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12 Volt LED Lamp Interferance Issue?

Bloppy

Subscriber
I am having an interference issue at my "up north" bunkhouse.
It is a 12 volt system with a led 14watt t8 bulb for night time interior illumination and a marine radio/cd player. What i am experiencing is when the light is on my radio reception is dead.
I used a second 100 ah battery just for the marine radio for a test and has the same results as using just one battery. Was thinking maybe the style of light bulb or my antenna is at fault,so I hooked up a 8w led emergency light for test and found the radio reception was fine with the 8w led light on. So i would say my 14w t8 dc bulb is evil. It sucks because I like these bulbs and have many, including my emergency lighting at home. So,is there anything I can try to do to get these 2 items to play well together? Would grounding the light fixture to earth ground help?
This is the bulb i have:
www.larsonelectronics.com/product/105115/14-watt-led-bulb-2-foot-t8-lamp-1750-lumens-low-voltage-dc-sub-zero-temperatures-40c
The bunkhouse is 2 1/2 hrs away so i am willing to try a few different ideas on a trip. Many thanks for any comments or suggestions
Jim
 

uglyblue66

Subscriber
Is it AM or FM? That could help folks determine what is causing the interferance.
I know flourecent lights kill Am bad as when I would try to play 1 of my old battery operated farm radios the buzz would cover up any stations that were not really strong.
The dc motor on a electric golf cart also interfers with a radio.
 

pegasuspinto

Active member
try a different bulb, make sure you just don't got 1 defective bulb

In all likelihood, your T8 LED is chineeze crapola and they completely left out ANY hint of radio interference suppression, and then outright faked any FCC compliance. It's just that simple.

Most LED lights include at least a switching power supply, which is plenty of electronics to cause radio frequency interference
 

Bloppy

Subscriber
Yes FM band, And yes I can try and another bulb. Will be going up in a week. I think I will buy a emi radio filter to take too if switching out bulb does not work. I guess I will start my list of things to try. Thanks again. Jim
 

Power

Active member
Would grounding the light fixture to earth ground help?
Jim
If properly done, it might help a little. Done wrong, could act as an antenna. If you have all metal piping to the well, could try a quick ground to nearest cold faucet.
 

Bloppy

Subscriber
I do have a couple 210 amp batteries but thought it was a little overkill for a 144 sf stick built bunkhouse. And do you mean an incandescent bulb or a non linear bulb? Was trying to use what I had on hand,and liked the amount of light from the t8. I thought I could use the traditional led emergency light bulbs but would use more power for the same lumens. You do have me thinking.
Power- no water there but will try the earth thing 2nd on my list.
thanks guys!
jim
 
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gnucklehead

Subscriber
pegasuspinto has it - - switching frequency, sometimes in the 100MHz range.. Try a different lamp, or scrap the T8 completely (could be the fixture)
 
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Kevin K

Subscriber
I just took a look at the link, and at 125 lumens/watt, it's an efficient lamp. But at $87.57 plus shipping :eek:, not for me. A quick look at Amazon suggested many more economical alternatives for 12 volt T8 tubes, mostly 18" length. Even though you may have to use two, still much more economical. The possibility of an early failure leaving me with an expensive piece of junk is enough for me to steer clear of this lamp.

Within the last year I replaced all the lamps in my home with LED's. Massachusetts is apparently subsidizing the lamps, so I took advantage of the offer. A Greenlite LED shoplight 43" long, single tube, 4000K, 23 watts, 2400 lumens cost $5. A MaxLite 100 watt equivalent standard screw in base (E26) bulb, 15 watt, 1600 lumens, 2700K dimmable or non-dimmable lamp cost $1. A MaxLite 100 watt equivalent flood lamp 13 watt, 1050 lumens, 5000K, cost $1. At these prices I can afford to do a complete switchover without worrying about being left with an early failure of an expensive lamp.

I do not have any AM or FM interference from these lamps. Somewhere on the to do list is borrowing a spectrum analyzer and checking the RF emission. I have a hunch anyone using the sub 30MHz amateur radio bands would have a problem.

So far I have had one early failure, a 100 watt screw in lamp. It was a power supply failure not an LED failure. Finding the failed part is on my to-do list, just as an interesting project.
 

