Need Reversing Polarity Motor Driver

[JimiRo]

I need to make a light mover for my vivarium. Instead of using two lights-one on each side-I want one light on a trolly to move back and forth, over and over again, with a pause of approx. 10 to 30 minutes on each far side, I have two large plants on each side of the cage that need the most intense light. It doesn't have to pause at each end, but it would be ideal if it could. Remember the motor needs a second or two delay before switching polarity so it won't damage the motor. My diagram shows the easiest thing that I could come up with, but I would rather make a timer circuit or something. The 30 rpm gearmotor is 12 VDC and less than 2 amps. Thanks in advance for any help.

 

[crutschow]

You certainly could make some sort of custom timer circuit if you really like to reinvent the wheel, but your design seems simple, inexpensive, and effective. Since my motto is KISS, don't see why you want to mess with that.

 

[JimiRo]

I was kind of looking forward to building my own circuit, if I could find the right plans, or get some help modifying an existing, archived circuit. It would also be cheaper to make a circuit, since I have to buy two $12 timers. I already had two 555 ICs and most of the other circuit components. But if you think it would be too difficult to find existing plans, I'll go with my diagram. I guess I can make enough room for the timers and power supplies in the hood or underneath the vivarium. Do I need any diodes or anything to protect one power supply from power coming back from the other power supply or is the protection already built into them? I've been collecting power supplies for years, and have a couple of drawers full of them. They're the kind that come with electronic equipment, such as keyboards, cordless phones, chargers, etc. I've even got one from the original 1980's Atari video game console. Also, my dual timer won't work the way I thought when I made the diagram. It was a timer I already had, but the instructions were missing and I assumed that the dual outputs could be set independently of each other, but that is not the case. I'll be using two individual Brinks single output, digital timers, instead of the dual output timer in the diagram. If you think my design will work alright, then I'll go with it.
Thanks for the time and advice.

 

[crutschow]

You bring up a good point about the power supplies. Connecting them the way you show would apply negative voltage to the positive input of the "OFF" supply and that would likely damage the supply. And diodes won't help to protect against that. Can't think of a way to protect them either.

But here's a simpler way. You could do it with one DPDT relay, one power supply and one timer. You cross-wire the relay to reverse the voltage when energized. Thus if you energize the relay for half the time and de-energize it for the other half you should get your required movement. See attached.

You can get a 120VAC relay and control it from your timer output.

 

[MikeMl]

This has come up before:

Read my posts here:

Thread 1

Thread2

 

[JimiRo]

I had actually thought about the relays before the two power supplies, but I wasn't sure where I could find 120vac relays, would 'The shack' carry them or even a hardware store?

 

[crutschow]

A short search of the Shack website produced this.

 

[MikeMl]

I had actually thought about the relays before the two power supplies, but I wasn't sure where I could find 120vac relays, would 'The shack' carry them or even a hardware store?

If the motor is 12Vdc, and you already have a single 12Vdc power supply, why not run the timer and relay on 12Vdc?

Here is a timer that is on for ~30 sec, and then off for ~30 sec. When the relay pulls in, the motor runs CW until the output shaft/carriage opens the CW limit switch, thereby stopping it. When the relay drops out 30 sec later, the motor runs CCW until the output shaft/carriage opens the CCW limit switch. As soon as the motor begins to move in the opposite direction, the respective limit switch re-closes.

The 555 timer chip can only sink 200mA, so the relay coil resistance must be 60Ω or more.

 

[JimiRo]

I was hoping for more like 10 to 15 min at each end, I found this countdown circuit kit, yesterday. It uses jumpers to pick from ten different second amounts from 8 to 8192, at the end of the count down the relay starts the motor until the power is shut off. I would like to simplify this circuit to do just one of the amounts. The 1024 second(around 15 minutes) countdown would be all I needed it to do. I guess I would need two of them, one for each direction, with limit switch. Or can your 30 second circuit be modified to allow more time?

The kits are available from Carl's Electronics, www.electronickits.com. It's part of the 3 kit combo.

What's the difference between a 555 and a 555cn IC?

 

[JimiRo]

I will definitely have a use for the 30 second circuit also, I'm a sign maker and have been wanting to make a kinetic sign to get more attention from the passing traffic. Thank you very much, MikeML.

 

[MikeMl]

You can use the timer kit you showed in lieu of the 555 timer i showed. You will need a double-pole double-throw relay in place of the single pole one in the timer kit.

The relay-limit switch-motor part will work with any timer, as long as the time period is at least as long as it takes the motor to run from one limit switch to the other.

You can change R1 (up to 5meg) and C3 (up to ~330uF) in my circuit to get a delay of R1*C1 = 5^6 * 330^-6 = 1650 sec = 27.5min.

**broken link removed**.

 

[JimiRo]

Thanks a lot, I would rather use your circuit than order the other one that I found. Yours seems to be a little simpler, and 27.5 minutes will work just fine. I forgot to ask earlier, do I need to use two separate power supplies, one for the circuit/relay and one for the motor? Is there any difference between the NE555 and a 555CN? I assume there is. I actually have some 555CN timers and a lot of other components that I got from a girlfriend's grandfather's workshop, after he passed away. They were just going to throw it all away. Thank you very much for all the help, it is greatly appreciated. I wish I could do something for you guys. I'm a graphic designer, so if you ever need any artwork or logos designed, vectorized, or cleaned up, just let me know.

 

[MikeMl]

You can try a single 12V supply. You may run into a problem where the inductive kick from the motor or relay may cause erratic timing of the 555. Get it running first without the motor connected and with a much smaller delay (you will grow old waiting for 27 min). Capacitors C1 and C2 are there to prevent spurious triggering, so they need to have very short leads (locate them close to the 555 pins). Layout is important. Wire the 555 circuit on a stripboard first. Do not run the motor/relay/limit switch wiring through the traces on the stripboard. Use #16 AWG or larger for any wire that carries the motor current.

Read the data sheet I linked. It will answer your CN question.

 

[JimiRo]

Okay, I guess I should have mentioned, I'm an artist, all my artist friends agree that we usually aren't to good at complex math. I barely made it through high school algebra, and haven't used it since. I've repaired broken boards with jumpers and replaced a lot of blown components for my musician friends, but this is the first circuit that I have ever made from scratch. I can build a model airplane, and I know my way around a soldering iron, so I thought I'd give it a try. So, can I use a 555cn, or not? I read the data sheet, but didn't understand about substituting different 555's. I don't know what tape, reels, and rails are, or MDIP, MSOP, and SOIC means. Are the pins arranged differently? Sorry for my confusion and ignorance.

 

[JimiRo]

Okay, if I understand it correctly, the only difference is the dimensions.

 

[MikeMl]

Okay, if I understand it correctly, the only difference is the dimensions.

I'm not sure, but I think the CN is the DIP, which is the one you want.