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Darrel · 03-18-2012, 03:35 PM

I have replaced all of the halogen (G7) bulbs in my puck lites. I picked up an LED replacement and have been trying it. It works fine and is brighter than the halogens and much cooler.
However at a campground with marginal OTA TV it displayed problems.
The station was usable but occasional pixalization was occurring. I fliped on the led bulb and the picture completely froze.

Turning off the LED restored the TV. Has anyone else seen this phenomenum?

Have a nice day - Darrel

gray ghost · 03-18-2012, 06:05 PM

I put LED turn signals on my motorcycle and experienced RF interference whenever signaling for a turn. Also picked up interference from the ballast of an HID headlight I installed. You may want to contact the company you purchased the lights from, they may have a fix.

wa8yxm · 03-19-2012, 07:03 AM

LED's do, in fact, generate RF all the way to, Well, visible light (Beyond Microwave) A good LED light maker takes steps to control this but in order to cut cost some leave the needed part out, IN bulk it might, after all, cost them 2¢ per unit. (And no, I'm not being facetious here, I'm being serious). By one's and twos, perhaps 50 cents to a dollar.

Radio Shack has it, a Capacitor A little ceramic disc job, about .1mmf should do it.

Solder it right across the leads of the light if you can do it and still get it in the socket. Or across the socket as CLOSE TO THE LIGHT as possible, the closer the better.

vermilye · 03-19-2012, 08:21 AM

It is usually the voltage regulators added to some LED lamps that cause the RFI. The advantage of the VR is the lamp works over a wide range of voltages & is unlikely to be damaged when your converter goes into the equalization mode.

There are inexpensive LEDs that do not have built in voltage regulation. While they may fail due to over voltage, some are so inexpensive that it still makes sense to use them to cure the RFI problem. I've used These from Hong Kong and have had no failures, but if I did, the $ is low enough that I ordered spares, & would just replace it. While the flat panel version may not fit your fixtures, they do make other non regulated versions. The companies change all the time so an eBay search is the best way to find them. Shipping from Hong Kong takes a couple of weeks.

BryanL · 03-19-2012, 10:29 AM

re: "LED's do, in fact, generate RF all the way to, Well, visible light" -- a diode generates RF on a DC signal? It seems this would be a significant inefficiency in light generation.

re: "It is usually the voltage regulators added to some LED lamps that cause the RFI." -- this one makes more sense as PWM from solar charge controllers can exhibit similar interference problems. The voltage controllers for LED's are PWM in a chip and you can get them with a remote control for $10 to $15.

I have seen one thread where the complaint was about a step light LED that didn't last very long. That may well have been due to just using a resistor to limit current and not limiting it sufficient for the LED heat dissipation available over time.

The LED tape strips are usually 3 LED's in series with a 150 ohm resistor to each 5 cm long module. This arrangement will usually keep the current through the LED's within current spec up to almost 15 volts.

That 36 LED light for $3 is interesting. The tape strips have 300 for $15. I can't tell what the panel is using for current regulation - is it resistors or a PWM chip?

I have seen some fluorescent tube replacements that brag about a wide input voltage range (10 to 30 volts or so). Those are obviously using PWM. Most of the SMD types that just specify 12v seem to use resistors only.

The panel with several bulb bases is a nifty way to replace bulbs. I've been using the tape strips and manual wiring and that's a bit more work. I haven't played around with the PWM controllers but the remote control and dimming capabilities do sound like fun to play with.

I also note the 144 lumens for 36 LED's in the panel. That seems typical for the 'cheap' SMD LED's. On the tape strips, I have seen some that have significantly larger output for quite a bit more money. The light efficiency per watt is about the same, though (similar to fluorescents).

vermilye · 03-19-2012, 02:08 PM

Most of the cheap flat panel LEDs use a resistor to limit current, however there is no way to be sure other than purchasing one & looking at it. I've been told some put a regulator in the adapter socket - if it doesn't also include on board current limiting resistors, that would be a problem if you cut off the leads & wire it directly, and since there is a regulator, it may still cause RFI if you keep the adapter.

The ones I purchased (the seller is no longer selling them) have on board resistors & no voltage regulation - In the case of my stove vent light I cut the connector & wired it directly & it is still going...

