Magnetic Question

[TimK]

I am working on a project that will use a series of small 24VDC electromagnets that must be turned on and off in sequence continuously 24 hours a day. Not sure if I will have to yet but may have to be able to reverse the polarity for a time after turning a magnet off. What electronic device could I uses to turn them on and off and possible reverse the polarity. I will probably use a small micro-controller to control the sequence simply because I can easily play with time delays. I know I can use relays but I don't think they would last long. The magnets will be small and draw less than 0.25 amps

Any suggestions would be great

 

[Sceadwian]

For simple on and off you would use single transistor with a diode anti-parallel with the magnet coil. The transistor switches the magnet on, the diode bypasses the inductive spike that occurs when the transistor turns off.

If you need faster off times you would need two transistors in a totem pole configuration, so that the second transistor could dump the coil current to ground causing the magnetic field to collapse faster (the diode will allow the current to go through the coil until it dissipates from the ohmic resistance of the coil)

If you need to reverse the current through the coil you need four transistors in an h-bridge configuration. Schematics for everything I've described are easily found searching Google for a few minutes.

 

[TimK]

Thanks for the reply, I will see what I can find, thanks for your help

 

[ronv]

Take a look at this one.

https://www.electro-tech-online.com/custompdfs/2011/06/sn754410.pdf