USB charging disrupts car radio

What about using a powerbank instead?

Play music via USB ....

Try a different cable, or use a different charger in a 12V socket.

Theo

This is clearly atypical behaviour, so it may be specific to your particular car or phone. You may get non-generic responses if you mention those.

RF is a crazy bitch. All sorts of things affect reception especially if the antenna is marginal or damaged.

USB plugin will affect the internal RF field of the car, which suggests that there is no external antenna at all, Even if he thinks there is

The powerbank could have other uses.

Second thoughts: I already carry a NOCO battery jump starter power pack[1] in the car for emergencies. That has USB outputs and running a smartphone wouldn't put a dent in its charge level. I wouldn't go out and buy such a thing for this purpose, but as it's already in the car it would be silly to not make use of it.

A powerbank will rule out the car, but it won't rule out the phone or the charging cable. It's possible the SMPSU in the phone is the source of the noise, potentially radiated by the cable. It's a good test nonetheless.

Theo

The phone has an internal SMPS? What is its purpose?

Many SMPSes. It charges the lithium cell from the USB input (which could be

They're all switching so potential sources of RF interference. Additionally touch screens use RF to detect fingers, which can be another source of noise.

Theo

I thought they were just transformerless regulator circuits, and didn't know there were such things as surface-mount transformers (

Most modern digital stuff runs on 1.8 or 3V

The charger will deliver 5V but the battery may be 7.4V

Lots of weensy SMPSUs - buck converters etc - manage all this.

Need not be a transformer. A simple inductor will do.

Not specific to cellphones. All electronics today uses them

e.g.

E.g. A raspberry Pi RP2040 chip requires 1.8v and 3.3V and the power source is typically up to 5,5V

It was more the size of the transformer or inductor which was the issue for a mobile phone. The smallest one in the ref I gave had a height of

You can buy surface mount inductors (you only need transformers if you want to isolate the supply for e.g. mains operation) that are very small indeed. The thing is that as the ability to chop at ever higher frequencies improves, the amount of energy you need to store in the ferrite for a given power level decreases.

There are a couple kinds of sockets in cars.

Legacy Battery ---- 25A ---------- Lighter --- Spring-loaded Fuse Socket Lighter Element

Modern Battery --- fuse --- SMPS ---------- Precise voltage outlet #1 (Accessory ---------- Precise voltage outlet #2 outlet)

The SMPS, if you draw current from it, is likely to make some RF interference while doing so.

If you were doing this, and had an external buck converter feeding the phone 14.4v 5V Legacy Battery ---- 25A ---------- Lighter ------ Buck Converter ------- Phone Fuse Socket

then the Buck Converter (a type of SMPS) could be making the electrical interference.

One test you can try: 12.000V Modern Battery --- fuse --- SMPS ---------- Halogen 12V 1A bulb ---- GND (Accessory outlet)

If every time you plug in a halogen bulb into the accessory outlet, the radio is suppressed, then it is the in-car SMPS doing that. When the halogen bulb is cold, it can draw more than 2 amps, but once it heats up, the power drawn will drop to the "rated current value", like 1 ampere. You would not want to use a 12V LED bulb, because the bulb might have an SMPS inside it. The Halogen bulb does not generate interference.

The reason we are starting with this part of the analysis, is to determine whether there is any *easy* way to fix this. If the in-car SMPS is buried somewhere, or it powers other parts of the car, you can't be playing with it.

If you determine you have a legacy design, and the socket has

There are SMPS all over the place, and we have to make sure the noisy ones are not being used.

If you place an auxiliary automotive battery on the floor of the car, next to you while driving, that battery can be a source of quiet power. You can then experiment with various converter types, and see if it is possible to make something work. The battery may last for some short trips, but might not be good enough for a 16 hour drive. And your converter should have a low-batt feature, so it does not drain the auxiliary battery below about 11V. Automotive batteries (not Leisure batteries), do not like being discharged all that much. You can't be draining them to 6V on each trip, and expect to get a lot of charge cycles from the thing.

Paul

Thanks though that's going to take a bit of working through.

The car is a 2010 Ford Focus and has a socket in the central console and one nearer the gear lever. I'll check more closely tomorrow in daylight.

However it does occur to me that I have a 12v leisure battery and a socket that I can clip on to plug the USB charger in. The USB charger is a budget unit with several outlets for different power output.

Testing that should isolate anything to do with the car electrics/electronics.