Battery surprise

Wed, 02 Aug 1995 23:55:11 -0500 (CDT)

Bought my UL with a defective onboard charging circuit, being assured the
batteries would not work. But at one point decided to try charging them
externally. One of then began to accept a charge, and after 14 hours at about
65mA, ran the machine for 52 minutes on slow speed and low backlight. Tried to
charge the other one, but the meter needle would blip briefly, then show no
charge at all. Recharged the first one, this time at 80mA. But it died after
60 seconds in the machine. Sort of cured me of wanting to mess with them, since
I had already decided to use the Renewals as per my previous posts, also since
I would have had to make up a charger (used a model RR variable power pack and
an ordinary VOM for my test charging). But the dead battery packs--I was
curious as to what was inside, and got the idea the easiest way to set up for
Renewals inside was to hollow out one of the originals, then put
contacts inside it for the 7 Renewal AA cells. Started the strange carving
procedure needed to remove just the label side of the battery case while
leaving the rest intact, including the full depth of all four walls. Boy did I
ever get a shock! Inside, in addition to six AA NiMHy cells, welded together
with heavy straps, four spot welds at each connection (in green shrink
wrapping--an earlier poster had written of blue shrink wrapped cells, and
nothing else inside--perhaps the original replacements?), were 2 PC boards with
15 electrolytic capacitors (12 of them wired in parallel across the output
contacts), 3 trimmer capacitors or potentiometers (not sure which, but can't
you just imagine--"Could you align the IF strip in my battery pack?" "Sure--let
me fire up the signal generator and the oscilloscope--OOOPS--they forgot to put
any access holes in the battery case!"), 2 integrated circuits, 10 discrete
semiconductors (transistors, diodes, rectifier packages), 2 chokes, and 17
small capacitors (may have been diodes--not certain). No wonder there are so
many battery problems! You have a complex AC power supply feeding more complex
circuitry inside the computer, which is feeding more complex circuitry inside
the battery pack! I can only imagine they did it to jack up the voltage out of
the six cells and/or make sure they didn't get overcharged--never had one, but
I understand the first round of replacement packs did good to run the UL for
5 min. Six NiMHy cells don't quite make 12 volts, I think, and perhaps the
discharge curve falls steeply. Why they didn't just go ahead and put in seven
cells with a dropping resistor I'll never know. I do see with all those
electolytics in there why my ammeter needle jumped briefly! (BTW, I did try
disconnecting all the electronic junk and charging those six NiMHy cells
directly--still nada.)

Speaking of which, I did finally get the battery pack case conversion done for
the seven AA Renewals. It was trickier than I thought--hard to get enough
resilient material to bear against the contacts in the narrow space--but I
managed. Took about 4 hours including the time to carve the case open and
remove the old innards--a lot of cutting little bits of sheet
brass, soldering, cementing things together. But it works and I have a UL
which, for 55 minutes or so, is completely self-contained, and the batteries
can be recharged in a Renewal Power Station anytime I want--also, I can use
ordinary off-the-shelf throwaway alkalines if I need to. This is mostly just
for quick entries, consulting my phone list--things like that. For long
sessions, I plug into that pack of size D Renewals at the bottom of my
briefcase--that should last about 15 hours if needed. A critical part of the
success of this effort was to pry off the contact holder at the bottom of the
battery compartment, then unplug the power connector to the motherboard and
remove the positive contact so that battery power could be fed to the DC IN
jack instead of into the motherboard at the usual point--otherwise, while
running off the AC power supply, the internal circuits might try to charge the
Renewal cells--BOOM!

Yet to be done is installing an on-off switch for the internal batteries, to
prevent their being discharged by the 50mA parasitic load. For now I'm using a
jumper (and taping it so it can't short out against the case or the floppy port
shell!). This could be the toughest part of all--there isn't much extra room
inside the UltraLite, and I don't want to damage anything!

Disclaimer/warning: Don't try any of this without a fair working knowlege of
electronics and mechanical things. Don't attempt to charge Ray-O-Vac Renewal
alklines in anything but a Renewal Power Station. Don't attempt to open up a
battery pack unless you really know what you're doing--the plastic is tough and
it would be easy to cut your fingers, get battery chemicals all over the place,

Any questions, I will try to answer them.

Mark Shields
"If we would teach children, we must first become children with them."
- Martin Luther