Relay circuit help for a pump in my car

Discussion in 'Automotive Electronics' started by merzatt, Apr 28, 2016.

  1. merzatt

    Thread Starter Active Member

    Jan 15, 2009
    37
    0
    Hello forum members,
    I would like to add a relay circuit to my car for auxiliary coolant pump. Currently pump is controlled by the AC control unit (AAC) without a relay. This pump known to seize and sometimes burns the circuit board of the AAC which is expensive. I would like to use the AAC as the signal to the relay and feed the pump from the battery nearby. I was told to place a protective (freewheeling) diode as well so that when the AAC stops the pump, there won't be a surge from the relay coil (I am a newbie and not sure what I am talking about here..)

    Please comment about my circuit below. Is the diode placed correctly? 14 V is the battery supply. Since this pump runs when the engine is running, voltage is approx 14 V due to charging. Can this extra 2V harm the pump? Pump also runs for 5 mins after the engine is off and at that time battery voltage is 12v.

    12 V on the left side is going to be my signal from the AC control unit.

    http://lushprojects.com/circuitjs/circuitjs.html?cct=$+1+0.000005+10.200277308269968+50+5+50 178+544+320+688+320+0+1+0.2+0+0.05+1000000+0.02+20 g+384+432+384+448+0 R+544+320+544+256+0+0+40+14+0+0+0.5 r+544+368+544+432+0+500 w+768+240+768+336+0 g+608+240+608+256+0 181+688+336+768+336+0+1840.5922678055792+30+12+0.4+0.4 w+512+432+544+432+0 w+512+352+544+352+0 w+608+240+768+240+0 w+384+432+512+432+0 w+480+352+512+352+0 s+320+352+384+352+0+1+false R+320+352+320+432+0+0+40+12+0+0+0.5 d+384+352+480+352+1+0.805904783

    RelayCtrl_merzatt_01.gif

    RelayCtrl_merzatt_02.gif
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,010
    1,530
    No your diode isn't in correct position. The diode goes in parrallel with the coil of the relay. To make life simpler for yourself, why not use one of the automotive relays with an internal diode? They do make such an animal. First link I found to one - http://www.altecautomotive.co.uk/5-...elay-with-diode-protection-altry18-2542-p.asp

    Here's a link on automotive relays that explains the different types and how to choose them - http://www.12voltplanet.co.uk/relay-guide.html

    To answer the 12V/14V question, even though they are called 12V circuits in a car, the ~14V is the real voltage when the engine is running. Don't worry about it. :)
     
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  3. merzatt

    Thread Starter Active Member

    Jan 15, 2009
    37
    0
    Thank you shortbus. Did some search and found TYCO single pole single throw horn relay, 1 form A, NOD (2x87). 12V, 30A inductive load with diode. available in the US.
    Tyco Mini Relay 12V SPST 40A V23234C1001X008 Waytek site

    I will install a 10 amps fuse between this relay and the battery.

    Terminal 85 -> [? resistor] -> AAC ground
    Terminal 86 -> AAC 14V (turn on signal)
    Terminal 30 -> [10 amp fuse] -> battery 14v
    Terminal 87 -> Pump
    Terminal 87 -> empty

    Is it necessary to install a resistor between 85 and ground?
    It has two terminal 87. Can I install an LED to the second terminal, so I will have a visual indicator when it is running.
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,010
    1,530
    Not sure what your asking? Can you make a drawing/schematic of how you think it should be wired.

    The two terminal 87 (A and B) are not the same, one is N/O (normally off) the other is N/C (normally closed or on). The N/C contact is 'on' when there is no power to terminal 85 or 86. If you want an LED to be on when pump is on, wire it to the same terminal as the pump. Again to save a hassle get a LED automotive indicator, they have a built in voltage resistor an a snap in housing/bezel around the LED. Just need to drill a hole and pop it in and connect. If you use a regular LED, you need to add a resistor and make some kind of bezel or holder for it. Just one of the many links for them - http://www.partdeal.com/red-led-indicator-light-12-24v-dc-8171-blue-sea-systems.html?zmam=74973193&zmas=1&zmac=4&zmap=77122764&gclid=CJC5mM_RtswCFYsCaQodm9oLsQ .

    Terminals 85 and 86 are the pull in coil terminals, they can be used interchangeably, one to ground and the other to the switch. No resistor needed.

    Terminal 30 goes to the power/fuse.

    Hope this helps you.
     
    Last edited: Apr 30, 2016
  5. merzatt

    Thread Starter Active Member

    Jan 15, 2009
    37
    0
    Sorry, I should have inserted the diagram. Here is the relay connections. No resistor, no LED. P=pump. How does it look?
     
  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,010
    1,530
    Should work
     
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  7. merzatt

    Thread Starter Active Member

    Jan 15, 2009
    37
    0
    It worked. Thank you.
     
  8. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,145
    203
    shortbus likes this.
  9. merzatt

    Thread Starter Active Member

    Jan 15, 2009
    37
    0
    Guys,
    I checked the HID relay which is controlled by another computer in the car. It has a LED and resistor inside. Since LED is cousin of diodes, do you think will it function as a protective (freewheeling) diode as well? Or should I add an external diode?

    Thanks
     
  10. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,145
    203
    The LED diode would be pointing in the wrong direction. Use a 200 PIV (Peak Inverse Voltage) diode or better.
     
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