#76 - Three Ways Ohms can Lie

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Can Ohms Lie? Relying on resistance measurements can often lead to a misdiagnosis. Demonstration of how reactance, temperature coefficients, insulation breakdowns, and voltage thresholds can cause loads to act very differently when energized vs. statically measured. Ohms don't lie, but don't always give you the whole story. Link to Meter used in this video: amzn.to/480nyLZ
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This video is intended for experienced or supervised technicians. Always take appropriate safety precautions when dealing with live circuits. For informational purposes only. Utilize the concepts in this video at your own risk.
#appliancerepair, #hvacrepair, #electrician, #ohmslie, #inductivereactance, #temperaturecoefficient, #electricaldiagnostics
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Опубликовано:

22 июл 2024

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Комментарии : 10

@TheTechCircuit 7 месяцев назад

Ohms don't lie, but don't always give you the whole story. This video is intended for experienced or supervised technicians. Always take appropriate safety precautions when dealing with live circuits. For informational purposes only. Utilize the concepts in this video at your own risk. The Tech Circuit or Steve Morrison assumes no responsibility or liability for any errors or emissions in the content of this video. The information contained in this video is provided on an as is basis with no guarantees of completeness, accuracy, usefulness, or timeliness.

@uxwbill 7 месяцев назад

This video explained something I had wondered but not really thought about or checked against a schematic -- why some gas stoves leave their igniter running even after the burner was lit.

@TheTechCircuit 7 месяцев назад

I'm forcing the centrifugal switch inward with my left hand in the beginning of the video so as to disengage the start winding. Only the main (run) winding is being statically measured - as stated in the introduction. That's the same winding the current flows through when the motor is running at normal RPM.

@kabandajamir9844 4 месяца назад

Please make a video on metal oxide varistor testing

@mikeadler434 4 месяца назад

👍👍

@DrHarryT 7 месяцев назад

Ohms law never lies, that's why they call it "Law" anyone who is worth their weight know that there are operational variables with respect to a device under load. For example, an incandescent lamp when the resistance is measured and the math [Ohms Law] is applied would indicate that the lamp will draw much more current than it actually does in operation. This is because as the filament get hotter its resistance goes down. In the case of the motor there is inductance and eddy currents and impedance that must be taken into consideration. Try locking the motor shaft and depressing the centrifugal switch into the run position and then measure the current, it then probably would draw 34A.

@TheTechCircuit 7 месяцев назад

Yep. That was the point of the video. To explain all that, and what the colloquial term "ohms lie" means.

@mohnewyork1082 7 месяцев назад

So mean to test this components you have to energize them and measure after few minutes measure ohm's? And use ohms low ?

@TheTechCircuit 7 месяцев назад

Some components, like those highlighted in the video act differently when energized vs. when you test them with an ohmmeter. In such cases, their behavior can be better determined by using current draw while energized.

@paradiselost9946 7 месяцев назад

theres another factor with the motor... BEMF. more pronounced if it was a brushed universal motor, admittedly. um... theres another strange effect ive seen with resistors, and that was on the gate of FETs... as per datasheet, you throw in a 4R7, and thats cool. scope the signal, and you see the ideal "square wave" with no ringing. reduce that resistance, and the ringing increases until you overdo the maximum ratings... oops. but increase it... 10R... start seeing that square wave developing a curve... and then, at say, 27R... the resistor starts burning out... woah woah woah! gotta go from 1W to a 5W! wtf? and then start exceeding 100R, and you can reduce that wattage again... (it does depend on the fet of course, take all numbers with a grain of salt...) it makes sense when you start thinking about it... at a low resistance, there may be a large current, gate charge... but the voltage drop across the resistor and the power dissipated is quite low. as it increases, the voltage drop and dissipation increases... until finally, it reaches a point that its simply limiting the current and at that point, dissipation reduces again.