0
\$\begingroup\$

I realize this is may be a noob question so please point me to the right place to ask it if this isn't so. Anyway, I'm trying to build a little magnetic blender using a spare laptop fan. I tried plugging the red and black wires (and every other possible combination) into a 9V battery but it didn't run at all. So I broke the whole thing apart and ended up with the motor inside:

enter image description here

When I plug the + and - ports from my battery to the metal things in the motor (A and B in the picture), it turns about half turn and then it stops, and when I switch the poles it runs a little more, and so on, always on the same direction. So I guess the poles need to switch intermittently, which I understand means I need AC instead of DC? Is there a way to easily have this motor work using a battery or power from my outlet using simple tools? I understand home current is AC, but I'd need a way to lower the voltage while keeping it AC, and I believe phone chargers all output DC.

\$\endgroup\$
0

3 Answers 3

3
\$\begingroup\$

You are on the right track, in thought process at least, not procedure.

Know that fundamentally, there is no such thing as a DC motor. All motors operate based on changing (alternating/rotating) magnetic fields which are produced by changing (alternating) currents. They are all "AC" so to speak at the lowest level. What goes into the coils is always some form of AC.

You only have motors that take DC and convert it into AC. The brushes on a brushed motor do this by taking the DC you put into the wires and making the current change directions through the coils when it turns, thereby producing the "AC", so that it can continue to turn instead of just turning a bit and locking up.

In a brushless motor, like your computer fan, electronics are required to do the job of the brushes. It needs some smarts. A computer fan has the electronics integrated into it, but it appears you might have ripped those out.

\$\endgroup\$
2
  • 1
    \$\begingroup\$ "fundamentally, there is no such thing as a DC motor." - not entirely true. en.wikipedia.org/wiki/Homopolar_motor \$\endgroup\$ Aug 7, 2020 at 22:09
  • 1
    \$\begingroup\$ @Br Oh, yes. I always forget about that one and someone always brings it up lol \$\endgroup\$
    – DKNguyen
    Aug 7, 2020 at 22:14
1
\$\begingroup\$

Try again with a working fan and then follow the instructions. The internal fan electronics commutates the DC with the Hall Effect magnetic rotor sensor.

Instead of guessing use, Red=+, Blk=- , yellow= tach out or don’t care

\$\endgroup\$
1
\$\begingroup\$

I'm guessing from the details you give that this was a 3-wire fan? the basic details others have not expressly given, but rather hinted at, are that PC fans don't run on just voltage. you cannot just put 9 volts on a 12 volt PC fan coil to run it or slow it down. it needs 12 volts, and data from a sensor showing it's speed and position to itself so it to know to turn and switch active coils to keep itself turning; called Tach. Yes, I know I haven't said anything new, I'm just adding some clarification that might be needed

\$\endgroup\$
1
  • \$\begingroup\$ All the ones I've tested would run (but slower) on 5V 9V should not be a problem \$\endgroup\$ Aug 8, 2020 at 10:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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