RF Interferance.

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xman
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RF Interferance.

Post by xman » Mon Oct 08, 2012 1:09 am

Well boys, I'm open to suggestions on this one and thought the pros around here may have some suggestions. I'm getting bad RF interference in my farm house both from the 12DC power wires and the AC power lines that run around the house. Some of the lights in the house run on 12vDC, these are 12vDC 4 watt LED down-lights. When these lights are on, the AM on the radio is very badly affected with noise. Some of the lights run on 240vAC, these are CFLs, and they run off the 240vAC generated from inverters mounted on the power board. The AC is badly affecting the FM on the radio. The radio's antenna uses shielded car radio lead and the antenna is mounted on the house's roof, outside the house. The radio reception was real bad until I had it's 12vDC power coming from a dedicated battery that isn't connected to the solar charging circuit so this battery needs to be manually charged. This did help but is still being affected by the AC and DC power wires going through the house. Just wondering if the radio's antenna lead should be grounded to the metal of the house like it is in a car but I don't use the metal of the house as a ground return. I'm up to using ferrite coils to see if that helps but not sure if that will help on both AC and DC circuits. Another alternative would be to run all the power leads on the house outside the house's metal panels but this is not what I'm after as moving the radio outside the house is not really a good suggestion. Any ideas?.

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Re: RF Interferance.

Post by professor_jonny » Mon Oct 08, 2012 7:33 am

Poor filtering in the inverters and inducted rfi from the cfl's

You could get an lc filter or sinewave filter on the output of the inverter to limit the rate of change in current/voltage ( also called a dv/dt filter) it will smooth out the power to a sine wave rather than a modified sinwave/pwm voltage vector transform lessining the rfi traveling down the 240v mains but that is only fixing half the problem.

As the inverters draw power from the battery's in a chopped up way you shuld install capicator on the input of the inverter you shuld have aprox 20,000 uf (.2 farad) for every 500w of inverter power a car audio cap would do the trick, it will reduce heating in the inverter and prolong its live also.

Make sure you ground the earth on the inverter to a suitable ground point or earth peg will help as as it will dump rfi to ground rather than raidiate it in side your house and bounce it off the metal walls.

Bc and es cfl lamps are very poor in their quality and filtering best to replace them with 12v led equalivants they wont have switch mode stuff in them so they wont radiate stuff in the power wires.

If you could run everything at 12 or 24v it would be best and ditch the inverters.

The cfl's in my house interfere with our baby monitor even the expencive philips ones do it.

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Re: RF Interferance.

Post by xman » Thu Oct 11, 2012 2:40 pm

professor_jonny wrote: As the inverters draw power from the battery's in a chopped up way you shuld install capicator on the input of the inverter you shuld have aprox 20,000 uf (.2 farad) for every 500w of inverter power a car audio cap would do the trick, it will reduce heating in the inverter and prolong its live also.
The inverters I'm using are only either 75 or 150watt units and only power one devise per inverter so real easy to track down exactly what's going on. What sized cap should I use on them?. Ill give it a go but I'd of thought seeing as the battery power is coming from 1000amps of battery bank and the wire connecting the inverter to the bank is 25amp rating, this wouldn't be an issue but..
professor_jonny wrote: Make sure you ground the earth on the inverter to a suitable ground point or earth peg will help as as it will dump rfi to ground rather than raidiate it in side your house and bounce it off the metal walls.
That I haven't done. As the inverters are in a plastic case, will the neutral output line do the job?.
professor_jonny wrote: Bc and es cfl lamps are very poor in their quality and filtering best to replace them with 12v led equalivants they wont have switch mode stuff in them so they wont radiate stuff in the power wires.
The guy I bought the 1st CFLs I bought off had 12vDC CFL units and suggested a cap on them to stop noise. I may try catching up with him and ask what to do about 240volt ones. The 240vAC CFLs I'm using are Phillips 5, 8 and 12watters by the way. I am also using 12vDC LED down lights and there problem is they interfere badly with the AM bands on the radio. The 240vAC CFLs and / or inverters interfere with the FM and the 12vDC LED down lights interfere with the AM bands on the radio. Also, if the battery powering the radio, ( Sony Car Radio by the way), is connected to the battery bank and solar charging circuitry, I get interference.
professor_jonny wrote: If you could run everything at 12 or 24v it would be best and ditch the inverters.
Well yer but the CFLs light up a room nicely where as the LED down lights are quite directional. But just to give you some idea, I can run 4 or 5 rooms of CFLs from 1 X 75watt inverter and it will draw far less DC amps than the 8 X 4watt LED downlights that only light up the under mezzanine floor area all be it very well lit up. Actually, like a kitchen bench. :lol: I'll grab the exact amp figures next time I go down but really, I was quite surprised how big a difference it actually was. The LEDs were pulling around 5 to 7 amps. The inverter, around 2. I really need a solution to stop this interference. It really was the last thing I was expecting with the radio antenna mounted outside the "Tin Box" that forms the house. I thought it, the tin shield, would have shielded the radio antenna from any interference. Seems like I'm getting interference inside either the aerial lead, the radio case or the radio's power leads. I'm to the point of trying running the radio and soon T.V., projector and God knows what else in the future, supply wires through metal tubing or grabbing some shielded supply wire to insulate the power wires. Another piece of info, the noise isn't affecting the USB MP3 playback so it is solely the radio being affected. That takes out the speaker wires being the source of the noise. I will move the radio to another location inside the house but it still needs to get power from the battery bank. This separate battery bit for supplying just the radio is bullshit and I'm expecting big dramas when I hook up the wind generators. Really seems strange I'm getting any noise considering the whole setup is basically that of a big car, metal body, car radio, 12vDC and power wires running everywhere including inside the metal body. Even the inverters I use are for charging laptops from a car lighter socket. Wouldn't really expect them to be a problem seeing as though most car lighter sockets are close to the car's radio normally.

