AC power on front panels

Gooijen, Henk henk.gooijen at
Sat Jan 14 11:02:44 CST 2006

Use a Solid State Relay with the proper rating at the AC switching side,
and operating on low-voltage DC at the input side. Nice to have is a SSR
which switches the load at AC voltage zero-crossing.
If you install the SSR at the rear side, you can keep the AC power leads
very short between the inlet, SSR, and the power transformer.
Now, you need a DC source, which is switched to the SSR input from
the console front side. Most SSRs operate at the input range of 3 - 32V,
so either install 3 NiCaDs, or install a small transformer with a bridge
rectifier and an electrolytic capacitor to smooth the DC. If you go for the
second choice, get a good quality transformer as it might be powered always.
If you go for the NiCaDs, you might consider a simple loader that recharges
the NiCaDs when the AC power is on the main transformer (unit switched ON).
- Henk, PA8PDP.


Van: cctalk-bounces at namens Richard A. Cini
Verzonden: za 14-01-2006 05:23
Aan: CCTalk
Onderwerp: AC power on front panels

            I'm playing around with my relatively new IMSAI and I was
pondering the following. The unit is constructed with the front panel power
switch unconnected and the corresponding terminals on the power supply board
jumpered together. There is a mains switch on the rear panel which takes the
place of the front panel switch.

            While for safety reasons I cannot disagree with the approach -
it's plain stupid to put uninsulated mains voltage in a low-voltage area
(and unpassable by UL evaluators I'm sure) - it detracts a bit from its use
because you have to reach behind the unit to turn it on.

            Has anyone come up with an elegant solution to being able to use
the front panel power switch while keeping it safe? I was toying with some
sort of low-voltage circuit (small LV transformer and relay, with the front
panel switch in the loop on the coil side). Another idea I had was to hot
glue a dielectric insulator board (that gray cardboard kind of stuff) over
the parts of the front panel that would be exposed.

            Ideas? Too much time on my hands?


Rich Cini
Collector of classic computers
Build Master for the Altair32 Emulation Project
Web site:  <>

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