RFI from Weed Whacker Charger on AM Band

I have had trouble with an annoying loud buzzing across the MW broadcast band inside and outside my QTH for the past six weeks. It appeared suddenly and basically wiped out most AM stations with the exception of very strong ones. So, after walking around the house with my radio it was apparent that the noise was being transmitted through the house wiring. The culprit was my weed whacker's battery charger that was in the garage. The noise was present when charging the battery and even when the charger was plugged in but without the battery inserted. Unplugging it was the answer.

Is there any way to prevent an appliance from causing interference through the house wiring? This device is apparently doing this. Thanks.

Not much you can do unless you want to get into the guts of the charger and add the appropriate capacitors and other components to prevent the RFI from being emitted in the first place.

i love listening to am radio when working outside but to do that i have to shut everything off such as woodshop flourescent lights ..all tool batt chargers all led and cfl lights in the home. just today ive got a new standby generator with the outdoor transfer switch/load panel about 5 feet from antenna bulkhead . ..i know that will be a problem with shortwave

My house is nearly 300 years old, and with several additions built on over the years and a standby generator added about 15 years ago, there are several "tiers" of wiring throughout. Add CFLs and a metal roof and you have a MW and SW reception nightmare. I am planning to eventually build an outdoor longwire, but in the meantime I took a chance and bought a cheap tunable loop, the Tecsun AN-200. It made an incredible difference both during day and night. A 5k daytimer about 15 miles from me was barely audible above the noise floor in the middle of the day with all the lights and AC off. Now with this antenna, I have to turn the RF gain on the radio down so it's not overloaded. Night time reception was the most improved as I can now listen to distant class A stations clearly and even some regionals. Very happy with my $20 purchase.

Every DOE class 6 AC adapter I've tested wipes out AM broadcast band. That includes an adapter that came with a recently purchased radio that receives AM broadcast band (unless you plug in the adapter, then you hear mostly white noise). That is why we had to take AM broadcast out of our BC365CRS.

The problem is the switching power supply in the charger. Call the manufacturer & see if they can help you. This unit is probably in violation of FCC rules. If the manufacturer won't help, call the FCC & make a complaint.

A friend in NH had a problem with similar interference that popped up on the 160 & 75 meter ham bands. We did some DF'ing (Direction finding) and found where we thought the RFI was coming from. We walked up to their electric meter (Nobody was home) with a RADAR ENGINEERS RFI Sniffer & confirmed that this house was the source of the RFI. He called the FCC, gave them all the info and 4 days later the RFI was gone. The problem was an AC adapter for a recently purchased router. It was replaced with a linear AC adapter, the kind with a transformer, diodes & filter capacitor. No square waves, no harmonics, no RFI !

Good luck,
Bob
N2OAM

But no compliance with current DOE laws. Manufacturers cannot import such an adapter any more. They all must meet DOE Class 6 which requires a noisy switching adapter. We are going to see more and more of this kind of thing.

Get an FT-240-77 ferrite core and wrap 5 to 10 turns of the chargers power cord through the ferrite very close to the charger. That should make a big dent in the RFI and can sometimes completely cure the problem. You can call Palomar Engineers and they will give you more potential fixes.

If it were my issue I would unplug the charger when the battery is charged. The battery is not generally going to lose much charge when the weedwhacker isn't being used.

Either that, or bag the cordless and get a corded or gas powered weed whacker.

Some of the corded ones are very good. I have had one since 2004 or 2005 that still works well. It will even cut small blackberry vines.

Thank you for the helpful suggestions.

Sounds like your weed-wacker charger is trickle charging 24/7 with an older nimh battery forever.

One easy solution would be to upgrade to a weedwacker that uses Li-Ion battery. While the charger may still be noisy, the fact that you never trickle-charge a li-ion battery, you could charge the battery and unplug it for a year or two without any usage due to a li-ion's very low self-discharge rate. So the time that the charger is making noise would be very limited.

Li-ion battery saving tip - don't store them fully charged. If you have no way to gauge the state of charge, at the very least, if you don't plan on using them within the upcoming 2 weeks or so, just charge them to full, and do a light job to "get them off the top end of charge". Either that, or just run the wacker for at least a minute or two before storing it away for the next season of usage. If you are going to use them within about 2 weeks or so, don't sweat the full charge too much - provided they aren't sitting around in a hot garage!

The long-term ability for a li-ion to hold a charge, means that not only will you probably enjoy the tool, but your radio noise will be limited for a very short time while you charge it up, and then pull the plug on the whole charging setup when done.

Fixed! A strange way to do it by upgrading to a different battery technology (limited charge time from possible noisy charger), just to get some peace between charges for radio listening, but it works.