Off-Delay Timer Issues

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Thread Starter


Joined Sep 29, 2011
Need some help on an off delay fan controller i am building. Its for an electronic fan on a car. The goal was to have the fan run for 10 min after the vehicle is shut off, then break the circuit.

I drew up this schematic and built a working prototype, and it works perfect on the bench. 10 min +/- 10 sec. However, upon installing my first build in the car i discovered that any other loads on the circuit (ie, headlights, radio, anything) will cause my circuit to reset and break break the connection prematurely. I tried integrating a 12v voltage regulator into the input, but the issue still remains. Even on the bench now, if add the presence of a light bulb to the circuit, it resets.

Any help would be appreciated.



Joined Jul 17, 2007
Sorry, but automotive modification topics are on the TOS restricted list, as per paragraph 6, which reads:

6. Restricted topics. The following topics are regularly raised however are considered "off-topic" at all times and will result in Your thread being closed without question:
  • Any kind of over-unity devices and systems
  • Automotive modifications
  • Devices designed to electrocute or shock another person
  • LEDs to mains
  • Phone jammers
  • Rail guns and high-energy projectile devices
  • Transformer-less power supplies
You might have a look in this thread:
There are a few websites listed where automotive electronics might be permitted. Keep in mind that automobiles are one of the most challenging environments to design electronics for; and even experienced engineers make mistakes that cost car companies millions.


Joined Nov 30, 2010
This reset problem is an excellent example of why we don't do automotive circuits. So many things can go wrong in that electrically noisy environment. An ignition or brake circuit that keeps resetting could cause a disaster, even a death.
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