UPS Battery Backup for Enlarger Power Smoothing

Dan Rainer · Friday at 10:00 AM

I have a Beseler 67 running off of a GFCI outlet in my bathroom darkroom. Recently, I've noticed that the lights in my house flicker ever so slightly when the AC cuts on. I'm a obviously bit nervous about this causing voltage instability during printing. Would plugging my Beseler into a cheap UPS battery backup be sufficient to smooth out a brief voltage drop?

koraks · Friday at 10:07 AM

Depends. The UPS will basically be a passthrough from your outlet to your enlarger as long as there's no blackout/brownout on the outlet. That means that any dips caused by the A/C coming on etc. will make it downstream to your enlarger just the same if (!) that's what's currently happening.

What you could do, is disconnect the UPS from the outlet when you're using the enlarger so that you work off of its battery. That should provide the enlarger with stable voltage. For a typical enlarger bulb this will be ok and it's 99.5% certain that any other associated electronics (timers etc.) will be fine with this as well. There's a tiny chance that some electronics may not like the AC waveform the UPS generates, which in some cases is more of a block wave than a sine wave, or something in-between, and/or something with lots of harmonics. Again, the chance that this will create any problems is small to the point of negligible. And a halogen enlarger bulb will be fine for sure. When the enlarger is not in use you can (temporarily) plug the UPS back into its outlet to allow it to recharge.

Note that many old-fashioned stabilizers like the big units made in the past by e.g. DeVere and possibly also the Durst stabilizers may not tackle these brief dips since they respond too slowly (the variac-based Deveres) or may not have sufficient headroom to buffer a brief brownout condition (the Durst units). So keep this in mind in case you have second thoughts about the UPS solution.

beemermark · Friday at 10:15 AM

You should be worried about why your air conditioner overloads your house electrical system. Applying a band aid to your enlarger doesn’t fix the larger issue. Fluctuating voltages negatively affects the electronics in your computer, appliances, TV, etc. Periodic voltage drops (and amperage increases) is also hard on the electrical circuit breakers leading to premature failure.

Dan Rainer · Friday at 10:23 AM

koraks said:
Depends. The UPS will basically be a passthrough from your outlet to your enlarger as long as there's no blackout/brownout on the outlet. That means that any dips caused by the A/C coming on etc. will make it downstream to your enlarger just the same if (!) that's what's currently happening.

What you could do, is disconnect the UPS from the outlet when you're using the enlarger so that you work off of its battery. That should provide the enlarger with stable voltage. For a typical enlarger bulb this will be ok and it's 99.5% certain that any other associated electronics (timers etc.) will be fine with this as well. There's a tiny chance that some electronics may not like the AC waveform the UPS generates, which in some cases is more of a block wave than a sine wave, or something in-between, and/or something with lots of harmonics. Again, the chance that this will create any problems is small to the point of negligible. And a halogen enlarger bulb will be fine for sure. When the enlarger is not in use you can (temporarily) plug the UPS back into its outlet to allow it to recharge.

Note that many old-fashioned stabilizers like the big units made in the past by e.g. DeVere and possibly also the Durst stabilizers may not tackle these brief dips since they respond too slowly (the variac-based Deveres) or may not have sufficient headroom to buffer a brief brownout condition (the Durst units). So keep this in mind in case you have second thoughts about the UPS solution.

I'm a bit concerned that a cheap UPS will have that horrible beeping alarm whenever its unplugged, with no option to turn it off. Not too pleasant while printing. I was hoping that a UPS would feed the power through a bank of large capacitors, even while not pulling off battery power. Thus smoothing out any power irregularities. I've also looked at isolation transformers (mostly medical surplus), but I've been hesitant to pull the trigger:

https://ebay.us/m/4TAe4S

beemermark said:
You should be worried about why your air conditioner overloads your house electrical system. Applying a band aid to your enlarger doesn’t fix the larger issue. Fluctuating voltages negatively affects the electronics in your computer, appliances, TV, etc. Periodic voltage drops (and amperage increases) is also hard on the electrical circuit breakers leading to premature failure.

I live in an older rental property, so there's not too much I can do unfortunately. I've brought it up to my landlord and he seems resistant to doing much about it.

koraks · Friday at 11:18 AM

Dan Rainer said:
I was hoping that a UPS would feed the power through a bank of large capacitors, even while not pulling off battery power.

They don't work that way, at least definitely not the cheaper units. Those generally switch over between grid and battery power depending on whether there's voltage on the outlet. Switching used to be a relay but is probably an IGBT these days. This also implies that there's a brief switchover blackout, but this is not very relevant for your application.

The beeping I can understand as a concern; you could just unsolder/disconnect/destroy the beeper.

