Strange electrical problem

[Pesty]

Hi,

I have a dab radio in the car.

The Ariel gets power from the head unit and I've earthed it on the chassis. All been working fine for years.

Today I've fitted an add a circuit which connects to a 12v to 5v converter then onto a camera. I've earthed the 12v converter to the chassis.

Camera works but when it's on I get no radio signal. Head unit fine.

I'm assuming ( I know nothing) that the Ariel unit and the 12v unit being both earthed to the chassis is causing an issue somehow.

Any ideas? Thanks in advance.

[anonymous-user]

Does the "step down" convertor (the 12v -> 5v thingy) have a switch mode DC-DC convertor inside? If so, i bet that the EMI generated is knobbling your radio reception (assuming you have checked there is no other more obvious wiring fault (missing ground/power wire etc)

[Pesty]

http://www.ebay.co.uk/itm/DC-12V-to-5V-3A-15W-Step...

This is the type of thing.

As soon as I unplug mini USB at camera side radio comes back.

Assuming there is some kind of interference I'm wondering if some kind of filter somewhere would help.

Both black wires from respective devices wired to an earth point on chassis. Wires in tact.

Edited by Pesty on Sunday 24th August 20:12

[anonymous-user]

you probably need a common mode filter on the power wires to the step down convertor.

Also, try earthing the unit to a different location

[Pesty]

Something like this before the step down?

http://www.ebay.co.uk/itm/TDK-ZJY51R5-2P-01-FILTER...


Getting way beyond my competence level I'll try a different earth point first.

Edited by Pesty on Monday 25th August 00:17

[Le TVR]

You need to try a process of elimination. While the DC-DC converter will generate RF noise it is usually in the 100kHz - 10 MHz range. The DAB radio is listening to 220 MHz and the RF noise is also likely to be coming from the high speed digital circuits in the video camera.

If you power the camera from batteries do you lose the radio?
If no then put a ferrite choke on the supply cable to the camera http://www.maplin.co.uk/p/ferrite-clip-on-hem3012-...
If you still lose the radio put the choke on the wire to the USB power socket.
If you still lose the radio put the choke on the power feed to the DC-DC converter.

etc. etc.

[Pesty]

Thanks Ill have a play.

They are only 2.99 cant i put them all three places

[Le TVR]

Pesty said:

cant i put them all three places

You may well have to!