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1-10 of 10 messages
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Page 1 of 1
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RFI FROM POWER INVERTER
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by KG6WSU on August 30, 2005
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I HAVE A 2KW RATED 12VDC TO 120 VAC POWER INVERTER I USE IN MY VAN. IT PUTS OUT A LOT OF RF HASH PICKED UP ON MY TRANSCIEVER WHICH IS IN MY HOUSE ON HOUSE POWER CIRCUIT.
HOW CAN I ELIMINATE OR REDUCE RFI HASH FROM INVERTER ?WIRE-MESH CAGE ? SHIELDED GROUNDED POWER CABLES IN AND OUT OF INVERTER ? INLINE FILTERS ? FERRITE BEADS ?
HAS ANYONE EVERY FIXED THIS SITUATION ?
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RE: RFI FROM POWER INVERTER
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by AA4PB on September 1, 2005
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Pretty much all of the above. You just have to experiment. Basically the RFI is generated by the switching circuits inside the inverter. It is possible for some of the RFI to be radiated directly thru the cabinet. Most of it is usually conducted out the power wiring which then acts as an antenna to radiate it. The DC input is most likely but the AC connections are also a possibility. Ferrite beads on the wires located close to the cabinet can help although you need lots of ferrite for the lower frequencies. On the DC side, ceramic bypass capacitors (lines to case ground) can be effective.
Use a cheap AM broadcast band radio to "sniff" around the wires and see if you can determine if there is one spot where most of the RFI is coming from.
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RE: RFI FROM POWER INVERTER
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by KG6WSU on September 1, 2005
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THANKS FOR INFO . WHAT VALUE OF BYPASS CAPS WOULD YOU RECOMMEND ? WHAT I WANT IS TO HAVE THE INVERTER POWER A LINEAR AMPLIFIER IN THE VAN FOR PORTABLE/MOBILE USE. I WANT TO POWER THE TRANCEIVER FROM THE SAME 12VDC VAN BATTERY,BUT WOULD THIS FEED INVERTER HASH BACK THROUGH THE BATTERY TO TRANCEIVER ?
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RE: RFI FROM POWER INVERTER
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by AA4PB on September 2, 2005
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I'd try 0.01uFd disc ceramics. More capacitance wouldn't hurt anything (and may help) but they need to be suitable for use at RF frequencies.
Most likely any RFI on the power leads will be radiated and picked up by the receiver antenna. It shouldn't hurt any to connect the radio directly to the same battery.
Since you are running the amp from the inverter you may also want to consider running the radio from your power supply connected to the inverter output. Although that is a bit less efficient, it would ensure that your radio always gets a nice regulated 13.8VDC. If you run it directly from the battery then the voltage input to the radio will drop as the battery voltage drops. Some radios don't do very well when the voltage gets below 11.5VDC or so. Almost none will work down to 10.5VDC which is probably the point where your inverter cuts off if it has an internal low-voltage cutout.
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RE: RFI FROM POWER INVERTER
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by KE5OK on August 30, 2009
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I have a small solar system. I use a 5kw inverter with a 10 kw surge. Like you I have hash. I found that it is coming from the DC side . Where you hook the Battery to. Not the AC side. Mine will even radiate when the AC line is not hooked to it. I can unhook the antenna from my rig and all hash stops. I tried several Caps. no luck. So far the best thing that I have done is to move the antenna. I don't know if you have that option , but it did help a lot. Good luck.
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RE: RFI FROM POWER INVERTER
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by WX7G on October 4, 2009
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Place one 0.1 uF ceramic capacitor from (+) to the metal case and one from (-) to the case.
Place one 0.01 uF ceramic capacitor (200 volt or higher rating) from each AC output to the metal case.
You have now done about as much as you can to reduce both differential-mode and common-mode RFI short of resorting to inductors.
Now for a 10 uH inductor. You will need some heavy wire for your 2 kW inverter. #6 AWG is an absolute minimum. Take a 3 to 4 inch diameter PVC pipe. Close wind 8 turns of #6 wire.
Between the inverter (with the 0.1 uF caps installed) place a 10 uH inductor in each DC power leg. Now place 0.1 uF caps from each power leg to the metal case.
You can do the same on the AC output side with the 0.01 uF caps.
You can experiment and see what works best; disconnecting the DC power and AC power 0.01 uF caps from the case and connecting them line-to-line may provide a reduction in RFI.
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RE: RFI FROM POWER INVERTER
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by WX7G on October 4, 2009
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For the AC side the inductor can be wound with #14 AWG. Close wind 20 turns on a 2" PVC pipe and you have 28 uH. Space the inductors at least one coil diameter to minimize coupling.
If you build the filter or try capacitors please tell us how it worked for you.
Ceramic capacitors are not the only thing you can use. Plastic dielectric caps will work just fine. I believe you can pick up the caps at Radio Shack and wind the coils form parts obtained at the hardware store.
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RE: RFI FROM POWER INVERTER
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by WX7G on October 4, 2009
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Filter design continued: With 20 uH of inductance on the primary there can be massive overshoot on power-up and during a load dump. To tame this place 10,000 uF or more across the inverter input (inverter side of the 10 uH inductors). A minimum 25 V volt rating will work but will not be rated for the maximum automobile system load dump spike. For this 63 volt caps can be used.
When running 2 kW this cap will still not be up to the 60 Hz ripple current job. Between the inductor resistance of 10 milliohms, the wiring to the battery, and the battery internal resistance there will be 20 to 30 milliohms minimum. A low ESR electrolytic cap will have an ESR lower than this and it will hog the inverter AC current and heat up. Use more input capacitance for higher power and check the capacitor temperature.
A low ESR cap is not needed or necessarily desired. For this filter (20 uH and 10,000 uF) we want 40 milliohms of damping resistance in series with the 10,000 uF cap. 14 milliohms if you use 100,000 uF.
Standard electrolytic caps will provide this ESR. The damping resistance helps tame power-up overshoot and damps the 360 Hz filter resonance.
I prefer to use low ESR caps and add surge robust damping resistors.
A good 12 volt, 2 kW RFI filter is not a trivial thing. You can see why nobody incorporates such a filter into the inverter or even sells them.
I see that MFJ sells a 12 volt RFI filter (MFJ-1142 I think). I'd like to get ahold of one and evaluate it.
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RE: RFI FROM POWER INVERTER
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by W8CAR on October 8, 2009
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First determine what type of inverter you have. There are two types-modified and pure sine wave. Most inverters are modified sine wave as they are fine for running microwaves, TVs and appliances you might have in a motor home. The pure sine wave type is more expensive but gives you almost the same AC as your home has. I used a modified sine wave inverter to charge my computer while mobile-I couldn't use my radio with the inverter on. I bought a nice pure sine wave inverter and it is very quiet with no noticeable RFI. I don't know how successful you will be with mods on a modified sine wave unit. QST recently had a review of several inverters and explained the basic differences and showed wave forms. Bottom line is you probably will have to spend some money to get a separate inverter to run your rig or pony up for a bigger unit for your entire vehicle.
Good luck!
Dan W8CAR
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RE: RFI FROM POWER INVERTER
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by N5LRZ on November 5, 2009
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Easy reply...
Since you are not in your van when you are in your house using your radio all you need to do is the following.
Put a relay activated by your igintion circuit in line with the power line to the inverther. When you take your key out of the ignition the relay will shut off all power to the inverter and the RFI will cease.
The auto shut off relay will also keep you from running your battery dead if you forget to turn off the inverter.
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