12v to 9v DC conversion

Walker34

Hi folks,
I need a 9v supply in my car, whats the best way to achieve this. I searched the web but cant find a suitable device like a cigarette lighter plug in. What resistors would I need to put in the circuit to drop the voltage from 12 to 9. Cant remember Ohms law or the associated formulas, so I thought Id ask the experts.
John

Pete67

It depends on how much power the 9V device is going to use. The volt drop across a resistor depends on the current flowing. A voltage dropping resistor is not really the way to go, depending on the load, the resistor could end up dissipating quite a lot of heat.

This, this or this might do the job, depending on model they supply up to 3A at a variety of voltages including 9V.

It would help if you said what device you are trying to power.

Walker34

Hi Pete67,
thanks for the prompt reply, that looks like the real "dogs"! Its powering a miniature wireless camera to watch for whoever is dumping rubbish in my side entrance. I used it before 2 years back because someone was stuffing my wheelie bin and the bin men were not taking it as a result. Ran it for a full night and at 4.00 am bingo! caught the guy on video.(a neighbor) I taped it and sent it to him without any message.
The camera is tiny but puts a significant drain on the battery. I used a jumpstart unit from Aldi hidden in the boot of my car to power it before, but that's long gone.
The unit came from china so the technical details were scant. Thanks for the url, looks good.

Pete67

Maplin have shops in Dublin if that's any help - one in Parnell St and one in Blanchardstown I think.

Just watch it does not drain the car battery overnight.....