Quote Originally Posted by KF7QLP View Post
Bought myself a mobile rig (12V power.) The info with it says it can draw up 13A, xmit'ing at high power.

In the car I can just tap its 12V system and in the garage I have a couple batteries and charger to power it.

I'd like to also use it in my (home) office but don't want to bring the loose batteries in and the Explorer won't fit through the door. It occurred to me that PC power supplies have a 12V tap and the first one I pulled up on newegg, a 500W unit at about $40, claimed it was good for 18A on each of two 12V taps.

I seem to remember that switchers, at least in the 'olden days' didn't like to fire up w/o some load. Is that still true of generic PC supplies, is the load included inside the ps case or has the design matured so that that's not true anymore (if it ever was.)

How 'bout ripple at high load. What's a number I should be shooting for? External filtering?

Any thoughts on using a PC supply to power a 12V rig?

Benton 21feb12
KF7QLP
Things haven't really changed. Typical computer switching supplies still need a load on the 5 V and often the 3.3 Volt bus to startup, and a connection to simulate the "power up" signal from a motherboard to start as well. Many of the newer supplies actually have lower 12 Volt capability than in the past.
The problems are multiple:
1. The "12 Volt" rail is usually +/- 10%, which is sufficient for hard drives and DC/DVD Drives in a computer, but many Amateur Radios will not work well, (some won't work at all) if the voltage falls below 12 Volts. They ARE actually designed for 13.8 Volts, +/- 10%, since 13.8V is the typical automobile system voltage when the engine is running.
2. The (RF) noise generated by such supplies can be horrendous; most of the supplies do NOT have any RF suppression or power-line filtering. (Open one up. You will see where the filter components are SUPPOSED to be mounted, but those spots are only provided when the unit is first submitted for RFI testing; once in production, the filter components are "conveniently" eliminated.

YMMV. You MAY be able to use such a supply, or you may be bitterly disappointed. And different brand supplies can vary widely; even different models from the same brand name may have widely different performance.