running a UL with sunlight

eh? ((no email))
Sat, 30 Oct 1993 22:17:17 HST


about running the UL from an external battery- I bought a used UL with a
broken backlight and kludge "cube" power supply. The previous owner had cut
the factory power connector off, and wired it to a cheap 500mv 12vdc cube.

The factory power connector was kind of flakey, so I punched a small hole in
the PCMCIA plastic cover, and installed a mini-phono jack, and have two sets
of cables, one that plugs into a 120vac->12vdc power supply, and one that has
clip leads that I can hook to a 12v battery. The factory plug has three
connections inside the UL, two are +/- 12vdc, the other I think is +5vdc for
the external disk/parallel interface (I don't know 'cause I've never seen the
factory power supply). Anyway- you'll have to pull the cover to check
connections, I can't remember which is which. One thing I been told is that,
if you run with an external 12v-only supply, the internal "main" battery will
not charge- dunno why that is (I don't have an internal battery either, so I
don't know how that charging circuit is supposed to work). There is a second,
long thin nicad battery, which DOES charge from the 12v-only setup, and that
is a 3.6v pack that powers the 1mb RAMdisk, so running your system with
12v-only will still allow your to keep your memory when unplugged.

I kludged a replacement inverter for my LCD backlight (the original inverter
was missing when I got the UL), and have set up my power plugs so that the
baclight is powered only when I am plugged into the AC supply- with this
setup, the UL runs about 100ma @ 12vdc (without backlight), and 400ma @ 12vdc
when the baclight is in use. This works very well for me- I'm using the system
to monitor my solarvoltaic/battery/inverter home power system.

So- all one needs to do is hook up a 12v battery to the 12v input to the UL.
If you want your internal main battery to be charged, you will have to plug in
the factory power supply occasionally (I've been told). With backlighting, you
will be using about 400ma * 12v * 24hr = 115 watt-hours/day, without
backlighting this drops to 30wh/day. Hook your 12v batteries to a PV panel
that puts out about 25 watts (6 watts w/o backlight), and you've got a
perpetual computer.

By the way, I used to have a Tandy 100 for this purpose- it used only
60ma @ 6vdc, less than 10% what the UL w/backlight uses... but not nearly as

Good luck to your friend- I'd be interested in hearing more about what he is
doing at that lighthouse.

aloha- joel.