CR Circuit for driving a motor
CR Circuit for driving a motor
(OP)
Hi guys, I want to design a CR circuit such that when a switch is closed a motor powers up slowly (as opposed to full torque instantaneously) and when the switch is opened the motor stops straight away. The motor has to rotate in both directions so the ciruit has to have a SPCO switch in it.
I guess that a diode has to be incorporated into the circuit to stop the motor from rotating in the opposite direction when the capacitor is discharging. Circuit design is not my strong point so if someone could offer any advice, it'd be very much appreciated. The circuit should be as simple as possible.
Thanks very much.
I guess that a diode has to be incorporated into the circuit to stop the motor from rotating in the opposite direction when the capacitor is discharging. Circuit design is not my strong point so if someone could offer any advice, it'd be very much appreciated. The circuit should be as simple as possible.
Thanks very much.





RE: CR Circuit for driving a motor
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RE: CR Circuit for driving a motor
Dan - Owner

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RE: CR Circuit for driving a motor
MacGuyver, I mean I hope that when the user presses the switch in direction 1, the motor rotates clockwise, but when he lets go (switch in centre position) the motor stops. Conversely, when the user presses the switch in direction 2, the motor rotates anti-clockwise.
I have an idea in my head, I'm just waiting to gain access to some software to test it virtually.
RE: CR Circuit for driving a motor
RE: CR Circuit for driving a motor
I also need the circuit to be as small and simple as possible. I'll hopefully be able to test my circuit tomorrow and put this debate to rest (fingers crossed!), but thanks for the help so far.
RE: CR Circuit for driving a motor
On the other hand if a timer relay is beyond your skill set, you may need more than free internet help to solve your problem.
Bill
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"Why not the best?"
Jimmy Carter
RE: CR Circuit for driving a motor
I had another look at timer relays and I guess I could make one, but I'd rather not. I'm going to test my circuit tomorrow on MultiSim and hopefully everything will be copasetic. If not, then timer relay it is.
I get that this problem probably seems simple to you guys, but I can't stress enough how little experience I have in this department, especially developing something independently.
RE: CR Circuit for driving a motor
One problem to be aware of is if the switch is opened then rapidly closed the thermistor will still be hot, its resistance will be near 0, and the motor will pull the full inrush current.
RE: CR Circuit for driving a motor
Concentrate on what you want to do instead of on possible secondary effects. You obviously want the motor to start slowly and ramp up in speed when you activate a lever (SPCO) in one direction. It shall then run until something happens (lever back to zero, I think) whereupon it shall stop as fast as possible.
The same thing shall happen in reverse when the lever is activated in the other direction.
If so, what shall the ramp-up time be? And what stopping time is acceptable (cannot be zero milliseconds). Fast stopping can be achieved by short-circuiting the armature (moderatletly fast) or plug braking (real fast) with reverse polarity until speed is zero.
I doubt if a SPCO will do the work. You need at least a DPCO if you want to reverse the motor (both leads need to be switched). BTW, the correct terminology used to be (and still is, in some quarters)SPDT (Single Pole Double Throw for the first switch type and DPDT for the second type).
Also, a CR circuit will make the opposite of what you want. An RC circuit will make the acceleration soft. Not the best solution from an efficiency point of view, but that is probably not very important in this case.
The capacitor needs to be an electrolytic one and that means that you have to be careful with the polarity. May be a problem when reversing the motor.
The inclusion of a diode: Yes, perhaps. Where do you want it?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: CR Circuit for driving a motor
What do you mean by an RC circuit being unsuitable as the acceleration is soft..? As for the diode, that was my idea, I know that a diode only allows current flow in one direction so I thought that should a CR circuit be used, then the diode be placed after the capacitor but before the motor (relative to the current flow).
Argh! I didn't think it would be this tough (or I would I be this bad).
RE: CR Circuit for driving a motor
"F" and "R" are two-pole cange-over switches for Forward and Reverse.
There are two parts. One for the reversing and braking and one for the ramping/soft start.
The discharge circuit has one error ("automatic drawing"): Remove the horizontal line going from D.R. to lower left connection of "R". If you keep it in circuit, you will burn out the D.R. resistor.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: CR Circuit for driving a motor
RE: CR Circuit for driving a motor
RE: CR Circuit for driving a motor
I'm guessing the answer is pathetically simple, but I think I've shown how lacking my knowledge in this field is already...
RE: CR Circuit for driving a motor
If your switch model has normal resistance (milliohms) and normal leakage (nA). And if you have ohms instead of any other unit for the resistors, if your capacitor doesn't have too much leakage and if it doesn't break down below 12 V and if you have the polarity right and if your motor model draws between a few milliamps and around 200 mA, then you should get something between 10 and 12 volts. Depending on how much load you have on the motor shaft.
Check also the current limit of your DC supply.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: CR Circuit for driving a motor
That about removing the wire to the discharge resistor.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: CR Circuit for driving a motor
Thanks for all your help again, you've decreased my hatred of electronics from a 10 to a 9 (it's no small feat)...
RE: CR Circuit for driving a motor
(Yes, correct wire removed)
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: CR Circuit for driving a motor