15 May
2011
15 May
'11
10:03 a.m.
For general use on old personal computer systems, S100, Kaypro, etc....
Would a 5A variac be sufficient?
On 110V mains (I assume you're in the States), A 5A variac will supply a
550W load or theresbouts. I would think that would be adequate for any of
the micros you mention.
And is there any write ups anywhere on how to use the variac when powering
up a system that hasn=B9t been powered up in > 10 years?
Other than 'don't'? :-). More seriously. most switch mode PSUs will do
odd things at low input votlages. They approximate a constant _power_
load, which means the mains current actually increases as the mains input
voltage decreases. If the supply is not well-designed (and a lot of them
aren't!), you can end up doing damage.
S100 machines do not normally have SMPSUS, so you can safely put those on
a Variac. But I am not sure what the point of doing that is. I would
remove the smoothing capacitors and test/reform them with a bench power
supply and series resistor, then check the transformer insulation with a
'Megger' (hgih voltage insulation tester), and then probalby power up the
transformer/rectifier/smoothing caps (i.e. with no boards in the
backplane) with a filament lamp in series wit hthe mainc.
-tony