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Author Topic: motor caught on fire! any idea why? Gavin Lewarne Master Film Handler Posts: 278 From: Plymouth, UK Registered: Aug 2009 posted 12-15-2009 05:20 AM                     Hi All, in the middle of a show last week one of our projectors drive motors literally caught on fire. Lickly nobody was hurt and the only damage seems to be to the motor itself. My question is this, why did it do it? As soon as i recieved the phone call i rushed in to do a damage assesment. When i got there the fire service were letting people back into the building and doing a safety check. Once they left, i isolated all power to that machine and removed the motor. Interestingly enough, the projector mechanism is undamaged and rotated freely with no roughness or binding. The drive belt was intact and in good condition. The motor housing had not mooved and even the motor itself was freely rotating. So what caused the blaze? apparently the flames were about 4 feet high and green, as if the coper in the windings itself was burning. The machine was running fine for 20 minutes when the motor just stopped and caught ablaze. I have checked the inverter output and all electrical wiring to the motor controls and within the motor itself and cannot find a problem. The motor is less than 2 years old and very clean. Got a new one on the way so will be up and running tomorrow, but i just dont understand why it happened Is worrying for the future considering the other machine has an identical motor on it  |  IP: Logged Rick Raskin Phenomenal Film Handler Posts: 1100 From: Manassas Virginia Registered: Jan 2003 posted 12-15-2009 07:21 AM                     Without dis-assembly it would be difficult to tell. You could do a visual of the internal components and look for damage. If there is a warranty, let the manufacturer or supplier deal with it.  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 12-15-2009 07:49 AM                     You may have had a motor that was not rated for invertor control, overheated windings and breakdown of insulation can be the end result.  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 12-15-2009 09:24 AM                        How long is the wiring run between the inverter and the motor, and is there a reactor (inductor) installed between the inverter and the motor? Reiterating what Richard said, was this motor rated for inverter use? An inverter connected to a motor with a short length of wiring (under 10 feet or so) won't cause any trouble, regardless of the motor's insulation rating. Problems start popping up with longer lengths of wiring between the inverter and motor, where the distributed capacitance in the wiring combines with the inductance of the motor windings to form a resonant tank circuit, resulting in high voltage spikes at the inverter output's waveform transitions (the inverter sends out a 6kHz or so square wave). These spikes may arc over between windings, eventually causing insulation breakdown, shorted turns, overheating, and finally, fire. That having been said, the overcurrent protection in the inverter should have protected against fire. The only case where it wouldn't have would be if you are using an inverter meant for a larger motor without properly reducing the inverter's overcurrent setting based on the reduced motor size.  |  IP: Logged Jim Cassedy Phenomenal Film Handler Posts: 1661 From: San Francisco, CA Registered: Dec 2006 posted 12-15-2009 09:49 AM                     A couple of years ago, I had a Century drive motor catch fire after the centrifugal switch on the starting winding went bad and "stuck". Since the start winding was never meant for continuous duty, the motor overheated and began melting the insulation off of the motor windings. Of course, this happened on my night off. (Staff Quote: "Gee, we smelled something burning but didn't think it was anything important.") For some reason it took a while for the main circuit breaker to kick off, and by that time even some of insulation on the wires inside the BX type cable running to the motor had started to melt. From what I was told, smoke and blue-green sparks began shooting from the motor before the whole thing seized and the breaker tripped. It took over a week to get the stench out of the booth. I had to replace the motor and a wholebunca wiring, including an external "slow start" circuit which totally melted.  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 12-15-2009 09:52 AM                        If he's running an inverter, then this is a 3 phase motor (induction or synchronous), and there's no centrifugal switch.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 12-15-2009 10:28 AM                     The older OEM motors on cnemecanica did hve issues with invertor control especially the low RPM ones as the little fan on the end of the shaft doesn't keep it cool enough I have usually put a small muffin fan on the end of those motors  |  IP: Logged Gavin Lewarne Master Film Handler Posts: 278 From: Plymouth, UK Registered: Aug 2009 posted 12-15-2009 11:43 AM                     i only have a 4ft cable run between inverter and the motor, so thats not the issue. Inverter still checks out just fine, as does an insulation test on the motor wiring. The circuit breaker never tripped! (but that too checks out OK) both motorts are rated for inverter use. The motor was only 2 years old and has never given us a bit of trouble until saturdays fiasco. The motor on the other machine is of similar age. and yes, the bloody stench is taking ages to go!  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 12-15-2009 12:05 PM                     What're the manufacturer and model of both the inverter and the motor? --jhawk  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 12-15-2009 12:11 PM                        It could just have been a manufacturing defect that took a while to become evident. There doesn't seem like anything about the installation that could have caused the motor to burn (reasonable wiring, no locked shafts), although it is odd that the inverter kept the motor running during what should have been an overcurrent condition. Then again, it could have been a high-resistance fault that generated enough heat to start the fire.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 12-17-2009 02:46 PM                        quote: Gavin Lewarne in the middle of a show last week one of our projectors drive motors literally caught on fire. Lickly nobody was hurt and the only damage seems to be to the motor itself. My question is this, why did it do it? Simple: It's the perversity of inanimate objects.  |  IP: Logged Gavin Lewarne Master Film Handler Posts: 278 From: Plymouth, UK Registered: Aug 2009 posted 12-17-2009 04:23 PM                     frank, do you mean how things that are not meant to break do so in a terrible way? yesterday, the battery on my dads car burst spewing acid all over the engine compartment. its a 6 month old beemer that now needs totally new engine electronics.  |  IP: Logged Ian Parfrey Phenomenal Film Handler Posts: 1049 From: Imbil Australia 26 deg 27' 42.66" S 152 deg 42' 23.40" E Registered: Feb 2009 posted 12-17-2009 05:10 PM                     Is there a possibility the problem is in the inverter and NOT the motor itself? A spontaneously combusting motor seems a rarity.  |  IP: Logged Rick Raskin Phenomenal Film Handler Posts: 1100 From: Manassas Virginia Registered: Jan 2003 posted 12-17-2009 05:41 PM                     Frank: I had a college prof who used that exact phrase. Today I guess it would be happens.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 12-17-2009 10:30 PM                     Was the motor properly fused, was the invertor fused? If the motor was thermally protected (internally fused) then the manufacturer may be liable.  |  IP: Logged

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