[roncallo]

Hello, if any of you have been following my Thread "Theirs a New One Coming", you will notice I'm working on an Arduino based controller for a PWM radiator fan. One of the challenges I have come up against is getting the fan to run a predetermined amount of time after engine shut down. I was trying to do this in code and control it using the Arduino but I was finding the code very difficult and also required running the Arduino at all times including with the key off and out of the car. So I am revisiting a hardware solution and trying to implement a 555 IC for a time delay after shut down.

The problem is all of the examples I have seen on how to do this involve grounding pin 2 of the IC to make this happen. I need to do something different. I need to activate the timer when power is removed form the system as in I turned the key off. I prefer to keep hardware down to a minimum and would like to avoid installing a relay if possible. I'm also not set on the 555, but its the only solution I have found so far.

If anyone has a solution to this it would be appreciated.

Adjustable Auto On Off Delay Timer Circuit Using 555 IC

A tutorial on how to make an adjustable delay timer circuit using 555 IC that can automatically turn on/off any output after a fixed duration. This electronic timer circuit is helpful when you need to power On/Off any AC Appliances after a pre-defined duration.

elonics.org

 

[GearheadGreg]

Almost all the delay-on-break relays that I'm familiar with require part of the circuit to remain energized, and in your case would be parasitic as soon as you remove the ignition key.
I ended up liking this relay called Fuji, they come in different configurations. This one is H3Y-2, now made by Omron. What I like is that it's not parasitic while it waits for either a momentary pulse of 12v or ground, and it's duration of circuit open\close is adjustable. You might be able to somehow rig it that when it looses power, it kicks the timer.

 

[andya]

Put a big capacitor on your Arduino board to keep power to it for long enough after power off. Andy

 

[roncallo]

Almost all the delay-on-break relays that I'm familiar with require part of the circuit to remain energized, and in your case would be parasitic as soon as you remove the ignition key.
I ended up liking this relay called Fuji, they come in different configurations. This one is H3Y-2, now made by Omron. What I like is that it's not parasitic while it waits for either a momentary pulse of 12v or ground, and it's duration of circuit open\close is adjustable. You might be able to somehow rig it that when it looses power, it kicks the timer.

Sound like what I already have. I'm really trying to replicate the function of this relay preferably in a solid state form on my PCB. And it only needs < 100ma current.

Beuler BU509TD 12 VDC Automotive 5-Pin SPDT Time Delay Relay with adjustable timing - Delay Off

Standard automotive style relayAdjustable time delay off with 2 seconds to 3 minutes timer with internal potentiometer20 amp / 30 amp rated contactsSPDT - Single pole Dual throwLow 1volt (1k Ohm) trigger voltage

www.qualitymobilevideo.com

 

[roncallo]

Put a big capacitor on your Arduino board to keep power to it for long enough after power off. Andy

Sound interesting, Would that be a polarized or regular cap. Any way of making the time adjustable say from 15sec to 120sec.

 

[roncallo]

Put a big capacitor on your Arduino board to keep power to it for long enough after power off. Andy

Looks like I found a good video on that. It starts at about 4:45. Also enhanced with a transistor at about 7:00. I will be playing around with it.

Thank you.

 

[roncallo]

Happen to come across this picture when I was searching for time delay circuits.

 

[Turbo510]

We use "super caps", about 1 Farad I think, for running the micro and a beeper for up to a minute as a power-fail warning. They are fairly small but only handle 5V.

 

[RaceDiagnostics]

Looks like I found a good video on that. It starts at about 4:45. Also enhanced with a transistor at about 7:00. I will be playing around with it.

Thank you.

Depending on the current taken by your Arduino, you may need a big capacitor. FYI, big capacitors tend to be electrolytic.

Here is how you would work out the size you need, or at least calculate the ballpark to start playing around with.

The electrical charge on a capacitor = it's capacitance x the voltage across it.

Total charge in a system is also = the current that is flowing x the time it is flowing for.

Rearranging gives.

The capacitance needed = (current taken by your circuit x time needed for the overrun) / the Voltage of the circuit.

You would also need a series diode before your capacitor to stop it also trying to power the rest of the car.

 

[GearheadGreg]

That's the MB repair tool I was looking for about 3yrs ago!

 

[107merc]

TinkerCad. Set up the circuit you have in mind and test it.

 

[RaceDiagnostics]

Sound interesting, Would that be a polarized or regular cap. Any way of making the time adjustable say from 15sec to 120sec.

Yes, you can make the time adjustable by turning on and off resistive loads on unused io on your Arduino. The more current you dump into load resistors the faster it will drain the capacitor.

 

[RaceDiagnostics]

We use "super caps", about 1 Farad I think, for running the micro and a beeper for up to a minute as a power-fail warning. They are fairly small but only handle 5V.

Supercaps are a good suggestion as they are fairly cheap for the capacitance. Three in series will be good for 16.5v but also will then give a 1/3 of the capacitance of course.

 

[roncallo]

Depending on the current taken by your Arduino, you may need a big capacitor. FYI, big capacitors tend to be electrolytic.

Here is how you would work out the size you need, or at least calculate the ballpark to start playing around with.

The electrical charge on a capacitor = it's capacitance x the voltage across it.

Total charge in a system is also = the current that is flowing x the time it is flowing for.

Rearranging gives.

The capacitance needed = (current taken by your circuit x time needed for the overrun) / the Voltage of the circuit.

You would also need a series diode before your capacitor to stop it also trying to power the rest of the car.

I'm not thinking the current will be too high. I'm estimating < 20ma to drive the three thermisters and the 3 LED's are only in use during engine start. I believe the Arduino itself will run under 20ma.

Interestingly enough I tried the two schemes in the video. The first method at ~ 4:45 with just a Cap in place would only light an LED for about 2 sec using the biggest cap I have of 2200µ. But with the second method the led stayed on for about 60 second.

I think I need to find one that will drop the voltage down to 7 volts in 60 sec when running at about 40ma. The Arduino Nano 33 BLE runs between 7 to 20V so it will shut off below that. I have only tried it with an LED so far. So next I will measure my current and see what I can work out.

 

[roncallo]

TinkerCad. Set up the circuit you have in mind and test it.

That looks pretty cool. I may give it a try

Thanks

 

[roncallo]

Supercaps are a good suggestion as they are fairly cheap for the capacitance. Three in series will be good for 16.5v but also will then give a 1/3 of the capacitance of course.

I did find an 18V 500000µf ultra capacitor. But its bigger than that relay, so not a solution.

https://www.mouser.com/ProductDetail/Cornell-Dubilier-CDE/DSM504Q018W075PB?qs=rQFj71Wb1eU8%2FgD2wfNHxQ%3D%3D

 

[cdk4219]

 

[cdk4219]

I have one if you would like to try it, I bought it and never used it, you can have it for nothing if you think you can use it. It does lots of things, and may be right up your alley

 

[roncallo]

I have one if you would like to try it, I bought it and never used it, you can have it for nothing if you think you can use it. It does lots of things, and may be right up your alley

Thats a lot closer to the size I need, but I need it in components that mount onto a PCB. Thanks for the offer

 

[roncallo]

Measured the current its running ~ 20ma when the LEDs blink on and settles down to about 15ma once they turn off. Thats with simulated resistors for the thermisters, simulation low temperature. Resistance gets lower at higher temperatures so current will probably see a peak of about 30ma.