Film-Tech Forum ARCHIVE: exhaust fan battery backup

This is topic exhaust fan battery backup in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Frank Cox (Member # 6258) on 11-13-2018, 12:17 AM:

On the (thankfully rare) occasions that the power goes off when I'm playing a movie, I always think that it would be wonderful if I had some kind of a battery backup on the exhaust fan that sucks air out of my lamphouse so the lamp doesn't just sit there in the heat.

The exhaust fan that I have is mounted on the ceiling and looks something like this:

I just have an ordinary light switch on the wall to turn that fan on and off.

Can anyone suggest the easiest way to get a battery backup into a setup like that?

Posted by Monte L Fullmer (Member # 2797) on 11-13-2018, 04:09 AM:

You can just disconnect the flex from the top of the unit and let the internal fans push the heat out for the time being.

Posted by Chris Markiewicz (Member # 1415) on 11-13-2018, 06:17 AM:

If you just need cooldown backup power maybe a good-sized UPS for that circuit? It only needs to provide power for about 10 to 15 minutes to cool the bulb.

Posted by Leo Enticknap (Member # 534) on 11-13-2018, 07:42 AM:

The first thing you need to figure out is what the power consumption of the fan is. If there isn't a data plate on it that tells you, a gizmo such as this one will.

Then you need to decide how long you want it to keep running if the power goes out. Let's say for example that the fan draws 2 amps (or 240 watts) and you want to keep it running for ten minutes. You then need to look for a UPS unit that can deliver two amps of line current for ten minutes. [url=https://www.amazon.com/dp/B0779LDRWZ/ref=sspa_dk_detail_3?psc=1&pd_rd_i=B0779LDRWZ&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=f0dedbe2-13c8-4136-a746-4398ed93cf0f&pd_rd_wg=rXLws&pf_rd_r=RC1Q9MKWCFH1B1XVG84Z&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&pd_rd_w=ND5QJ &pf_rd_i=desktop-dp-sims&pd_rd_r=707f748c-e749-11e8-8227-afb9b27696c9]This one[/url] claims to be good for 68 minutes at 100w, and so would be more than adequate for our example.

That having been said, UPS units are useless if either an automated safe shutdown sequence is initiated if the power goes out, or there is someone in the booth to do this manually. This means initiating the shutdown sequence of the projector (including lamp) and server, then cutting the fans after a predetermined interval. A PC connected to the UPS by USB that detects a power outage that way and then sends IP commands to the various devices would work. Some more sophisticated UPS units have serial and/or GPIO outputs, too, which could work directly with an automation controller to achieve the same thing.

Posted by Monte L Fullmer (Member # 2797) on 11-13-2018, 05:17 PM:

Sorry, I was taking the post as if a power drop in the exhaust fan circuit, not the entire building. Yes, a UPS would probably help.

Posted by Marcel Birgelen (Member # 6801) on 11-14-2018, 03:54 AM:

For equipment running on 12V, 24V or 48V I've used ordinary automotive lead batteries in combination with battery chargers in the past.

The problem will be getting a DC fan in the correct range and for this specific application. So the best bet is to connect the fan to an UPS, maybe a small UPS, you don't need a lot of kVA to keep the fan running for 15 or so minutes.

Posted by Tony Bandiera Jr (Member # 2365) on 11-14-2018, 08:09 PM:

Good idea to back up the main exhaust fan on a UPS, but a very important warning:

Make absolute certain that the UPS is a "True sinewave" output!

Common motors will not take kindly to the normal "modified sinewave" outputs of a typical UPS. The stepped waveform puts uneven current stresses on the motor...if you're lucky, the motor will only run hot and trip out its thermal overload protection. The usual outcome is a burned-up motor, shorted motor windings, and often catastrophic damage to the UPS itself.

You also MUST oversize the UPS to allow for the startup current of the motor, otherwise the UPS will shut down when the motor tries to start (or will blow internal fuses.)

A much safer and better bet would be a small generator (even the $400, 3200w one from Harbor Freight will do nicely) that you can quickly connect to the exhaust fan either by "cord and plug" or one of the small transfer panels available... THIS ONE would be ideal for this application. (You can find similar ones in Canada through your stores up there.)

I guess I would amend my advice to forget the UPS, one of the right specs and size would probably cost more than a generator and the transfer switch I linked above..and would be less reliable IMHO.

Posted by Carsten Kurz (Member # 5396) on 11-15-2018, 07:10 AM:

Why not have a common UPS for projector head (if applicable, not all projectors offer split supplies) and exhaust fan?

Our system does that.

That said, I think if the bulb goes off, there is not much further heat that needs to be extracted. I would think that the exhaust fan will run off slowly, not stop immediately, so the peak will still be extracted, and then the bulb will not contribute much more. Keep in mind, whatever you are adding, might become an additional single point of failure.

- Carsten

Posted by Gordon McLeod (Member # 33) on 11-15-2018, 07:35 AM:

All motorsthat are CSA approved made after 2000 must be invertor drive approved because almost all motor drives are a very choppy mess

Posted by Mark Gulbrandsen (Member # 72) on 11-15-2018, 10:22 AM:

This one would run it for around 8 to 10 hours or a full screening day. Along the wall behind that guy are rows and rows of batteries. This is just the inverter cabinet. This is at a transmitter site and is used to keep 14 high power DTV transmitters on the air for the ten minutes it takes to warm up this generator.... A UPS for an Imax booth is very similar in size to this.

Posted by Leo Enticknap (Member # 534) on 11-16-2018, 03:02 PM:

So if you wanted to perform an electric chair mass execution during a power outage, you'd be all set with one of these rigs!

Posted by Mark Gulbrandsen (Member # 72) on 11-16-2018, 04:57 PM:

Well... It's 440 volt 3=Phase!! Should do that job adequately...

Posted by Frank Cox (Member # 6258) on 11-16-2018, 05:01 PM:

"And did you enjoy the movie, Mr. Smith?"

"I got a big charge out of it, thanks."