Archive: 12v Relay timer

Discussion in 'The Completed Projects Collection' started by StevePage, Apr 19, 2006.

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  1. StevePage

    Thread Starter New Member

    Apr 19, 2006
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    I want to make a timer that will trip a relay to turn on a pump every 10 minutes. Thats easy, what I can't figure out is how to make it turn the pump on at 10 minutes, then run the pump for 1 minute, and then start over. This is a project for my fishing boat, I need to conserve my battery, but I need to keep my fish alive also. The way it is setup now it will run untill I turn it off, I need it to run for 1 minute every 10 minutes untill I turn it off. Any help would be appreciated. I'm poor and would like to build it myself, I have found products that cost 75-100 dollars that will work but I'm trying to not spend much money on it. Thank you!

    I think this will work but its expensive and "overkill"

    http://www.ab.com/industrialcontrols/produ...-hnc_specs.html
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    You should be able to do this with some batteries, an 8-pin PIC like the PIC16F675, a transistor switch, and an ON/OFF switch. You can get everything you need from Microchip in their PICKit1 which is $35.00. I don't think it gets much cheaper unless one of the folks here has a 555 solution.

    Think of the fun you'll have learning to program and doing the whole thing youself with a little help from your firends.
     
  3. StevePage

    Thread Starter New Member

    Apr 19, 2006
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    thank you, I'll try to figure it out. I may have to repost for some help :D Whats the web address of Microchip?
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    I was being serious about learning to program a micro controller and the PICKit1 is an excellent way to start. For the price of $35.00 you get a board for programming parts and prototyping simple circuits. It also comes with a CDROM that contains development software, and two blank parts you can use.

    To design the electronics we should start with the relay. What can you tell me about it? Part numbers, coil resistance, any ratings or other data you may have. the basic idea is to connect one side of the relay to a positive voltage, the other side goes to the collector of a Bipolar Junction Transistor(BJT). The emitter goes to ground. The base is connected through a resistor to the microprocessor. We also need a diode across the coil to limit the voltage on the collector when we turn the transistor off. Here is the idea of the relay driver without the component values.

    [attachmentid=1386]
     
  5. StevePage

    Thread Starter New Member

    Apr 19, 2006
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    What I have is an Attwood 1250 gph pump running at 3amps full load. I have a 12v power source at 1100 amps (marine battery) Does this help with the relay value? I think I could just use a basic automotive relay, I have one of those and the diagram for wiring is simple, I don't have the electrical specifications on it but it says it will handle 30 amps so it may take more power than a 555 has to trip it.

    [attachmentid=1387]
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    On your automotive relay the 30 Amps refers to the relay contacts. They should be more than suitable for running the pump. The relay has one end of the coil connected to ground. The other end is connected to a source of 12V power. Do you have the ability to connect the relay coil to a 12V source and measure the current in the coil. This will tell us what size transistor switch is required. Alternatively, can you measure the DC resistance of the coil?

    I think the PIC12F675 will solve the timing problem. There are probably other parts that would work but this one comes with the starter kit.
     
  7. n9352527

    AAC Fanatic!

    Oct 14, 2005
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    You can also use 555 timer configured as an astable with 11 mins period and 10/11 duty cycle. Have a look in this page, specifically the 555 in astable mode (Fig. 9b). Just copy the circuit and calculate the R1, R2 and C values to give you 11 mins period and 10/11 duty cycle.

    Use a switch to turn the whole circuit on and off, and use a transistor buffer to drive the relay. The output would be inverted (i.e. high for 10 mins and low for 1 mins), to fix this use a PNP or PMOS transistor or use the NC contact of the relay instead (the motor would be off when the relay is energised instead of the other way around and this would use a little bit more battery juice). If you are using BJT, don't forget to set the appropriate base current with a resistor and as Papabravo mentioned, don't forget to select a suitable transistor (current and voltage rating).
     
  8. StevePage

    Thread Starter New Member

    Apr 19, 2006
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    [attachmentid=1399]
    Will this work? Just wanting a second opinion, I got this in an email and I'm not 'inclined' enough to read it correctly.

    [attachmentid=1400]
     
  9. n9352527

    AAC Fanatic!

    Oct 14, 2005
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    You need to find out how much current the 555 can sink. If it is higher than the relay needs then you need to buffer it with a transistor. I have a habit of buffering the output anyway, probably a good idea even when the 555 can drive the relay directly.
     
  10. pebe

    AAC Fanatic!

    Oct 11, 2004
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    The LMC555 will sink 50mA.
     
  11. JohnnyD

    Well-Known Member

    Aug 29, 2006
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    I'd definately go down the 555 timer route. The NE555 can sink and source 200mA. I measured the coil resistance of a standard 30A automotive relay and it was around 70ohms so it should draw around 170mA @ 12v.
     
  12. Chris Wright

    Well-Known Member

    Jul 26, 2006
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    Is it just me or are others having problems with the attachment links in this thread not showing up?
     
  13. cenee

    Member

    Apr 20, 2006
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    Try this circuit. Use a 7812 if you want to use a 12 volt relay, just make sure that your wall transformer for this 555 circuit (pump separated) is at least 2.5 volt more than your voltage regulator; but no more than 18v. Good Luck.
     
  14. JohnnyD

    Well-Known Member

    Aug 29, 2006
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    cenee - that circuit looks good. There might not even be a need for the transistor on the output of the 555, if the relay coil consumption is under 200mA.
     
  15. Chris Wright

    Well-Known Member

    Jul 26, 2006
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    RadioShack has an automotive SPST relay (275-226) with a coil rated at 12vDC/400 ohms which would only draw 30mA.

    (They have two other SPDT relays rated at 12vDC/80 ohms and 12vDC/320 ohms drawing 150mA and 38mA respectively and are half the cost, but are special order.)



    Good stuff! But is the 7812 needed since the input source is a 12v marine battery in the boat?
     
  16. JohnnyD

    Well-Known Member

    Aug 29, 2006
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    You could use a 78L12 as they are much smaller and capable of supplying all the current you'd need (less than 100mA). I'd definately regulate the voltage because of the fluctuations if the battery gets charged, etc...

    Using an NE555 means you won't need the transistor.

    Should be a nice simple circuit when it's done. good luck :)
     
  17. cenee

    Member

    Apr 20, 2006
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    ------------------------

    Ups, you are right. If the power suply is a DC battery, no need to use a voltage regulator. The signal is clean enough with a DC source.
     
  18. JohnnyD

    Well-Known Member

    Aug 29, 2006
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    Its just that the thread creater said it was going to be installed in a boat, and I'm guessing they have altenators like cars.
     
  19. richbrune

    Senior Member

    Oct 28, 2005
    106
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    Yep, and most boats have a voltage regulator that operates at about 13.5v. I think you'll be okay without the 12v pos v reg, don't worry if your timing cycle doen't seem exact, 555 circuits used for long duration never are. There are integrated 555 timers with x10 counters that are quite accurate.
     
  20. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Nope, only 100mA !

    And if you want to use a voltage regulator giving 12V with an input of 13.5V, you need a low drop device.
     
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