OMRON Twin Timer Relay - Battery Driven Fuel Pump

Thread Starter


Joined 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?