Jack Hottel

Subscriber
As noted above the interference is generated by the driver inside the LED tube. These are similar to the electronic transformers currently used in many wall warts. They use a high frequency oscillator to drive a ferrite transformer to change the voltage desired then rectify & regulate that to drive the LEDs. The wave form produced is nothing like a sine wave and consequently splatters harmonics all over the radio spectrum. Try capacitors of various sizes across the inputs to the tube and from each input to ground if you have one. If the fixture is metal ground to it also.
A power line filter might help, as would a filter on the antenna input to the radio. Ground the radio and keep the antenna as far away from the light/power lines as possible. A portable AM radio makes a good sniffer to find exactly where the interference is radiating from. If directly from the light tube, wrap the tube in metallic window screen and ground that. Have fun.
Jack Hottel
 

Power

Active member
I just took a look at the link, and at 125 lumens/watt, it's an efficient lamp. But at $87.57 plus shipping :eek:, not for me. A quick look at Amazon suggested many more economical alternatives for 12 volt T8 tubes, mostly 18" length. Even though you may have to use two, still much more economical. The possibility of an early failure leaving me with an expensive piece of junk is enough for me to steer clear of this lamp.
.
Maybe not. I have had LED failures. Contacted company. They send a replacement. Some send postage paid for return of defective bulb, some say discard it.
 

Power

Active member
And they say 50,000+ Hours... DO save your receipts :D
I did not need receipts. They asked for information off bulb. I think they get manufacture date from that.
People were very pleasant, asked what kind of fixture used in, base up or down, if on dimmer, how many hours/ day used.
 

Bloppy

Subscriber
Kevin-The link for the bulb was for information only. I got them for under 20 dollars each a while back. DC t8 always seem to cost more than the Ac t8's.
Jack- it is a metal light fixture and already have a plastic housing ready to try if the grounding does not work. And thanks about the tip about using an am radio as a sniffer and the metal screen. all good to know!
Ron- no fancy on/off switch,trying to keep it simple.
I appreciate all the info guys.
Jim
 

dkamp

eMail NOT Working
Hey Blop-

When you say 'marine radio/cd player'... are you referring to an AM/FM stereo reciever with CD that's intended for marine environment, or... are you referring to a Marine VHF 2-way tranciever?

If it's the former, then the bandwith which your interference is occurring, is between 88 and 108mhz... and 550 to 1800khz.

If it's the latter, then it's 156-158mhz or so.

The former is much wider in it's scope, than the latter, and as a result, the design of the radio reciever is a substantial weakness with respect to interference rejection.

To complicate further, common AM/FM radios use a 455khz IF stage for both AM and FM reception, and if your lighting is generating noise with harmonic products in that vicinity, and that noise is getting into the reciever's IF stage, you'll get NOTHING out.

The downside to diodes, is that they're naturally noise generators. All you have to do to make a diode of ANY type generate noise, is to pass current through it... so an LED light is nothing more than a broadband RF noise generator that's very efficient at radiating around 4.3Thz as well.

The lamp is probably sending enough crap RF noise backwards through the power line to radiate substantially.

You could try to add noise filters to the lamp's power leads, but do it as CLOSE to the lamp as you can get. Putting a .1uf capacitor close to the lamp's power leads will help quench RF, as would putting inductance on BOTH of the power leads.
 

Bloppy

Subscriber
dkamp- radio is just a moisture resistant stereo and not a 2 way.
After reading your post last night I did some reading about the capacitor thing -so I would solder the cap between the power wire and the ground wire close to the light as possible?
If so,sounds like only a 2 dollar try -I like
In the same reading I did stumble on what BTPost was saying about the Ferrite Core on the wire.
I guess I am going to the electronics store monday. (Its a old time CB radio shop).
Never knew about the the troubles with some led 's before now,
I guess I have been lucky. And last week I thought maybe it was my antenna was picking up the interference. Did not occur to be it would be transmitting down the power supply. Thanks to you all,I have good attack plan.
Jim
 

Power

Active member
In the same reading I did stumble on what BTPost was saying about the Ferrite Core on the wire.
I guess I am going to the electronics store monday. (Its a old time CB radio shop).

Jim
I get my ferrites for free. Seems TV sets, computers, microwaves, monitors, printers..etc all have them. When they are scrapped, I clip out the ferrites, and put them in a plastic box.
 

dkamp

eMail NOT Working
Yep, another source for ferrites is on video monitor cables, keyboard cables, and other data cables... if there's a big lump of plastic an inch or three from one end connector, it's a ferrite... clip the wires off on the connector side, and pull 'em through. Feed your power leads through it. You could also use toroids, and wrap the power leads (both) around the donut a few times.
 
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