reverse polarity circuit

Discussion in 'General Electronics Chat' started by synaps, Apr 5, 2009.

  1. synaps

    Thread Starter Member

    Mar 26, 2009
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    hi can you show me how to wire the circut below

    i have 2 turning trays that travel 6 inch up and 6 inch down we start with it 6 inches up i have it wired with a polarity 6 pin dpdt toggel i need to know where to mount the toggel in order to change direction after it stops at 6 inches down if i put the switch in the center and the tray trips it the reverse happens right then or will it finish the cycle to the limit switch which is set at bottom and top of the unit
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    If I understand your requirement, it is more conventional to use limit switches to change a motor's direction of travel. A single DPDT toggle switch can't be placed to do that function automatically.

    We need more details, though. Is the motor AC or DC? Can microswitches be placed where the trays will make predictable contact?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    What is a turning tray?

    Ok, so you have a total travel of 12 inches.
    I think you mean that you have it wired with a DPDT toggle switch so that current flows forward through the motor when the toggle switch is in one position, and reverse throught the motor when the toggle switch is in the other position?

    If the DPDT toggle switch is connected to a brushed DC motor in such a fashion that changing the switch position causes the direction of current flow through the motor to reverse, then the motor will change direction right away. However, this is very hard on the motor, and I don't recommend it.

    Instead, a DC brushed motor's terminals should be shorted together until the motor is stopped. Shorting the motor's terminals acts as a brake, causing the motor to stop more quickly than if it was just coasting. Once the motor is stopped, the power can be re-applied in a reverse direction.

    If the motor is a capacitive start AC motor, it will continue in the same direction.
     
  4. synaps

    Thread Starter Member

    Mar 26, 2009
    21
    0
    I AM SORRY I EMAILED YOU THE RESPONCE I AM A NEWBY
     
  5. synaps

    Thread Starter Member

    Mar 26, 2009
    21
    0
    hello me again
    has anyone thought about my problem to automate the curing oven.
    i have 2 tables 12x18 one above another like they are stacked they start out with the front tilted up at 30 deg the timer switch kicks on a simple screw shaft will move the tables down 12 inches then stop this is done in cw rotation then after 3 hours and by fliping the dpdt switch change polarity of the motor and bring the tables back home to +12 then stop for 3 hours what i need is to automate the dpdt switch to change polarity without me tripping it i need to know where to mount the toggle or rocker switch so that before the table hits the limit switch it will turn on the polarity switch, so that when the timer kicks back on it will be in reverse this cycle runs 24 hrs a day 7 days a week for 4 weeks then the part is cured the timer is a programmable digital timer that can program 20 different cycle times in 24 hours than you
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Assuming we're talking about a DC motor and N/C limit switches, one of the two attached circuits will run up-hold-down-hold-up-hold... The drive for the transistor would be a 3hr-High/3Hr-Low timer.

    ken
     
  7. synaps

    Thread Starter Member

    Mar 26, 2009
    21
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    i am sorry but i dont understand the switch where do i place it at the end of the cycle is it a push button switch and what type of timer are you showing here and the relay is what sorry for the ignorance this is the first time project for me i am the formulation chemist is there any way you can simplify thisthank you
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    I added a cheap 24 hour timer that plugs into the wall. I replaced the resistor/transistor/diode/DC-relay with a 120VAC relay and plug that connects to the timer. Are there already limit switches in the unit? If not, not knowing how the motor/trays are arranged, I can't tell you where to place the "normally closed" switches (Probably "microswitches") to stop the tray in the up and down.

    I hate to discourage you, but this is about as simple as it gets for an automatic motor reversing system. Is there someone that can assist you in the wiring?

    Ken
     
  9. synaps

    Thread Starter Member

    Mar 26, 2009
    21
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    ok i am sorry about my ignorance i just have problems reading these drawings an i am by myself no help just me if i am thinking right i already have the programmable timer and it is set at 12-6-12-6 so on each setting is on for 11 min then i have anoher timer that kicks on with opposite polarity at 3-9-3-9 so on this is how it is set up now but i only want to use the one timer and one power supply reason is i burn my power supplies up.
    anyway i hook the wall timer to the wall and to the walwart set it the power comes out and goes to this switch then comes out to the motor ok where do i put the switch i do not have limit switches on it now but i want to install them when i change to this switch so can you tell me where to put the switch at in the circuit i know where you probably think i should put it ha ha thank you for your time
     
  10. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    My circuit can be implemented with one timer:
    12p(on)-3p(off)-6p(on)-9p(off)-12a(on)-3a(off)-6a(on)-9a(off)-12p(on).........

    The motor voltage is 12VDC, right?
    What is the current or wattage on the motor?
    What is the voltage/current/wattage rating of the power supply?
    What is the motor RPM?
    How far does the motor/tray move "after" you remove it's power?
    What is the temperature in the curing oven?

