0
\$\begingroup\$

I want to run a small DC motor (which is operated on a 1.2V 600 mAh cell battery) using 12V charger. Now the problem is that when I connect the motor to 12V, 5V, 3.3V the motor starts pulsing (I mean starts for 0.5 second and turn off for 0.5 seconds and the loop keeps on), but when I connected 3.7V 18650 cell battery directly to it, the motor start to rotate at full speed. Furthermore I connected the motor to 5V power supply but again the power supply turns off and on again repeatedly. Last but not least, when I connect the terminal of power supply to one of the terminal of motor due to sparking it start rotating normally, but without sparking it keeps on pulsing.

Kindly tell me how to run the motor smoothly and what components should be used? Basically I'm trying to power Kemei Hair Trimmer using 12V charger.

enter image description here

|improve this question
\$\endgroup\$
  • 4
    \$\begingroup\$ A 12 V power supply is ten times higher than the manufacturer chose. This will end badly (if it's not over already). You need to limit the current or voltage. \$\endgroup\$ – Transistor Jul 25 '19 at 9:40
  • \$\begingroup\$ You need to buy or build a 1.2 volt output buck regulator. Product recommendations are off topic here so do some digging around and report what you find. Note that you need to know the stall current of the motor on 1.2 volts to do a proper selection. \$\endgroup\$ – Andy aka Jul 25 '19 at 11:15
  • 1
    \$\begingroup\$ one more thing i run it using a 5v 2A charger and it works but motor was rotating too fast at 0.9 A but when i use 5v 1A charger it didn't work, why? \$\endgroup\$ – user6631276 Jul 25 '19 at 11:23
  • \$\begingroup\$ This type of project is rarely practical; it would be better just to use the sort of battery it was intended for, or to see if maybe it will run from an NiMH cell which you could take out and charge in a charger. \$\endgroup\$ – Chris Stratton Jul 25 '19 at 15:46
  • \$\begingroup\$ What type of motor is this? Did the hair trimmer provide a pulse to the motor? \$\endgroup\$ – Voltage Spike Jul 25 '19 at 15:54
0
\$\begingroup\$

Your power-supplies are not capable of putting out enough power to run the motor, as a result, when you connect the motor, the power-supply goes into shutdown.

Maybe add a DC-DC buck converter with a input current limit between the supply and the motor, set the current limit such that the power-supply is happy. Search "CC-CV DC-DC Buck" for some examples, prices start at around $1.50

|improve this answer
\$\endgroup\$
  • 1
    \$\begingroup\$ Then what is the optimal solution for power supply? NO.1= 5v 2A charger with some resistance or No.2= I have to use resistances to divide the voltages using resistor using 12v 1A charger? one more thing the motor runs on 0.9 Amps using 5v 2A charger but on its orignal cell battery it uses 1.34 v and 0.34 Amps. \$\endgroup\$ – user6631276 Jul 25 '19 at 11:37
  • 1
    \$\begingroup\$ one more thing i want to ask is that using 12v 1A charger when i rub the teriminal against the one terminal of the motor after some spikes or small ignition the motor start working normally but without spikes it doesn't work, why? \$\endgroup\$ – user6631276 Jul 25 '19 at 11:39
1
\$\begingroup\$

You have already discovered that speed is proportional to voltage. Current is proportional to load torque when the speed is stable. However the current require to start the motor is higher than the current required for steady speed. Attempting to start the motor with too much voltage is apparently causing your charger to shut down. As soon as it shuts down, the current ceases, so the charger recovers and tries again.

DC motors work best when connected to an electronic speed controller that limits the current. With the current limited to the proper level, the motor doesn't try to get up to speed quite as quickly.

For a small motor that doesn't need speed adjustment, you can use a power supply that can either supply as much current as the motor requires to start or limits the current somewhat by internal resistance and is not harmed in the process. Small batteries can power small motors that way.

