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Author Topic: Under cabinet lighting transformer RFI  (Read 3381 times)
K2MK
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Posts: 467




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« on: May 26, 2007, 06:29:43 AM »

I have 12 volt lighting under my kitchen cabinets. The manufacturer is Seagull and the system uses a 60-150 watt 12v transformer into a total of 15  xenon bulbs. There is very noticeable interference on 80 and 40 meters as well as on a portable AM radio.

I tried ferrite beads on the 120VAC input cable and on the low voltage output cable. The only improvement was when I added the beads to one leg of the output cable. I have two beads on there now which yields a minor improvement. When I add more than 2 beads, the bulbs start to dim and the beads get quite warm.  Suggestions welcome.
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N3OX
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« Reply #1 on: May 26, 2007, 08:40:01 AM »

"When I add more than 2 beads, the bulbs start to dim and the beads get quite warm. Suggestions welcome."

That's a little pathological.  What's the output voltage as seen by a DMM?  Is it 12VAC or 12VDC? Maybe it's high frequency AC, which would be really pretty terrible.  If it's 12VDC+noise, putting some inductance on the output apparently makes the supply do something unstable... if it were DC+noise and you put beads on, the bulbs wouldn't dim unless choking the HF stuff caused the power supply to malfunction.

Also, what kind of beads are you using?

The quick fix would be to just scrap the power supply and buy a 150W 120V:12V transformer.

Dan



 
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K2MK
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« Reply #2 on: May 26, 2007, 06:09:01 PM »

Hi Dan:

It is just a 12V transformer not a power supply. The output under load measures 8.8Vac. I had some Amidon FB-(43)-6872 ferrite beads on hand. Amidon says their material #43 suppresses 20-400MHz. Maybe that's my problem. I didn't use the correct beads. Their materials #73 and #77 suppress 1-40Mhz.

Mike K2MK
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WA7NCL
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« Reply #3 on: May 30, 2007, 02:19:44 PM »

Sounds like it is a switching system at high frequency.  

You need to use large clip on ferrites (many hams use them to make baluns).  You need to use them common mode.  That means you put the power and return wires thru the same ferrite.  You can wrap several turns bifilar thru the clip on core as well.  The ferrite will serve as a common mode choke but not impede the flow of HF current to the light.

This may or maynot help.

You still might be getting interference on the mains side.  You can try the common mode choke approach on the AC mains side as well.  Put both the hot and neutral tru the same ferrite.

I have some of these in my house as well.  We almost never turn them on so they are not a priority for me.  But when they are on, they wipe out HF in the house.
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K2MK
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« Reply #4 on: May 31, 2007, 06:28:17 AM »

Thanks for the ideas. I'm also waiting to hear from the manufacturer of the lighting system to see what they say.
Mike, K2MK
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KE3WD
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« Reply #5 on: June 10, 2007, 07:40:56 PM »

Many gas bulbs actually emit broadband RF.  

We used to hold the police and fire HTs of a yesteryear generation up to the neon tubes above the bench for the quick and dirty receiver go/no go check of the RF input transistor etc.  

Kind of an eyebrow raiser that chokes would get warm on the low voltage AC line described -- if that voltage is at 60 Hz.  My gut bet is that the "transformer" is at a much higher frequency.  

Something tells me that there is more circuitry to those xeon lights, maybe behind the sockets.  

Luck,


.
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K2MK
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« Reply #6 on: June 11, 2007, 04:31:35 AM »

Thanks for the suggestion. I took my AM radio and placed it near the transformer and near the bulbs and the noise source is definitely the transformer.

The manufacturer got back to me and agreed to replace the transformer with one that usually solves such RFI problems. The link to that transfomer is:
http://www.seagulllighting.com/Ambiance%C2%AE-Lighting-9460-12.html

The transformer that I now have is:
http://www.seagulllighting.com/Ambiance-Lighting-9458-12.html

I had read elsewhere on the web from a different manufacturer (Kilcher) that they use a toroidal transformer for RFI problems. I'm hoping that this manufacturer (Seagull) has done the same.  Seagull calls it a magnetic transformer which I suppose could be a toroidal type. I'll report back after the exchange is made.

Thanks to all,
Mike K2MK
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K2MK
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« Reply #7 on: June 11, 2007, 08:47:32 AM »

Problem solved.

I picked up and installed the new transformer and it completely solved the RFI problem.

Mike K2MK
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N3OX
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« Reply #8 on: June 25, 2007, 11:26:58 PM »

Dunno if you're still reading this, but I assume the new transformer is about five times heavier than the old "transformer."

Is that right?
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K2MK
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Posts: 467




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« Reply #9 on: June 26, 2007, 06:44:30 AM »

It was definitely much heavier and quite a bit larger.
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N3OX
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« Reply #10 on: June 26, 2007, 11:27:07 AM »

Yeah, I think the new one is ACTUALLY a transformer and the old one was a switcher, and a bad one at that.

This is an unfortunate development in power supply naming convention Sad

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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