2
\$\begingroup\$

I'm currently trying to design a circuit for my car which will switch itself OFF or ON depending on +12V signal from ACC(accessory) cable.

Car is providing me a +12V battery power, +12V accessory power and ground, i would like to make a circuit which detects +12V on ACC and then uses +12V from battery power.

Obvious solution is to use relay switch, but I'm curious are there any other options how it can be done ?

I'd be grateful for example circuits :)

\$\endgroup\$
8
  • \$\begingroup\$ Why? Only difference between Accessory and Battery is that Accessory is switched on by the key... essentially a manual relay. \$\endgroup\$
    – Passerby
    Commented Feb 15, 2015 at 21:52
  • \$\begingroup\$ @Passerby: On quite some systems accessory is regulated to 12V while battery is 12.xV or 13.xV when the motor is running. Additionally this regulation current limits accessory to a few amps max. \$\endgroup\$
    – PlasmaHH
    Commented Feb 15, 2015 at 21:56
  • \$\begingroup\$ because on this particular acc cable only 100-200mA load is allowed/suggested by manufacturer - and my device will draw ~500mA-1A \$\endgroup\$
    – NoderBlade
    Commented Feb 15, 2015 at 21:56
  • 1
    \$\begingroup\$ That would be important in the question. And @plasma I have yet to see a car where that is the situation. \$\endgroup\$
    – Passerby
    Commented Feb 15, 2015 at 22:12
  • \$\begingroup\$ @Passerby: Try any of those that me and my family had in the last 10 years \$\endgroup\$
    – PlasmaHH
    Commented Feb 15, 2015 at 22:26

1 Answer 1

2
\$\begingroup\$

Here are options:

  1. Transistor with a heatsink if need be
  2. Infrared LED along with phototransistor with heatsink if need be

I would only suggest you use these options if you have the components laying around, otherwise you would just be reinventing the wheel as a solid state relay(SSR) is typically made out of one of the options above.

\$\endgroup\$
5
  • \$\begingroup\$ doesn't a mechanical relay switch also use power constantly because of electromagnet is working constantly ? (in case of monostable switch - because that's the only one I'm interested in) \$\endgroup\$
    – NoderBlade
    Commented Feb 15, 2015 at 23:37
  • \$\begingroup\$ @NoderBlade Good point, I'm curious which one uses less energy. \$\endgroup\$
    – Addison
    Commented Feb 16, 2015 at 0:45
  • \$\begingroup\$ I found this one - it looks promising i think docs-europe.electrocomponents.com/webdocs/130e/… \$\endgroup\$
    – NoderBlade
    Commented Feb 16, 2015 at 0:49
  • \$\begingroup\$ @NoderBlade That does seem nice. Only 300mW of power for the input, which at 12V input is 25mA. \$\endgroup\$
    – Addison
    Commented Feb 16, 2015 at 1:09
  • \$\begingroup\$ Mechanical relays use power while the coil is energised (activated) but not very much, and your car generates a LOT of electricity (typically 50-100 Amps @12v) when running so ~100mA to keep a relay on is a flea fart in a hurricane. \$\endgroup\$
    – John U
    Commented Jun 10, 2015 at 14:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.