18 Sep
1998
18 Sep
'98
5:16 p.m.
At 10:19 PM 9/18/98 -0500, Wirehead wrote:
On some (static memory and other) cards the linear regulators get quite hot
with the high input voltages. Doesn't help here that the 117 Volts is
sometimes 122 Volts or higher. For these systems I run them with a 12V
transformer wired as a 120 to 108V step down (buck) autotransformer. I first
tried with a variac to see how low the voltage can go, usually below 100V
with supplies with a lot of "margin", such as many of those open frame
linear supplies. It also helped a Heath H-19 terminal which also has a
linear power supply.
A slightly related matter, I found that some XT motherboards can run on only
5 volts, using a 1.44 floppy. I did this many years ago using a 12 Volt
battery directly as input to a 5V regulator as power supply. Not very
noteworthly now with all the portables.
-Dave
I measured the voltages across a power connector
and got 9.4V, +17.56 and
-17.86. A little high but I attribute that to a lack of a load.
Actually, I think most power supplies in S100 mainframes tend to run a
bit high so they can handle the load and because it doesn't matter since
each board has it's own regulators anyway.
Anthony Clifton - Wirehead