Voltage Stabilizer Options

[aduncanson]

I fired up my 8x10 Elwood with its 500 Watt incandescent bulb to make a print for the first time the other day and after making a test strip and deciding on an exposure time, I put an 11x14 sheet of Oriental Seagull in place on the easel and started the exposure. As I watched the image projected on the paper it was clear that my electrical supply voltage abruptly dropped and that my exposure was not going to be good.

I suppose that I could look for a Zone VI timer, but that is not my preferred approach. Is there an inexpensive (~$80) voltage stabilizer available. Does anybody make due with a computer Uninteruptable Power Supply?

Thanks for your help - Alan

[photographs42]

I have at least one or more voltage stablizers you can have for shipping cost. I'll have to dig them out to tell you what model they are. Let me know if you are interested.
Jerome

[Nathan Potter]

500 watts is a lot of power to really stabilize well. I would suggest the best way would be to run it with a DC voltage regulated supply. 120 volts at 5 amps should do it. It doesnt really need to be variable but could be to be more versatile. Tough to buy one for $80.00 though - try ebay.

Nate Potter PEI, Canada

[nolindan]

Look for a "CVS" series Sola constant voltage transformer on ebay or at a surplus industrial supply house. Do not buy a transformer rated for more power than you need - these things draw the nameplate power rating from the wall no matter what load they have on them: a 2,000 watt Sola will draw 2,000 watts even with no load. A CVS transformer will keep the voltage constant to better than 1%. .

The voltage stabilizer boxes with all the LED indicators on the front panel, sold for computer use, are useless for stabilizing an enlarger, in fact they often make the situation much worse. They consist of a transformer with 100, 125 and 150 V taps and a pair of relays that switch between the taps at low voltage and high voltage conditions. Figure voltage regulation to be 25% or worse.

[Kevin M Bourque]

I used a Sola on an enlarger and it worked well. They're heavy suckers, and they buzz while they're running. The get the job done, though. Definitely look for one on eBay.

[Peter De Smidt]

Nicholas is right. The affordable ones for computers are completely worthless. I bought at $80 tripp lite, way back when. The Sola CVS is the way to go.

[aduncanson]

Thanks all for the great advice. I have confidence in this group (particularly when they agree.) By happy coincidence a 750 Watt Sola CVS just closed on eBay, and I got it for $10 & $50 shipping, or within my $80 objective.

Interestingly, in researching this I found an engineering handbook that said that a 5 Volt change in the line voltage can make a 14% change in light output. And I expect that the case is actually significantly worse since the shorter wavelength blue and green light are probably disproportionately affected.

[Peter De Smidt]

Nicholas will correct me if I'm wrong, I'm sure, but I think you want to hook the CVS directly into the wall, and then plug your timer into the output of the CVS, with your enlarger plugged into the timer, of course. I seem to remember that these big transformers aren't happy being switched on and off a lot, which would happen if you put the CVS between the timer and the enlarger.

[PenGun]

I plug all my important stuff into voltage regulators.

http://www.apc.com/resource/include/techspec_index.cfm?base_sku=LE1200

Works well.

[Peter De Smidt]

That one might work well for computer equipment, but it's not even close for an enlarger, with an output regulation of +6% to -12%.

[PenGun]

That one might work well for computer equipment, but it's not even close for an enlarger, with an output regulation of +6% to -12%.

I guess you are right. I thought that was the voltage swing it would maintain true voltage within. Oh well.

[rdenney]

Most computer UPS's I've investigated don't stabilize voltage. They just kick the battery-powered inverter in when the voltage runs outside the acceptable range. They also filter transients. But they expect voltage regulation to be done by the power supplies of the computers attached to them. Since most of those devices run on DC, the regulation in the supplies is much easier to do.

The Sola is a true AC regulator.

But it's also worth considering where one might be getting fluctuations in the voltage. I find that the service voltage from the power company is usually very stable. But if I have stuff plugged into a branch circuit that also supplies a heavy and sudden power user (such as an appliance, or, worst of all, a laser printer), the branch can see fluctuations in voltage at the end of the branch that are unseen at the power panel. Depending on where your darkroom is, you might be just as well of running a unique branch circuit from its own breaker in the service panel, just to serve the darkroom.

