OMRON Twin Timer Relay - Battery Driven Fuel Pump

Discussion in 'General Electronics Chat' started by jameseraymond, Oct 25, 2012.

  1. jameseraymond

    Thread Starter New Member

    Oct 25, 2012
    Hi all, I’m new to the forum. I use CNC/PLC forums frequently and figured it was time to join this circuit forum. I need HELP! haha

    I am trying to figure out what twin timer relay I need and if my design will work?
    I’m trying to run a fuel pump off a standard 12v car battery (150Ah or so). I want the pump to turn ON for 20 minutes and off for 60 minutes and keep repeating an infinite amount of times. (While the battery is charging of course)

    I am looking at OMRON’s twin timer “3CR-F8N 12DC”
    Basically I would be using the flicker mode with t1=20 minutes ad t2=60 minutes.

    My first concern is that the car battery when charging will be receiving about 10 amps and 14.4V (I think). This means that the relay could see a fluctuation of battery voltage. When the battery is at 20% (should never get that low) it would see 11.58V and when it is 100% it would see 12.6V. When the battery is charging it could see 14.4V.
    The specs on this relay state:
    Rated Supply Voltage: 12 VDC, ripple: 20% max.
    Operating voltage range: 90% to 110% of rated supply voltage.
    Seeing how 14.4V is outside of the rated supply voltage range, will I have an issue with the relay when my battery is charging (which would be ALOT)?

    Also, looking at the pin schematic I had a few questions on how to wire this. FYI: I will only be using one side of contact outputs (right side)
    Do I have to connect pins 8 & 7 together with a jumper? Or is this done internally?
    Then I connect my pump (+) to pin 6 (Normally Open) and my pump ground to pin 2?
    When pins 2(-) and 7(+) are connected to the power supply the pump will turn on for t1 (20min) and off for t2 (60min) and repeat? Am I looking at this correctly?

    Anyone have any other ideas or can help me out?
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    yes link 8-7 and take your pump feed from 6.