Electrical - Using cigar lighter to charge phone interferes with radio reception... | Ford Escort Owners Association (FEOA)
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Electrical Using cigar lighter to charge phone interferes with radio reception...

Discussion in 'ICE (In Car Entertainment)' started by gimpel, Aug 28, 2020.

  1. gimpel

    gimpel FEOA Member

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    Greetings,
    When I plug a USB adapter into the cigar lighter jack, my radio reception decreases. I guess the transformer in the adapter is causing interference with the antenna cable? or maybe it is affecting the radio itself? perhaps by feeding a signal back through the wiring.
    I plan to relocate the lighter jack to a better location, and want to install another lighter jack as well in the rear seat compartment. I wonder if moving the location of the USB adapter will fix this problem, or whether I should shield (and ground) the wiring to the lighter jack? or power the lighter jacks off another 12V wire, like the dome light circuit?

    AFN...

    gimpel
  2. neuspeedescort

    neuspeedescort Moderator Staff Member

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    are you using the phone for anything or just charging it?
  3. denisond3

    denisond3 Moderator Staff Member

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    I added two extra 12 volt outlets to my escort, for use with charging cell phones and running the GPS on long trips. I added wires from an inline fuse I added near the battery, running into the interior. One outlet was in the console below the ashtray, the other was on the back of the rear console section next to where the shoulder belts emerge.
    Both of these outlets are connected full-time, i.e. even when the ignition is off. I dont recall any interference with radio reception with my system.

    It was a little bit of trouble running the two wires from underhood into the interior. Since my car doesnt have a cruise control, I used the hole for that which is under a rubber plug next to the brake vacuum booster - at about the 10:00 position. If my car did have cruise control, I could have used the hole for the clutch master cylinder, since this car has the automatic trans. That hole is covered by a metal plate what unbolts.

    The 12 volt accessory sockets dont have the metal fingers that work with a cigarette lighter, but I dont smoke. I had to search fo find the non-cigarette lighter type of 12 volt accessory socket. Some auto store folks didnt even seem to know there was a difference.

    Later I added these same 12 volt accessory sockets to two my other escorts, each of which get used on long drives. We live in two places seasonally, and keep a couple of escorts registered in both places: S0 we own five 2nd gen LX escorts.
  4. gimpel

    gimpel FEOA Member

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    I did some tests so I could answer fully... and BTW, I cannot disassemble the adapter without destroying it, but research online shows it does not have a transformer, but either an IC chip or linear regulator circuitry which may contain an LC circuit which could create RF interference... also, the cigar lighter is at least eight inches away from the radio, the antenna cable is definitely shielded, so seems feedback through wires to the cigar lighter is more suspect?

    12V accessory plugged into the cigar lighter does not cause interference...
    USB fan plugged into USB adapter does not cause interference...
    USB cable plugged into USB adapter does not cause interference...
    As soon as I plugged an android device onto the end of the cable (2 different phones, 2 different tablets, and one apple Ipod) the interference begins and continues as long as it is plugged in, even with a 100% charge, when the circuitry of the battery or phone is supposed to halt actual charging... even with device powered down, shut off... and positioning of the device and cable has minimal effect on the interference.

    I am not impressed with the stock radio or antenna in this car anyway, or the similar '98 Tracer I had a few years ago (same problem). I have bought a new audio system which I will install as soon as I get the dash kit, and at that time will connect to a CB antenna mounted on the trunk or roof which may solve my problems. At the same time, once I have the dash console open, I will examine and possibly shield or install a filter on the 12V to the cigar lighter.

    I dont listen to commercial radio (high power) but rather distant and/or lower power stations, which is why this is a concern for me... And my new system will allow me to input my media through an integral USB port or Bluetooth...

    thx for responses...
    denisond3 likes this.
  5. marclar

    marclar Administrator Staff Member

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    a usb plug in charger uses a 'step mode' power supply, or a 'buck' converter to lower the voltage to a steady 5v. this process creates a TON of noise due to the high frequency collapse of the magnetic field in the inductor... this power and ground are connected to the same feed area the radio.. thus backfeeding all the 'noise' in to the radio.

    best way to avoid this would be to run a dedicated power and ground to its own charger.
    neuspeedescort and denisond3 like this.
  6. neuspeedescort

    neuspeedescort Moderator Staff Member

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    bingo Steve!
  7. zzyzzx

    zzyzzx FEOA Member

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    You need to use a more expensive adapter.


    Basically, the cheap adapters have a little unshielded switching power supply to reduce the voltage to 5V for the adapter that puts out a lot of interference. Now, if you used a regular voltage regulator, like one in TO 220 case:

    [​IMG]

    You would need an additional heat sink to get rid of the heat:

    [​IMG]

    Which would take up much more space AND require some air flow for cooling.

    So the little adapters use tiny switching power supplies, so that it doesn't generate so much heat. But it needs to be shielded since the way a switching power supply works it converts the 12-14V DC power to an AC signal, at (whatever frequency) and then converts that to 5V DC for the USB charger. It's the AC signal frequency (or maybe even a multiple of it, depending upon how dirty the AC signal generated is) that's causing the interference. This signal is either literally transmitted over the air, or on the car wiring to places all over the car that aren't designed to protect themselves from errant signals that is causing your issue. This problem is easily avoidable by properly shielding the adapter, but because things are cheaply made, that doesn't often happen. It's easy enough to do too. The inside of the adapter would need to be coated with a conductive coating that would be grounded, or the working parts of the switching power supply should be a a little metal casing which would be grounded and look something like this:



    [​IMG]
  8. zzyzzx

    zzyzzx FEOA Member

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  9. gimpel

    gimpel FEOA Member

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    Thx...

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