Voltage stabilizer: UPS or constant voltage transformers for regular bulbs?

[~andi]

I'm looking at voltage stabilization for plain old tungsten bulb enlarger running at mains with bulbs up to 250W and a timer-switcher (Mains outlet -> Stabilizer -> Timer -> Enlarger). My main goal is to get a steady 230V AC (or better yet 220V to prolong bulb life) even out short peaks/drops and noise induced by e.g. switching on other devices or switching power supplies. Research left me with the following options:

- constant voltage transformers (CVT). Transformer/capacitor in a resonance circuit. The only halfway affordable "under the table" product I could find in the EU is this: http://www.block.eu/en_US/products/589824.htm
- standard UPS. There are plenty of inexpensive ones. The discriminating factor for price seems to be the time the UPS can deliver energy when mains it out. Some allow regulation down to 220V (a plus).

I'm not certain which way to jump.

I found a couple of threads about this on apug mainly concerning cold light head fluctuations or LV/DC stabilized power supplies (not applicable here).

On the internet I did not find anything contradicting the use of an UPS, but also none recommending it for my kind of application. Some recommendations pro CVT, none against it. Also the CVT seems to interrupt the earth connection to the mains. I'm not sure if that is such a good idea (or do the capacitors take care of that?) The CVT is 410 Euros, a UPS can be had for 80 Euros.

Thank you very much
Andi

 

[Leigh B]

Hi Andi,

CVTs are ancient technology from the 1930s. They work well when you have a constant load.
With a transient load (enlarger lamp on/off) they will exhibit voltage drops and spikes at turn-on.
The magnitude and duration of those variations are not large, but they could affect exposure.

The only way to change the output voltage is with a variable transformer (Variac) between the CVT and the load. It lets you adjust the voltage to whatever you want, from 0 to full and even higher.

The UPS is obviously a more modern solution to the problem.
Some of these are spec'd to attenuate noise from the power source (AC line).
They are really not designed for your application, but should work fine.

They will also suffer from the turn-on transient as described for the CVT.
But given the active control circuitry, the magnitude and duration will be less.

Get one rated at least twice the power of the load (the enlarger lamp + timer + ???).

Also the CVT seems to interrupt the earth connection to the mains.

What you're seeing is a different type of transformer, called an isolation transformer. It unfortunately shares the name with vintage products that performed different functions.

The modern product protects patients in a hospital from transients on the AC power line.
These don't care whether the load works properly or not.
Avoid any product that interrupts the mains ground.

- Leigh

 

[bernard_L]

Be aware that some UPS units operate as pass-through as long as the line voltage is present (been there). This does not meet your purpoose.

 

[~andi]

Thanks Leigh, this confirms a vague feeling I had about the CVT units not being the right thing. Thanks for making it obvious and so eloquently at that. Those spikes would not be nice for the longevity of the lamps either, I guess. The ground-lift thing I came to mention because the CVT product linked in the original post seems to separate the earth from mains as well (the text says this somewhere and the plug on the picture does not have the ground lugs). I had a bad feeling about this.

I'll check out UPSs now. The maximum load would be 250W lamp (mostly 150W or 75W though) + Stopclock Pro (whatever little power that consumes) + LED safelight (probably negligible with a 135mA wall wart). So with 600-700W I should be fine.

Bernard, I didn't know that. Important information indeed. Thanks

Andi

 

[wombat2go]

I worked for a manufacturere of cvt ( ferro-resonant constant voltage transformers ), but more than 40 years ago.
I know they were sold to photo processors, and i don't recall switching transients being a problem with the ferroresonant type.

One time i went to a photo processor to see the problems they were having with color wedding photos, and a CVT solved it.
The regulator for photo printing using incandescent lamps needs to be of a type that accurately holds true rms regulation.

If the cvt has a resonant filter, it is inherently fairly accurate for true rms because the output waveform is pure
( As I recall, within 1% or so THD)
At that time I was working on development of solid state replacement for cvt, and we had difficulty getting accurate
and fast true rms feedback.

I see that resonant cvt are still available from the inventor and major supplier, and not too costly.
But if it is necessary to adjust the color temperature of the lamp, a downstream controller will be required.
(I thought the color enlargers already have that (?)

