What Size Capacitor for 2 Minuite Output?

Anyone know what size capacitor I would need to get about a 2 minute output using this relay wiring?
https://www.the12volt.com/relays/relaydiagram22.html




Thanks,
Travis

Forget it!

But assuming 12V & a 60 Ohm relay coil and a relay dropout of ~4.5V, a 2F capacitor.

Bah! I've got 3 or 4 hanging around!

Ok, so that's out. Here's what I'm trying to do:
I want to activate a relay by pushing a momentary switch, I want it to stay on for 2 minutes then shutoff if no more input is given.

Any help would be greatly appreciated!

Thanks,
Travis

DEI 528T timer.

I believe two minutes is the max amount of set time. Have used one for years on my bed lights with a neg alarm aux. Easy to use, install and find. Should be under $20 with shipping.

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'14 F-150 Platinum.
Not giving up my class A/B yet...

1 min is max for the 528t. I need more than that.

Travis

Just remembered, my alarm is 60 sec out and the timer is another 60sec.
Giving me the 2 minutes.

Another option is the Inpower SSR timers available on Waytek's site.

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'14 F-150 Platinum.
Not giving up my class A/B yet...

Search for timer circuits. There are so many!

I also need the relay to stay active when the truck is running....

... and yet turn off after 2 minutes...

After 2 minutes with the truck off. If the truck is on, and the button is pushed the relay would activate and stay activated, until 2 min after the truck is shut off.

So a cut off circuit 2 minutes after IGN off?
So a recently oft posted latching relay circuit with a 2 minute IGN off delay timer... maybe an RC fed MOSFET that breaks the relay's 85 to GND...

Basically, yes. Its for a pre-heater for fuel filters on a diesel pickup.

I need to jump in the truck, push the button for the heaters to come on. They need to shut off after 2 minutes, unless the truck is running, then they stay on constantly. Once the truck shuts off the heaters need to shut off (they can stay on for the 2 minutes, for ease of design).

Travis

That's another change - albeit possibly pedantic...
Do the heaters stay on once triggered as long as the IGN is on (plus 2 minutes), or once triggered as long as the engine is running (within 2 minutes, plus 2 minutes after engine off)? I assume the latter.
Point being, if the engine stalls - or is not started - should or can the heaters stay on?

Not really a change in design but different wording.

The longest I want the heaters to stay on is 2 min (approx.) without the truck running.

Think of it operating just like the original diagram I posted with a 2F cap, as you suggested.

Travis

Yeah, so it isn't IGN controlled, but "engine running" controlled.

Does it have a charge light or switched/sensed airflap or electronic injection or electrical tacho signal?

Ok, I'll simplify it a bit now that I fully understand what you are asking.

If the key is on, the heaters can stay running.

Ok, so the latching SPST relay I've recently described in other threads with relay power from (fused) battery +12V and the "on" pushbutton from IGN +12V. The off button can be omitted.
The relay powers the heaters and a timer circuit. The timer relay is normally closed between GND & 85 of the latching relay.
The timer is triggered by the -ve going IGN off signal. When 2 minutes is up, the timer relay opens to de-energise the latching relay which also disconnects the timer (and reconnects latching relay 85 to GND).
The timer trigger (to IGN +12V) must handle +12V despite the timer being unpowered, otherwise the timer needs to be powered from IGN +12V.

Another job suited to a PICAXE 08...

I think I'm following you. Just to be clear, I can use a pushbutton to activate the timer before the key is on, correct?

I'll look into the picaxe 08....

Thanks,
Travis

Also, can you link me to the SPST relay diagram you are speaking of? Is it one of the ones in the list?

Thanks,
Travis

latching relay? tho that may no longer be relevant...

No - I have been describing an IGN-on system.
If you want an anytime trigger then that's a +12V (constant; battery) timer.
IMO that's easiest as separate timer tho the heater may share the same relay (ie, diode connect signal outputs to relay 86).

Chances are that whatever suitable timer you find can be used for both, or a single timer used with appropriate control logic/circuitry.
But look at the (PICAXE) 08M2. Tho it requires serial interface programming plus input/output circuitry plus the programming learning curve (ie, hack existing PICAXE web projects) it overcomes any standby consumption problems (it takes something like 14uA as opposed to the 10mA used by 555 timers etc) and is infinitely configurable. EG - one output and 5 inputs; easy to add conditions like "if engine not started or it stalls, turn off after n minutes"; etc.   

There are also Arduinos & Stamps etc tho IMO they are overkill when a thumbnail sized 08M2 can to the same.