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Sherlock Ohms

Case of the Reversed Power Switches

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Beth Stackpole
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Blogger
Back to the basics
Beth Stackpole   2/17/2012 7:12:41 AM
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Now that is a Sherlock Ohms tale I can relate to. How many times does the root cause of the problem end up being something so basic, but likely often overlooked because you're searching for the complicated problem.

naperlou
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Blogger
Wiring Problems
naperlou   2/17/2012 9:55:55 AM
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Ah, the old crossed wiring problem.  While you might think this would be easy to catch, it obviously isn't.  It is good that they were able to diagnose and fix the problem without any long term consequences. 

 

When I was working on satellites we were warned about the reversed sign problem in attitude control systems.  Surprisingly one got by the extensive testing and the satellite was sent into deep space instead of into near earth orbit (oops!).

 

Rob Spiegel
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Re: Wiring Problems
Rob Spiegel   2/17/2012 3:12:53 PM
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Wow, Naperlou, how often does that happen? I would imagine the satellite mistake was a multi-million dollar goof. Can a mistake like that be corrected? Could the satellite be brought into near orbit?

Walter
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Silver
Case of the Reversed Power Switches
Walter   2/21/2012 1:15:01 PM
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This incident sounds a lot like the one I had contributed where one of three pumps was running without power.  There was a bad check valve and the other two were driving it backwards.  In the case of the Reversed Power Switches also, the one blower was driving the other backwards.  Just because a motor is spinning does not mean there is power on it.

KGround
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Iron
Re: Back to the basics
KGround   2/21/2012 4:48:59 PM
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Maybe this would be worth a case by itself, but since it is similar in nature, I add it here.

Today I discovered the hard way that you can reverse a split capacitor motor by forcing it to turn bbackwards while the motor is running.  If the connected equipment can overpower and stall the motor and cause it to turn backwards it will happily reverse direction and continue running in reverse until the next time the power is turned off and back on.  I had seen this before (not knowing exactly what i was seeing) on larger motors of several Hp with failing capacitors driving pumps against back pressure, but this present incident is with nearly a new fractional Hp motor.  Thanks to the folks at Brother tech support for educating me on this. 

George Merriman
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Iron
Similar problem
George Merriman   2/21/2012 5:29:28 PM
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Some time back I checked into a motel while on a road trip. The weather was mild, but the room became very warm after a few hours. I went to the air conditioning control and turned on the cooling. The room became warmer. The more I turned down the temperature the warmer the room became.

I called the desk and asked for another room. When the night manager came to help me move rooms he explained that they had been having similar problems since the air conditioning system was upgraded a few weeks earlier. The wiring for some of the room controls had interchanged so that my control was setting the temperature for another room and visa versa. Someone checked into the other room after I arrived and felt that the room was cool, so turned on the heat in my room. I started getting warm, so I turned on the cooling in the other room. One thing led toanother, and I was roasting while the other person was freezing!

Jon Titus
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Blogger
Re: Similar problem
Jon Titus   2/21/2012 6:01:29 PM
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In 1985, when Cahners Publishing Company, then the owner of Design News, moved into a new building the staff had a difficult time regulating the temperature. The HVAC people had mixed up the thermostats so the editorial groups regulated the temperature on the executive side of the building and vice versa.  The execs got cooler and thus turned up the heat on the editors (literally), who then adjusted their thermostat to further cool the execs. The initial solution was to place locked plastic enclosures around the thermostats, but the editors--many of whom were engineers--quickly subverted the "lock out" and the cycle repeated itself until someone got the HVAC guys in to check out the system. They uncrossed the controls.

Bill Carton
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Iron
Re: Similar problem
Bill Carton   2/21/2012 7:39:54 PM
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The crossed thermostat problem bit my wife and me one cold night in New England, but with a much faster time constant.

We had accidentally flipped over our dual-control electric blanket while remaking the bed.

Her control and mine were each slammed to opposite stops within 3 minutes.

Hilarity ensued as I did the troubleshooting. That was 30 years ago, and it still gets laughs at cocktail parties.

Tool_maker
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Platinum
First Job
Tool_maker   2/22/2012 6:50:39 AM
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I love stories of first real work experiences. We all start our jobs with book learning and abstract theories only to run slam into the real world. My first concerned a bandsaw with a spring loaded tensioner. Every time I broke a blade, the spring unloaded with a loud bang and was quickly followed by catcalls and ridicule from all of my new coworkers. Finally a veteran tool & die maker told me the problem was the blade welder on that particular saw and that I needed to weld the blades on another machine. But I was not told until I was properly humbled. Sort of an initiation  I guess.

Txema
User Rank
Iron
Stability
Txema   2/22/2012 9:33:43 AM
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I never thought of a case of unstable control by switching the remotes of HVAC systems... really funny!

Next time you need some cooling, try to roast your neighbour!!! -lol-

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