Car USB sockets blank out FM radio

[Guest]

I have bought several car USB adaptors, two which fitted in the cigarette lighter socket and another which had a 12v lighter plug going to a box with 2 12v sockets and a twin USB socket. I want to power a tablet for use as a satnav and a car cam. The USB sockets always interfere with the radio making it useless even if they are not powering anything. I have not heard anyone else complain of this but it must be common as it happens in my own 2 vehicles, (Hijet and Fiesta MK6), and in my partners 4 year old Ford KA. I think I need a USB supply that uses a 7805 regulator. Does such a thing exist or will I have to make my own?

 

[Someone Somewhere]

Typically, the first bits to be cut out of a cheap power supply is anything relating to noise. Coils, capacitors... all going to disappear. Get a good one from a reputable manufacturer, and you'll likely be fine.

7805s are solely resistive, and would be thoroughly cooked by the excess heat - they're incredibly inefficient, especially at high relative voltages. They're rated at one amp (most phone chargers are two), and dissipating seven watts without getting hot enough to burn you is going to mean either a reasonably large heatsink or a fan.

 

[spdragoo]

Yes, it's quite common for car USB chargers to interfere with the radio receiver. Happens in mine all of the time...except that I only notice it on AM stations as a staticy whine. And even then, I get more interference going through a railroad or highway underpass than I do from the charger.

 

[Vlad Rose]

Yes, it is due to them not being grounded properly; thus giving off Electromagnetic Interference. This can also happen as Someone Somewhere had mentioned. You can try getting a USB extender and splice a wire off it to mount to a metal piece in the car for grounding, but may not fix it.

I had a few USB adapters that were like that as well. The interference would disappear if I had my hand on either the adapter itself or the connecting USB cable from it; meaning it was grounding related.

 

[Guest]

Looks like I'll be making my own then, a simple 78S05 for each output will be fine as they are 2 amp devices. I have no problem with needing a heatsink or inefficiency. I am fed up with buying switch mode devices only to find they all interfere to some degree regardless of price.

 

[hemopapde]

You can try getting a USB extender and splice a wire off it to mount to a metal piece in the car for grounding, but may not fix it.