# Programmable polarity switch for DC circuit

My question concerns a future research project in electrocoagulation (water treatment) I am planning right now.

I will have a lab power supply connected to two (or more) plates in water. The operation will run in a galvanostatic mode, meaning I want to have a constant current through the system as one of the major outcome determining factor is the charge density through the plates (e.g. $$\mA/cm^2\$$). The plan is to procure a lab power supply that can supply up to 30 A, since that is at the higher end of the range I want to test. My measuring probes and the power supply will be programmable, meaning I have the possibility of centrally controlling the electrical inputs and the data collection of experiments from my computer.

One thing that I want to test is reversing the polarity of my electrodes to counteract electrode passivization, i.e. switching the anode and cathode during the experiment. I would like to do this in a programmable fashion as well. For example, either at timed intervals or maybe when a certain voltage drop has occurred due to the increased resistance from the passivization.

Given that I have all required signals connected to the computer, what would be the way to solve my problem? The programmable side will not be an issue for me, I am mostly interested in the best way to solve the problem.

Requirements:

• Switching circuit should be able to handle up to 30A passing through the switching side.
• Programable

Thanks in advance!

## 1 Answer

Use a H bridge / motor controller (where your anode and cathode replace the motor).

Image source: multiple motor h bridge?

• Would it work interchangeably? A DC motor would be an inductive load and the between the electrodes in my circuit it would be a resistive load. I've searched around a bit, have not found an H bridge/ motor controller board that can handler higher currents yet. Also searching around for high current DPDT programmable switches, but I can't find any of the shelf products. – Aquapuer Nov 29 '19 at 10:33
• No, not interchangeably, but one way: if it can switch a inductive load, it can also switch a resistive load. But not necessarily the other way around – Huisman Nov 29 '19 at 10:52
• @Aquapuer Searching internet for "30A brushed motor controller" yielded e.g.: robotshop.com/en/medium-power-motor-controllers.html or nl.rs-online.com/web/c/automation-control-gear/… (nl.rs-online.com/web/p/dc-motor-controllers/7736844). These are suggestions how to search, I didn't go into details if it fits your application. – Huisman Nov 29 '19 at 10:56
• Ok, thank you. I think you've pointed me in the right direction. – Aquapuer Nov 29 '19 at 12:54