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12v DC Motor Speed Control

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Apr 23, 2013
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I have a very simple problem but could use some advice. I have a basic knowledge of elementary circuits but need some advice and I apologize if this happens to be answered in another post I would appreciate it being pointed out. I have a very small pump with a brushless magnetic dc motor it is 12V DC supplied from a 120V AC plug in wall transformer(rectifier?) it draws 0.6A running 7.2W(?) I would like to be able to vary the speed of the pump. I know you can use a POT to adjust the speed, any suggestions? I would like to put the control board or POT into a gang box or small NEMA box. The area might have some water issues, it is for my home brewery. The issue is the flow into the pump inlet is less than the discharge of the pump, I have a ball valve on the outlet but having it 75% closed does not help the issue. The pump will run for 5-10 minutes then stop on overload(?) then restart after a few seconds I think varying the speed is my best bet. Any suggestions on how to properly do this. I am open to a kit or building my own either I can be able to do. Thank you for all your help.

" small pump with a brushless magnetic dc motor " these have an electronic controller IC associated with them. it might be fitted inside the motor case. Unless you can gain access to this IC you cannot change the speed. But you can have an external variable "pulsed" power supply that turns the motor on for say 2 Seconds, off for 5 right up to on for 6 Seconds off for 1, or what ever you fancy. One point is that these sort of motors take a big surge of current to get them started.

I cannot get into the motor area without cracking the motor housing, so if it has an IC I guess I am out of luck other than a 'Pulse' power supply which I am assuming is a PWM controller. Any recommendations for a DIY one or an off the shelf one?

Hi TurkFebruary
I know you can use a POT to adjust the speed,
No it is not a good idea because it is pretty dissipative .
any suggestions?
If you want control it's speed you can easily use a 555 timer to create PWM and then apply it into a totem pole and then a mosfet or perhaps a darlington pair . and then using a simple LC filter and then it s ready to use !
Thus you can easily and without high value of dissipation , change the speed of your motor .

Best Wishes

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