Reversing DC Polarity at a Set Interval?

Thread Starter

frontier92

Joined Jan 28, 2021
1
I'm making a DC colloidal silver generator (planning to use four rechargeable 9v batteries). The positive and negative wires that clip to the silver rods must be switched every few minutes throughout the process so the two rods wear evenly. The process takes several hours. Is there a simple way to reverse them at a set interval with a switch or dial at the project box rather than having to disconnect the wires and reconnect every few minutes. It would be great if I could set the interval and leave it, but if I can't do that, I'd be okay even if I had to flip a switch back and forth. Thank you in advance!
 

djsfantasi

Joined Apr 11, 2010
7,689
I'm making a DC colloidal silver generator (planning to use four rechargeable 9v batteries). The positive and negative wires that clip to the silver rods must be switched every few minutes throughout the process so the two rods wear evenly. The process takes several hours. Is there a simple way to reverse them at a set interval with a switch or dial at the project box rather than having to disconnect the wires and reconnect every few minutes. It would be great if I could set the interval and leave it, but if I can't do that, I'd be okay even if I had to flip a switch back and forth. Thank you in advance!
Yes.
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First, you could use a DPDT relay to switch polarity on a schedule. The question is how to turn the relay on and off.

We need to know more about your application. Are the periods for each polarity equal? 10 minutes on one way, 10 minutes on the other way? By the way, this time is important to answering your question. Is it a few seconds, a few minutes or longer?

If you can code, the absolute easiest way is to use a microprocessor. If you’re unfamiliar with them, then a uP that can be programmed with the Arduino IDE is the easiest to learn. A Nano Arduino clone is small, inexpensive and would fit your bill. Then, a MOSFET (or transistor), a couple of resistors and a DPDT relay would fit the bill.

For timing, a 555 IC comes to mind, but it’s not good for long periods.

One could use a counter IC, like a CD4060, but you might need additional counters for really long periods. Plus the MOSFET, resistors and relay.

You could also use an H bridge to reverse polarity, but in my opinion, that’s overkill.

So... answer the following questions.
  1. How much current will pass through the solution? (9V batteries may not last several hours in your application)
  2. How long will each polarity pass through the solution before reversing?
  3. Can you program? (Follow up. Have you used a microprocessor, like an Arduino or PIC before?)
  4. Have you used a MOSFET before? A BJT (transistor)
  5. Do you know how to wire a DPDT switch or relay to reverse direction?
 

crutschow

Joined Mar 14, 2008
27,171
Here's a circuit using the CD4060 that can go from less than a minute up to a 24 Hour period in the astable mode (remove D1).
You can use either version of the circuit.
If you select a DPDT relay, it can reverse the current direction as djsfantasi suggested.
 
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