# What do they call this?

I need a circuit that switches the positive and negative between two separate terminals at a specific interval. This is for dispersing copper in water for a project that I am working on. I want to reverse the polarity of the conductors so they will be "self cleaning" and I want to prevent bridging. I have seen this done before on a device that put silver in water but I have no idea what the circuit is called in order to do a search for it. Can anybody tell me how this is done.

Thanks

## Answers and Replies

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You could use a relay connected as a reversing switch, like this:

[PLAIN]http://dl.dropbox.com/u/4222062/Reversing%20switch%204.PNG [Broken]

Your solution is the rectangle in the middle. The switches are contacts on a relay.
You would need a double pole double throw set of contacts on the relay.
The left diagram might be when the relay is not activated and the right one might be when the relay is activated. The coil of the relay is not shown.

Can you see that this circuit reverses the polarity of the supply to the rectangle in the middle? This circuit is commonly used to reverse the direction of small DC motors.

A similar arrangement using transistors instead of switches is called a H Bridge.

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My first attempt at this was with a relay and a 555 timer, and it worked OK. I wanted to do this with a circuit and eliminate the moving parts. The silver thing that I saw did not use a relay -- Well... At least I did not hear a relay activating. I was told later on that it was done with a circuit. I guess I figured that this application had a name and I just didn't know what it was. Like when I look for other circuits that use the 555 timer or current limiting circuits.

Thanks

The solid-state version of what you want is called an H-bridge, and is usually used to run DC servo motors that need to reverse direction. They are pretty easy to build out of discrete components if you don't have high-frequency issues. And there are a number of ICs that work nicely at around 2Amps. Google can be your friend here.

Seems like the expression "phase reversal switch" comes to mind, but I think that applies to AC equipment. Perhaps yours would be called a polarity reversal switch?