Inverter noise, RF and audio ?

It's time to pick an inverter for power tools and computers (mental power tools).

I'm pretty sure (after lots of reading) that we don't need a true-sine inverter at exorbitant cost, but it has to be better than a square wave.

In addition to the wave form we're also worried about audible (fans or transformer hum) or RF (SSB jamming) noise.

We need something between 1500 and 2000 watts.

Suggestions and comments ?

Thx.



-Sven

Sven,

I am also starting an inverter hunt. What did you learn that led you to the conclusion that true sine wave wasn't needed for electronics? I have a flat screen tv and would charge computers with an inverter. I would love to dodge the cost of a true sine wave machine, but was afraid the tv and ipod player would suffer.

RF Interference

The difference between a pure sine wave and a square wave is th odd harmonics contained. For 60 Hertz, that is harmonics of 180, 300, 420, 540, 660, 780, etc.
The spectrum of a square wave appears as a porkeypine ready for war. And extends into the RF

Dan,

Dan Morehouse said:

I am also starting an inverter hunt. What did you learn that led you to the conclusion that true sine wave wasn't needed for electronics? I have a flat screen tv and would charge computers with an inverter. I would love to dodge the cost of a true sine wave machine, but was afraid the tv and ipod player would suffer.

Click to expand...

It was mainly the feedback I got when I was on the cruisers' forum and reading others' prior discussions. Then I tried using one of those cheap 300 watt auto inverters to charge the Powerbook, iPad, Kindles, Sonicare and also the Dewalt 18V batteries, they all worked fine and I couldn't tell any difference in heat generation. Since we don't have the SSB yet I can't tell how it would react but I assume we'd shut down the inverter (and some of the LED lights) when needed for radio silence.

I'd love to see a comparison of the waveforms of the various inverter products out there; square wave, so-called modified sine wave and claimed pure sine wave. I wonder how honest those claims are.

It would also be nice to see the various ones compared relative to efficiency and stand-by draw.

Finally, how much audio noise do they each make; can you mount one on a bulkhead next to a bunk ?

I don't suppose Practical Sailor has done a comparison recently ?



-Sven

RE: Inverter

A small motor generator set mmight suite your needs much better. A DC motor running off 12V DC driving a Generator for 115 V AC. The commutators brushes on the motor would produce some noise. But they can be sheilded. Your computer will also generate RF noise and may interfeer with the SSB.

Vagabond39 said:

A small motor generator set mmight suite your needs much better. A DC motor running off 12V DC driving a Generator for 115 V AC. The commutators brushes on the motor would produce some noise. But they can be sheilded. Your computer will also generate RF noise and may interfeer with the SSB.

Click to expand...

For small sensitive loads you may be right but the energy inefficiency would be a killer !

Thanks,



-Sven

Since they went to all the trouble to invent pure sine wave inverters, you'd think they had solved a very serious problem...especially given the fact they cost SO much more. It would be interesting to see if someone had a demonstration set up at, say, a boat show that made it obvious why you needed (or didn't need) to spend twice as much for an inverter. My electric tools probably don't care if it's square. But I don't want static muddying up the picture while watching "Moby Dick" or "The Perfect Storm". THAT would be a real disaster.

Inverter efeciency is another factor to consider. Power out equals power input times efficency. Typicaly around 75% ie. 100 Watts at 12 V DC input 75 Wats of approximately 110 V AC out.

With the caveat of knowing just enough about electricity to be dangerous, I have to throw out this question on the square versus sine wave coming out of the inverter. Does it matter if the device connected to the inverter is powered by a "brick"? - e.g. your laptop, TV etc. is likely to have a transformer (brick) in the power cord that is stepping the voltage down and I believe turning it into the right stuff for whatever the device is. This would make me think that the brick will take care of issues of square versus sine wave coming out of the inverter. I know that here at work we've got probably 100 laptops running in trucks off simple (cheap) inverters, and we've never had any failure issues that we would identify as bad power out of the inverters. We do get failures along the lines of the laptop falls off the back of the truck and they drive over it though....

tHE digital WORLD IS A WORLD OF SQUARE WAVES, PULSES, AND ODD HARMONICS. They work well. And plastic cases may have an layer of aluminium foil for shielding. It may even be grounded. However RF is generated in a broad spectrum of frequencies far exceeding the computers clock frequency. Sensitive radios will need proper effective shilding and distance not to be affected. The Antenna mounted on the mast, and coaxial cable to the radio help minimize interference.
Tools are usualy not affected. The inductance of the motors, the metel field magnets and armature, and the phase shifting capacitor ensure reliability.

Right - so if I'm following this correctly, what we're really talking here then is not about the "quality" of the electricity coming out of the inverter, but the inverter emitting EMI that affects other devices - yes?

Emerald said:

Right - so if I'm following this correctly, what we're really talking here then is not about the "quality" of the electricity coming out of the inverter, but the inverter emitting EMI that affects other devices - yes?

Click to expand...

No, it is the quality of the sine wave coming out of the inverter. Some motors will get extra hot if fed a square wave but I do not know what it is that determines which motors (induction, brush or whatever). I believe some chargers also are less efficient when fed a square wave but don't know that for a fact.

As far as I have been able to tell from lots of opinions you can still get by with a square or "modified" sine wave inverter in many/most cases.

The EMI is a second concern.



-Sven

CORRECT. Altho many radios today use digital synthizers and digital audio, converted back to analog for the speaker, the quality of the sine wave and shielding determine the amount of interference. Altho todays radios use mkuch lower voltage than those of the ww ii ERA, THE RF INPUT CAN BE CONTAMINATED.
As for Battery chargers, the peake pvoltave may be lower for a "modified sine wave" and lower the out put voltage.
However, why use an inverter to chatge a battery, when the battery power will only produce 75% of the power to the charger that was taked from the battery to produce it! And How efficient is the battery charger. Can you get even one half of the required power back to the battery?

Sven said:

No, it is the quality of the sine wave coming out of the inverter. Some motors will get extra hot if fed a square wave but I do not know what it is that determines which motors (induction, brush or whatever). I believe some chargers also are less efficient when fed a square wave but don't know that for a fact.

As far as I have been able to tell from lots of opinions you can still get by with a square or "modified" sine wave inverter in many/most cases.

The EMI is a second concern.



-Sven

Click to expand...

OK - gotcha at last

Vagabond39 said:

However, why use an inverter to chatge a battery, when the battery power will only produce 75% of the power to the charger that was taked from the battery to produce it!

Click to expand...

Lugging around a 65 lb AGM battery to brush my teeth with the Sonicare doesn't sound like too much fun



-Sven

Ah, now I get it.
Battery to inverter.
Inverter to Charger.
Charger to Battery.
perpetual motion.
And perpetual dead batteries!