.
Not a bad start, but not a finished design.
As you say, the assembly work is pretty amusing at times.
>(I'm a fan of embedded processor systems)
Me too, I design them for a living.
I recently did a thermal printer with a processor dedicated to
battery charging (small NIMH pack)
500kHz switching regulator plus reverse pulse charging entirely in
software. No "charger chip" or SMPS chip, just a processor, mosfet,
inductor, diodes, and support R's and C's.
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