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Reverse polarity switch with delay for DC motor

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Reverse polarity switch with delay for DC motor

Postby rogue_bird » Fri Jun 05, 2009 6:23 pm

I am trying to get a DC motor to run in one direction until it reaches the end position then stop and switch polarity so it will run the other direction when power is reapplied.
Then do the same thing at the other end.

1. timer turns power on for 1min. (7:00am -7:01am)
2. motor runs in one direction until it hits stop position, say 30sec.
3. power to motor turns off when it hits stop position and delays for the 1min. timer to end/turn off main power. also reverses polarity so that.
4. next time the main timer comes on (8:00-8:01) it dose the same thing in reverse direction.

Thank you in advance for any help. This is an important home project that needs to be 100% reliable.
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Postby pebe » Fri Jun 05, 2009 9:44 pm

What voltage and current is the motor?

Is it the power supply to the motor that is switched?
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Postby rogue_bird » Sat Jun 06, 2009 2:06 pm

I am using a deep-cycle 12 volt battery to run the motor.
The motor is rated @ 12 VDC, 2A at full load.
It is actually moving an arm up and down and I need it to stop and wait at each end. I could put a switch on the arm that gets tripped at each end. I am still a little confused how to do this properly and don't want it to run as soon as it changes polarity of the incoming power as I need it to stay there for some time before it needs to move the other direction again. It needs to be automated as I am not there to do this manually.

Thank you for your time on my project.
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Postby pebe » Sat Jun 06, 2009 2:13 pm

OK. I'll draw up a suitable circuit for you.
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Postby rogue_bird » Sat Jun 06, 2009 2:19 pm

pebe-
thank you so much.

I hope I was clear. I don't need the main power timer in the design.
I just need the delay timer included so that it won't start to move again as soon as the arm gets to each side, so the main timer has time to kill the power and wait for the next timed event to go the other direction and do the same thing on that end.

I know I said that the switch could be on the arm. I thought it would be easier as it seems that it would only need one switch. I rather have the switches on either end of the stops. this way they are not on the moving part. either way will work.
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Postby pebe » Sat Jun 06, 2009 7:48 pm

Hi rogue bird, here’s the circuit.

The motor is switched by two single pole change-over relays in an ‘H’ arrangement. Normally, the two ends of the motor are connected to 0V. When one of other of the relays is energised, the motor will turn one way or the other.

IC1 is a 555 timer wired in a bistable mode circuit. When IC1 is triggered, it switches on REL1. It is triggered ‘on’ by taking TR to 0V, and reset to ‘off’ by taking RES to 0V. When TR and RES are both at 12V, the IC stays in its last commanded state. IC2 is wired in an identical circuit.

This is how it operates. Assume the arm is at the top. The limit switch S4 was closed when the arm hit the top stop. The time switch has just put 12V on to the supply rails and the 555s are powered up.

The capacitors C1 will hold the TR pins low for a split second and IC1 will be triggered on. The same would apply to IC2, but it cannot be triggered on because S4 is closed, keeping it in its reset mode. REL 1 energises and S1 changes over and puts 12V on the LH side of the motor while S2 stays unchanged, so the RH side of the motor remains connected to 0V. The motor starts to run, taking the arm down. The limit switch S4 opens up but IC2 can’t trigger on because C1 has charged up via R1 to 12V, so TR is no longer at 0V.

The motor will continue to run until the arm is at the bottom. Then S3 will close and reset IC1. REL1 will de-energise, S1 will change over, and the motor will stop. There it will remain until the timer ends and the 12V supply to the 555s is disconnected.

Next time the timer comes on it will be IC2 that is triggered (IC1 cannot trigger because S3 is closed). REL2 energises and S2 changes over, turning the motor in the opposite direction. The arm will rise until the top limit switch, S4, closes and resets IC2. Then it will stop, ready for the next timed period. So now we are back at square one.

I hope that all makes sense. Just shout if you have any questions.

Good luck with your project.
Attachments
555 Motor reverse.GIF
555 Motor reverse.GIF (8.66 KiB) Viewed 143921 times
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Postby rogue_bird » Sun Jun 07, 2009 12:56 am

Thank you so much! I'll let you know how it goes. I am very grateful for your help. I hope I can get it all put together properly now. I owe you one.
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Help building this circuit

Postby darrena » Fri Sep 25, 2009 8:28 pm

Hi
I am trying to build an automatic door opening circuit for a duck house using a linear acuatuator on a 24v dc circuit.
i need the door to open at a set time when the mains timer goes off and then close an hour or so later so needing the polarity to change.
I understand the circuit you have described will do this ????

I know little about electronics and wondered if you would be kind enough to list the required components and describe how the wiring diagram should look!

Any help appreciated

Kind Regards
Darren
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Postby pebe » Sat Sep 26, 2009 9:01 am

The circuit would operate a solenoid, but you would need an external timer that switched the 12V on for a short period, and switched it on again for a short period an hour later.

You would still need the limit switches to turn off power to the solenoid at the ends of its travel.

But there is nothing to hold the door in its last commanded position so it would need to have neutral balance so it would stay in position.
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Postby rogue_bird » Tue Sep 29, 2009 1:04 am

pebe-

Thank you again for your help. It worked out GREAT. Let me know if there is anything you need :shock:
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Postby bad coffee » Tue Feb 16, 2010 9:27 am

Would it be possible to use one 556 instead of two 555's?

bc
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Postby rogue_bird » Tue Feb 16, 2010 3:11 pm

bad coffee wrote:Would it be possible to use one 556 instead of two 555's?

bc


Yes you can.
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Postby bad coffee » Fri Feb 26, 2010 11:05 pm

I built this circuit with a 556, and it's working great. Thanks for the help.

B
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Postby rogue_bird » Sat Feb 27, 2010 12:13 am

bad coffee wrote:I built this circuit with a 556, and it's working great. Thanks for the help.

B


Excellent, Good to hear. what are you using it for?
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Postby bad coffee » Sat Feb 27, 2010 8:04 pm

Chicken coop door! We're getting our first three chicks next week! Since I ordered the parts from mouser, I figured I'd make three or four and sell the ones to recoup my investment. I've got less than $25 in each one. If I fix the one I fried a relay in they go down to under $20. It doesn't include 12v 2A wallwarts or motors/actuators, though. Still $50 for an auto opener is a pretty good deal.

B
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