inexpensive timing relay circuit

Discussion in 'The Projects Forum' started by strpdbas, Dec 24, 2008.

  1. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
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    newbee
    I would like some help building a timed, motor reversing circuit. I am building a prototype bi-directional, rail mounted, HID light mover. I am using a Hurst (mfg.) synchronous 10rpm, reversible, gear drive motor. The motor has 4 leads, 2 blue, 1 red, 1 black. There is a .68uf cap across the red and black leads.When current is applied to the blue and red leads the motor runs CW rotation. Switching the current, using a S.P.D.T. reversing switch, to the blue and black leads produces CCW rotation. The motor is rated @ 115vac 7.5w. Both the motor and the controller will move along the rail. I can use adjustable stops at each end of the rail to activate a micro switch (one on each side of the controller). When the switch hits the stop I want to have a delayed on time of about 10 seconds (can be fixed or variable dwell). After the delayed on time power is restored to the motor reversing the motor direction and repeating the cycle. Economy is a major consideration. I have found a supplier of a solid state relay to perform the entire process but they cost $85.00 ea. I am hoping I can purchase the less sophisticated components on EBay for a lot less money. Any help would be appreciated.
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    OK.

    1. You have two micro switches, mounted on either sides of the moving controller driven by an AC motor and will be triggered by mechanical stoppers.

    2. You can control the motor rotation direction via a SPDT relay.

    3. When micro switch activates, you want an adjustable time delay of ten seconds. In this time period, motor is not running.

    Because of requirement 2 & 3, you will need to use two relays. One to control the motor direction and one to control the motor power. The scheme of the design will then be:

    1. A set/reset flipflop, sets and resets by the respective micro switch on either side. The Q output of this flipflop control the motor direction relay.

    2. A 555 one shot timer, triggers via both micro switches and disconnect the power to the motor. After a time of ten seconds, reconnects power.

    Do you want a circuit drawn up for you?
     
  3. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
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    :) I would be eternally grateful for a ckt. diagram. I have thinking about this so hard my head hurts. Thanks in advance for your help.
     
  4. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Here it is. If you have questions about the circuit, please ask here. It can look intimidating but actually it is quite straight forward. Takes some times to understand how it works first.

    [​IMG]

    It is often good if you have your location filled in so people know where you are from as sometimes it is difficult to get some electronic parts in certain countries.
     
  5. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
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    WOW, you are the man. Thanks for responding so quickly. I hope you don't mind if I contact you again in regard to the schematic. I will study it carefully. Have a healthy and prosperous New Year, and thanks again for your help.
    As far as location goes, I'm a Yank from NY.
     
  6. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Hi strpdbas,

    You can ask questions here and get a much faster response than using PM. Your question is related to purchasing parts so are location specific and forum users in NY or USA can point you to better shops than I.

    You can use the 2N7000, which is much more common and easily available. Just put in "2N7000 N-CHANNEL MOSFET" into Google and you'll get lots of hit. Other possible equivalent is BS170. Compare their offer prices and don't pay more than 10 cents for each though.

    You can build it on a solderless bread board but please take care of the mains voltage on the relay terminals.
     
  7. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
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    OK, I'm new to using forums and am still feeling my way around. I assume that a majority of members are in the UK, a country I would like to visit before I die!!
    Thank you
     
  8. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Visit UK? Why not. A dollar will soon worth more than a Pound. :D

    Do keep us posted on your progress.
     
  9. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
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    0
    I will keep that in mind, let me know when the pound = dollar and I will book my plane fare. LOL
    A few more questions, please pardon my ignorance but I want to get this right the first time and am excited to begin.
    I assume the limit switches are momentary and are used to activate the appropriate side of the circuit. When the switch hits the stop it releases the other half of the ckt, activates the time delay (adj. with R3), then reverses the motor direction and repeats the cycle.
    I am building the power supply. I intend to use a 120vac/12vac tx rated @ 1A. attached to a full wave bridge. I assume C9 is for power conditioning. Is this OK?
    Do you have any recommendations on the type of caps. I use? I am considering radial electrolytic for all. It is my understanding they can be installed either way, except for C8 & C9. I don't see a C3 in the diagram, is this correct?
    I am in the process of ordering all of the components. So far I have managed to find everything I need, including a solderable PCB and enclosure for about $17.00 US.
    Again, many thanks.
    strpdbas
     
  10. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Yes, momentary one will do. The proper sequence of event is: limit switch struck the stopper. Motor is power OFF first before its direction is changed. There is a 23ms delay between these two events. So when the motor direction is changed, there will be absolutely no electric current from the mains going into it.