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Re: RF Interferance.

Post by professor_jonny » Thu Oct 11, 2012 8:15 pm

The problem with battery banks it they are unable to supply instanious current at the frequency an inverter really needs the power in ac runs at 50 hz and the power switches on and off in pwm at probally 100 times per cycle of the sine wave power the frequency it draws is in the order of kiloherts.

If the inverters were bigger they probally would cause less interference as you would not be hammering the capicators in them so much and would possibly have better filters in them and bigger cap banks, using a cap around 7 to 10k uf on each would be the trick but a car audio cap would suit.

In a car the altenator is able to switch the regulator up quickly and capacitance of the mass of wires helps this problem as all the power wires have capacatance between the metal frame then there is the fact that all the devices in the car computer clock etc usually have capicators in them to.

earth the chasi of the unit to ground don't earth the neutral or earth pin

Are you using constant current drivers with your led lights or are they intergral type ?
below is a constant current led driver with 9 to 50 volt input cc 1000ma it depends on the lamp info im guessing you have led's with drivers on the lamp?
seperate drivers are definatly better quality than the built in ones and also offer the point that as the battery voltage gets lower your lights dont dimm.

http://nz.wellforces.com/ac-dc-power-su ... -wire.html

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Re: RF Interferance.

Post by dan » Tue Oct 23, 2012 1:11 pm

Thanks for the replies, they've been really helpful to my similar problem.

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Re: RF Interferance.

Post by xman » Wed Oct 24, 2012 11:50 am

@ PJ, haven't got back to you on this as I haven't really had time when I go down to stuff with the radio or wiring. I can say the last time I went down it was raining lightly and the interference was noticeably less. Rain grounding the aerial to the metal of the metal farm house you think?. I'll try moving the radio and aerial to a less "wired" location in the building and see how that goes and also throw a noise suppress on the radio's power wires and see what joy I have. If these measures don't work, I'll be asking more about the other parts you recommended. Thanks as always P.J. for taking the time to share your knowledge. It is always appreciated.

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Re: RF Interferance.

Post by xman » Mon Nov 05, 2012 2:15 am

Well I had a bit of time to do some tests and found the interference is only on the radio both AM and FM and not at all there when using the USB input as the source so I guess that rules out the power wires being the source of the noise and leaves only the radio antenna and it's extension lead. I'm yet to try grounding the antenna's shielding but thought I would ask if anyone has any further ideas. Then again all the interference may disappear when I relocate the radio and it's antenna away from the battery/ power distribution room. Don't really know.

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Re: RF Interferance.

Post by professor_jonny » Mon Nov 05, 2012 10:28 am

The tuner is real sensitive to voltage and interference, as it has to pick up waves in the air that are virtually voltage free.
It will be the tuner picking up inteference in the power wires or radiated within the building.

If you had a scope you could check the inteference against the source?

What kind of radio is it like a cheap boom box or ?

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Re: RF Interferance.

