Power Supply Thoughts. Curious on other peoples set ups in the booth.

[Mark Gulbrandsen]

One potential problem with the UPS idea: most UPSes are designed for computers and don't output a normal AC sine wave when on batteries. This "dirty" power is fine for computers, but may not be for sound equipment, video projectors, automation systems, etc.

I've heard of places like hospitals (which need uninterrupted power) using things like motor-generators with giant flywheels to provide continuous power if the street power fails and the generator(s) needs time to start and stabilize. This seems like overkill for a cinema, but maybe not for locations with regular power outages.

It depends on the type of UPS one buys if it outputs a sine or square wave. The ones I used are by Tripp-Lite and they are regenerative. So they put out a generated sine wave all the time.They have alkso been really reliable, only requiring normal dust and battery maintenance at regular intervals.....

[Frank Cox]

My wife has a fancy sewing machine. I've been told that I can't put it on a UPS so I just have it on a Tripplite surge suppressor, which I guess is the best I can do for it.

[Marcel Birgelen]

Like Mark indicated, it really depends on the type of UPS you're using. Essentially, there are three types of UPSes when it comes to the type of output they generate:

• Stepped square wave models: The cheapest form, they produce an output more like a stepped square wave than a pure sine wave.
• So called "modified sine wave" models, mostly found in the mid-range that produce a smoother output, but still not a perfect sine.
• True sine-wave UPSes, which produce a perfect sine wave output.

True Sine Waves are only useful in scenarios like this:

• Highly sensitive, analog measuring devices.
• Old audio-equipment without modern power supplies
• Devices running on electric motors running on AC, especially 3-phase models: This probably includes Frank's or rather Frank's wife's sowing machine. Electric motors driven directly from AC from the grid, tend to run very hot and can become damaged after prolonged use with choppy power supply.

Most modern equipment will handle choppy UPS power just fine though, as long as the energy delivered in one cycle is the same as a pure sine would've delivered. Most modern PSUs have sufficient capacitor capacity anyway and their output only needs to be a smooth DC feed.

As for flywheels: I'd never trust any really critical systems like hospital equipment to any passive-standby systems and the flywheel systems I've seen are usually of the passive-standby type. Also, flywheels also remember me of Chernobyl... where their idea of no-break was the turbines spinning out after losing steam power. We all know how that worked out...

[Steve Guttag]

There is a forth. The "Double Conversion" (aka Zero Transfer Time) UPSes that also product pure sine wave. A big distinction is that the protected devices never see a transition to UPS as they are always on the UPS power. With Line Interactive UPSes (which can have pure sine wave output) there is a finite transfer time between the failed city power and the UPS backup. Some devices will "see" this glitch and respond poorly.

Tripplite's worst feature is if its batteries fail, it doesn't self-bypass and put you back on city power, if available, it plays possum and appears COMPLETELY DEAD...no fan, no LEDs...nothing. Put in new batteries and magically, it comes back to life. They also can have fan failure, particularly if they are not kept clean so pay attention there too.

[Marcel Birgelen]

There is a forth. The "Double Conversion" (aka Zero Transfer Time) UPSes that also product pure sine wave. A big distinction is that the protected devices never see a transition to UPS as they are always on the UPS power. With Line Interactive UPSes (which can have pure sine wave output) there is a finite transfer time between the failed city power and the UPS backup. Some devices will "see" this glitch and respond poorly.

A Double-Conversion-type UPS itself doesn't say anything specific about the output it produces. Double-Conversion UPSes are usually the most expensive models and usually produce pure sine-waves though, but there is no such guarantee. Old models actually used a generator to produce the sine wave, as high-power semiconductor technology improved, most of them switched to high-power thyristors.

Like you indicated, any critical system should really be secured by double-conversion style zero-break systems, as they're constantly operating under load. It's not just the risk of the small interruption in the power-feed upsetting devices (many devices do have PSUs that can handle even a break or brownout of a few seconds pretty well), the problem is that the highest risks of batteries and other stuff failing is during the initial peak at transfer. Since there always is a gap and most devices tend to buffer for a few seconds, those devices need to make-up for that gap and will thus draw a much higher peak-load on the UPS during transfer. Some UPSes use supercaps to overcome this, but many don't...

