Electrical noise question

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Electrical noise question

Postby Waliczek » Tue Jul 19, 2005 10:00 pm

On my last campout, it took my small B/W TV 7" and I plug it into the cigerette socket I installed in my cabin. TV work great. I then reach up and clicked on the vent fan in the roof, and then the static started, I could not tune it out. I apparently need a filter of some kind. Does anyone out there who know a lot more then me , can advise. What kind of Filter? and How to install it? Maybe a simpler fix is in order.
Thanks for any help.
Tom
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Postby madjack » Tue Jul 19, 2005 10:04 pm

...goto Radio Shack and see if they have a RF filter that will clip to the power cord of TV...they should have one that is about 1.5/2" long and .75" dia that will fit around the cord
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Postby Waliczek » Tue Jul 19, 2005 10:18 pm

I do have a radio shack several miles away. I will be there before noon tomorrow. However, past experience with that store shows me that the clerks are not very knowledgeable about much. At least you have given me something to ask for. (excuse me for ending the sentence with a prep.)
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Postby madjack » Tue Jul 19, 2005 10:25 pm

...whenever I shop at a Radio Shack and need something out of the ordinary, I always ask for the manager, they usually at least know their stock...the little pimple face kids, well I try to avoid them, 'cause they frown on you slappin' 'em for being stupid
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Postby SteveH » Thu Jul 21, 2005 8:18 am

Tom,

Although I agree with MadJack, the noise can be coming in on the DC line, I'd double check as DC motors used in fans have commutators and brushes, and they create sparks which translates into RF noise being generated.

The way to double check for shure is to run the fan and TV with the TV powered by a seperate battery. If you still have the noise under those circumstances, the noise is coming in as RF and cannot be filtered out with DC filters.

If you determine the noise if RF noise, you can put a couple of capacitors on the power lines going into the fan soldered to the fan case, and possibly reduce it, but probably never totally eliminate it.
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Postby An Ol Timer » Thu Jul 21, 2005 12:57 pm

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Last edited by An Ol Timer on Thu Jul 21, 2005 1:03 pm, edited 1 time in total.
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Postby An Ol Timer » Thu Jul 21, 2005 12:58 pm

Noise ( an ac signal in the high frequency range ) of this type is usually created by the brushes arcing and is in a broadband across the RF spectrum.
A capacitor allows ac to pass and blocks dc, whereas an inductor does the opposite allowing dc to pass while blocking ac.
A simple filter on the power lines to the fan should have an inductor ( RF choke ) in each line and a capitor across the lines.
This allows the dc to flow unimpeded while shunting the ac across the lines effective shorting it out.
The filter should be placed as close to the source of the noise as possible.
A capacitor from the case of the fan ( if metal ) to the low side (-) would also shunt noise.
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Postby Waliczek » Thu Jul 21, 2005 3:20 pm

I have made a list of all of the idea's and this Sat. early, I am going to start The search. Thanks to all for your advice. I will keep you posted. If additional ideas come to mind, please pass them on, so I can add them to the list.
Tom
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Postby Waliczek » Thu Jul 21, 2005 6:19 pm

Additional information from a question off another forum.

The entire trailer is 12 volt, running straight off the battery, solar charged.Research so far points to the type of motor in the 12 volt fan, and it's close proximity to the TV. My other source feels that the motor is emitting a low grade frequency, and because of the closess to the TV (about 2ft), it does not have time to filiter out. I Can't move the TV further away ( It's a teardrop) He suggests a simple shield. Believe it or not, he suggested a metal soup can, cleaned, and cut to surround the small electric motor, with about 1/2" clearance or more if possible. I am going to try this. It seems so odd, and simple, what if it worked.
Tom
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