How can I reverse polarity to a motor using relays?

Difference in high to low dc voltage

What would be considered low and high amperage using the relay operations listed in previous posts. Also, with using the relays to automate motor control with signal coming from computer, is there feedback or current that can feed back to computer? I think this thread is awesome.

To find the relay suitable,find the current draw,an analogue ammeter is probably the best,but if you are sure the motor draws 10 amps or less you can safely use a mulimeter.If you wish to use a multimeter to read high ampage you must use a suitable shunt. So, what is the Voltage and current rating of the motor you wish to control?

motor ratings

I have a DC motor. 1/8 hp, @ .9 fla.. 30 rpm 75 lbs in. 90vdc

I have hooked up my operation to a DPDT switch that I manually control in front of desk. I wanted to use the powering on of the computer to turn on a relay- hit a switch at top of travel and stop motor. When I turn the computer off I would like a pause (timer) to verify that I have not just reset computer and then allow motor to travel to bottom and hit switch at bottom to stop. Then it would just be continuous from there.

Also, I am using a dc motor controller with potentiometer but this small drive does not have a switch for direction. Thats why I used DPDT. Some have said this would be easy to accomplish but I am not very good with relays. But I am trying. Thanks for all the help.

My motor is 9ovdc baldor. 1/8 hp at .9 amps.

I wanting to complete an operation like this thread has talked about. I manually do this operation with a DPDT switch but would like to do this automated. By this I mean I want to use either a 3.3v or 12 vdc signal from my power supply to turn on a control relay and send lift up and hit a switch at top to stop motor, then use that switch to activate my down relay. Which at the bottom there is a switch also to stop operation.

I thought maybe I could put a digital timer between the top switch and the down operation to make sure that I have not reset system. So this gives me a 1 minute or so to make sure the system is off before it travels down to bottom switch.

I am using 120 ac to my drive and letting the drive do the controlling. I would use the computer power supply to control the relays, thinking this would be safer because teh two circuits would be isolated from each other.

I am just not great with relays, but trying though.

Thanks.

Ron and tblo163, thanks a lot!
Im building a solar tracker for my senior design project and this diagram is exactly what ive been looking for. Thanks for the quick response and help!

kirkhan

Use with a arduino

I guess i overlooked some specs and the drawing youve given uses a switch to control the motor direction. How can i use 2 different inputs to control direction with the relays?

You just need one double-pole double-throw relay:
**broken link removed**

thanks colin55, but im limited to 5v power supplies that come from a arduino board. Do you have anything that i can use with that?

Simply connect the circuit to the 5v supply.

kirkhan said:

I guess i overlooked some specs and the drawing youve given uses a switch to control the motor direction. How can i use 2 different inputs to control direction with the relays?

Click to expand...

I have attached a basic schematic of what I believe you are looking for. The circuit is an expansion of the circuit Eric posted back around post #6. This allows one PIC out for CW rotation and one for CCW rotation.

There are several ways to go about doing this. For example to totally isolate the motor circuit from the PIC an opto coupler could be used.

Generally I like to drive the motor and relay circuits with a separate discreet power supply as PIC chips really seem to dislike noise from the motor and relay coils.

One problem is if you want to drive a 5 volt motor it will require over twice the current of a 12 volt motor to do the same amount or work. The same holds true for the relay coils.

Something open for discussion with the circuit Colin posted is the full wave diode bridge using 8 diodes rated at 1 amp. Given a choice I would not parallel the diodes but use 4 diodes rated at 3 amps. Only to say I would not do it or configure the bridge that way.

Also there are turn key chip solutions out there that will do what you want done using an H bridge to drive a motor with PIC inputs so that is an option. Much of all of this depends on how big the motor is and the current it will draw. I did not include a fuse scheme in the schematic but fusing should be a consideration.

Ron

Thanks a lot Ron, this circuit looks like something simple i can build in no time.

The 5v supply is just switches. The motors have their own power supply coming from a solar cell. They both, combined take 500mA at 12v. So do i still need to fuse the lines or is this power consumption so small that if can be ignored?

Also, i had a quick question about your diagram, this might sound stupid but what is the purpose of the transistors? Are they there to not allow random voltage spikes to set the coil?

Thanks,
kirkhan

kirkhan said:

Thanks a lot Ron, this circuit looks like something simple i can build in no time.

The 5v supply is just switches. The motors have their own power supply coming from a solar cell. They both, combined take 500mA at 12v. So do i still need to fuse the lines or is this power consumption so small that if can be ignored?

Also, i had a quick question about your diagram, this might sound stupid but what is the purpose of the transistors? Are they there to not allow random voltage spikes to set the coil?

Thanks,
kirkhan

Click to expand...

First the reason for the transistors. If you look at your PIC data sheet you will likely find the maximum current out of a DO (Digital Out) pin of your PIC is about 20 mA. That is hardly enough to pull in any relay. Thus we use a transistor to interface the PIC to the relay. Matter of fact you could use a TIP120 transistor with a 1KΩ base resistor. The idea is we drive the transistor into saturation using it as a switch and the transistor switches the relay. In general, do not exceed 20 mA per pin.

I think I read you were using an Arduino and if so you may want to give this a read. There is a section on motor control that includes some of the H bridge chips I mentioned earlier.

I would still fuse the motor simply because if for any reason the motor gets into a stall configuration things will get ugly as the motor begins to try to draw current well exceeding its ratings.

Ron

hi,
Another advantage of this type of relay drive circuit, is the dynamic braking action of the motor when the relay contacts short out the motor.

From what ive read, a H bridge does exactly what i want it to and i dont need all those relays and transistors. Thanks Ron for the diagram though.
I am going to go with the link you sent me and making changes for my circuit. (**broken link removed**)

Thanks again Ron,
kirkhan

Hi Ron, off of what ive read the H bridge does exaclty what i need it to and eliminates the need for the relays and transistors. I think im going to go with that part and use the tutorital on the website you gave me (**broken link removed**). Thanks for the previous schematic, i will go back to that idea if this doesnt work.

kirkhan

Hi Ron, off of what ive read the H bridge does exaclty what i need it to and eliminates the need for the relays and transistors. I think im going to go with that part and use the tutorital on the website you gave me **broken link removed**. Thanks for the previous schematic, i will go back to that idea if this doesnt work.

kirkhan

Hi Ron, off of what ive read the H bridge does exaclty what i need it to and eliminates the need for the relays and transistors. I think im going to go with that part and use the tutorital on the website you gave me. Thanks for the previous schematic, i will go back to that idea if this doesnt work.

kirkhan

Hey. I'm new here and wanted to see if u guys can help me. Its basically the same premise as the motor reversal issue. I just bought 2 power folding side mirrors for my truck. My truck is not equipped for them so I have to build my own controller. Polarity determines whether the mirrors extend or retract. I could easily do it with a manual switch, but of course it has to be cooler than just that. I'm trying figure out the simplest circuit I can design using the installed mirror directional control switch. When its in the neutral position I want to be able to nudge it left/right and have the mirrors extend and retract. A momentary switch type of thing. But, I also want them to extend when I turn the vehicle on, then retract when I turn the vehicle off. Anyone here have any ideas how I might accomplish this with the least amount of headache? Or setting my car on fire!!!

You can do it another way to.

1) one relay acts just to turn the motor on
....a) SPST if you just want on
b) SPDT if you want brake and on

2) 2nd relay changes direction (DPDT)

Ok. But how would u get the mirror to retract when the vehicle is turned off?