# reversing electromagnet polarity

Discussion in 'General Electronics Discussion' started by comdoc, Oct 13, 2010.

1. ### comdoc

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Oct 13, 2010
How to electronically switch polarity of a small stator electromagnet (0.5 ohms) as tube magnet rotor (magnetized across diameter) spins? Stators are opposed; stator #1 needs to attract S pole while opposite stator #3 attracts N pole; shaft rotates 90 degrees, power to 1+3 switched off, and power to 2+4 switched on...then stator #2 attracts S pole while stator #4 attracts N pole...etc. Plan to use 12V DC 2 amp power supply and Hall effect sensors. Motor has 4 circuits to solenoids spaced at 90 degrees around shaft; each circuit resistance about 4 ohms. What components are needed for timing?

Thanks,

comdoc

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
As far as I can tell, you need nothing for timing, you simply place the hall effect switches in the appropriate place to detect when polarity should be reversed.

Use an H Bridge to reverse the polarity.

3. ### comdoc

3
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Oct 13, 2010
Thanks, Steve. But it's not when polarity is reversed--rather it's where. One coil is turned on and at the inner end is polarized (ie N) at the same time the opposite coil is turned on and polarized in opposite direction (ie S). These opposing coils are on the same circuit. Should I place Hall sensors at 90 degrees apart around the rotor magnet? Thanks, comdoc.

Last edited: Oct 14, 2010
4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
You place the hall effect sensors such that they detect when the rotor is in the appropriate position to reverse polarity on the stator winding.

That is what I meant by "when"

You may have a third issue,

1) Hall effect sensors to detect when to change polarity
2) ???
3) H Bridge to change polarity

Obviously something needs to control the H Bridge. The hall sensors may only give a quick pulse to say that the polarity should be reversed.

(2) Could be an SR flip-flop

Last edited: Oct 15, 2010

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Oct 13, 2010