This Weekend's Finds

From: Tony Duell <ard_at_odin.phy.bris.ac.uk>
Date: Mon Aug 18 08:48:38 1997

> [My ascii circuit diagram]
>
> > That looks like a voltage regualtor, which is strange, since I'd have
> > expected a constant current charger for the NiCd. Of course a lot of
> > machines just use a resistor to limit the charging current (and to get you
> > to buy more expensive battery packs)
>
> It does to me, too! By "to get you to buy more expensive battery packs"
> do you mean that the packs are more expensive, or that they wear out
> faster?

I mean more {expensive battery packs}. The packs themselves are the same
price (but more than the cells that make them up), but they don't last too
long.

Of course it's normally possible to make up suitable replacement packs
from individual cells. One of my HX-20's has a homebrew pack in it (4 2/3C
cells, I think), and my RK05's have retraction batteries that happen to
be used in cordless telephones. They were a lot cheaper than the genuine
DEC part, and work just as well.

> Good point. 50mA then (8 < V < 12) based on the 14 hour rate on the
> battery label. Looks like 9V is about right...

As I said, try it. An adjustable PSU is very useful here, but good ones
are not cheap.

IMHO a good bench PSU is a very useful piece of equipment when restoring a
classic computer - more useful than say a logic analyser. You can power up
odd sections, test machines without repairing a defective PSU first,
test/align motors, lamps and solenoids (and, for example, make sure an
optical tape reader will work at a lower lamp intensity), etc.

I like the 30V 10A Velleman one that Maplin sell. It's expensive (\pounds
230.00 as a kit), but it works well.

> Philip.

-tony
Received on Mon Aug 18 1997 - 08:48:38 BST