555 Timer: Electric Choke Control

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Joined Aug 20, 2011
Need a timing circuit to control Bosch 30amp SPDT relay which supplies current to an automobile electric choke. Ideally looking for about 5 minutes. After searching here and google I found the attached circuit, which is stated to be an adjustable (per the 1Meg pot) 1-10min timer.

Using a RS std 555 8 leg IC and all component values shown, but no LEDs/bleeper, just my VOM hooked up to the pin3 output and a stopwatch to determine timer duration. Using small (2amp) 12v battery charger as supply, actually about 15.5v. Used stripboard to mock up the circuit and have triple checked all connections. Can't seem to make it work. Apply supply voltage and pin3 ramps up to same voltage but doesn't timeout. I've run the circuit for 20minutes without timeout. I've bypassed the pot, figuring that should get me a quicker timeout, but nothing.

Anyone see an issue with the circuit?...or can suggest a better approach? TIA.


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