# Project that has reverse polarity to motor

Discussion in 'The Projects Forum' started by Jonnieb2013, Apr 21, 2013.

1. ### Jonnieb2013 Thread Starter New Member

Apr 19, 2013
8
0
Hello,

Real novice here so excuse me.

I am undertaking a project which involves sending current to a 12v motor. I then need to swap two wires over to reverse polarity to get the motor to run the other way. I have attached simple diagram of what I need to achieve.

My question is, is there a way of doing this via a relay so that when I push the switch it powers the motor and it runs in one direction and then push it again it reverses the direction?

If that is possible then is there a way of getting a timed relay for say 4 seconds as I want the motor to run for 4 seconds as soon as I push the button and release it?

2. ### GopherT AAC Fanatic!

Nov 23, 2012
8,025
6,785
You need a circuit with 4 transistors (preferably MOSFETS ) with 2 n type and 2 P-types known as an H-Bridge.

Google " H-Bridge" for a good starting point. Your drawing is definately in the right direction.

3. ### Jonnieb2013 Thread Starter New Member

Apr 19, 2013
8
0
Thanks

The red + wire has to be the same wire for each circuit so this is the common wire, so then I need an H bridge relay, not a DPDT relay?

4. ### Jonnieb2013 Thread Starter New Member

Apr 19, 2013
8
0
Would a dpdt momentary rocker switch work by any chance, without the need for a relay or H bride?

Ideally I would use my existing switch, with this in mind would I then need the relay/H bridge (DPDT ?)

How would I wire it up?

5. ### crutschow Expert

Mar 14, 2008
19,805
5,543
A DPDT switch or relay will work to reverse the motor. Just wire the motor to the wiper of each pole. Wire one side of each NO contact to the power. Then cross-wire a jumper from the NC contact on one pole to the NO contact of the other pole. Do the same for the other NC and NO pole.

If you want momentary or time operating then you need to add another relay and timing circuit to turn the power on and off.

6. ### Jonnieb2013 Thread Starter New Member

Apr 19, 2013
8
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Thankyou very much for your help,

I am a novice, you coudnt do a very rough sketch could you as a guide?

What I want to do is push the button once (without holding it down) and then the motor runs for 5 seconds, push the button again and then the motor reverses for 5 seconds.

I guess I would need a relay that holds 5 seconds of charge???

JB

7. ### t06afre AAC Fanatic!

May 11, 2009
5,939
1,227
What you want to implement is often done using some micro-controller. Your tasks can be done with almost any common controller and some relays or a H-bridge

8. ### Jonnieb2013 Thread Starter New Member

Apr 19, 2013
8
0
Can you give me some examples of what I need, pictures or links as I dont know, how do I enable 5 seconds on the motor by only pushing the button once?

thanks guys, appreciate it.

or could I use something light this, a light delay that is controlable from 1 to 60 seconds? (keeps the power going from 1 to 60 seconds)

Last edited: Apr 22, 2013
9. ### Jonnieb2013 Thread Starter New Member

Apr 19, 2013
8
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Do you know how I would wire up this relay?

rgds
J

10. ### tubeguy Well-Known Member

Nov 3, 2012
1,157
198
You could use just the momentary DPDT switch. but you would have to hold it down for as long as you wanted the motor to run. (That is provided the switch can handle the motor current.)

I must point out that immediately switching directions is hard on a running motor (and also hard on what it's driving). It's better to have a short pause for deceleration before switching directions.

If using relays, it would be good to use 2 SPDT relays so they could both be off for a short time before switching directions.

Edit: @ SPDT relays also also can provide braking for a quicker stop.

Last edited: Apr 23, 2013
11. ### Jonnieb2013 Thread Starter New Member

Apr 19, 2013
8
0
Thankyou

Yes, the motor stops for quite a long period until such time I want to reverse it.

I have attempted a wiring diagram for the dpdt switch as attached, not sure if its right or wrong or indifferent and whether there is automatically a bridge between points 5 and 7 and 6 and 8 (to send power to the motor) or whether I need to physically wire these together?

I have shown the main switch at the top. Is it best to have this on the live wire or earth?

Can someone guide me if the wiring looks correct as I don't want to blow anything up? or should the live and earth be the other way round I think along the lines of what was said in post #5:-

A DPDT switch or relay will work to reverse the motor. Just wire the motor to the wiper of each pole. Wire one side of each NO contact to the power. Then cross-wire a jumper from the NC contact on one pole to the NO contact of the other pole. Do the same for the other NC and NO pole.

Once this is mastered then I want to take it a step further and then add some form of timer that will keep the power going for 1-10 seconds after a single push of the button.

Last edited: Apr 24, 2013