Here is a simple scheme for 12V approx 10s OFF Relay. It’s very easy to build. Scheme and part list are shown below.
- R1 – 6.8 Ω
- R2=R3 – 100 kΩ
- D1=D2 – 1N4007
- T1 – 2SD892 (Darlington NPN transistor)
- C1 – 100μF/25V
alternative (if you cannot find 2SD892 transistor you can use one below)
- T1 – BC517 (this one has higher hfe than 2SD892, so you also have to change capacitor)
- C1 – 33μF/25V
- BROWN – ignition (+12V)
- GREEN – to relay (No.85)
- RED – constant power supply (+12V)
- BLACK – ground (-12V)
If you want to change delay-off time, you can change the capacitor. For longer delay use higher value capacitor, for shorter time, use lower value capacitor. Change only capacitance, not voltage.
Buy one 4-pin car relay (NO-normally open)
Bring constant power to relay pins No.86 and No.30.
Relay pin No.87 will give power (+12V) to DC-DC converter when ignition is ON and 10s after ignition is off.
And here are the images how I have coupled it along with DC-DC converter.
Thanks to rjc_147 who pointed out for D2 diode & Credit to Razor AMD for the content.