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Inverter filter??

Old 07-12-2005, 11:33 AM
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Default Inverter filter??

I have a 750w & 300w inverter setup to run small 110 devices so as to not be constantly running the gen. On the tv I'm getting a slight rolling line across the screen no matter which tv is on which inverter. It appears the clipping is inherrent in the inverters when the DC power is cut and inverted at 180deg to create the AC power. Is there a filter or line conditioner that can clean up the inverted power. Thanks.
Old 07-12-2005, 03:04 PM
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Default Re: Inverter filter??

What you need is a AC line filter. It looks like a transformer but is a band pass filter to pass 60 HZ AC and impede the harmonics induced by the chopper circuitry of the inverter. Check out MTE CORP. www.mtecorp.com figure out your total load (including inrush) and have them size a unit for you. I use these reactors on motors up to 600 HP and the cleaner waveform is better for the windings.

Monstro

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Old 07-12-2005, 04:02 PM
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Default Re: Inverter filter??

Old 07-12-2005, 11:07 PM
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Default Re: Inverter filter??

If you only want to clean up your TV screen and not try to clean up the total inverter output try this 5 buck idea first:

http://www.radioshack.com/product.as...05&site=search

Just put it on your TV power cord...
Old 07-13-2005, 07:02 AM
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Default Re: Inverter filter??

one inverter is strictly for the main stateroom tv but the other one is for the saloon tv and any other small devices such as vaccuums etc. I think I would prefer a clean line for those devices so as to not shorten their life any. Thanks.
Old 07-13-2005, 04:17 PM
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Default Re: Inverter filter??

Teh problem is the inverter. There are basically two types - pure sine wave and modified sine wave. It sounds as if you have a modified sine wave.

The pure sine wave inverters are more expensive, and I dont' think a filter could easily negate the affects of the cheaper inverter. I have a 600 watt modified sine wave inverter, and chose to live with the line rather than spend the bucks for a pure sine wave one.

It also appears that some modified sine wave inverters are less noisy than others. I have a Xantrex that does pretty well, and a small no name that is absolutely horrid.
Old 07-16-2005, 07:57 PM
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Default Re: Inverter filter??

Inverters 101
The original inverters started with large transistors fired by an oscillator circuit to chop the DC into a 60 HZ square wave. The positive transistor will turn on and conduct +60 volts to generate the upper part of the wave. The negative transistor will turn on and conduct -60 volts to generate the lower part of the wave. The resultant square wave output has a peak-to-peak voltage of 120 volts measured from the top of the positive cycle to the bottom of the negative cycle. -_-_- The immediate transition from positive to negative voltage is hard on motors and transformers. Not to mention the 60 Hz hum.
The next step was PWM or Pulse Width Modulation. The positive going cycle transistor was turned on and off rapidly with the duration of the on time increasing until the middle of the cycle and then decreasing until the end of the positive cycle. - -- --- ---- --- --- -- - On 1, off, on 2, off, on 3, off, on 4, off, on 3, off, on 2, off, on 1, off . This is repeated for the negative cycle. This output is coupled to a transformer and the output looks like a scratchy sine wave.
The next variation was to sine code the transistor output. The first transistor turns on for one beat at a lower voltage with the voltage increasing proportionally to the transistor on time. On 1 @ 10 volts, off, on 2 beats @ 20 volts, and so on.
This was a great improvement in the waveform. Now the good part.
The closer the output looks like a true sinusoidal wave the higher the peak to peak voltage must be. When you measure the voltage at the outlet and find 120 VAC. That is RMS or average voltage. RMS is Root Mean Square. A more complex computation than average. The achieve 120 VAC RMS the peak-to-peak voltage of the waveform must be 190 to 212 volts.
At this point our PWM inverter output has a fairly good waveform but still contains harmonics. An interesting point is that a square wave is comprised of the base frequency modulated with an infinite number of odd harmonics.
If you add an output reactor the reactor will impede or filter the harmonics that distort the output waveform.
This is probably more information than you wanted so I won’t go into how the reactor works. Although if you like math the formula is 2 X pi X frequency / henrys of the reactor. This will show the impedance for each harmonic.

My next job will be a test pilot for Trojans.

Monstro
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