    You will get about 16V across C9 with that arrangement. If you are using 12V relays, they might need series resistors but it will be fine just for short time testing purpose. I assume some voltages would be dropped by the 2N7000 too. In an actual test you can measure these voltage and determine if and what series resistor is needed.

    Only C8 and C9 need to be electrolytic, for others any type of non polar, non electrolytic capacitor with 50V working voltage will do. The requirement is very relax.

    The capacitor designation is probably out of sync as I deleted extra component when I finalize the schematic.
     
  11. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
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    In regard to the power tx, what would be the lowest amperage rating I would need to operate thie ckt. still using the 120vac/12vac winding? This is the single most expensive component. Also, do you think I should try to find relays with a higher voltage coil?
     
  12. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    Transformers are usually sold and listed based on VA rating.

    The (VA) rating of the transformer in this design depends on how much current the two relays take. Consider the small handling power of the relay I would say 200mA total for the relays is sufficient. So a 3VA power transformer is good.

    Relay coils can usually withstand quite a range of voltages within 5~10% of their rated voltage. I doubted you can find any relays rated for 13V or 14V. You don't need big relays, just tiny ones with a contact current and voltage rating to suit your application.
     
  13. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
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    Can I use a 12.0 2.5va? I can't find 3va. Also, could I use a 12.6v unit?
    I'm almost there!! I found a pretty cool program PCB123 (free download). You can select the board size you want to use, drag and drop components etc. The only difficulty I am having is laying out the board wiring routes. I will probably hard wire the first unit to make sure it works properly. If it does I probably will attempt making my own pcb. I'll keep you informed of my progress unless you are getting tired of hearing from me. Thanks again for all your help.
    Joe
     
  14. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    The transformer's rating fine but the secondary voltage is too high. These small rating transformers has bad voltage regulation and without load could gives out 13~14V AC. This would cause the rectified voltage become too high like 18 to nearly 20V.

    What is the next lower voltage available? e.g. 10V or 9V? You can try a 10V one.

    Forget about PCB at the moment. Make one that actually works and then decide on how to make it fit on a small PCB.
     
  15. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
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    What relay coil voltage would I need if I were able to find both? In other words if I use a 6V tx do I use a 6V coil? If I use 10V tx can I use the 12V coil or must the coil voltage match the tx voltage?
     
  16. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
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    What about using an open frame tx? Is their output voltage more stable?
     
  17. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Yes and yes. Use 6V relays if the tx is 6V and a 12V relay if the tx output is 10V.

    Normally these compromise don't become a factor because most knows that the tx rms voltage becomes higher after rectification and smoothing so will add a voltage regulator IC in order to get a fixed voltage DC output.

    For your application, adding a voltage regulation IC just cost more and produce heat with no additional advantages.

    The bad voltage regulation problem of very small transformer (less than a few VA)is related to the use of thin winding wiring of the transformer, not its packaging.
     
  18. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
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    I have found all of the parts I need to put this thing together. I have a few questions regarding the resistors. First off are 1/4w 1% metal film resistors OK? He has all sizes, however you call for 2.2k, and 330k. He has 2.21k and 324k and 332k. All others are an exact match.
    In regard to the PCB I would not consider them until I get the first unit working. I just thought the design program was pretty cool.
    Regards, Joe
     
  19. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    The resistance values are not critical. Any 5% resistors, carbon film or metal film will do. 2.21K and 332K are perfect.
     
  20. strpdbas

    Thread Starter Active Member

    Dec 24, 2008
    99
    0
    OK thanks. One last before I break out the soldering iron. Regarding the bridge rectifier, can I use a KBK-08? It is rated @ 4A/800V.
     
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