Rick "noting also that a 14% change in light output is only 0.2 stops" Denney

[aduncanson]

rdenney's intranymic set me off on a task to quantify the disproportionate effect of voltage reductions on the amount of blue-green light produced by a tungsten bulb. Specifically, I did the following:

- Applied Planck's law of black-body radiation,

- Used 2900K as the normal color temperature of the enlarging bulb (per the Focal Encyclopedia of Photography),

- Performed numerical integration over the range from 380nm to 700nm to represent all visible light,

- Found the color temperature necessary to reduce the visible light output by 14% (2849K),

- Looked at the change in light output from 380nm to 500nm to represent the range to which enlarging paper is sensitive (per an Oriental data sheet),

I found that a 14% (.22 stop) reduction in all visible light coincided with a 18% (.28 stop) reduction in light between 380nm & 500nm.

Other points:

1) A 0.2 stop error in exposure while not dramatic, is certainly enough to cause me to remake a print.

2) Nobody said that brownouts were limited to 5 Volts or a 14% change in visible light output. The fluctuations I observed on my easel were dramatic, possibly approaching a whole stop, to my very uncalibrated eye.

[rdenney]

rdenney's intranymic set me off on a task to quantify the disproportionate effect of voltage reductions on the amount of blue-green light produced by a tungsten bulb. Specifically, I did the following:

I bow in shame.

It's "internym", by the way, though I like your variation. (This was the subject of heated debate by the world-class debaters of the alt.folklore.urban newsgroup back in the deeps of Internet time. Back then, the dreadful "epenthetic" was the ridiculous alternative.)

But back to the topic at hand. We live in the country and get power from a rural electric cooperative, and I don't think I've ever seen voltage fluctuate that dramatically except during stormy weather, at which time darkroom work would not be my first choice in any case. Being rural, our water is fed by an electric pump, and when the power goes out (for which a brown-out is usually a harbinger), the water flow stops soon after. I'd hate for that to happen with a load of prints--or, worse, negatives--freshly placed in the washer. Other than those occasions, our voltage rarely fluctuates by more than a volt or two. (There was the case, however, of them dialing it up too high after an extended outage such that we had 132 volts coming into the house. After I had to repair a couple of fried power supplies which I had incorrectly attributed to a surge, I measured it.)

Clearly, your power is more variable than ours, so extra action is necessary for you. I was just pointing out that for many folks, the weight, inefficiency, and buzz put out by a true AC voltage stabilizer might not be worth the trouble, and that those fluctuations in their darkroom might be caused more by house wiring than by the power company.

Rick "not prepared to perform an integration of hardly anything any more" Denney

[nolindan]

Nicholas will correct me if I'm wrong, I'm sure ...

Oh, dear. To have acquired a reputation as a tireless pedant at such an early age.

Nevertheless:

A Sola seems like a beast that you don't want to trifle with, and the common perception is that the timer should be placed between the Sola and the lamp and the Sola should be fed it's quota of electricity at all times lest it go on rampage.

However...

Placing the Sola between the timer and the enlarging lamp is the correct application. Indeed the Sola is such a beast that it doesn't even deign to notice being turned on and off at your will.

As a practical matter you don't want the Sola running all the time - the buzzzzzz will drive you nuts and don't forget that a 750W Sola will pump 750W of heat into your darkroom whenever it is on. If you have a 750W Sola running a 500W lamp then the Sola will put out the difference of 750W - 500W = 250W as heat. If the lamp is off and the Sola is on then the Sola will now pump out the full 750W of heat all on its own.

Sola's are quite indestructible - turning them on and off won't harm things a bit. The only things in a Sola are a transformer that is 3 times the size it needs to be (it has to do with the design of ferroresonant power supplies) and an oil/paper capacitor. Sola's, due to their high 'leakage inductance' don't draw any surge from the line when they are turned on. The combination of a Sola and an incandescent bulb places less stress on the timer's relay than an incandescent bulb alone. And when the incandescent bulb fails the Sola will shield the timer from the transient short circuit that a failing bulb creates.

[neil poulsen]

Nicholas will correct me if I'm wrong, I'm sure, but I think you want to hook the CVS directly into the wall, and then plug your timer into the output of the CVS, with your enlarger plugged into the timer, of course. I seem to remember that these big transformers aren't happy being switched on and off a lot, which would happen if you put the CVS between the timer and the enlarger.