Post by xman » Mon Nov 05, 2012 11:21 am

Sony car radio. :oops: I picked a car radio thinking it would be best for a 12volt install in a metal building actually. I may see how it goes when I remove it from the power room away from all the inverts and power leads but still I'd of thought being a car radio using car antenna and extension lead would have worked quite well. Still, I am happy I have worked out it is only the AM and FM getting any interference as it is this unit I'm using as the amp for the Xbox wall install. Maybe when I move it I will be actually able to use the booster I made for the radio antenna as well. It has been useless with the current interference I get on the radio. By the way P.J., all this effort you've put in on my problems makes me feel I owe you a trip down the farm on your next Aussie visit.

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Re: RF Interferance.

Post by professor_jonny » Tue Nov 06, 2012 5:55 am

It is part of what i do at work i do stray voltage and harmonics stuff, specially to do with varible speed drives and smps, its one of my hats at work :-)
I help write standards and codes of practices in that area.

I'd' put an earth on the inverters to an outside peg or stake then put a car audio cap across the battery bank and see how you get on. make sure you shed frame is earthed also legally it has to be if there is mains in there.

car radio shuld be prity good i would of guessed?

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Re: RF Interferance.

Post by xman » Tue Nov 06, 2012 8:19 am

Hmmm, actually been thinking about the shed's earth and all this time I have been presuming it to be earthed quite well already but now that I think about it. it is only dynabolted to the concrete slab and has no direct earth to a stack as such. That may well help somewhat having a slack and a cable to the steel of the shed's frame. The concrete of the slab may be a poor conductor?. May explain why the interference is reduced when it rains, water between the metal of the shed and the ground?.
Also thinking the antenna's lead may well be insulated better if it is feed through a copper tube which is earthed. I have a cap from a car coil that may suit being placed across the radios power wires.

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Re: RF Interferance.

Post by xman » Mon Nov 26, 2012 3:16 pm

Well I tried giving the shed a good earth, car jumper leads connected to the steel balcony rails and a copper pole driven in the ground 100mm. No good. Made Jack Shit difference actually. Looks like it's an aerial issue. Next visit, I'll relocate the radio and the aerial and see if that gives any joy. Also re-connected the solar to charge the radio's battery just to see if it added any extra interference, it didn't.

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Re: RF Interferance.

Post by professor_jonny » Tue Nov 27, 2012 12:32 am

100mm earth peg ? the legal length is 2mt it will give you a poor earth you wont even get down to the wet stuff below.

copper is not very good as an earth peg same with galv covered steel as it will corode/rust over time stainless 316 16mm 2mt long peg will set you back 20 to 30 dollars at a guess.

I'd be looking at filtering the mains down stream of the inverters and the incomming to the inverters from the battery bank a car audio cap in paralell to the battery and some dual layer eletrilitic (ac) caps like what you would find on a run circuit of a motor and see what happens, it shuld not be too expencive.

if the radio is on its own supply (seperate car battery) does it still get interference ? within the building/ outside ?

then start removing things to track down where the source is.

if you had a scope capable of measuring up to 20mhz you would get a 500 ohm resistor put a trailing lead to your earth peg and measure the voltage across the resistor connecting the free end to sources of stray voltage, any current flow to earth of siginificant current will cause the resistor to have a volt drop which you can measure.

the scale shuld be 500mv and any thing over 1 division (500mv) would be concidered high.

as the out side walls are tin it could be considered a faraday cage which could be the source of the problem.

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Re: RF Interferance.

Post by xman » Thu Jan 10, 2013 4:11 pm

Well I moved the radio away from the power distribution room in the farm house and had success with the interference with the AM but the 12 volt DC LED down lights are still an issue with the FM. Looks like I found the issue-
http://www.emcrules.com/2011/07/radio-i ... hting.html
Now how the hell am I going to sort this out without changing the LED bulbs themselves?. I can't go changing the 12 volt power supply because these bulbs are being powered direct from the batteries that are 12 volt. I'm thinking a capacitor wired across the LED down light power pins may fix this. Just need to work out what value to use. Interestingly, I'm having this same issue with the digital radio I have in the city house. Put the LED lights on in the kitchen and the digital radio in the next room receives no signal and as a result, no sound output. Turn the LED down lights off in the kitchen and the radio comes back on just fine. This was never an issue using the old halogen down lights. Another solution I have read is by using a different power supply when powering the LED down lights from an AC source. I can't do this down the farm however, what about an isolation transformer?. :ugeek: May be well worth a try I think. As you can see, I'm still working on this issue but it really required me to move the radio's location to prove a few things first and now that this is done, I can continue to find a possible solution I hope. I'm quite confident now I'm not the only one on this site experiencing these issues with new generation LED down lights and maybe not yet but as time goes on, I'm sure more will be effected by these issues.

