Re: Automobile Cell Phone Charger RFI

Dennis Smith

Many chargers for mobile phones have sensing circuitry and a data circuit to charge at full speed, without the corrected signal the phone will not allow a charge over a small amount, the signal needed for Apple devices is different from many Android devices as far as I am to establish. this is why some multi-port chargers often have ports specifically for indicated for Apple devices and Android devices, often appearing to perform poorly when the wrong port is used. I have in one example an Android phone that will 2/3 charge in 10-15 minutes from nearly dead and fully charge in 30 minutes from a good quality fast charger, but my 90W 6-way charger with ports marked Apple and Android and one specifically marked for Samsung/Huawei, that on certain ports doesn't charge anywhere as quick except from one port, however my GF who has loads of Apple devices finds the same port doesn't charge her phones at all, but the others do. (the port that doesn't charge is supplying current, but only enough to keep her phone powered neither using the battery power, nor charging it.

The switching circuits in good quality chargers are often regulating the drawn current and helping to prevent overcharging causing either phone damage or worse an explosive fire. So just regulating the voltage and making several Amps available to the phone to use when and if needed, just won't work as you might expect. 

So, making a power supply for a mobile phone to drop 12V to 5V might work for older phones quite well, a newer phone will charge at a less than optimal speed.

Dennis Smith

On Fri, 31 Aug 2018 at 00:19, doug <dmcgarrett@...> wrote:

On 08/30/2018 03:21 PM, Rick Ellison wrote:

I have a 4 port charger that makes listening to FM barely hearable and totally wipes out AM. I had never thought of using SDRC to track it down.


73 Rick N2AMG

I am sort of surprised that your device contains a switcher when all you need is 5 Volts DC from a 12 to 15 volt cigarette lighter socket. I would put a 5V series regulator in the charging device and it
would make no RFI at all. Perhaps there is one made like that. I have a two-port lighter plug with USB jacks on it. I will take a look and see if it generates RFI. And my phone came with a separate
charging cord compatible with a USB jack, which the AC charger has on it. (And IT is a switcher of course, sind it plugs into the houshold AC.)
In the meantime, Does the device you have have a built-in charging cord that goes to the phone, or do you use a separate USB to phone cable? If it's a separate cable, then disconnect it and see
if the RFI goes away sufficiently to listen to the radio. If it does, then get some ferrite snap-on RF chokes and run the charging cord thru about three of them right next to the lighter socket. And you
can wind a coupe of turns of the cord thru each choke.
If that doesn't work, you will have to find a charger made with that series regulator. They are almost certain to exist.

--doug, WA2SAY, retired RF engineer.


Am 29.08.2018 um 22:08 schrieb Kriss Kliegle:

Noticed a charger I picked up from one of my favorite electronic surplus sites made listening to FM difficult while charging the phone.
Did some tests on 99.5Mhz with the SDRplay and a 27" (68.6cm) whip located nearby.

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