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Author Topic: Problem with Century Starting Too Fast Don Furr Jedi Master Film Handler Posts: 509 From: Sun City, Ca USA Registered: Nov 2002 posted 02-15-2009 04:31 PM                     Here's the deal. I've just installed my newer SA/RE-3 equipment and noticed that motor is starting WAY to quickly. It's a GE 1/4 HP, 1800 rpm version. It has the "deep" flywheel installed but using 6K reels it snaps the film. It's coming up to 1800 rpm PDQ. Is there a cap kit or some other way to slow the start time? HELP!!  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 02-15-2009 04:54 PM                        Are you using floating-hub takeup reels? With 5" or larger hubs? Fixed-hub 6000' takeups _will_ snap the film unless you have the takeup tension set just perfectly. You really want the 7" floating-hub reels, but those can be hard to find. I just went through the "projector starts too fast" issue myself. I have the 1725 RPM async motors, for which there is a Century slow-start kit (resistor that goes between a start winding and the AC line). I don't know if these apply to the 1800 RPM motor, which is probably a sync motor. With the sync motor, you could use an inverter drive (TB Woods E-TRAC, or similar) to control the ramp-up.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-15-2009 05:21 PM                     You would want to also switch to a 3-phase motor if you went to a motor controller too. A poor man's slow start for a sync motor is a HIGH-WATTAGE resistor and a time-delay relay...have the resistor in line just for the first couple of seconds so it is more of a two-stage start. It isn't great but I've seen it work with some success. I much prefer inverter drive...very smooth starts. Steve  |  IP: Logged Don Furr Jedi Master Film Handler Posts: 509 From: Sun City, Ca USA Registered: Nov 2002 posted 02-15-2009 05:55 PM                     If I change this 1800 rpm motor to a 1725 non-sync will that fix the problem?  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 02-15-2009 06:22 PM                     I do some shift work at a drive in using a Century that unit has a 1725 rpm induction motor on it. Ramps up quite smoothly. It's the belt driven model, not the direct drive version. True, those Sync motors, esp those Leeson models, really get the rpms up quite quickly. -Monte  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-15-2009 06:30 PM                     You'll also have to replace the pulleys and drive belt to go to 1725rpm. Sync is the more desriable since it gives you perfect pitch. 1/4 hp is way too large!! About 1/5th to 1/3rd HP is better for a 35mm version. You can also place a large power resistor in series with the start capacitor or start winding depending on motor style to lower the start torque. Actually there IS a very good single phase motor controller that is British made. It will not work on capacitor start or run type motors though. Its speed is very accurate. Will get back on this tommrrow as we have them in the parts room. Mark  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-15-2009 06:48 PM                     I usually just put a 1.5ohm 200watt wirewound resistor in series with the motor and leave it there All it does is rob some of the starting torque and unless you have a low mains voltage its dropacross it while the motor is running is negligable  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-15-2009 07:21 PM                     I agree Gord. A wall dimmer will also work just fine on split phase motors and gives you variable adjustment of starting torque. I've never tried this on a sync motor though so can't say if it'd work or not. Mark  |  IP: Logged Don Furr Jedi Master Film Handler Posts: 509 From: Sun City, Ca USA Registered: Nov 2002 posted 02-15-2009 07:40 PM                     I just inspected a pair of newer Strong 5 Star sound heads....they both have 1/4 hp 1800 rpm motors, but there are two caps on top. What purpose does the 2nd cap. serve?  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 02-15-2009 07:51 PM                        That's a capacitor-start capacitor-run motor, then. Those have high starting torque, and the run capacitor ups their efficiency.  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 02-15-2009 08:05 PM                     quote: Mark Gulbrandsen A wall dimmer will also work just fine on split phase motors and gives you variable adjustment of starting torque. I've never tried this on a sync motor though so can't say if it'd work or not. Mark Um, slow your roll there Mark. A run of the mill wall dimmer is NOT rated to handle any kind of motor or inductive load, and would probably result in either the motor or the dimmer going up in smoke. Not something worth the risk, even if it might work... Dimmers made for low voltage track lighting MIGHT work if they can handle the current rating of the motor. Now a variac or the old style resistance dimmer would probably work well. However. any sort of setup as above assumes that there will be someone who knows what they're doing to actually start the motor, as leaving it unattended at low enough of a setting will burn up the motor. Better solution is to add the resistor to the start windings and leave the incoming line alone..or go to a three-phase motor and inverter. quote: Mark Gulbrandsen 1/4 hp is way too large!! About 1/5th to 1/3rd HP is better for a 35mm version. While I agree with this, why is virtually every projector set up from the factory with 1/4 horse motors?  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 02-15-2009 08:47 PM                        My Grandmother's old Maytag (with the wringer attached) had a 1/4 hp motor that is EXACTLY the same as the old Century R3 Hoover motor. "In those days" there was not the selection of models. Surely we used whatever motor was available. Louis  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 02-15-2009 08:57 PM                  Hot Tip, Mark: 1/3 hp is bigger than a 1/4 hp...  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 02-16-2009 12:21 PM                        |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-16-2009 01:18 PM                     quote: Tony Bandiera Jr Um, slow your roll there Mark. A run of the mill wall dimmer is NOT rated to handle any kind of motor or inductive load, and would probably result in either the motor or the dimmer going up in smoke. Not something worth the risk, even if it might work... HAve done it many times for location work. It actually works very good! The dimmer will blow before any damage could occur to the motor but a standard 15 amp wall dimmer works just fine. quote: Phil Hill Hot Tip, Mark: 1/3 hp is bigger than a 1/4 hp... I'm aware of that Phil. I was just stating the range of motors I've seen on Centurys over the years. Mark  |  IP: Logged

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