    A bunch of photos would help in determining how to arrange the limit switches. That is the critical part.

    Ken
     
  11. synaps

    Thread Starter Member

    Mar 26, 2009
    21
    0
    ok
    the motor is 12-24 vdc gearmotor
    1 amp power
    power supply 12 vdc 1.5 amp
    motor speed 10 rpm
    motor does not move without power
    enviroment 160 deg c 65% humidity
     
  12. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    This would require that the limit switches be outside the oven. I'm assuming the motor is outside of oven.
    Pictures of how the motor links to the oven case and the internal trays will help.

    Ken
     
  13. synaps

    Thread Starter Member

    Mar 26, 2009
    21
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    is there such a switch that when a tray trips it stops changes polarity then when power is added again starts in the opposite direction
     
  14. synaps

    Thread Starter Member

    Mar 26, 2009
    21
    0
    yes the motor is outside of oven and i am sorry but i cant send pictures i can tell you the motor is just a linear gearmotor with the screw shaft comming out of it going to the aucuator and turning the table move up and down the shaft the motor and shaft are stationary
     
  15. synaps

    Thread Starter Member

    Mar 26, 2009
    21
    0
    can someone answere my question is there a switch for a brushed dc gearmotor that will start-stop-change polarity-start thanks
     
  16. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    That's my circuit, but because of the oven temp and humidity, the limit switches can't be placed inside the oven where the travel-nut on the linear screw, or the tray positions could trip them.

    Without seeing the physical drive arrangement, even sketches, I'm afraid that can't help much more.

    Is it possible that one doesn't have access to a digital camera in this day and age? ;)

    Ken
     
  17. synaps

    Thread Starter Member

    Mar 26, 2009
    21
    0
    ok please lets say temp and humidity is no factor can you explain how your circuit would work like do i need 2 switches one when table goes down hits switch stops then change polarity timer kicks on in 3 hrs runs tray back up then hit switch on top stop and reverse then timer kicks back on and runs it down again if this is it then when the tray hits switch 1 and then leaves to go to switch 2 trips this one when it comes back to switch 1 how does it switch it back or is there like a push button that it just hits and not flip like a toggle or rocker
     
  18. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    OK this is speculation. The sketch is how I see the tray tipping mechanism. The motor with a lead screw moves a lever arm back and forth tipping the tray(s). I added two options for placing the lever-arm Microswitch limit switches. The photo is the type of switch that I'm thinking about.

    Ken
     
  19. synaps

    Thread Starter Member

    Mar 26, 2009
    21
    0
    ok i see, i can do option a now the switch that i use is what type a dpdt 6 pin lever switch i will jump it over and then when the nut hits it on the down it will change polarity i dont think this will hurt the motor it is only traveling 10 rpm but i can put a 2 second relay in it before it gets to the polarity switch so if i turned the timer off then the trays will transverce back and foward constantly they come down hit switch a change direction back home to switch b then back to switch a and so on is this right?

    needed
    name of switch is it a dpdt 6 pin lever switch
    place them at each end of the cycle
    place relay right before polarity switch if necassary
    wirring comes out of power supply going into switch a come out of switch a to switch b then to motor just reverse leds on switch b from a please let me know if i am correct if so i will wire this tonight thank you

    sam
     
  20. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    I don't think you quite understand, the relay "is" the polarity switch. It functions like the DPDT (double pole-double throw) 6-terminal manual switch you were using. The timer is flipping it, instead of you. Maybe the fact that in my schematic the 6 relay contacts (upper right) and the relay coil (lower right) look like separate things.

    The limit-switches are SPDT (single pole-double throw), with only three contacts: C (common), NO (normally open), and NC (normally closed). You will use only two contacts on each, the C and NC. These provide a current path to the motor, until their button/lever is pushed.

    The timer turns the relay on and off every three hours, reversing the polarity and direction of the motor every three hours. Just as if you are flipping you switch.

    The limit-switches just cut the power to the motor when the UP or DOWN limit is reached.



    With the relay off, its contacts select the polarity that drives the motor in the DOWN direction until the DOWN limit-switch is contacted.

    This opens the DOWN limit-switch contacts and shuts off the power to the motor. The motor just sits, holding the DOWN limit-switches contacts open.

    Three hours later the timer turns the relay on.

    The relay's contacts reverse the polarity, and through the UP limit-switch, drives the motor in the UP direction.

    When the UP limit-switch is contacted, the power to the motor is again cut off. The motor just sits, holding the UP limit-switches contacts open.

    This repeats every three hours.

    Does this help? Or would a physical wiring sketch help more?

    Ken
     
    Last edited: Apr 7, 2009
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