# Auto polarity reversal

#### wachanna

Joined May 26, 2021
12
Good day chaps, im flambustered with curiosity in search of how to automatically reverse polarity every minute. I have in my possession a 1 horse power 12 volt DC motor, which, if i hook up to a conveyor belt, i want to reverse the direction every minute, but, in order to do that, i would need to manually unhook the power cables from my power supply, and reverse the polarity. Living in the current year we do, it seems there just must be a way to use modern day wizardry to switch the polarity every minute automatically by using some sort of circuit, but since i am no pro, nor even had a class about this stuff, i have not a clue as to how to make such a circuit, so pretty please with the kindness of your beautiful hearts, could you please help me figure this out?

#### drc_567

Joined Dec 29, 2008
1,156
Numerically, converting horsepower to watts, the 12 volt DC motor would require about 65 amps DC (745 watts/12 volts=65 amps) at minimum. So figure on that amp rating, and maybe a little extra, in whatever switching mechanism you decide on.

Joined Jul 18, 2013
28,488
A circuit using four suitably sized SCR's would do it, but instant reversing a 1HP motor is not a good idea with some pause in between to allow a stop first.

#### ScottWang

Joined Aug 23, 2012
7,396
If you don't want to use general relay then I'm thinking to use a 555 and set to one minute, and some transistors, some P, N MOSFETs to build a H-bridge driver, each P, N MOSFET in series with a low values resistor, seperated the P, N, P, N MOSFETs, and each MOSFET in parallel with some MOSFETs to increase the current, N type in parallel with N type, P type in parallel with P type.

* it seems too frequently to reverse the polarity for one minute.

Note :
Don't forget to add the heatsink for the MOSFETs.

#### crutschow

Joined Mar 14, 2008
33,976
A circuit using four suitably sized SCR's would do it
How would that work with a DC motor?

#### Ya’akov

Joined Jan 27, 2019
8,964
If you are using the motor at full power this probably isn't emopugh current handling but this is an example of something remade: https://www.amazon.com/Forward-Reverse-Control-Two-way-Timing/dp/B07P9NZ5WN/

You could build your own circuit, but you might want to start with a commercially built timer module and do the switching part. As @MaxHeadRoom mentioned, you are going to have to pause between direction changes to avoid damaging the motor, they don't like suddenly changing direction at all.

#### LowQCab

Joined Nov 6, 2012
3,928
With a few Modifications this Circuit could do the job.....
It stops the Motor before Reversing direction, and then smoothly ramps-up the Motor Speed.
.
.
.

Joined Jul 18, 2013
28,488
How would that work with a DC motor?
Similar method to the SCR bridge used in DC TM motors, just configured for polarity change.

Joined Jul 18, 2013
28,488
I have in my possession a 1 horse power 12 volt DC motor, which, if i hook up to a conveyor belt, i want to reverse the direction every minute,
Is this a permanent fixture that can utilize mains power?
Or a mobile device of some kind?

#### crutschow

Joined Mar 14, 2008
33,976
Similar method to the SCR bridge used in DC TM motors, just configured for polarity change.
I'm not familiar with that method.
So how is the SCR shut off with a DC supply?

Joined Jul 18, 2013
28,488
This is why I asked in #9 if mains power was available,
But in the case of the T.M.'s the SCR is used on the output of the bridge rectifier in order to ramp up the 200vDC, it turns off every time the ripple transits through zero.

#### wachanna

Joined May 26, 2021
12
If you are using the motor at full power this probably isn't emopugh current handling but this is an example of something remade: https://www.amazon.com/Forward-Reverse-Control-Two-way-Timing/dp/B07P9NZ5WN/

You could build your own circuit, but you might want to start with a commercially built timer module and do the switching part. As @MaxHeadRoom mentioned, you are going to have to pause between direction changes to avoid damaging the motor, they don't like suddenly changing direction at all.
https://www.google.com/aclk?sa=L&ai...6rezwAhVeIDQIHZU7ArcQwg96BAgBEBk&dct=1&adurl= I found this. It doesnt have the power requirements for my 1 hp motor but its a clean simple design i could play with. What could be installed to the manual switch side to make it automatically reverse polarity every minute? My first thought is 2 time delay on/off circuits, but i need a circuit i can trust will only have one way on at a time. How can this be accomplished?

#### Ya’akov

Joined Jan 27, 2019
8,964
https://www.google.com/aclk?sa=L&ai...6rezwAhVeIDQIHZU7ArcQwg96BAgBEBk&dct=1&adurl= I found this. It doesnt have the power requirements for my 1 hp motor but its a clean simple design i could play with. What could be installed to the manual switch side to make it automatically reverse polarity every minute? My first thought is 2 time delay on/off circuits, but i need a circuit i can trust will only have one way on at a time. How can this be accomplished?
A timer and a bistable multivibrator (flipflop), both can be gotten as modules. You would use one timer that pulsed each minute and the flipflop would switch state on each pulse.