reversing polarity control SOLVED

Hi I have a reversing polarity 2 wire12 volt motor control .max out put 5 amps . I need to increase the rated out put to at least 15 amps. I would therefor like this unit to control 2 relays which I can use to increase power. How do I make the one unit control 2 relays so when the polarity is in one direction nuber one is active and when the polarity is reversed number two is active

by swaninlet
March 28, 2018

2 Answers

Answer by Foxx

Put a diode in series with each relay coil. Connect the diode polarities so that in one case current flows into the coil and in the other case current flows out of the coil.

ACCEPTED +1 vote
by Foxx
March 28, 2018

Answer by swaninlet

Many thanks , much apreciated Best regards

+1 vote
by swaninlet
March 28, 2018

The motor is used to control a rudder. This some times involves rapid changes with the motor sometimes needing to pulse in either direction when changes are small . Thinking about it this may couse sparking and delay using mechanical relays. Is the same circuit you provided suitable to use with solid state relays

by swaninlet
March 30, 2018

Solid state relays such as the "SSR" available from Adafruit normally accept a logic level control input which is positive so to use this you would have to break the control signal into "left rudder" or "right rudder" Beyond this I don't know enough about your application to say a lot. eg: type of motor (ac?, dc?, stepper?, size?, voltage rating?), type of control(proportional position regulator?) etc. Also the technology level you are using (relay and contactor?, PLC?, microprocessor such as Arduino?).

by Foxx
March 30, 2018

Hi many thanks for your comment . Here is what I am wanting to achieve . I have A Raymarine SPX 5 auto pilot on my boat. This drives a very small DC motor which turns the wheel. I am up grading my stearing to Hydraulic this has a pump in the system to be driven by an auto pilot system . I would very much like to use my existing controls and units , to do this I need to increase the load capacity . Hence the relays . My knowlage of electronics is very limited. I would also like to make something that can do the job . Reasons much cheaper than buying a whole new set up and it means I understand the working so could make repairs in the future. With all of this in mind what info should I try and obtain to make it easier to give advice. I live in a remote part of the world where we have to order in bits which takes a long time to get here so simplicity and basics is what I look for. I would also like to take this opertunity to thank you for being so kind as to comment on this subject.

by swaninlet
March 30, 2018

The more I look at this the more I think you were on the right track in the beginning. I checked on the Raymarine XPS5 and they seem to be pushing it for tiller control, not wheel control but it must be adaptable to either. Beyond that they block me out of their website. I've worked out an elementary (schematic) diagram for you using 2 relays plus appropriate transient (spark) suppression which would control a reversing valve on the hydraulic cylinder which you are proposing. If you could give me an email address I will send you a print of this diagram. It's based on a number of assumptions on my part so take a close look at it before using it. My email address is

by Foxx
March 30, 2018

Many thanks for your generosity . I will send you an e mail and will attach the service manual that I have found for the XPS 5 . You are right that they push it for tiller control but they also sell it as a wheel pilot . Which I have. They sell the SXP 30 which is for larger motors such as hydraulic .But pretty expensive and not many availiable being an old model. Will continue conversation by mail

by swaninlet
March 30, 2018

Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account

Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers

Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.

About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.