This may be naive, but how about leaving the Sola CVS turned on turning a relay off and on between the CVS and the enlarger?

[rdenney]

This may be naive, but how about leaving the Sola CVS turned on turning a relay off and on between the CVS and the enlarger?


That will just add more transients that will need capacitors to reduce arcing. You could use a solid-state switch designed to minimize transients, but the only one I can think of designed for this purpose is a NEMA load switch designed for use in traffic signals.

I agree that switching a big transformer power supply will do it no harm, as long as the surge-absorption capacitor is good. I worry about those old wax-paper capacitors, especially if they haven't been used and have been allowed to dry out. If it's been off for years, I would power it up gradually the first time, assuming you can find someone with a Variac.

I agree that it will help absorb transients going into the enlarger that will actually reduce stress on the bulb.

I don't recall the power rating of my Time-O-Lite, but I have used it to power a bank of bulbs with no issue, and it didn't even blink at the 300-watt monster that I had in an old Solar 5x7 diffusion enlarger. I seem to recall the Time-O-Lite was rated for 750 watts of lamp load.

But my Gra-Lab is rated for 600 watts of bulb load and 1200 watts of resistive load. There will be inrush current on the Sola's transformer. Does it have an inrush current limiter? I don't really know why the bulb load rating would be half the resistive load rating.

Rick "a traffic signal geek" Denney

[jp]

I've read that bulbs draw more power when cold for a fraction of a second, especially as they age. Resistance of a conductor changes with temperature.

Solid state relays are used to blink tower lights at night (the red obstruction beacons). These lights have traditionally been 620w incandescent bulbs inside keg sized housings. There is a spare bulb and spare wire as well.

The lights are gradually being swapped for LED lighting at $3000/fixture plus labor, to save on electricity and tower climbing labor.

I rebuilt one of the blinking controllers a few years ago when one of mine got damaged by water. It's a simple 555 timer IC circuit that operates the solid state relays, and the solid state relays control the 120v going to the bulbs.

[nolindan]

a 14% change in light output is only 0.2 stops

A 0.2 stop error when exposing film is trivial, but paper is a lot contrastier than film. Grade 2 1/2 MGIV is 0.4 stops per A. Adam's Zone. So a 14% change is 1/2 a zone - a noticeable amount. At less than 1/4 zone difference one is chasing ghosts: I can see a 1/4 zone difference in the inspection tray but can't for the life of me see what all the fuss was about the next morning when I can barely tell the dried prints apart.

[Peter De Smidt]

Contrast grade also matters. Grade 5 is much more sensitive to exposure changes than grade 1.

[Ginette]

I look around on the Bay for theses Sola CVS but didn't see any info about the max watts. What about the "sine wave output" ex: 23-23-210-8 or 23-22-112-2 ?
My intention is to use this kind of unit for stabilize compact fluorescent photo bulbs, mine are 45W , 5,600K, generally a shooting set-up of 8 to 10 bubs = 360-450 Watts total.

[aduncanson]

The Sola ID plates list the output capacity in V.A. for Volt-Amps. Volt-Amps are equivalent to Watts if the load is essentially resistive, like an incandescent bulb. Where the load includes significant net reactance (inductance or capacitance) there is a phase difference between the voltage and the current. Then the power consumed (Watts) is the voltage x the current x the cosine of the phase angle. This means that for a reactive load, the V.A. needed will be higher than the power consumed. Given the ballasts used in fluorescent fixtures, they may be significantly reactive. (I don't know - somebody else here might.)

It might be easiest to just measure the current drawn by your lighting set up and multiply by the voltage to find the V.A. capacity you need.

[Ginette]

Thanks you for trying to explain to me but "cosine of the phase angle" is like Chinese for me. Electricity is not my domain at all.
First question : if Compact fluo lamps are "reactive", it will serve nothing to try to stabilize it ??
Second question: I don't have any idea how to mesure my lighting set-up :(
This is what I have: 3 softboxes like this http://www.lincoinc168.com/brpe4xfllihe1.html
and the Sola unit is this one: Sola Constant Voltage Transformer , Catalog No.: 23-13-030-2, Harmonic Neutralized Type CVS, Input V. 95-130, Freq. 60Hz. Va. 30 (item #120449489578 on the Bay)

Is any one use this kind of lamps for shooting?
Maybe the wrong forum for this but the Voltage Stabilizer discussion made me think about trying to solve the color variation I observe using theses lamps. I used it only on digital, still not have test it on film.