I've seen flat panels with anywhere from 9 to as many as 48 SMDs - the number does not indicate how bright they are since different boards often use different SMDs. About all you can go by is the Lumen spec.

Darrel · 03-19-2012, 03:27 PM

Thanks for the Ideas. I guess I just thought that a diode worked on DC and RF interference wasn't a factor. The little peanut (G7 I think) bulbs in my puck lites are too small to modify but the fixture sounds like a good place to try the MMF capacitor that Wa8yxm suggests.

Have a nice day - Darrel

SCVJeff · 03-20-2012, 01:08 AM

Like Jon mentioned, it is not the LED causing the RFI, it's the switching regulator contained in the lamp itself. There are things you can do: twist the Dc +&- together and get some common mode rejection, and add ceramic caps on the lamp itself. 90% of the noise is being radiated either out of the switcher, or back down the DC line. Unless you are an accomplished solderer..er... and can clip and tack the leads less than 1/8", you stand a good chance of making the problems worse. I did some measurement testing/ fixing with my analyzer awhile back and it can be improved quite a bit. I twisted up the wires from the switcher to the LED's, then tacked .001uf caps in & out of the swxr, as well as the LED board on mine and made a significant difference.. Don't remember where, but I poster the problem and fix results on the spectrum analyzer in a post several months ago.

Pull all but one lamp out and start trying things and use a TV as your gauge. You might end up killing it before you're done with all the tacking of parts on it, but hopefully the end result will work out for you

Dunner · 03-20-2012, 03:42 AM

Quote:

Originally Posted by BryanL

That 36 LED light for $3 is interesting. The tape strips have 300 for $15. I can't tell what the panel is using for current regulation - is it resistors or a PWM chip?

I just bought 6 of these.

White Car Interior Light Panel 48 LED SMD +Adapters New | eBay

By PWM regulation, do you mean something like an LM7812? If not, is seems very easy to wire one behind a socket.

D

She and I · 03-20-2012, 06:11 AM

[QUOTE=Dunner;1119312]I just bought 6 of these.

White Car Interior Light Panel 48 LED SMD +Adapters New | eBay

I purchased 10ea 36 led smd's from this vendor (Exrell) and sodered the wires to the back side of the switches they worked great for about 3 day's.then started flashing 3 led's at a time then they (the 3 led's) quit working..some have lost 6 or 9 led's.contacted Exrell replacements are supposed to be in the mail

So........I guess I need a better source.
Richard

Dunner · 03-20-2012, 06:58 AM

I had another type lost in the mail. Vendor sent me another one. I made sure to tell him I wasn't trying to rip him off and he thanked me for it.

BryanL · 03-20-2012, 08:21 AM

re: "By PWM regulation, do you mean something like an LM7812?" -- no. that's just a buck voltage controller for a fixed 12v output.

See TPS92001 LED Lighting PWM Controller - Texas Instruments | DigiKey -- hobbyists tend to use 555 based circuits - see LED Dimmer Circuit - Lighting -- but the PWM microcontrollers are getting to be very inexpensive, too, and much simpler in terms of parts and wiring.

I note that the TI part functions at up to 1 MHz - frequencies like that can be a lot of fun to keep in the circuit and not cause RFI. John and Jeff had some good suggestions (hams do have a lot of experience with this sort of thing!)

SCVJeff · 03-20-2012, 09:49 AM

It's not the primary 1MHz switching, it's the square wave harmonics of that all the way out to 500MHz+.

wa8yxm · 03-20-2012, 10:18 AM

I have a friend who designed and built a "Gated Noise Source" he tested it across many Ham Radio bands, from HF to VHF to UHF and even hung it in front of a microwave horn belonging to his employer and sat it there. The noise source was a diode foreward biased.

Though he used what is called a "Pin-Diode" The fact is LED's do much the same thing.

(Noise sources are used in tuning radios, they generate what is called "White noise" that is all frequencies are represented at the same level, So if you are tuning a radio you need not worry about "Being on frequency" Gating the noise source at a nice audio frequency, say 1,000 Hz, means you can tune by ear.. When you get the radio tuned for the best signal to noise performance the tone is the loudest. Thus Ted's gated noise source, which has exactly ONE control on it's front panel (ON/OFF) and which you can build for under 50 dollars (Under 25 back then) outperforms professional units he used prior to bulding it which had commas in their price tags.