slightly on topic; battery chargers for cordless drills.

[marc rosen]

Hey All, I wonder if anyone out there notices this phenomenon when charging the batteries on your cordless drills or other tools. I have three brands of cordless drills. My oldest is a Dewalt 12 volt, followed by a Bosch 14.4 and the most recent is a Festool 12 volt. When I am charging the Festool we get some interference (buzzing/humming noise) in any radio we play in the house, both AM and FM. The Bosch and Dewalt do not cause this interference. Does anybody notice this? Thanks in advance for your responses. Marc

[CW]

Chances are that the one making the noise is a switching supply and the other two are transformer type.

[Mike]

I had a similar problem with 2 chargers. One was a 12V Dewalt and the other was the power brick for a laptop.

A Ham radio operator at work said I could bridge a .05mf ceramic capacitor across the AC line on the Dewalt charger and that would filter out the noise. I never tried it because the charger died before I got around to it.

The brick was replaced by the vendor, but that didn't solve the problem. I later noticed that I had the same brick at work, so I tried it and it made no noise. The difference was that the work brick had no ground. So, I got a cheater plug to defeat the ground and the noise went away. I'm not sure why they felt the need to put a ground on a sealed chunk of plastic, but they did. BTW, the only time the noise was noticeable was when the laptop was jacked into my receiver for use as a media center. It didn't cause noise otherwise.

My take is that both devices have a design flaw, but that is just my humble opinion. It was not like either of the devices were inexpensive, but they seemed to be cheaply made.

Mike

[Steve B]

Mine did it, then I plugged the charger into a different circuit, and it stopped instantly.

Steve

[Leon]

I have heard this can happen in older wired homes.... If your wall outlet has equal sized holes that will permit you to plug in the appliance in either dirrection, up or down, try unpluging the charger, rotate the plug

180 degrees, and replug.

[Swingman]

On word ... "Ground Loop". :)

A perplexing problem that can have you chasing your tail. As Leon suggests, switching the plug polarity can solve it, but often it does not.

On a wall charger with a three pronged plug, "lifting" the ground with a two prong adapter might do the trick.

WARNING: The latter can be a shock hazard with case grounded tools/devices, but I wouldn't worry too much about that with a battery charger.

If neither of the above work, then you need to take a look at the proximity of things like fluorescent fixtures, close by RF inducing sources, the device, and its connecting wires, acting as an antenna, etc.

As a former recording studio maven and owner, I can tell you that isolating the source of a hum on an electrical circuit can be as much an art as it is a science.

No more than a battery charger is used, if the first two suggestions don't work, I'd be tempted to live with it.

Good luck.

[clare]

A good isolation transformer (like a OneAC) will usually solve the problem if it is a ground loop - and often even if it is EMI coming back the power lines. For the latter, a ferrite on the power cord often helps too (on the AC cord of the isolation transformer)