Back EMF with potential relay operation
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- Опубліковано 19 жов 2016
- A short video to show you the higher voltage created by the induction motor on the compressor to disengage the potential relay.
Here we have interfaced the potential relay coil within the electrical box to show the back emf compared with source voltage in
(please note Australian rated power supply)
Thank you.
Here I am, back 4 years later brushing up on my back end understanding. Still a great video. Surprised there aren't more likes and comments.
Iv seen two different ways on wiring a potential relay. One where power starts from common and another where power Starts from the run winding and goes goes through common. Can you make a video showing how you wire one up
Yes i can make a vid, i have a relay case with all the components than can remote fire a CSR refrigeration motor . Now I have to go and make that for you. Thanks for viewing sir
Is common on a compressor neutral??
The way these compressors whould be wired is with the phase to the common via the thermal overload. This way phase is cut to the motor on a thermal overload fault. You can wire it with the common as a neutral feed out via the overload but in fault the compressor is still under a potential charge. Most systems I have seen bring phase to the overload and common providing you have the polarity right at the electrical box
I've been scratching my head, trying to better understand how the steady state back EMF can be higher than line voltage coming in. An intuitive first look sends a red flag, that our observation is trying to violate the first law of thermdynamics. In a single motor, back EMF from generator effects will naturally grow as rpm increases, to the point that there is an equal balance, with steady state rpm and low antegrade current overcoming mechanical resistance. I'm guessing that back EMF for a simple motor would only be higher during faster states of passive spin, such as regenerative braking of a vehicle where kinetic energy is converted back into stored energy in the battery. In these HVAC motors with dual windings, is this higher steady state voltage possible because antegrade current through the run winding overdrives the rotor, spinning so fast that the back EMF on the start windings exceed incoming voltage? Are potential relays ever used in motors that do not have dual windings?
Potential relays are used in refrigeration compressors that do not disengage the start winding. These are basically permanent split phase cspacitor motors thst use a capacitor start. The relay only disengages the start capacitor. I have not seen them anywhere else. They dont use current relays on high torque single phase compressors as this would add unwanted resistance to the run or main winding. Other than that most other types of older ac motors use centrifugal switch, like a pool pump or just simple split phase design. Thanks for asking