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Author Topic: Strong 77 008 Power Supply Ventilation David Kilderry Master Film Handler Posts: 355 From: Melbourne Australia Registered: Sep 1999 posted 04-22-2004 11:41 PM                        We operate a Strong 77 008 continuous power supply (rectifier) at our Lunar Dandenong Drive-in Theatre here in Melbourne Australia. It is 160 amp maximum current and has the three rotary phase controls on the front. My question relates to the fan forced ventilation through the unit, at present ours sucks from the grill on the top of the unit and blows the hot air out of the bottom. Coventional wisdom would have this flow going in the other direction i.e. heat rises so pull from the bottom and evacuate from the top. Which way is the fan supposed to spin? Which way does yours go? The reason I ask is because this unit has activated the heat cut-off on several occasions on hot evenings. It need 2 - 3 minutes to cool and then will operate again. We run 5,000 watt xenon lamps at around 140 amps. We use Strong lamphouses on all three screens but with the other two using Ushio Xebex power supplies. The Strong power supply is the only one to exhibit this problem. David Kilderry  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 04-22-2004 11:47 PM                        I don't know about the Strong units, but sometimes large enclosed power supplies have their air intake at the top, so as not to suck in dirt and debris from the floor. I agree it's counter-intuitive, as heat rises.  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 04-22-2004 11:48 PM                        In most any device you want the fan to be sucking air into the unit, not blowing it out of the unit. So you want the fan turning in the direction that sucks air IN through the surface it is attached to. Cooling fans placed in the top are usually there to prevent heat build up in the top (caused by rising heat). It's almost always more effective to push air down and out the sides than depending on enough static presure to push the hot air out the top via a fan at the bottom.  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 04-23-2004 12:17 AM                        I wonder if your fan was replaced at some point with a motor that turns the wrong way? I've had several of those power supplies, and they all have pulled the air through the bottom & blown it out the top. It could also be that your safety switch needs replacing. Those things get touchy after awhile.  |  IP: Logged Rick Long Jedi Master Film Handler Posts: 759 From: Toronto, Ontario, Canada Registered: Nov 1999 posted 04-23-2004 12:18 AM                     These units have handles on them giving the misleading impression that "handles up" is the way to install them. The problem with this, as you have noticed, is that the air is taken in at the top of the unit, passed by a hot bridge, transformer, ect. and then exhausted through the bottom outlet, only to rise, as hot air is wont to do, and be sucked in again. This recycling of hot air results in the bridge-mounted heat sensors cutting out. (Hot-air recycling is not only limited to rectifiers - I have known several service managers who also had this habit). The cure is to lay the rectifiers flat so that the recylcing condition is eliminated. Be aware, however, that our experience is that once these heat sensors have been activated more than a couple of times, they become much more sensitive, reacting to normal heat variations as well. Probably best to replace these as well.  |  IP: Logged Ken Layton Phenomenal Film Handler Posts: 1452 From: Olympia, Wash. USA Registered: Sep 1999 posted 04-23-2004 12:49 AM                     We had two of those rectifiers at the Sunset Drive-in theater in Tumwater, Wash. I distinctly remember them blowing air out the top as Jack has stated.  |  IP: Logged David Kilderry Master Film Handler Posts: 355 From: Melbourne Australia Registered: Sep 1999 posted 04-23-2004 02:43 AM                        Excellent advice everyone, thank you. We will look to reversing the air flow and replacing the heat sensitive switch. It has activated several times now and it appears to have become more sensitive. The unit was installed two years ago after life at another drive-in, that was in an even hotter climate. David Kilderry  |  IP: Logged

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