Does this sort of device exist?
I was wondering if you could buy a sort of "timer" that switches the direction of an electrical current at certain time increments.
My intended setup is the following:
I have a coil of wire with both ends hooked up to some sort of power source (a set of batteries, an adapter plugged into a wall socket). When applying a current through the wire, the solenoid should create a magnetic field. However at a certain time, the current should switch directions, creating a magnetic field in the opposite direction.
For a duration of time, I need a current travelling through one direction of a conductive wire, and after the time increment (which can be adjusted via the device im inquiring about) is over, the current should switch directions. Essentially, all the device should do is switch the leads of the wire to connect it to the opposite ends of the power source, except do so at certain times.
Also, the device should switch the current direction within a very small time period, perhaps even several milliseconds. I am not sure if such a thing exists, but if it does, could any of you send me a link of where to find one? thanks.
- Steve CLv 68 years agoFavorite Answer
don't know of a monolithic device, that does precisely what you're wanting, even at a slow speed.. An old fashioned device that might be used kind of like what you're wanting was called a vibrator- and was part of the system used to generate the HV needed for spark ignition from DC, they work somewhat like a DC door bell by using electromagnetism to throw a contact out of contact, which interrupts the magnetic field. spring then pushes the contact back into contact, and cycle starts again. Put a transformer electrically in series with a door bell/ a vibrator and you should get AC across the transformer's unconnected terminals.
Alternatively you could go for full H bridge. see http://www.mcmanis.com/chuck/robotics/tutorial/h-b... .
Switches could be relays if you really want - but total number of switch open/closes would be limited-semiconductor switches usually better. alternate the opening and closing of pairs of switches *across* the powered device. use something like a 555 timer with 50% duty cycle to generate a square wave at the frequency you want the *voltage* to switch direction.
You seem to be wanting to power magnetic coils by your device. They'll have a fair inductance, and inductance functions kind of like inertia, and that tries to keep current flowing once it's started. You might have difficulty getting much flow of current at all at high frequencies. Another thing you'll have to be careful of with AC is current and voltage can end up getting out of step, and non intuitive things can happen like having current flow backwards against a voltage for some of the time. Current should still alternate though, you just have to be careful how you calculate the power your cables/device need to cope with. there can be a fair bit of math involved see http://en.wikipedia.org/wiki/Electrical_impedance
- billrussell42Lv 78 years ago
A fast DPDT relay would reverse polarity in milliseconds, but with an inductive load, you have to be aware that you can get huge voltage transients.