[rdenney]

First question : if Compact fluo lamps are "reactive", it will serve nothing to try to stabilize it ??
Second question: I don't have any idea how to mesure my lighting set-up :(


The lights you linked require 160 watts for each box (four 40-watt fluorescent fixtures). Three of those is 480 watts. A 750VA power conditioner will be fine, even if the fluorescent fixtures are reactive with a reduced power factor (which I just don't know).

The "560 watts" in parentheses in the listing is intended to provide the wattage of incandescent lighting that would provide the same light output. 40-watt compact fluorescents are usually compared to 140-watt bulbs in terms of light output.

Rick "wondering what color correction these would need" Denney

[aduncanson]

Being a reactive load does not imply that stabilization is not useful.

Each of your of your softboxes light will require 160 Watts. Sources on line (You know how reliable they can be.) estimate the power factor for compact fluorescents to be as low as 0.6. These figures imply that you need a capacity of 3*160/0.6 = 800 Volt Amps or greater. That Sola has an output capacity of only 30 Volt Amps and will not do.

[Ginette]

Thanks, this is more clear now.
This will be quite big and heavy. I look at models and their VA on their website (http://www.sola-hevi-duty.com/products/powerconditioning/cvs.htm)
Will 3 smallers units (one on each sofbox) do the same job ? Even if they all on the same circuit (hope it is the same term in English than French!)

Thanks all for the great advice. I have confidence in this group (particularly when they agree.) By happy coincidence a 750 Watt Sola CVS just closed on eBay, and I got it for $10 & $50 shipping, or within my $80 objective.

Nice bargain, can you indicate me the item number that I look your model.

[aduncanson]

Here is the item that I bought 180373725418. I had noticed that they seem to no longer have a 750 VA model in their line. It is a beast.

Three smaller units should work, but like Rick I am wondering exactly what color correction you need. I am not sure that fluorescents change color with voltage fluctuations the way that incandescents do. Their (frequently poor) color seems to be determined by the phosphors that are used. The pernicious thing about power fluctuations in the darkroom is their unpredictability and the need to redo prints. When shooting digital, you should be able to notice the problem, either by eye at the time of the exposure or by reviewing the captured image immediately after, then re-shoot immediately with little trouble. (Said just like somebody who does not have to put up with the problem.)

[rdenney]

Thanks, this is more clear now.
This will be quite big and heavy. I look at models and their VA on their website (http://www.sola-hevi-duty.com/products/powerconditioning/cvs.htm)

This sort of power conditioning requires large transformers, and they are indeed big and heavy.

The 1000VA model, considering a .6 power factor, would supply 600 watts continuous for compact fluorescent fixtures (the Sola models will handle momentary surges well above their rated output). That would be fine for the 480 watts consumed by three of the units you linked.

There is a 750VA model in the portable units, and I would definitely recommend that you use a portable unit. The hardwired units you linked will require installation by a qualified electrician. The 750VA model will be marginal with those lights at a .6 power factor, providing 450 watts instead of the required 480. But I'll bet they would handle it. And you should investigate the actual power factor of those fixtures--they might not be quite as bad as .6.

To power one of these fixtures, you need a 267VA supply. Again, their 250 might be sufficient, especially if the power factor is even a little higher than .6. But running 3 of the 500VA models would be less efficient than running one 1000VA model.

According to the specs, the 750VA model will draw about 9 amps, and the 1000VA model will draw about 12 amps. A typical branch circuit in a house is designed to supply 15 amps, so it should have no problem, as long as that branch isn't sharing the circuit with something else that is pulling very much current. If have a branch circuit rated at 20 amps, it will have more headroom. Anything greater than that will require a special plug. You could also run the unit from a 240VAC branch circuit (though you'd probably have to have this specially wired), in which case the above amperage requirements would be reduced by half. If your studio is in your basement and the power panel is nearby, having an electrician install a special circuit might not be that challenging. In that case, the hard-wired model might indeed be preferable. But I suspect you can just plug it into the wall, and make sure not to plug other power consumers into that same branch.

