View Full Version : Circuit needed to reverse DC supply polarity every 3 minutes

02-19-2010, 11:04 AM
I have a DC supply (12v, 0.1A) that I want to reverse the polarity every 3 minutes or so. The reversal needs to be done automatically as the unit is used fort 3 hours each time. Also I need to be able to manually set the reversal interval between 30 seconds and 5 minutes.

I have another 12v DC supply, but where the current maximum is 2A. I need to do the same with that. This supply is in a damp environment. The other supply is in a dry environment.

Anyone have any ideas of simple circuits that will do that?

02-19-2010, 12:19 PM
u can also use an h bridge with a 555 timer

02-19-2010, 10:46 PM
For slight symplification use 555 & DPDT relay.

02-20-2010, 08:54 AM
Thank you for your advice.

I am a relatively new to electronics. I am also proficient with a soldering iron.

But when it comes to integrated circuits I am lost. So I am unfamiliar with the 555 chip.

I know what a DPDT relay is, but not much about the solid state version.

Are there any simple tutorials that would help me understand how to make the circuit I need?

The DPDT relay needs to be switched every 3 minutes or so. Plus the ability to manually set the interval between switching to between 30 seconds and 5 minutes (for experimental purposes) is important.

02-20-2010, 11:37 AM
Can you tell us what you are switching the polarity to?...a motor perhaps?


02-20-2010, 11:42 AM
Can you tell us what you are switching the polarity to?...a motor perhaps?


It's a colloidal silver generator. That's simply a couple of silver wires in water. By electrolysis it generates colloidal silver. The switching is to reverse the current every so often to avoid silver oxide building up on the wires.

02-20-2010, 12:01 PM
Model railroading has many set-able auto reversing circuits. This is used if you have a round track and you want the trolley to go in one direction for a few min then reverse for a few min. You could add a relay to the output to handle higher voltages.

Here is a very adjustable model, you most likely can find off the shelf varieties.

02-20-2010, 05:03 PM
Check AAC books at top of page. volume VI, chapter 8, for 555 circuits,& Bill Marsden's LEDs, 555s, Flashers.
As you need only a few micro amps, a single 555 & a one transistor invertor will provide alternating reversals. Set 555 as close to 50 % as possible. 'would suggest one meg pot from pin 3 to 2 &6, with switch selected capacitors for a short & long time periods. My printer-scanner is down so cannot send print--Help!!