From: tonya@hpldsla.sid.hp.com (Tony Arnerich)
Newsgroups: rec.photo
Subject: Re: stabilizers
Date: 1 Sep 92 18:23:03 GMT
Organization: HP Scientific Instruments Division - Palo Alto, CA

bjs@uts.amdahl.com (Barry Sherman) writes:

> I recently obtained a sensitive enlarger meter for the first time.  Actually,
> it's a (used and obtained through incredible hassles) JOBO Colorstar 2000 
> color analyzer.  The exposure meter portion seems to be quite sensitive.  
> Sensitive enough to measure bulb brightness fluctuations due to lamphouse 
> heat-up and current fluctuations.

> ...

> on the enlarger.  Then I turned the air-conditioner on and off several times,
> imitating the way that its thermostat turns it on and off while I'm working.
> The indicated exposure time jumped up and down by ~5-8% every time I varied
> the air-conditioner on or off.  This does not make me happy!  I've had some
> problems with inconsistent results in color printing and suspect that this
> may account for some of them, 

Absolutely.

>                               although, interestingly, the Colorstar did
> not indicate any change in the color of the light from the enlarger during
> these fluctuations.  (It's sensitive to 1cc color changes.)

Recall that the Colorstar is subject to the same fluctuations. How does it
behave in brownouts? Just another fly in your ointment ... :-(

> My first attempt at a solution will be to switch the air-conditioner to a
> different circuit, although I don't expect that to make any difference, since
> all my circuits are drawing from the same feed lines.

This will help in that it will eliminate the voltage drop across the house
wiring (breaker to the outlet). Be sure to turn off all significant loads
on the enlarger/analyzer circuit: especially fridge or other intermittent
devices.

The voltage drop in the power company's wiring (their transformer to your
breaker box is less significant due to larger gauge wire, but it will still
be there.

For the best results, power the air conditioner off the opposite 110V line
coming into your house. Your house gets 220V in the form of two opposed
110V lines, plus "return", for three wires total. Usually adjacent circuit
breakers feed off opposite incoming lines. 

>                                                        So I'd like to
> get a voltage stabilizer.  Of course, there's no hope of finding one designed
> specifically for my colorhead.  But I've seen generic-looking boxes labeled
> "voltabe stabilizer" in electronic stores.  My questions:

> * Does one just buy a "110 volt" voltage stabilizer?  

You could. Many devices can perform this function. There are "power condi-
tioners", "stabilization transformers", and some "uninterruptible power
supplies" that have this feature. The latter device steps down and rectifies
to 24VDC (unregulated), which then feeds an inverter to step up to 110VAC.
The better ones do this at least; the cheapo ones merely switch directly
to the incoming AC line when the power meets certain loose specs - not what
you want. Any of these devices might be found at a good computer store.

> * Are they rated as to current capacity?  (My 2 bulbs draw 400 watts total.)

They better be! 400W is no big deal in the world of computers, so this
rating shouldn't be difficult to find.

> * Since my lamps are 24v I assume that I want a stabilizer that my step-down
  > transformer will plug into.  I.e.  I assume that I want a 110 volt
  > stabilizer and it will be inserted between the step-down transformer and
  > the wall outlet.  Or do I want a 24v stabilizer to be inserted between the
  > transformer and the bulbs?  Or does it matter?

I never heard of anybody building a 24V stabilizer. An advantage of doing
the job at the 110V end is that most things will plug in - like your analyzer,
for instance. Think about that for 1 millisecond and you'll get a very good
idea.  :-)

> * In other words, I, in my state of ignorance, have no idea what to ask for
  > when I to into the store.  Any knowledgable suggestions?

I don't know if your equipment cares about sinewave vs. squarewave. If so,
most inverter-type stabilizers won't do for you. The transformer-type will
work great. I got the following listings out of American Design Components'
catalog (# (800) 776-3700, New Jersey - I have no affiliation with these
guys):

- Constant Voltage Transformer $49.95 Item #25561 Input: 95-130 VAC,
  output 120VAC 8 amp capacity

- Omnipower AC regulation & battery backup $399.95 Item #29116 450 Watts
  (Not listed as to square or sine wave output)

- Line Stabilizer/Conditioner $89.95 Protects against brownouts, spikes
  Made by Tripp-Lite  Item #29119

- "Micro-UPS" Item #29034 $199.00 Square wave 60+-1 Hz 400watt battery backup
  and over/under voltage correction, 20ms switchover time

- Tripp-Lite battery backup Item #29114 $349.95 450W, brownout/transient
  protection, 2ms switchover time (from incoming line to battery).

I'd recommend either cat #25561 or #29119, because of their lower costs.
The transformer is almost certainly sinewave output. It *is* massive, though:
3"x5"x7", and *solid*. But then, you won't be moving it much after you set
it up.

Also, don't buy a unit that is *just* capable of handling the load - go for
a safety factor of at least 1.5X, preferably 2X. To convert amp ratings to
watts use Volts * Amps = Watts.

- Tony
Newsgroups: rec.photo