Electrical – A relay that can switch from one source to another – what’s that called

dcrelayremote controlswitches

I want to be able to use a microcontroller to select the power source, from among two, for a 100A DC application.

All the relays I see are ON / OFF, rather than a selector.

So, I'm looking for something with 5 connections:

  • Signal input (say, 3.3v digital, which when activated causes it to "switch")
  • Power input 1 (which I'll connect to a battery bank)
  • Power input 2 (which I'll connect to an AC Adapter)
  • Power output (which I'll connect to the load)
  • Common ground (for the voltage of the signal input)

I'm probably not searching for the correct piece of equipment, but I can't seem to determine what this might be called.

Best Answer

If the ground/common/negative side of your circuit can remain connected, then you need to "switch" only the "hot"/active side (voltage not disclosed) side. That can be done with a SPST (Single Pole, Single Throw) switch or relay.

However there are several things to be aware of if you want to do something like this:

  1. CURRENT Switching such a high current will require a large and expensive relay. These are becoming harder to get and more expensive as this kind of switching is done with semiconductors (transistors, thyristors, etc.) here in the 21st century.
  2. VOLTAGE Switching a high voltage will require essentially a "mains-rated" relay which will add even more to the price.
  3. DC vs AC Switching DC is more difficult than switching AC. Because AC naturally passes through 0V many times per second (50Hz or 60Hz) Breaking high-current DC requires a special kind of relay designed for such applications. This will add even more to the price.
  4. CONTROL VOLTAGE You will not find any relays that can switch 100A @ ???V which can be operated from 3.3V. You will need probably a multi-stage relay driver circuit to allow the 3.3V logic-level to control another circuit with enough power to activate such a large relay.

You make it more difficult to answer your questions when you do not include the working voltage. It limits us to generic answers which may not be applicable to your situation.

Related Topic