I'm creating a motorized Chinese turning table aka a motorized Lazy Susan but i'm worried that if the circuit stops powering the wheel to a direction, the table will continue to turn due to its momentum and create reverse voltage which will end up damaging the circuit.
it would really help if someone would explain me why i don't have to worry or what i can do to prevent this. thanks in advance.
(see attachment for a nice drawing.)
electrical components for the project include:
Wall socket to 12V DC adapter, max3A
You always have to have protection against reverse voltage because the inductance of the motor windings alone can produce it. This has nothing to do with the action of the motor as a generator when there is kickback - especially through a gear chain that can't really function efficiently in reverse.
Please post your circuit for more detailed feedback.
You chose a good H-Bridge driver. It has a nice protection circuit built in for inductive loads. They use the "MOSFET substrate diodes" as the protection circuit. They tell you the H-bridge output Connects directly to the motor or other inductive load. Breaking can take several forms, turn off the drives and that I believe gives you the soft braking, this is causing the back emf to be passed through the substrate diodes. Enabling the outputs of both 1/2 bridges to high or low will force dynamic breaking. Dynamic braking works because when the power is turned off to the motor the load causes the motor to spin making it a generator. Shorting this current causes it to brake rapidly but less and less as the speed diminished. When the motor is stopped there is no breaking. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
Note here that there is no "reverse voltage" from a motor overrun. The back EMF of the motor is in the same direction as the applied voltage, when you open the switch, the voltage across the motor simply falls back to a lesser voltage as the motor continues spinning and the voltage across the switch is only a small proportion of the applied voltage at that point.
This is a completely different effect to that of interrupting the current through an inductor.
However this specifically applies to permanent magnet field motors, which is nevertheless the vast majority of small DC motors and all "brushless" motors. May not apply to car starter motors.
aarg is absolutely correct. I would suggest you study Lenz’s Law, Faraday's Law, Ampère’s lawAmpère’s law and the Maxwell’s equations. From this you will find that if a charge is put on an inductor it will not charge instantly but will take a time constant dependent on circuit parameters. If that circuit is opened for example a switch the magnetic energy will discharge immediately and the voltage will rise until the energy is consumed or limited by the external circuit. A common example is the clamp diode placed across an inductor such as a solenoid. If the voltage did not reverse the diode would never conduct. That is also why a MOSFET will clamp the transient. The (avalanche) UIS rating of the MOSFET will tell you how much it will tolerate. As far as motor I have yet to see one that is not inductive, they work because of magnetism and the coils that produce it. When a motor is driven instead of being driven it becomes a generator. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
ItHappenedAgain:
I'm creating a motorized Chinese turning table aka a motorized Lazy Susan but i'm worried that if the circuit stops powering the wheel to a direction, the table will continue to turn due to its momentum and create reverse voltage which will end up damaging the circuit.
Have you built it?
If not, do so and find out, all part of being a "maker" "inventor" "experimenter".
Motor drivers have suitable protection against back EMF, I would say you are overthinking your project.
Tom....
