| Electronics > Beginners |
| Losses in inductors |
| (1/2) > >> |
| ZeroResistance:
So lets say I have a electromechanical relay with a coil rated for 12V and 12ohm, which means its rated wattage is 12W. If I give it 12VDC, a current of 1A flows thru the coil and it the magnetic energy attracts the contacts of the relay. However when I calculate the power I^2 * R lost in the resistance in the relay it turns out to be same as the rated power 12W. My question is if I give the relay 12w some of it is converted to mechanical energy and some is lost in the winding resistance. So would it be correct to say that if I use I^2 * R that would the power lost in the resistance of the winding of the relay. But then how does one deduce how much energy was converted to mechanical and how much was lost? TIA |
| Zero999:
Electrical energy is only converted to mechanical energy when the power is initially applied to the coil. Once the relay is activated, all of the energy from that point onwards is converted to heat. Relays also have hysteresis. 75% of the rated voltage is required to activate the relay, but after that, the voltage can be reduced to around 10% of the rating and the relay will remain energised. If the force and distance of travel required to switch the relay contacts, is known, then the amount of energy required to activate the relay can be calculated, which can be used to work out the efficiency. |
| ogden:
--- Quote from: Zero999 on January 21, 2019, 11:34:59 am ---If the force and distance of travel required to switch the relay contacts, is known, then the amount of energy required to activate the relay can be calculated, which can be used to work out the efficiency. --- End quote --- Relay is one of the most inefficient "motors" known. Who cares - it is 0.00000001% or 0.000001% efficient? Number is irrelevant anyway. |
| ZeroResistance:
--- Quote from: Zero999 on January 21, 2019, 11:34:59 am ---Electrical energy is only converted to mechanical energy when the power is initially applied to the coil. Once the relay is activated, all of the energy from that point onwards is converted to heat. Relays also have hysteresis. 75% of the rated voltage is required to activate the relay, but after that, the voltage can be reduced to around 10% of the rating and the relay will remain energised. If the force and distance of travel required to switch the relay contacts, is known, then the amount of energy required to activate the relay can be calculated, which can be used to work out the efficiency. --- End quote --- Isn't the current flowing into the coil and into its resistance while the relay is doing work in attracting the contact? |
| schmitt trigger:
This book, has an excellent explanation related to the energy conversion on a solenoid (which is what a relay is, a solenoid pushing some contacts): https://www.amazon.com/Electric-Machinery-Fitzgerald/dp/0073660094/ref=sr_1_2?s=books&ie=UTF8&qid=1548081614&sr=1-2&keywords=electric+machinery+fitzgerald |
| Navigation |
| Message Index |
| Next page |