Need help with auto switching Reverse polarity circuit ..#2

Thread Starter


Joined Mar 25, 2022
Here is what I am wanting to do and cannot figure out how to accomplish it. I want to use 3 9v Batteries in Series and run +/- 27v in to a circuit and I want +/- 27 also out of the circuit. Heres where I am unsure. Although I know I could use a switch to manually change polarity. I am wanting a timed circuit to swap polarity. The timing is not too critical but needs to be between every 2-3 minutes to swap the polarity. Also would be nice to have a way to protect the out going 27v leads as they are going to be electrodes to have some sort of protection in case they were to touch and short out. Thats not absolutely critical but would be a nice feature. I have been stuck for 2 weeks trying to figure out how to get a circuit built that will allow for auto switching of polarity. Any help and assistance or ideas would be GREATLY appreciated.

A little more info I am building a Colloidal Silver Generator the Silver Electrodes go in distilled water. The reason for reversing polarity a time intervals and back and forth is to ensure one electrode is not eroded over time faster than the other. The process takes 2-3 hours so a manual switch would be a daunting task to baby sit the generator. If some one is willing to help me complete a circuit that will work, I would be very appreciative.

Thank you
Rodney W3LDR
Amateur Radio Operator
Hi Rodney, Were you ever able to put together a polarity switching circuit for making colloidal silver? Is yes, would you be willing to share the circuit with me? I would appreciate it very much.

Mod:Created new Thread, link to old.
Last edited by a moderator:


Joined Jan 23, 2018
The simple scheme is an "H Bridge" with FET devices and a R/S flip-flop to alternate which part of the bridge is active. Given that the exact time is not critical, a simple RC feedback to the set and reset will reverse states every so often. Use a CD4013 FF and 4.7 meg resistors from "Q" to "R", and from "Q-bar" to "S". The outputs will be from the Q and Q-bar. The capacitors will be from the S and R inputs to the supply negative. Probably a bit more will be required to drive the transistor gates.