Dan Rainer said:
I've also looked at isolation transformers (mostly medical surplus)

An isolation transformer is just a 1:1 transformer. Whatever fluctuations on the primary side will be transferred to the secondary side. It has no buffering or filtering function etc.

qqphot · Friday at 12:59 PM

I run my Durst 184 8x10 enlarger using essentially a UPS system as power source, but it is of the kind which is continuously online; that is to say, power to the load is always supplied by the inverter, and power to the inverter is supplied either by mains power or battery if mains should fail. I started using this because the original power conditioner for the Durst color head caught on fire quite spectacularly during a printing session once. Sagging voltage with incandescent lamps can be a problem especially for color printing since not only intensity but color temperature changes with voltage.

This kind of UPS is suitable for stabilizing power to an enlarger because the output is quite closely regulated and not subject to voltage drop due to external loads. A UPS which passes mains power directly to the load until mains power fails would need to be forced to run on battery while printing.

Kino · Friday at 1:31 PM

I tried a Sola Constant Voltage transformer on my enlarger with a digital Gralab timer and the timer freaked-out. I suspect a mechanical timer would have been fine, but no-go for the Gralab...

bobequus · Friday at 4:42 PM

I think this overthinking a small problem. For B&W a small fluctuation during a 15-30 second exposure will most likely not be visible. I'd venture to say my Time-O-Light has more variability. But to be sure. . .
Next time you are printing and you see this happen, immediately make a second print with the exact exposure. Process the same as the one which saw the glitch. Compare. See a difference? Then a constant voltage setup (not UPS) might be called for. Might save a buck or two.
Bobby

AnselMortensen · Friday at 4:58 PM

The root cause of this issue as an A/C compressor starting (or over-amping).
Maybe try setting the thermostat to a higher setting while printing to keep the compressor from kicking in ?
You could even pre-cool the house to a lower setting before the printing session.

hwy17 · Friday at 5:00 PM

If I wanted to achieve the goal of a power supply that is unaffected by source power supply voltage fluctuations I would use a double conversion system.

You can get double conversion aka "always online" packaged UPS systems.

I would probably build one instead out of a Meanwell 12v power supply, lead acid battery, and a victron phoenix or morningstar inverter.

I don't have the darkroom experience to say whether this is worthwhile though.

I disagree with the notion that minor light dimming in a house when the A/C kicks on is always cause for concern. It won't happen with a very well built electrical system but it's fairly common and well tolerated by TVs, Computers, etc. as long as voltage isn't dipping below around 110.

DREW WILEY · Friday at 5:08 PM

Ansel M's solution is the most logical. Just turn off the AC when the enlarger is being used. It sounds like your circuit is just plain overloaded. Not a good sign in general. Going down a path more expensive than your enlarger itself might or might not improve anything, print-wise.

hwy17 · Friday at 5:10 PM

Dan Rainer said:
I've also looked at isolation transformers (mostly medical surplus), but I've been hesitant to pull the trigger

A medical isolation transformer will provide very little compensation for this. During the precise moment that the A/C kicks on there is a much larger voltage dip for a fraction of a second that the isolation transformer will absorb some of, so you would see slightly less instantaneous flicker, but as far as brightness while A/C compressor is on vs brightness when A/C compressor is off you would still have the same steady difference through an isolation transformer. They're 1:1 voltage in voltage out.

Nicholas Lindan · Friday at 6:25 PM

As bobequus stated, a small dip as the A/C turns on will have little to no effect. If, however, the A/C drags the power line down when it operates then you may see some effect. If the living room lights don't dim a little when the A/C kicks in then you are OK.

The common UPS units for small computers won't be any help as they are made to switch over to battery power when the power fails and not when it dips by a few volts. You can expect a 10-20V dip when the system is running on the battery. An expensive unit that runs on the battery all the time, using the power line to keep the battery charged, gets around the problem but this is massive overkill.

If the power line voltage gets dragged down by the AC, and not merely blipped, then the most cost effective solution is a ferroresonant constant voltage transformer; these are commonly made by Sola. Don't get a larger ferro than you need - ferros draw a constant current independent of the output load, so a 500W ferro with a 75W enlarger bulb will draw 500W; get a 75W ferro instead.

Plug the transformer into the timer and the enlarger into the transformer. If this sends your timer into a tizzy then you need a new timer.

gordrob · Friday at 7:32 PM

I am using a Sola 500 watt Constant Voltage Transformer and have it wired as set out by Nicholas. It is connected to a GraLab 500 digital timer and have never had any issues with the timer acting up. The transformer only draws current when the GraLab is turned on for printing

Don_ih · Friday at 8:25 PM

I wouldn't worry about the power fluctuation impacting enlarging. I can't see how it could be significant unless your exposures were less than 2 seconds.

Nicholas Lindan · Friday at 9:44 PM

Nicholas Lindan said:
....If the living room lights don't dim a little when the A/C kicks in then you are OK....

That should read: "...don't dim when the A/C is on then you are OK..." A slight dimming when it kicks in can be ignored.

MattKing · Friday at 9:50 PM

FWIW, this is much more of a potential concern if you are printing colour than black and white.
Or of course you are working in a high volume production environment.

UPS Battery Backup for Enlarger Power Smoothing

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