I need to get a pump running at different speeds so I ordered an electric motor, a potentiometer and a power supply adapter. I put them all together and they worked, however the potentiometer got burnt out.

These are the items:

Electric motor: RS PRO, 12 V dc, 3000 gcm, Brushed DC Geared Motor, Output Speed 1425 rpm

Potentiometer: RS PRO, DC Motor Controller, 6 → 15 V dc, 3 A, Panel Mount

Power adapter: JnDee™ 12V 6A 6 amp 72W AC/DC POWER Supply ADAPTER Transformer ## Great For CCTV, LCD Monitors, TVs and Powering LED Strip ## (12V 6A)

And this is what happened with the controller:

enter image description here

I am trying to find where the problem is. Is the power supply not giving a non-digital dc input? Is the current rating (3A) of the potentiometer being different to 6A given by the power supply?

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    \$\begingroup\$ The device is rated for 3A, you put a 5~6A rated motor on it. If it has a load that current is likely to be higher. I would get a "controller" rated for at least 10A or more. or build your own with some Mosfets, there are plenty of tutorials online. (Also the load is not directly on the potentiometer). \$\endgroup\$ – Wesley Lee Aug 2 '19 at 10:25
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    \$\begingroup\$ That's not a potentiometer. That's a DC motor speed controller with adjustment by potentiometer. The motor is rated at 5 A. Your controller at 3A. It might work if not heavily loaded. \$\endgroup\$ – Transistor Aug 2 '19 at 10:28
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    \$\begingroup\$ @WesleyLee, would you be able to tell me if one of these speed controllers would be any good? uk.rs-online.com/web/p/dc-motor-controllers/2442670, uk.rs-online.com/web/p/dc-motors/8347584, uk.rs-online.com/web/p/dc-motor-controllers/0440486? \$\endgroup\$ – Roxana Radu Aug 2 '19 at 11:09
  • \$\begingroup\$ yes, this controller looks much better \$\endgroup\$ – Mike Aug 2 '19 at 11:12

When you select a motor, controller and power supply, you must start with the motor. Then select a controller that is adequate for the motor. Finally select a power supply that is adequate for the controller.

For the motor, you first determine the speed and torque that the load requires. The motor that you selected appears to be capable of supplying 3000 gram-cm of torque at 1450 RPM at the output of the gear. It requires 12 volts for full-speed operation and appears to require 5.28 amps to produce rated torque. Saying "appears to" indicates that the wording of the specification is not completely consistent throughout all of the product description.

In selecting the controller, the maximum output voltage must 12 volts. Higher voltage would make the motor run faster. Running the motor a little faster might be ok, but it is better not to do that. The maximum output current must be at least 5.28 amps. It would be good to select a controller that can supply 150% of the rated motor current. The motor will tend to draw more current when it starts and during acceleration. The controller needs a "soft start" or a "current limiting" feature. If it lacks that, the motor may draw up to 10 times the rated current momentarily when it starts. It is better to prevent that rather than selecting a controller that can supply 10 times rated current.

All three of the controllers mentioned in your comment appear to be adequate. Two of them have current limit adjustments that will protect the motor from overloading if they are properly adjusted. One is self protecting, but will not protect the motor as well as the other two will.

The power supply must be selected to provide the voltage and current required by the controller. The output voltage and current may need to be a little higher than the controller output voltage and current because of losses in the controller. If it doesn't matter if the motor can not quite reach full speed, the input voltage does not need to exceed the rated motor voltage. If the controller does not limit the motor voltage, it will be limited by the power supply voltage. The power supply may not need a current limiting feature. If it has such a feature, the controller output current may need to be higher than the momentary current limit of the controller.

I would be inclined to use a simple power supply that has only a fuse to protect it and depend on the controller to protect the motor.

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You put a motorcontroller for 3A on a motor of 5.28A.
So better change the motorcontroller

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  • \$\begingroup\$ Thank you for your answer. Would you be able to advise if I would use this speed controller, would my motor start from 9V speeds instead? uk.rs-online.com/web/p/dc-motors/8347584 \$\endgroup\$ – Roxana Radu Aug 2 '19 at 13:50
  • \$\begingroup\$ No, the supply voltage is in the range 9 ... V the output is 0 ... 12V. The module should be fine. \$\endgroup\$ – Mike Aug 6 '19 at 11:18

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