Bad Texas Instruments Pressure Sensor

Discussion in 'Off-Topic' started by #12, Jun 7, 2014.

  1. #12

    Thread Starter Expert

    Nov 30, 2010
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    Post #17: "If you can remember the commercial on TV, don't buy that brand". You will end up paying for the advertising. Even if you catch a big brand name product on sale and the price is reasonably close to the other options, parts you can only buy from the manufacturer will be incredibly expensive.

    From people that do Trane air conditioners regularly:
    The Trane motor in this example has an average MTBF of 3-5 years.
    Replacing only the control module (over $200) results in a 30% fail rate in the next 90 days. That causes a free house call and an unhappy customer.
    You can't just drop in a PSC motor of the same HP and RPM ratings because the squirrel cage is so over sized that a generic motor doesn't stand a chance.

    This is a constant torque design for a stepper motor; 4 permanent magnets on the rotor and 18 coils around the perimeter. This means the RPM of the squirrel cage can be very low. The RPM is pretty much not related to the number of poles. Great for efficiency and quiet running. (A big fan running slowly is a lot more efficient than a small fan running fast.) Power2/Power1 = (RPM2/RPM1)^3 That means a little more RPM costs a lot more power. The squirrel cage that came with this machine needs about 2.3 HP at 1050 RPM. The label on the OEM motor says 1050 RPM and 1/3 HP. This one must be running at about 450 PRM to use up 1/3 HP. Calculating from the 18 coils around the perimeter, the motor would sync at 400 RPM on a 60Hz power supply if it was a PSC motor. I don't think I have ever seen a PSC motor rated at 400 RPM, therefore, I can't buy one.

    Each Trane fan motor is programmed by Trane. For example, 13 minutes to go from 60% power to 100% power, in order to dump more humidity in the first 13 minutes of runtime. This can be achieved by simply running a PSC motor at a lower speed than the maximum rated speed, and this method has been working properly for at least 50 years. It's called, "Sensible heat ratio", as in: How much energy is dedicated to Fahrenheit change compared to how much energy is dedicated to humidity removal.

    And, no, I didn't just pull these numbers out of my a$$. This is the result of 3 days of part time research on the Internet, personal interviews, and reference books accumulated over the last 30 years.

    "It's hard to stop a Trane", unless you don't have $500 for a 1/3 HP fan motor.
     
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