 

[tedr1]

Has the variation of the AC supply been quantified by use of a voltmeter? Where I am the AC supply is constant within a few percent, this amount may be smaller than the stability specifications of the CVT and UPS, which are designed to eliminate large variations of source voltage, it is possible there would be no net improvement.

 

[~andi]

Tedr1, I have no data except some ad hoc Voltage measurements and observations. I have a simple multimeter (metex M-4650) I trust, but its not capable of recording over time.

Here's the situation (there's no real problem, I'm just looking to optimize here and there):

- we have fairly stable voltage here of 246V. 230V is the nominal mains with a ~10% tolerance (so the OK range is 207-253V)
- I have a lot of bulbs which are rated for 220V, i'd like to use them longer
- color printing is of no concern, i do b/w only
- when the office laser printer is switchted on (cheap samsung b/w of recent vintage), the light flickers for a brief moment
- especially in the evenings those brief light flickers happen once in a while, it's really very very brief, maybe 1/4th of a second, but i really can't tell

With a CVT/UPS I thought could even out the supply a bit and have a fixed reference voltage for the bulbs and not the 10% tolerance, especially prolonging bulb life and as a precaution. The voltage going down below 230V I think is unlikely since the power companies here err on the + side because of grid stability.

Andi

 

[~andi]

Tedr1, I have no data except some ad hoc Voltage measurements and observations. I have a simple general purpose multimeter (metex M-4650) I trust, but its not capable of recording over time.

Here's the situation (there's no real problem, I'm just looking to optimize here and there):

- we have fairly stable (between days) voltage here of 246V. 230V is the nominal mains with a ~10% tolerance (so the OK range is 207-253V)
- I have no idea of brief interday fluctuations, always measured in the evenings
- I have a lot of bulbs which are rated for 220V, i'd like to use them longer
- color printing is of no concern, i do b/w only
- when the office laser printer is switchted on (cheap samsung b/w of recent vintage), the light flickers for a brief moment
- especially in the evenings those brief light flickers happen once in a while, it's really very very brief, maybe one cycle, but i really can't tell

With a CVT/UPS I thought could even out the supply a bit and have a fixed reference voltage for the bulbs and not the 10% tolerance, especially prolonging bulb life and as a precaution. The voltage going down below 230V is probably unlikely since the power companies here err on the plus side because of grid stability.

wombat, would it be possible to name the supplier you mentioned (or is it the one linked to in my initial post?)

Andi

 

[Chan Tran]

If your 250W bulb is a 24V unit I would use a 24VDC power supply. It would supply much more stable voltage than an AC voltage stabilizer.

 

[~andi]

Chan Tran, good thinking. Thanks. However, it's a 220V bulb, LED safelight and timer/switch (Stopclock Pro) all on mains. There are many options for a stabilized/regulated low DCV power supply. I prefer the tungsten opal bulbs as source of light though.

 

[ac12]

Most common UPS (that I know about) are pass though. So you get the the voltage fluctuations within the designed upper and lower bounds of the UPS.
When the voltage drops below the lower limit, then the UPS kicks in.
You then need to check the specific UPS, cuz the output could be a square wave or a stepped sine wave or sine wave. The cheaper UPS are likely to be square wave. Some electronic devices don't like the square wave, but a square wave should be fine for an incandescent bulb.

A full time UPS is a more specialized and expensive device.

 

[wombat2go]

Hi Andi,
I was looking at Sola, and they are available on Amazon.
However, for b/w, I would suggest you don't need such a regulator.
To check, you could cut some test strips and run them by varying the timer ( say in 5% steps)
Cover the paper with black card with a slot cut.
That will roughly simulate varying lamp voltage in 2.5% steps.
I have not done that in such small exposure changes and it would be useful to get an indication of the effect on the print.
Or, if you can borrow a variable autotransfomer, use that to do a real test of sensitivity to voltage.
Another way to test is to use a camera or spot meter to measure the reflection off the paper while changing voltage.
I used that method to check corner fall off on my old condensor.

 

[AgX]

- we have fairly stable (between days) voltage here of 246V.
- I have a lot of bulbs which are rated for 220V, i'd like to use them longer

For that a plain transformer would be sufficient.

 

[AgX]

If your 250W bulb is a 24V unit I would use a 24VDC power supply. It would supply much more stable voltage than an AC voltage stabilizer.

It only would do so if it is stabilized.