Rick "thinking it would just be easier to plug the lights into the wall and not worry about minor voltage fluctuations unless it becomes a noticeable problem" Denney

[Peter De Smidt]

Ginette,

What are you photographing with this setup? It's gotta be possible to get decent light from this type of things, as expensive professional units are available.

The output of regular fluorescent bulbs varies with the temperature of the bulbs. They start off fairly dim, get brighter when they warm up, and then get a little dimmer again when they get too warm. That's why when they're used in enlarger heads it's best to run them with a timer that has a light-output sensor, one that varies the time according to the light output. If the compact bulbs are the same, I doubt that using a voltage stabilizer will help much.

[Ginette]

I will try to explain a little more even if English is not my native language, please excuse the non-sense sentences!

I work on location for more than 2 months for photography a collection of sacred vases and other silver objects (like a bunch of spoons). It was taking full size objects pictures and also all the marks on it (vey tiny, some are not visible to the eye).

As silver and gold are highly reflective, I made my own diffusion tent and consider that my set-up didn't vary and that I should obtain consistent color output in my digital images.

So it is why I suspect that color variation (magenta-green axis) may be caused by voltage variation.

I choose theses compact bulbs because they didn't emit heat like tugsten and this can be dangerous for fire so close from my diffusion material ( ripstop nylon) and also for my own confort as I work very close to the lamps. Flashes will not be a good choice because I have really to see the exact light on the objets, really tricky to photography silver objects.

Lamps are open all days long or sometime closed for the lunch. I always let them open for at least 15 minutes before starting to take pictures.

Rdenney, you told about their "MCR Portable Series (http://www.sola-hevi-duty.com/products/powerconditioning/mcr_port.htm)" ? Is this will be appropriate for lamps, they didn't talk about in theirs applications.

[Peter De Smidt]

Having spent a good portion of the last year doing this type of thing for Kohler Company, couldn't you build your light tent and then use flash heads in, say, 20" dishes with diffusion caps on the dishes? That way what you get with the modeling lights would be very, very close to what you'd get with popping a flash. Compact flash bulbs have very poor CRIs, and even those with better CRIs give off light with a very spikey spectrum. And as I said before, I doubt that voltage fluctuations are causing the problem.

[Nathan Potter]

Ginette may not have adequately defined her problem. I think she implies above that the color temperature of her fluorescent source is varying over time and also has implied that this is due to a line voltage source variation. As mentioned above the light from fluorescents comes from the phosphor coating on the inside of the bulb. This is not a classic black body spectrum but emission from electronic transitions in a solid state material. As mentioned by others here and in other threads it is a spikey spectrum adjusted to produce a sort of equivalent 5000K + black body by mixing a selection of different phosphor emitters. People who use such fluorescents for photographic purposes use color correction filters to better approximate daylight.

I have never heard of significant color changes occuring while using such lights once the bulbs have stabilized or by variations in line voltage but I think other users of such bulbs may need to comment about this here.

Nate Potter, Harrington ME.

[Ginette]

Yes I was aware that fluorescent have not a full spectrum. I was thinking that this implicate that some colors may not be rendered exactly as they supposed to be but I expect that a given color reddition will be consistent.

[jp]

The other issue with fluorescents (and other non-incandescent lights) is the shutter speed. If you shoot a high shutter speed (probably unlikely for product photos), you can capture the lights going on and off in a 100/120hz flicker. (for each voltage peak in a sinewave.)

This is a real problem sometimes affecting random images when shooting sports indoors in existing light.

[rdenney]

For this sort of project, I would invest in real studio lights that have flash tubes mounted in the same heads as incandescent modeling lights. The modeling lights are small enough not to cause excessive heat, but large enough to render the effect.

This need not be that expensive. Some years ago, I bought a nicely complete Speedotron Brown Line 1600-ws system, including the power pack, two large heads, two small heads, and a wide assortment of modifiers. The cost of that was about the same as three of these fluorescent units. And because it is used, it will be worth about as much at the end of the project as at the beginning. (If you do buy an old flash system, make sure it either has or you buy extra a low-voltage sync interface.)