Try the lowest voltage power supply that you can find. You can probably find a 3-volt supply. You can limit the speed by putting a resistor in series with the motor. If you use one to three diodes in series with 3 to 5 volts to limit the voltage, the motor speed will be somewhat less effected by load variation. That may also be easier than figuring out the resistor value.

Based on information in a comment that should be added to the question:

on its orignal cell battery it uses 1.34 v and 0.34 Amps.

To reduce the voltage of a 3 V supply you need to drop to 1.34 V. That means 3 - 1.34 V = 1.66 V across a series resistor with 0.34 A or 1.66/0.34 = 4.8 ohms.

|improve this answer
\$\endgroup\$
  • 1
    \$\begingroup\$ i have used 3.3v using Micro USB MB102 White Breadboard Power Supply Module( DC7-12V ) directly but didn't work but with 3.7v 18650 cell battery it worker why the power supply keeps turning on off again and again? \$\endgroup\$ – user6631276 Jul 25 '19 at 12:11
  • 2
    \$\begingroup\$ Most electronic power supplies shut off if the output current exceeds the rating even for a small fraction of a second. Batteries don't protect themselves. They have internal resistance that heats up and reduces the voltage as current increases. \$\endgroup\$ – Charles Cowie Jul 25 '19 at 12:55
-1
\$\begingroup\$

If you want to run on 12v ypu will require at least 5A supply. It is not worth it because the brushes inside the motor wont last a day and motor will be too fast for any practical application.

Solution: Open the motor carefully. Pull the rotor out, Unwind and remember the pattern (Its always same direction for all coils.) Count the number of turns while doing so. Increase turns count to at least 4 times (Assuming you are going to use 12v) by using thinner wire and re assamble motor carefully. (Try not to bend those thin brushes in the process or the motor is gone). Run the motor and if speed is still too high for you application, Increase turns to 5-7 times original with even thinner magnet wire and you are done. You can now run the motor with 12V 1A supply.

I have done the same to run a 1.5V motor on 3.7 lithium ion battery with same speed.

I have the same exact motor in my trimmer.

EDIT:

Solution2: Use a power resistor in series with motor. For your motor, You need 3.6 voltage drop across resistor and current should be 0.4A, That gives us 9 Ohm resistor. Use two 4.7 ohms (2W or more) in series which gives 9.4 ohms. If that is slow for you, use 4.7+2.35(Two 4.7 ohms in parallel to get 2.35 ohm). That will speed things up.

|improve this answer
\$\endgroup\$
  • \$\begingroup\$ Thanks Vikas kumar, its good to hear that you have exact motor, but i don't want to open a motor, i have run the motor using 5V/2A charger and it run but too fast i think using resistor i can reduce its speed. but using 12v/1A charger it keeps pulsing so i think opening motor is kind of risky while using 5v/2a charger is safe what would say? \$\endgroup\$ – user6631276 Jul 25 '19 at 16:05
  • \$\begingroup\$ @user6631276: Absolutely. Use a power resistor in series with motor. For your motor, You need 3.6 voltage drop across resistor and current should be 0.4A, That gives us 9 Ohm resistor. Use two 4.7 ohms (2W or more) in series which gives 9.4 ohms. If that is slow for you, use 4.7+2.35(Two 4.7 ohms in parallel to get 2.35 ohm). That will speed things up. \$\endgroup\$ – Vikas Kumar Jul 25 '19 at 16:39
  • \$\begingroup\$ Thanks @Vikas Kumar the problem is solved! using 5V/2A charger! \$\endgroup\$ – user6631276 Jul 25 '19 at 19:42
  • \$\begingroup\$ I'm sorry, but working or not, this approach only makes sense for very low resource cases. If you can land magnet wire, you can get the right components to do this the right way. \$\endgroup\$ – Scott Seidman Jul 26 '19 at 10:56
  • \$\begingroup\$ I see, the better answer is in the comments. Can you edit your answer to include it? \$\endgroup\$ – Scott Seidman Jul 26 '19 at 11:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.