 

[CMoore]

It seems like A Lot of times, the AC Regulation is worse than what normally occurs on your Mains during the course of a day, but.....Check out the two links below. It is probably all 120 VAC because of where i live, but they probably have a link for what "Normal Countries" supply to their homes.
I am not saying any of it is right for you, but they are both well regarded names in their field.
It seems like, maybe, DC Regulation works to tighter specs than AC.?
Good Luck

Look and see what Furman has.
https://www.amazon.com/s/?ie=UTF8&k...vqmt=e&hvbmt=e&hvdev=c&ref=pd_sl_52f9pouvx5_e

and also Tripp-Lite
Dead Link Removed

 

[Leigh B]

It seems like, maybe, DC Regulation works to tighter specs than AC.?

As a general rule of design, DC regulators can be many orders of magnitude more accurate than AC regulators.

That's because DC regulators are dealing with steady-state conditions.
They can easily achieve accuracies of 0.01%, even tighter with slightly more effort.

In contrast, AC regulators are dealing with constantly-varying amplitude.
The instantaneous voltage is easily distorted by characteristics of the load.

- Leigh

 

[CMoore]

Hey Leigh-
Yeah, that sounds logical.
Thanks for the info.

If this is just to run his light source.....does anybody make a High Voltage, Regulated, DC Power Supply.?

 

[Leigh B]

does anybody make a High Voltage, Regulated, DC Power Supply.?

Of course.

There are hundreds of them available.
Check Mouser, Digi-Key, Newark, Allied, etc, and hold onto your wallet.

Dead Link Removed
www.digikey.com
www.newark.com
www.alliedelec.com

Then there's the question of how you would control that using the darkroom timer.
Most have remote control of some sort, but usually not designed for relay control.

- Leigh

 

[~andi]

Rrrr... more power. No, I'm pretty sure I don't want to run my enlarger on 230V DC... I doubt it would work very well with either. Afaik the tungsten bulbs are designed for AC. I feel I have to issue a warning here if someone without expert knowledge should find this thread in the future:

Dealing with high-voltage DC - you really, really, really, really should know what you're doing and be extra careful. It can be extremely dangerous.

I don't see a practical application in a hobby darkroom besides a tube amp for entertainment.

Andi

 

[AgX]

Afaik the tungsten bulbs are designed for AC.

Incandescant lamps work the same with AC or DC current.

Dealing with high-voltage DC - you really, really, really, really should know what you're doing and be extra careful. It can be extremely dangerous.

DC current is less dangerous than 50/60Hz AC current.

(Less dangerous, it does not mean safe... Though 120V DC is still tolerated as touchable by safety regulations!)

 

[zilch0md]

Rrrr... more power. No, I'm pretty sure I don't want to run my enlarger on 230V DC... I doubt it would work very well with either. Afaik the tungsten bulbs are designed for AC. I feel I have to issue a warning here if someone without expert knowledge should find this thread in the future:

Dealing with high-voltage DC - you really, really, really, really should know what you're doing and be extra careful. It can be extremely dangerous.

I don't see a practical application in a hobby darkroom besides a tube amp for entertainment.

Andi

I thought he was shopping for a 220V AC voltage regulator.

 

[AgX]

Yes, but then the idea came up that DC supplies could cope better with peaks in the mains.
However those supplies typically deliver 12/24V DC and not 120/230V DC.

A plain transformer 230V/220V then would not compensate mains fluctuations, and likely not short time peaks either. Though others would be more competent to discuss the latter (core saturation and such...)

 

[Chan Tran]

My old dichroic head in the Besseler CB7 has 2 200W bulbs but they are 24V. The enlarger originally came with a transformer to supply power to these bulb. I replaced the transformer with 2 24VDC 10A regulated power supplies. One for each bulb. The voltage is rock steady. In fact in coming AC power can be anywhere from 100-250V and the output is still 24VDC.

 

[~andi]

Thank you very much to all of you for your help and input.

I have my solution: Variac for the 220V bulbs.
I conclude stabilization is not worth the effort in my case.


Andi

 

[Gerald C Koch]

Are you sure that a voltage stabilizer is needed? The stability of the output from generating plants is far better than it was 50 years ago. Such a device MIGHT be useful when doing color printing but offers little utility for B&W even for VC papers.