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| Newbie: windings relationship to voltage |
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| rthorntn:
Hi, So say I'm building a device, it must use 48v DC. Among other things the device will have a motor and direct acting solenoid, say i'm building them myself, I'm trying to figure out what makes a motor and/or solenoid a certain voltage, is the following correct: - they both use electromagnets? - they both use windings? - they both use inductors? So what governs the optimal voltage to be put through a motor or solenoid? Thanks. Richard |
| Brumby:
--- Quote from: rthorntn on September 02, 2018, 12:24:49 am ---Among other things the device will have a motor and direct acting solenoid, say i'm building them myself, I'm trying to figure out what makes a motor and/or solenoid a certain voltage, is the following correct: - they both use electromagnets? --- End quote --- Yes --- Quote --- - they both use windings? --- End quote --- Yes. Windings are what create an electromagnet. --- Quote --- - they both use inductors? --- End quote --- Inductance is a property arising from having a current flow through a conductor. Windings produce greater inductance because of the multiple turns of wire grouped together. --- Quote ---So what governs the optimal voltage to be put through a motor or solenoid? --- End quote --- Heat. A simplistic answer I know, but heat is often a limiting factor where voltage and/or current considerations look ok. The basic effectiveness of a motor or solenoid relate to the current flowing and the number of turns in each winding - but the geometry and materials used are also important. The actual calculations for designing your own motor and solenoid are something I will leave to the experts. We are bound to have someone here with a better handle on that than myself. However, if I want something particular, I'll just use my requirements and look up specifications of products already available. |
| IanB:
First you figure out how much current the device needs to do its job. Then you arrange that the resistance/impedance/reactance of the device is such as to limit the current to what is desired. For the solenoid it is just resistance, for the motor it will depend on load and speed. Also, most DC motors need some kind of control or regulation over their speed otherwise they will not run in the manner desired. You can't just stick a voltage on them and hope for the best. Even for solenoids, you might want to control them to vary between the pull-in force and the holding force so the coil doesn't overheat. |
| rthorntn:
Thanks, so for motors, current determines the torque, voltage determines the speed and the maximum voltage is therefore about efficiency and reliability? So in the same motor, provide it with either 5V or 12V and it will draw the same amps? If so, let's say the 12v motors current is 1A, so at 5V it will consume 5W and turn at "slow" RPM, at 12V it will consume 12W and turn at "fast" RPM (the torque will stay the same) but at 24v the extra speed will probably cause reliability issues? |
| IanB:
--- Quote from: rthorntn on September 02, 2018, 02:30:24 am ---Thanks, so for motors, current determines the torque, voltage determines the speed and the watts it can dissipate as heat is determined by its design? So in the same motor, provide it with either 5V or 12V and it will draw the same amps? If so, let's say the motors current is 1A, so at 5V it will consume 5W and turn at "slow" RPM, at 12V it will consume 12W and turn at "fast" RPM (the torque will stay the same) but it will also have to be able to handle the extra 7W of heat? So if you want a small 48v motor with low torque and high speed, to power a fan blade, it needs to be very low current, otherwise it will generate a lot of unnecessary torque and heat? --- End quote --- Well, no, I didn't say any of that. Also, an ideal motor is not supposed to dissipate any power as heat. Any heat is wasted power and represents a loss of efficiency. Of course real motors cannot be 100% efficient, but even so most of the electrical input power is supposed to leave as mechanical output power. Very little is supposed to be turned into heat. |
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