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Re: RF Interferance.

Post by professor_jonny » Fri Jan 11, 2013 4:31 am

just of it is that the led fittings have built in switch mode powersupplys and to make them cheap they omit filtering in an above post i asked if the drivers were intergral or seperate, seperate drivers are definatly better quality than the built in ones and also offer the point that as the battery voltage gets lower your lights dont dimm below is a sample but you would need to buy new fittings to work with them which is the bummer.

this is an external constant current driver but it does not nesesserally mean they have filtering built in just more likley as of the space constraints with in the led bc and es fittings.

http://nz.wellforces.com/ac-dc-power-su ... -wire.html

The best way to reduce rfi being emitted is to filter it with an lc filter the freq you want to reject determines
The values of the components tipically you want to reject high frequencys above 10mhz.
the inductor will be in series to limit inrush one on both + and negative of the supply and the capicator will be in paralell that will filter what goes through the inductors, you can buy such devices but all you need ia s ferrite ring and wrap 10 or so turns seperately on a single ferrite of solid core enamel coated copper wire and some suitably rated electrilitic caps preferabally ac double layer versions probally around 1 to 2 uf.

you could also look for a dc low pass filter on the net which was just a quick search:
http://www.alibaba.com/showroom/dc-low-pass-filter.html

this is the tupical thing that they omit from the fittings to save space and cost:
http://www.alibaba.com/product-gs/59752 ... ilter.html

The 5th order harmonic of the switchinng freq is the one that causes all the issues normally as it would be close to the freq of radio signals.

In nz and australia there will be a new code of practice (ecp) that will cover pds (power drive systems) and any product that converts power from on source to another (switch mode power supplys etc...) until that comes in to play the market will get flooded with cheap un filtered fittings.
in theory they shuld be covered by asnzs3000 but of current there is one person in nz(mark epsom) that is contracted by the goverment to police it and i dont think there is much more in australia, they only catch the big fish and only when a complaint is made.

There will most likely be a saftey standard introduced with led tubes also so that the power is only applied at one end of the fitting to aviod any one pluggin it one end with their fingers at the other end, the problem arises as the large inrush from the smps caps charging can cause shock and death, which does not happen with traditional tubes as they need the filimant to connect the circuit.

what they will do is put power on each end of the fitting and join the two pins at one end of the tube to complete the circuit so that either end is not live as they are not connected in any way to the other end.
there is problems with this if they fit in a traditional led tube fed from both ends or a traditional tube it will blow the fuse at the switch board so they are debating some mechinism to counter this maybe something intergral to the tube.

I know it does not help us in nz and australia yet but soon these problems will be distant future soon (hopefully).
i know as we at work have been helping to draft these codes as we have a lot to do with variable speed drives.

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Re: RF Interferance.

Post by Lion » Thu Sep 28, 2017 7:12 pm

I had the same problem with interferance. When the LED lightbulb was on my Xbox was squealing (I blame the foxconn power supply).
I've ordered the Xbox Protection Cord (X800925-100). I didn't have very high hopes, but to my surprise — it works! No more annoying noise, problem fixed. :mrgreen:
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Re: RF Interferance.

Post by professor_jonny » Fri Sep 29, 2017 4:56 am

Lion wrote:
Thu Sep 28, 2017 7:12 pm
I had the same problem with interferance. When the LED lightbulb was on my Xbox was squealing (I blame the foxconn power supply).
I've ordered the Xbox Protection Cord (X800925-100). I didn't have very high hopes, but to my surprise — it works! No more annoying noise, problem fixed. :mrgreen:
For any thing to make the xbox psu do that I would replace the led lights with something better as it might damage other things in your house.

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Re: RF Interferance.

Post by Lion » Sun Oct 01, 2017 1:21 pm

The weird thing is that just the Xbox with a Foxconn PSU had such problems. I had an another one (with Delta one I think) and no such thing occurred.
I'll replace the LED anyway though. :D

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Re: RF Interferance.

Post by Lion » Wed May 23, 2018 6:20 pm

Yup, it was the PSU. After I replaced it with a Delta PSU the noise has disappeared. :D

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