[Steve Guttag]

Marcel, are you aware of any double-conversion type UPSes that don't produce a pure sine wave output?

[Marcel Birgelen]

Marcel, are you aware of any double-conversion type UPSes that don't produce a pure sine wave output?

Yes, we actually owned a couple of them. Those were MGE branded Galaxy UPSes, I think they were commissioned around 2003, both in the 10kVA range, which used to power our equipment room with our VMWare server farm and storage. While being true on-line UPSes, the output those units generated wasn't a perfect sine on the scope, even with zero load on them. Apparently, later models produced a pure sine wave output and there was an "i" version, targeted at medical solutions that did. They have since been replaced with a bunch of APCs, which do produce a pure sine, which we located in a "shed" outside. I don't like the notion of having such large batteries in the same room we store a lot of data...

Maybe you heard about the recent datacenter fire in France at one of the biggest cloud providers? According to recent updates, the fire most likely started in one of their UPSes. I've seen buildings burning down due to UPS fires before...

[Gary Wachter]

Check out Eaton Double Conversions UPS series. They don't suffer from the APC battery charging issues and "going dead when needing it most" Tripp-Lites. They also have a great single rack mount transfer switch / PDU (EATS120) with programmable transfers, power and environmental monitoring. Feed one input from the UPS and the other from Utility (or another UPS).

[Mark Gulbrandsen]

Check out Eaton Double Conversions UPS series. They don't suffer from the APC battery charging issues and "going dead when needing it most" Tripp-Lites. They also have a great single rack mount transfer switch / PDU (EATS120) with programmable transfers, power and environmental monitoring. Feed one input from the UPS and the other from Utility (or another UPS).

Yes, I almost went with them originally, but went with the Tripp Lite's instead because the availability was a lot better. BTW, Tripp Lite makes basically the same rack mount transfer switch as Eaton does. All but a few of my customers just elected not to get them. But on the other hand I have only had a few go dead due to bad batteries, and that was out of over 300 installed.

[Marcel Birgelen]

Models differ between Europe and the U.S. (different voltages and different sockets), but over here Tripp-Lite and EATON STSes are actually the same models, as in, Tripp-Lite STSes are built by EATON. Also, EATON quite recently acquired Tripp-Lite.

[Steve Guttag]

The problem with most ATS (Automatic Transfer Switch) is that they are much more complicated than they need to be for MOST installations. They are trying to second-guess the UPS' power and have a lot of uneeded sophistication built into them (checking frequency of the power, voltage range...etc.) and, as such have their own set of timings before switching. All of this comes at, what I consider, a very hefty cost. Price out most ATSes and you will be shocked. You could pay more for an ATS than for the UPS! All that MOST systems need is a simple relay with the coil of that relay powered by the primary power (UPS) and if that power drops out, so does the relay leaving you with city power on the normally closed contacts of the relay. We're talking about maybe $50 or so technology for a relay, box and appropriate cords/receptacles. It shouldn't be $700-$1000 just to back up a UPS that doesn't fail gracefully. I'm sure there are systems that need the extra sophistication offered by these high-dollar ATSes but that just can't be the vast majority. It definitely doesn't have to be for digital cinema. I've done the relay based system and it works perfectly and have had zero lost shows as a result of a UPS failure. Conversely, I've had commercial ATSes cause show issues due their over-thinking how/when to switch to the secondary power, particularly in a brown-out situation where it sees primary glitch (transferring itself to battery back up) and the secondary go/come back.

[Marcel Birgelen]

ATSes and STSes come in all sizes, flavors and price ranges. Many of them are pretty complex and need to be, especially the three-phase ones for big zero-break installations where stuff matters. You don't want your hospital to go dark when one unmonitored phase craps out, for example.

But yes, I agree that most in-rack STS/ATSes are over-engineered and overly-expensive as a result. There is also a bit lack of competition in this field. I think it's nice that most newer ones do have an IP interface, but even this doesn't justify the costs of most of those 1U in-rack things anno 2021.