I would expect that these so-called daylight-corrected fluorescent tubes have a mix of phosphors that blend to produce the visual effect of a 5000K average. The actual effect of the color depends on the sensor's sensitivity to the various spectral spikes provided by those different phosphors--that may be different than our eyes, or even than a color balance meter. And if the phosphors start dim, brighten, and then ultimately dim a bit again as they warm up, then I would not be surprised if the different phosphor colors do so differently, which could cause a color shift during that warm-up process. I would want to leave the lights on for at least a half hour before expecting real consistency, but I don't see how that would be a problem in this sort of a setup. I just don't see that minor voltage fluctuations could be an issue.

I wonder if these lights were really intended for video or ebay-style product photography where critical color balance is not as important. (That will get the video gurus lighting their torches and grabbing their pitchforks.)

I never have to worry about color shifts with the flash tubes on my old Speedotron heads, though. They are a bit blue, but consistently so and easy to correct.

By the way, another way to obtain diffusion is to turn the lights into reflectors rather than shooting through diffusers, and sometimes that helps you solve a reflection problem, too. Obviously, part of the problem is seeing a reflection of the lights in the silver items you are photographing. I have photographed polished brass tubas, and am familiar with that issue.

Rick "who has faced similar problem situations in the past" Denney

[nolindan]

Whoa ...

The lamps in these softboxes are 4 x 40W CFL - being equivelant in light output to 4 x 40W incandescent.

The power draw is probably no more than 50W per softbox. Four boxes would be less than 200W total.

OTOH, 4 x 40W of CFL isn't a whole lot of light. If you used 75W equiv. CFL bulbs the power would be 90W (or less)/box. CFLs don't like heat - make sure there is adequate cooling before relamping with higher wattage bulbs.

You should test first to be sure that line voltage fluctuations are the real cause of the problem. If you can, borrow a 'Variac' that will let you vary the voltage to the lamps - take pictures at high voltage and low voltage and see if there is a color shift. Also, send an email to the softbox manufacturer and the manufacturer of the bulbs.

The first suspects in the case of a color shift are the film and the processing.

[rdenney]

Whoa ...

The lamps in these softboxes are 4 x 40W CFL - being equivelant in light output to 4 x 40W incandescent.

No, the bulbs are rated at 40 watts, and put out the light of a 140-watt incandescent bulb. They are rated for 2400 lumens of output. Here's the spec for the bulb by itself:

http://www.lincoinc168.com/brppphhirafl1.html

Rick "noting that this is the smallest CFL offered by this company" Denney

[Ginette]

No, the bulbs are rated at 40 watts, and put out the light of a 140-watt incandescent bulb. They are rated for 2400 lumens of output. Here's the spec for the bulb by itself:

http://www.lincoinc168.com/brppphhirafl1.html

Rick "noting that this is the smallest CFL offered by this company" Denney

In fact I use now these 45W ones (http://alzodigital.com/full_spectrum_lighting.htm) more closer to 5,500K daylight than others one which are super daylight 6,500K.
It is the max wattage indicated for the 4 sockets head. For close work, it is just right for me.
Looking at, they even said that the lamps are "FULL SPECTRUM LIGHT BULBS" but I don't trust this. CRI stated at 91.
My Minolta Color Meter give reading around 5,300 to 5500K for my set-up.

@ Nolindan
"The first suspects in the case of a color shift are the film and the processing." -`I'm in digital for this assignment. But we are not supposed to talk about this here :rolleyes:
But your idea to test the voltage variation is bright! Any suggestion for a Variac unit?

@rdenney
"The modeling lights are small enough not to cause excessive heat, but large enough to render the effect"
What will be approximatively the output of theses modeling lamps"?

[rdenney]

@rdenney
"The modeling lights are small enough not to cause excessive heat, but large enough to render the effect"
What will be approximatively the output of theses modeling lamps"?

I think mine are in the range of 25 watts or so. Maybe 40 for the big ones. The light output is enough to see the lighting effect, but much less, of course, than the flash tubes.

Rick "recognizing that these are pretty old-fashioned lights these days" Denney

[nolindan]

No, the bulbs are rated at 40 watts, and put out the light of a 140-watt incandescent bulb.

You're right, not that you need me to tell you...

I think I must have read 'equivalent to 140W incandescent' to be 'four bulbs are equivalent to 140W' and somehow missed the big '560W' in the title.

Getting old...

Anyways, neat bulbs. Think I will get some.

[aduncanson]

I had forgotten that this thread had ventured so far from my original topic. That does not bother me, it is not mine to direct. Never-the-less, I did want to complete the tale I started since there turned out to be a lesson to share.

