# control speed of motor (help)

Discussion in 'General Electronics Chat' started by fadelo, Apr 12, 2011.

Apr 12, 2011
22
0
hi there

I was thinking of what is the simple way to control the speed of a motor

I'm planing to build a circuit consisting of tow motors..

while surffing the net I found topics about the motor controller and it's the

first time to hear about it!

mmm what about using a variable resistor??

regards

Last edited by a moderator: Apr 12, 2011
2. ### Wendy Moderator

Mar 24, 2008
20,772
2,540

Apr 12, 2011
22
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I will try to look for it
regards

Apr 12, 2011
22
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mmmm

ok I have a 12v dc fan 0.19 A .. it operates at 5 v mostly

how could I possiblly increase the votage taken by it in order to i
ncrease the speed?

what if I connect a capacitor ? would it be useful?

Im using 12v battery 3 A

Regards

5. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
Does you fan happen to be from a computer or other electronic device?

John

Apr 12, 2011
22
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no I bought it from an electronics shop who sell most what student need for making projects...

my idea is to decrese the speed of a fan by conncting different values in series with a rotary switch so every position has a vaoltage drop which make the fan slower

and it work pretty good

but what about if I wanted to increase the speed even faster? what I could do??

what is the simple method ever?

I connect a 300v 240 micro farad capacitor but nothing changed

thnx

Apr 12, 2011
22
0

8. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
Is the fan a brushed or brushless design?

John

Apr 12, 2011
22
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I couldnt tell really but I did connect a 224 capacitor in parallel with the fan and from the sound it seems faster and it took half the time to reach maximum speed (edit the power factor I guess)

ok here is another issue

this is my circuit it's quite simple the idea is to reduce the speed of the fan by resistors!! it's working good.. what I was trying to do is to put
LEDs between each position of the rotary switch so when I start at the fan with low speed a Yellow LED turn on .. when I change the rotary switch to the second position a red Led is turn on it doesn't matter if they where all on when I change to the last position ??
I'm still trying

any help

10. ### hgmjr Moderator

Jan 28, 2005
9,030
214
There is a problem that arises when attempting to use a resistor in series with a motor to control its speed. That problem is the potentially severe loss of torque that results. As you apply a load to a motor, it draws more current from its power source. With a resistor in series with the motor, this increase in current results in a larger voltage drop across the resistor as the load on the motor increases. With more voltage dropped across the resistor there is less voltage available to power the motor. The motor is then more prone to stall due to voltage starvation.

It is for this reason that most of the members will recommend that you use PWM to control the speed of your motor. It may mean a bit more complexity to the control circuitry but the result is a motor that provides the maximum torque for the speed change range.

I notice that you have used resistors to control the speed of a fan. This is permissible as you do not usually make heavy torque demands on a fan unless you are trying to achieve negative or positive levels of pressure. However, the use of PWM on the fan will give you the best fan performance across the range of operating speeds.

hgmjr

Apr 12, 2011
22
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thnx a million.. now I can understand
what's wrong with using the resistors
I will give it a shot and try to design the
PWM
thnx again

12. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
I hope you are aware that PWM with a standard DC brushed motor will only decrease speed. It will not allow you to increase speed greater than its speed when directly connected to your supply.

If you still want to increase speed, you need more voltage or a different type of motor. More voltage can be provided by a boost converter, but that is more complicated.

John

13. ### strantor AAC Fanatic!

Oct 3, 2010
4,302
1,989
Another idea, if you are happy with having the 3 speed selection would be to put 3 voltage regulators.

Apr 12, 2011
22
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what I was trying to do is to put
LEDs between each position of the rotary switch so when I start at the fan with position one,, a Yellow LED turn on .. when I change the rotary switch to the second position a red Led is turn on it doesn't matter if they where all on when I change to the last position ??
I'm still trying any help?

15. ### hobbyist Distinguished Member

Aug 10, 2008
773
62
Hi,

will something like this work for you?