Capacitor question

[Garypowell]

I have the same fuzzy TV reception when in the bedroom on the external antenna and I turn on the LED reading lamp over the headboard. I have read most of the posts and since I know the antenna wire runs up there close to the 12 volt wires I have self diagnosed that is what the problem is. Some may recall I installed a new Jack Antenna and shorted out one of the overhead lights with a screw. Fortunately I was able to pull a new wire through the ceiling to repower the light.

Someone who knows about these things always writes in and says to use a .001 Microfarad 35 Volt Ceramic disk Capacitor. I went to Radio Shack today to pick one up and could only find ".001 Microfarad 500WVDC.

Its the 500WVDC part that concerns me. It is a little tiny thing....two in a package.....but will this work?

I keep looking at the "500" and the "VDC" and wonder if it is too big (a value/voltage) or something to be effective.

Thanks in advance.

 

[dave10a]

The 500wdc means works with voltage up to 500 vdc and will be not problem at any lower voltage. However, I am not sure this will solve your problem because you most likely have coax cable which offers shielding or significant attenuation from external noise sources. However, the 12vdc usually gets noisy when the charger is being used because most chargers are switching regulators that are noisy-- especially ones used for RV's. That is why AM reception of radios and TV video for RV's will demonstrate static or noise. If you turn off the charger (unplug the 120ac feed) and if the problem goes away then I would believe that is the problem-- otherwise the 12vdc supplied by the battery with nothing else functioning is "clean power". Also when using a capacitor to clean up the power, it should be installed as close as possible to the noise source to minimize inductive reactance in the wiring. The size of capacitor depends on the frequency you are trying to attenuate. The lower the capacitance the higher the frequency. In other words, a .001 will attenuate a sharper wave front (spike) than a .01. I have used .5 to .001 to eliminate alternator noise and on-off switch noise or Spikes. To determine the correct value requires measurement using an oscilloscope other wise its trial and error.

 

[Garypowell]

Thanks Dave. The problem showed up after installing an LED bulb in one of the reading lights. Turn it off the fuzz goes away. Turn it on fuzz in the TV picture.

I changed all the bedroom and closet lights about 2 months ago with no problems with the TV picture. Then about a month after that I ordered and installed the LED reading lights.....the problem started then.....and only with one of them.

Thanks again

 

[TedS]

Replace the 'noisy' led.

 

[Garypowell]

I'll choose the $.55 cap over the $10.00 LED.

 

[dave10a]

I'll choose the $.55 cap over the $10.00 LED.

All devices should be in compliance to FCC rules for emitting RF and EMI. It is likely that particular LED has a problem that should be covered under mfg warranty because it is emitting radiation. However, if the LED is close to the TV and is causing interference it could be normal and in compliance. Try swapping the LED with another one to see if the noise stops, if it does take it back to the store and tell them that it is out of compliance and should be replaced under warranty. It is worth a shot--- especially if the capacitor does not work. The FCC will support your claim

 

[Garypowell]

It just occurred to me that I could swap the two LED's in the bedroom reading lights and see what happens. Can't remember the exact name where I bought them but it in Earth City where many on the forum buy from....just need to get out the paperwork. Something like Super Bright LED's.

I have one LED that the pins broke off and they have agreed to swop out so I could ask. I guess I thought all LED's had a small amount of interference and it was just the luck of where the wires were located such that a problem showed up.....

 

[danemayer]

In the other thread on this subject, I linked to a white paper on LED design. In order to maintain constant lumens output and constant color temperature, there is switching circuitry on the LED assembly. As the 12V input voltage level varies, the circuitry responds to manage the LED output. The switching circuitry is going to vary by LED type and source, and perhaps even by lot. And as the Power Converter changes between its 3 voltage levels, the circuitry will do different things.

Don't know if this is the problem, but there's lots of possibility. Testing with an incandescent bulb in place of the LED might be revealing.

 

[JohnDar]

In regards to LED's and TV interference, all of the 12V bulbs in our rig, except the reading lamps over the bed and sofa, have been changed to LED's and we have not experienced any problems from them. The OEM fan in the bath still causes problems, though. It's being changed to a Heng this season.