Twin Timer Relay (OMRON) - 12v Battery Fuel Pump

[james.e.raymond]

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). We 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” [url]http://www.ia.omron.com/product/item/h3cr3009e/index.html[/url]
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?

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 (1 pump)
[img]http://www.ia.omron.com/product/item/DIC0010/img/E00000385197.gif[/img]
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?

[pebe]

You might do best to have a word with Omron. I see there is a box/tab at the top RH side of their data sheet where you can contact them about the product.

If they say that your battery voltage range would be outside the spec of their relay, then you might like to consider using their 24V version fed from a boost converter like this:

http://www.ebay.co.uk/itm/10A-12V-80V-D ... 62100?pt=L

The converter will accept a wide range of input voltages and give a stable settable voltage output. The limitation is that the output voltage must be at least 2V higher than the input voltage – hence the need to choose the 24V version of their relay.

To answer your other questions: yes, you will need to connect pins 7 & 8 ( contacts and coil terminals are usually isolated in relays, because you may have an AC coil but want to switch DC power), and yes, connect up the pump as you suggested.

[james.e.raymond]

I will actually have access to 120VAC. This design is going to be used for pump testing so it will be sitting in the lab.
So i should probably power the coil terminals with 120VAC, pins 2(-) and 7(+).
I can connect my 12V battery (+) to pin 8, (-) to pin 2.
Then I connect my pump (+) to pin 6 (Normally Open) and my pump ground to pin 2?
This way i wont have any issues with the voltage fluctuation.
I just need to order a 120V twin timer relay that can switch DC power?
I think this will work right: [url]http://www.ia.omron.com/product/item/h3cr3007r/index.html[/url]

[pebe]

It could be dangerous to connect your battery to pin2 (the mains connection).

If you don't want to connect your pump directly to the battery, then connect mains to pins 2&7, battery to pins 1&8, and pump to pins 3&6.

[james.e.raymond]

"It could be dangerous to connect your battery to pin2 (the mains connection).'

Yes u are definetly correct. Not sure what i was thinking on the connecting the battery ground to the AC power supply ground.
I will probably connect the pump directly to the battery gorund rather than use the other contact output. But i could do that if needed.

[james.e.raymond]

I just noticed that the Contact Output rating for this OMRON twin timer is only 5A.
H3CR-F8N AC100-240V 50/60HZ [url]http://www.ia.omron.com/product/item/h3cr3007r/index.html[/url]
[color=#FF0000]"Switching capacities (resistive load (cos(phi)=1)): 250 VAC 5 A, 30 VDC 5 A
Minimum applicable load: 10 mA at 5 VDC (failure level: P)"[/color]

My pump with initially draw 11A and then settle down to about 7A. I will be over the 5A rating ........
Does anyone know of a twin timer similar to this one that has 10A or higher contacts?
Or maybe i need to use this timer to control another relay that does? Any ideas?

thanks for help so far pebe!! Really appreciated!

[pebe]

I would use the timer to control a heavy duty (20A?) relay. They are not expensive and in the event of contact failure, they would be cheaper to replace than the Omron timer.

[james.e.raymond]

So I have come up with a design. See the attached Schematic & Component Specs.

TWIN TIMER: [url]http://www.ia.omron.com/product/item/h3cr3007r/index.html[/url]
POWER RELAY: [url]http://www.ia.omron.com/product/item/g7j_1020b/index.html[/url]
30A SMART CHARGER: [url]http://www.iotaengineering.com/dls30.htm[/url]

When the timer is powered on (120VAC) it will turn on the Power Relay (120VAC) for 20 minutes (tON). While the Power Relay is on, the Pumps will be on (~12VDC Battery). After 20 minutes the Power Relay will turn off, shutting the pumps off for 60 minutes (tOFF). The cycle will then repeat an infinite number of times. On for 20minutes, Off for 60 minutes (All day, everyday until testing is done). While this is happening the "smart charger" will be charging the 12VDC Battery continuously as needed.

I am concerned with the pump draw of 7-11 amps EACH, 28-33 amps total! What will this do to the battery? Will it effect the battery even though the battery will be continously charging? Is the 60 minutes off cycle enough? Should I only test 12 hours a day and let the battery charge the other 12?

Let me know what you think?
Any other concerns to worry about?

[pebe]

It was not obvious from your initial post that you only wanted to test fuel pumps. If you have not already purchased the various items you specified, then I think you could take a simpler approach.

As you have mains available, then why not power the pumps directly from a 12VDC supply derived from the mains, and forget the battery. If you had a 4-output, ring-of-four counter with an output to 4 terminals and with a 20minute dwell at each count, then you could connect a pump to each output. The counter would then run three (or four) pumps sequentially via switching FETs or relays; with each one being on for 20minutes and off for 60minutes. The maximum continuous power you would then require would be only 12V at 11A. PC ATX power supplies can deliver 15A and are quite cheap to purchase.

Would that be a better approach?