Removing noise from car charger - Page 1
Forum section: electronics / beginners

author: AdamSparky
author_rank: Newbie
timestamp: March 13, 2012, 09:07:58 am
content: I have tried a few car iphone car chargers and they all introduce noise into the speakers through the iphone (which is playing though the AUX input).I have decided to hard-wire one into the car so I can charge my phone and keep the cigar lighter free for other use.I'll just use a +5V reg chip to step down from 12v and then use a few resistors to supply the 2.7 and 2.06v to the data lines of the USB cable. (As explained here:http://www.ladyada.net/make/mintyboost/icharge.html)What is the best way to stop the engine nose from passing though this circuit? Would I put a capacitor between +12v and GND before the circuit or put a cap after the regulator between +5v and GND? Is there a better way to remove noise?CheersP.S. Just discovered the radio show and love it! Listen to it in the car all the time. Have also been working my way though the video shows.

author: T4P
author_rank: Super Contributor
timestamp: March 13, 2012, 09:55:32 am
content: LC filter / LCLC filter

author: Zero999
author_rank: Super Contributor
timestamp: March 13, 2012, 11:51:49 am
content: Are you sure it's not a ground loop problem?Try using an isolation transformer to connect the iphone to the stereo.

author: wkb
author_rank: Super Contributor
timestamp: March 13, 2012, 01:12:00 pm
content: Quote from: AdamSparky on March 13, 2012, 09:07:58 amI have multiple el-cheapo USB chargers from China feeding my iPhone. Never did that give rise to noise, I used them in multiple car models / brands.I must note that I fed the audio to the car stereo using Bluetooth. So no analog connection. What happens if you use the iPhone without charger connected? Is that noisy or not?

author: sacherjj
author_rank: Frequent Contributor
timestamp: March 13, 2012, 01:36:39 pm
content: Quote from: wkb on March 13, 2012, 01:12:00 pmI've found most of my noise pick up to be using non-shielded 3.5mm audio cables, so I agree with your assessment. However, I have had one car that was extremely noisy on the power buss and had to filter the power to keep the noise down.Although one of my el-cheapo-USB chargers did add some noise to my system and almost crap to my pants, when a filter cap blew and I though someone touched off a .22 shell in the cab.

author: Ajahn Lambda
author_rank: Regular Contributor
timestamp: March 13, 2012, 05:19:51 pm
content: Automotive environments can be very. . . fascinating, regarding noise. Most auto manufacturers install filter capacitors in their wiring harnesses, typically near the ignition system components (this is NOT the same as a 'condenser' as found on an old point-contact system) to reduce EMI. Most I've seen are rated between 0.1 and 1 µF.A few common things I've found which introduce noise to the power bus are bad spark plug wires, a failing alternator (usually it's the rectifier at fault), and poor grounds (corrosion at connections to chassis ground, poor connections between engine and chassis, or even the shielding wrapped around harnesses with digital signals).IFF those aren't the source of the interference, I think your plan to build a filtered supply into the car is a fine idea. You might want to include protection against transients.

author: AdamSparky
author_rank: Newbie
timestamp: March 14, 2012, 06:34:21 am
content: Quote from: wkb on March 13, 2012, 01:12:00 pmThere is no noise when the iphone is running from batteries, as soon as I plug in the charger a distinct whine can be heard.

author: sonicj
author_rank: Frequent Contributor
timestamp: March 14, 2012, 06:51:02 am
content: Quote from: AdamSparky on March 14, 2012, 06:34:21 amground loop. use a isolation transformer.