mariomoskis
New Member
yes,i refer about average current(which is really across my motor)
so ithink that i am right,yes?
so ithink that i am right,yes?
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You can put a resistor in series with the motor, but I wouldn't recommend it because the motor needs a high current to kick-start it.
yes,i refer about average current(which is really across my motor)
so ithink that i am right,yes?
Because a motor is not a simple resistive load. It has resistance and inductance. Also, when rotating, it acts as a speed-dependent voltage generator opposing the applied voltage.Why won't applying 6V at 50% duty_cycle create same average current in the motor as applying 3V continuous ?
before try with another transistor i saw that maybe i can do it with a power opeartional amplifier like follow voltage(3V) with 1A output,like this:
View attachment 62416
but i have this question:
if the supply voltage for the amplifier must be 5V,
why when i have supply voltage=6V with duty cycle 50%,the motor is already consumes the 0.3A maximum that it can? and i see too that the voltage at the output of the amplifier is higher than at the input,but it shouldn´t happen?
and i see too that if i increase the supply voltage for the amplifer to more than 6V,the motor is gonna comsume more current,why is this happen?
Sorry, I seem to be missing something here.Why doesn't the OP use a 5V motor to match his 5V power supply?
I would agree with most of it, except :Also I am not sure if my analysis at post #46 is correct/complete
In view of the above I'm not sure about 'ridiculously lower'.So, can I conclude that -" You can apply 6V to a 3V motor, but the duty-cycle needs to be ridiculously lower and should be judiciously calculated.
I agree.It won't follow a linear pattern like that in a resister." ?
But I also said I didn't recommend it.i did your suggest,i put power resistor in series with the motor
I can't recommend any value.but which is the higher value that i can use?
I don't know. Possibly the switching time of the opamp is affected by load conditions. Anyone else know?why when i put 1ohm resistor the operational get little hot?
so,the problem is that i need supply voltage 5V because i just have one supply power and i have another circuits which have supply voltage 5V and it can´t be less
the motor must be that,(1.5-3V),i don´t have load!
and i have two transistors 2n2222a or BD135,so is there a way to get 3V across my motor with duty cycle 100%??
@alec_t
There is two way to control the current into your motor. (which is what really matters)
i) You use Supply Voltage much greater than the motor ratings.
i.a) Then you need to use PWM at very low duty_cycle.
i.b) You need the transistor with much higher peak current rating than the average current that flows through motor.( Ipeak ~= I_avg / K where K is the duty_cycle ).
1.05A is stated in the datasheet to be the current at maximum motor efficiency. That is not necessarily the same thing as the maximum motor current in all circumstances, so for reliability you need a circuit to cope with a possibly higher current than 1.05A. Certainly adding a gearbox will increase the average current above what you are experiencing now, because of the added friction of the gearbox. The peak current will occur when the motor is stalled.i am gonna put a gearbox in my motor,so current will be 1.05A as we saw in the datasheet of the motor?
Yes.that current with the gearbox could be higher than 1A?
A digital meter (if that's what you used) set on the current range will not give an accurate measurement of a variable pulsating current.i put a amperer to see the current at the output of the amplifier and it is 0.3A,
Good.and generating the pwm with a module of Compactrio ni9401(digital output) instead of the 555, the AO don´t get hot and it is working well
I don't know your circuit layout so can't say definitely. But if you have this set up on a breadboard then there is lots of stray capacitance which could affect pulse rise and fall times and hence power dissipation.why i have this two differents situations??
Yes. At least, it can be reduced (not entirely eliminated) by using a correctly designed pcb which minimises conductor lengths.there is a way to don´t have that stray capacitance?
That is good practice; but it won't solve any stray capacitance (or stray inductance) problem.i put a capacitor beside the power supply,but it has the same behaviour