[LargeFormat] A UPS for an enlarger voltage regulator? Wacky idea?

[Don Feinberg]

In a word, "not suitable for purpose".  A UPS for a computer does two
things:  keeps the voltage up by use of a battery and inverter when the line
voltage goes to zero (or less than 90-ish volts), and clamps down spikes.
It has no effect whatever during normal voltage fluctuations.

What you really need is either of:

1.  What are sold as "enlarger voltage regulators" (Beseler, Vivitek, Omega,
others).  These are simple (small and light) SCR-based devices, and they
work.  But to work, the output voltage has to be set below the minimum
voltage that the device is designed to correct for.  For example:  device is
supposed to correct for variations from 95 to 125 volts.  So the device gets
set to, say, 90 volts.  Result:  voltage is very stable, but your enlarging
times are doubled.

2.  What's called a "constant voltage transformer".  This is a special type
(heavy!!) of transformer which "self-compensates" for input voltage
variations.  In use, it actually compensates about +/- 5%, far and away well
enough for enlarging.  These are devices, then, which produces something
like 117 vac for an input range of something like 95 to 130 vac.   So they
are close to ideal.  Downside:  The one I use, good for about 300 watts
continuous, weighs on the order of 15 kg and is physically large.  I bolt it
to the wall under the enlarger bench....

Actually, I combine the constant-voltage transformer with a Variac (another
heavy device); using this combination, I'm able to set the exact (well,
within about 1% or 2%) voltage that I want to have in the darkroom.   This
way, I set to, say, 115 vac, and the voltage at the enlarger is always 115
vac  +/- 1%, and my enlarging times are reliable +/- 1% or so.

Don Feinberg
donf@cybernex.net




> I would like to put a voltage regulator on my enlarger to minimize
> fluctuations.  Would a high-end computer battery backup -- i.e.
> uninteruptable power supply (UPS) -- accomplish the same thing?  I don't
> mean a power strip, but a battery backup that's supposed to deliver a
steady
> supply of "conditioned" voltage (whatever that is) to a computer.  I
happen
> to have one on hand.
>