I found a 750 VA rated Sola CVS transformer for a great price. After I wired it in (along with some other handy darkroom mods) I was disappointed that the enlarger lamp still dimmed noticeably during exposures. But NOT while focusing.

I took the implication to be that the contacts of my tired old, 1000W rated, Time-O-Lite P-72 timer were not up carrying the current demanded by the enlarging lamp. I might have cleaned up the Time-O-Lite, but my experience with that sort of thing is not good and I have been tempted to switch to one or another "f-stop" timer which is absolutely not rated to switch the Elwood's power. So I bought a contactor (relay) instead (for about half the price of the Sola by the way.) It is now wired in and my enlarging lamp output seems to be rock solid.

Perhaps, I did not need the Sola, but since I got it at a good price and am happy with the results, I have no complaints. However, others might want to consider how their timer might be degrading their enlarger's exposure consistency.

- Alan

[Peter De Smidt]

Glad you eventually figured it out. F-stop timers, such as those by RH Designs, are really wonderful, btw.

[neil poulsen]

. . . I suppose that I could look for a Zone VI timer, but that is not my preferred approach. Is there an inexpensive (~$80) voltage stabilizer available. Does anybody make due with a computer Uninteruptable Power Supply? . . .


FYI: Were you to get one, you would also need to get a sensor. They don't come with sensors, and the sensors are no longer available. Metrolux timers also become available on EBay from time to time. Again, still need to sensor.

[Robert Billups]

I have a Metrolux II complete with footswitch and nulling probe, and sensor for light head...in like new condition that I am selling. An incredible piece of equipment that is no longer being made. Find some literature on this and see what you think as it is much more than an exposure stabilizer. Since I bought it several years ago I no longer was faced with trying to hit a moving target when printing. Indredible!

I am prepared to take serious offers over a period of two weeks beginning March 8, 2010.

[danjenson]

Most computer UPS's I've investigated don't stabilize voltage. They just kick the battery-powered inverter in when the voltage runs outside the acceptable range. They also filter transients. But they expect voltage regulation to be done by the power supplies of the computers attached to them. Since most of those devices run on DC, the regulation in the supplies is much easier to do.

The Sola is a true AC regulator.



SolaHD offers variety of ferroresonant power conditioners to protect equipment from all power problems other than a complete loss of power.

[danjenson]

SolaHD offers variety of ferroresonant power conditioners to protect equipment from all power problems other than a complete loss of power.

http://www.clrwtr.com/Sola-Power-Conditioners.htm

[Eric Woodbury]

Light sensors for Zone VI timers can be made with common parts available today. They are nothing more than a photo diode, albeit a rather large one, with a light IR stopping filter. Sensors for MetroLux are available, as well, new from the manufacturer. Even a few MetroLux are still available from the manufacturer, even though the company is currrently on a hiatus for a bit longer, I realize. For this I apologize.

A few other notes about some of the above in no particular order and only to the first order of accuracy:

CFLs don't flicker in any real sense. They operate at much higher frequencies than line frequencies. CFLs don't change color with voltage, as noted. They change intensity with temperature and if there were multiple CFLs, they would be different intensities based on their local temperature.

With old timers (electric, not people) and big lamps (500W) a contactor is certainly a good idea. Too bad there is not some easy way to switch over to a low voltage halogen lamp. A lot more light per watt and the low voltage is easier to deal with usually. See lamps for big color enlargers.

Yes, tungsten bulbs are very low resistance for about 200 milliseconds after turn on. The helps them heat quickly. It also stresses the filament.

I would not run a 500W/120V tungsten bulb on DC. I believe the unidirectional current would cause filament migration and prematurely erode the filament.

Indeed, series regulators are bulky for high power. If you are rolling your own, consider a shunt regulator. This might be smaller, lighter, and cheaper, but requires some headroom. Just a thought.

I wouldn't worry too much about power regulation without testing first. Power in my neighborhood is quite stable.

Paper exposure is very sensitive to small variations in exposure. Repeatability needs to be about 1% or better. This is because the highlights are so dependent on the threshold of exposure. This is a good test for any system. Make several 'identical' exposure right at the threshold of exposure. Process together and see if you can tell the difference.

Have fun.