ARRL

Forum Home - Rules - Help - Login - Forgot Password
Members can access, post and reply to the forums below. Before you do, please first read the RULES.

electical noise from lithium-ion battery charger

Sep 24th 2011, 21:36

K5WOR

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Folks next door have 2 Ridgid battery charger for drills. One is a 24 volt and the other is a 12 charger. The 12 charger generates a white noise from about 20 Mhz to at least 50 Mhz. I am about 100 feet away and 10 Meter is totally gone! Full scale on my Yaesu FT-1000 S-meter. Unplug the 12 charger and inoise is gone. The 24 volt charger makes some noise but only about half that of the 12 volt unit. I am sure it's due to the switching PS in the units and maybe could be fixed, but should it have to be fixed or is some wrong here??
Richard
Sep 29th 2011, 12:28

W1RFIAdmin

Joined: Jul 25th 2011, 14:25
Total Topics: 0
Total Posts: 0
Below 30 MHz, the FCC Part 15 rules limit conducted emissions from devices. The premise is that on HF, small devices do not radiate well, but the wires they are connected to do, especially the AC power lines.

The "legal limit" for noise from Part-15 regulated devices marketed to residential environments (Class B environments) would typically be at S7 or so from a neighbor's house located 100 feet away. Fortunately, most devices don't operate at the limits all of the time on all of the frequencies, so although (as hams know) interference does happen, it is not a constant thing for everybody.

The League has converted on of the Lab offices to be a "C63.4" conducted emissions test room. In our experience, although most devices have emissions at or below the limits, some do not. We have seen some import battery chargers operating at 30 dB over the FCC limits. Ouch.

The level of noise you describe is stonger than I would expect. If you can supply the Lab staff with the model number of the charger, we can get one and start by looking at its conducted noise. It may be faster to let us borrow your unit for a fast test, if you have a cooperative neighbor. It's also possible that the unit is somehow defective.

You may be able to control the noise two ways: In some cases, hams and their neighbors work out a social solution, where he will agree to charge his batteries during times you don't operate.

You can also try filtering. The noise is generally generated differntially, so an AC-line 'brute-force" type filter would be my first choice. SOME of the outlet strip "surge protectors" also have EMI filtering, but we've never looked closely at them to see just how they are made. (A project for the Lab, or a volunteer test engineer, if someone wants to be ambitious.)

You can also try a common-mode choke, or may also need one. I'd recommend #31 ferrite material. A toroidal core will work best. Amidon, Dan's Small Parts and Palomar should sell the material. I know that Dan has FT-240-31 cores that are large enough to accomodate a few turns of wire of the AC line cord of the offending device. Google the companies for their web sites.

73, Ed Hare, W1RFI
ARRL Lab
Technical forums moderator
Oct 6th 2011, 16:17

K5WOR

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Hi Ed
The main charger is a RIDID 12 Volt Lith-Ion model 140446001 (R86049). So far the folks next door have no problem keeping it unplugged when not it use. However I will try to do something with it. Even with cheap SW portable at 50 to 100 feet it's just a HUGE white noise machine.
Richard

Back to Top