Can I use a 12v relay for controlling a 3v or 5v dc motor?

Hi, I have some tiny 3v and 5v dc motors. Can I use a 12v relay as shown here:http:// ww.instructables.com/id/Super-Easy-Reversible-Motor-Control-for-Arduino or should I get a 3v and a 5v relay respectively?

Lambo

I didn't look at that page but assuming its a standard relay design then yes you can use a 12V relay.

The 12V refers to the voltage required on the coils for them to turn on properly. There should also be a amp rating, that refers to the contact ratings, the terminals also have a volt rating but its usually so high that you usually hit the amp limit first.

If you have a 12V power supply that can switch on and off, you can power your motor through the contacts (NC/NO) with no issue. They are electrically isolated, one the relays strongest attributes.

Just make sure you know which terminals are coils and which ones are common, NO, NC contacts to avoid damaging the motor or relay.

Do not try and connect a 12V relay directly to the arduino's output pin. You need the output to go through a transistor and you need a diode across the relay coil.

You will still need to feed the proper voltage for the motors through the contacts.

I see, so the value on the relays are their operational requirement then? Not some maximum value. Hm, still a bit uncertain. If I am controlling the 3v DC-motor (with voltage regulator I assume? Or voltage divider? Resistors?) and some other 4.8-6v servos from a 4xAA battery power, I should use a 6v relay then, and power it all from the 6v, right? And not using the Arduino's power at all? Hm, but how will I be able to control the speed of the DC-motor?

Sorry that my one tiny question suddenly turned into a few more.

The 12V refers to the voltage across the coil for it to properly and consistently switch.

The other contacts have no electrical connection to the coil, when the coil is activated it acts like a magnet and pulls a lever/slider which mechanically switches the contacts.

http://www.glolab.com/relays/relays.html

Meaning when you wire your motor on 3-5V you would likely use the COMMON and NO contacts as you would a switch. When you apply the proper voltage to the coil, you close the switch.

and some other 4.8-6v servos from a 4xAA battery power, I should use a 6v relay then, and power it all from the 6v, right? And not using the Arduino's power at all?

Detailing your power system is something you will need to do at some point. Start with your highest voltage device and pick a power supply or battery that runs those devices. Make sure the supply's AMP capability is at least twice your projected use. You can then regulate down and run the lower voltage devices off a regulator.

Many will tell you the Motor Supply and the Logic Supply should be different (isolated). That's certainly the safe way. If you have 6 or 12V available it hurts nothing to run your relays off your motor supply. Whether you run it off the Arduino's supply or the motor supply is moot, since you need a transistor anyway. I know of only a few relays that can be driven from a logic output and their contacts are too small to run your motors.

Hm, I think some is clearing up a bit. Thanks all! Still miles away though. But what happens with a 6v relay when my battery pack drops below? Should I get a 5v or even a 3v relay and use a voltage regulator to bring it down?

A 6V relay will probbly work at 5V but it will not be as reliable. As you bring the voltage down there will be a point where it stops working.

If you have a 5V arduino the it is simple to use a 5V relay although you still need a transistor to boost the output current. You will not find many 3V relays. There is no need to use a regulator to drive the relay if your supply is so close to the working voltage.

What Mike said + most relays will give you a "minimum pull-in voltage. See if that falls within your projected low battery voltage.