# Using a relay to reverse polarity of a circuit.

I am new to using a relay and would like an efficient way to reverse the directions of motors. I have a set-up of 3 motors running off two relays and would like to be able to have a master relay or something to reverse the direction these motors travel. Thank you for your help.

What motor?
How often will you be reversing the motor?
You can use a H bridge to reverse DC motors.
You can use a DPDT relay to reverse motors.

What you think you want to do can't be done. Need to double or triple the number of relays depending on the setup of which motors are to behave identically.
Meaning, use a proper controller or have a mess of relays.

Sorry, I wasn't very descriptive. I am using an Arduino and the whole circuit will be reversed at once so I can just reverse the battery, surely that's possible.

If all you have is single pole relays it would take 4 to do it right, can be done with 2 but that means using NC contacts, not good with motor loads. Have you thought about your kickback diodes? They will be short circuits if you reverse polarity on them.

Then a DPDT relay can do that, reversing the battery is just the same as reversing a motor for
a relay. Make sure to use a single DPDT relay that is break-before-make. Any other arrangement
could cause a dead-short due to timing differences between relays, which for the battery is not
acceptable.

I assume that the motors are isolated from the Arduino, ie the Arduino controls the relays but is
isolated from any part of the motor wiring itself.

If physically changing the positive and negative leads at the battery will truly achieve what you want, then 2 NO/NC relays at the battery can work.

Hi,
You will need two relays;
One to STOP/START the motor, that is apply power.
One to FWD/REV the motor, that is to swap polarity.

Can you please post a copy of your existing circuit, in CAD or a picture of a hand drawn circuit in jpg, png so we can advise properly on adding the reverse feature?

What size/voltage/current are the motors rated at?

Thanks.. Tom..

I just laid out a circuit board for someone that uses this relay to do that.

http://www.futureelectronics.com/en/technologies/electromechanical/relays/signal-relays/Pages/4749057-AZ830-2C-12DSE.aspx?IM=0

His application is pretty low voltage and current but he has been using them for at least 3 years without problems. Basically he charges and discharges a test cell.

outofoptions:
I just laid out a circuit board for someone that uses this relay to do that.

http://www.futureelectronics.com/en/technologies/electromechanical/relays/signal-relays/Pages/4749057-AZ830-2C-12DSE.aspx?IM=0

His application is pretty low voltage and current but he has been using them for at least 3 years without problems. Basically he charges and discharges a test cell.

Note that relay has a polarised coil, connect it the wrong way round and it will not work.

Tom...

TomGeorge:
Note that relay has a polarised coil, connect it the wrong way round and it will not work.

Tom...

I believe there is a magnet in those relays which biases the armature.
This takes less current to operate than normally would be needed.

Has anyone taken these apart to confirm this?

.

TomGeorge:
Hi,
You will need two relays;
One to STOP/START the motor, that is apply power.
One to FWD/REV the motor, that is to swap polarity.

Can you please post a copy of your existing circuit, in CAD or a picture of a hand drawn circuit in jpg, png so we can advise properly on adding the reverse feature?

What size/voltage/current are the motors rated at?

Thanks.. Tom..

Actually need two SPDT relays. Normal position applies power in one polarity. Activate either of the relays will open the circuit. Activate the second relay, while the first is still activated and the power polarity is reversed.

I ran my Peltier experiment this way to cool, wait 15 minutes to stabilize the temp, then set the Peltier to heat for 30 minutes, off to stabilize, then back to cool.

Paul

Hard to find DPDT relays with 5V coils, the current required for DP coil is higher, they are more expensive because they are less plentiful. (I guess).

Paul_KD7HB:
Actually need two SPDT relays. Normal position applies power in one polarity. Activate either of the relays will open the circuit. Activate the second relay, while the first is still activated and the power polarity is reversed.

Can't work surely, you can't reserve polarity with single pole. Or have I missed something?

MarkT:
Can't work surely, you can't reserve polarity with single pole. Or have I missed something?

TWO relays. Cross wire the NC and NO pins to the + and - supply. Take the power to drive the device from the common.

Paul

Ah, I've got you, that avoids the issue with dead shorts that I warned about in #5 - I'd imagined the battery
between the commons (which would need a single DPDT to be safe).

Sound obvious now

For us who need a visual aid

.

larryd:
For us who need a visual aid

.

Reverse the connections to either relay and you will be good.

Paul

edgemoron:
Hard to find DPDT relays with 5V coils, the current required for DP coil is higher, they are more expensive because they are less plentiful. (I guess).

Check, Mouser, Digikey, E14, RS, ebay.
I have more 5V coil DPDT in stock than SPST at work.
Cost because extra hardware involved, no matter what the coil voltage.
Tom....

edgemoron:
Hard to find DPDT relays with 5V coils, the current required for DP coil is higher, they are more expensive because they are less plentiful. (I guess).

The one posted above comes in 5V. That's the one I designed for. I just didn't spend a lot of time looking up the specific one. I think the guy building these boards gets them surplus at some place around San Francisco.