Author Topic: How to increase the starting voltage slowly in steps  (Read 1663 times)

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Offline ajoseph88

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How to increase the starting voltage slowly in steps
« on: September 21, 2015, 08:02:36 pm »
At start, how to increase the starting voltage slowly... The starting voltage is 5V, and it is used to control the speed of dc motor, so at start the motor should start smoothly, increasing speed gradually... to limit the starting current... So I need to increase this control voltage 0 to 5V gradually at start.
I tried to make use of RC charging time constant, it works, but I need it only during start... if it remains through out the operation, then the speed response is very slow... because of capacitor charging and discharging... 

The 5V is given to the microcontroller, which changes the ADC, which controls the speed of the motor...   

Any help, much appreciated... 
« Last Edit: September 21, 2015, 08:11:42 pm by ajoseph88 »
 

Offline Psi

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Re: How to increase the starting voltage slowly in steps
« Reply #1 on: September 21, 2015, 08:08:16 pm »
Soft motor start is the term your looking for
It's a  a motor controller feature
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline jitter

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Re: How to increase the starting voltage slowly in steps
« Reply #2 on: September 21, 2015, 08:17:23 pm »
I tried to make use of RC charging time constant, it works, but I need it only during start... if it remains through out the operation, then the speed response is very slow... because of capacitor charging and discharging... 

Can you bypass the RC network with (e.g.) a relay after the motor has spun to full speed?
 

Offline IanB

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Re: How to increase the starting voltage slowly in steps
« Reply #3 on: September 21, 2015, 08:21:14 pm »
Can you do it digitally inside the microcontroller? When the controller receives an "on" signal it can gradually ramp up the PWM to the required value. When it receives speed control inputs it can pass them straight through without filtering them.
I'm not an EE--what am I doing here?
 

Offline ajoseph88

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Re: How to increase the starting voltage slowly in steps
« Reply #4 on: September 21, 2015, 09:00:09 pm »
I tried to make use of RC charging time constant, it works, but I need it only during start... if it remains through out the operation, then the speed response is very slow... because of capacitor charging and discharging... 

Can you bypass the RC network with (e.g.) a relay after the motor has spun to full speed?
It makes sense, i'll try...
 

Offline ajoseph88

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Re: How to increase the starting voltage slowly in steps
« Reply #5 on: September 21, 2015, 09:02:59 pm »
Can you do it digitally inside the microcontroller? When the controller receives an "on" signal it can gradually ramp up the PWM to the required value. When it receives speed control inputs it can pass them straight through without filtering them.
I tried that, but if I try to modify or do anything with the ADC value or firing delay value inside the program, the value gets messed up... I'll still keep trying different ways to do this by program...
 


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