Square-waved question - Page 2 - Fiberglass RV


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Old 06-09-2007, 07:33 AM   #15
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Thanks y'all for the encouraging replies, and thanks, Byron. Gina, time will tell whether I can break away from the mousey thing, maybe a Bluetooth mouse is going to happen. I think I will approach it much like you do, enjoying doing what I have to do in pleasant surroundings right outside or inside the Burro.


The only thing is, I must apparently learn to cope with the latest and the greatest thing from the laptop manufacturers: shiny, mirror-like screens. Whose "brilliant" idea was this anyway? Waxpaper, anyone? Steel wool?
I use an inexpensive Logitec wireless mouse with my laptop. It's smaller than a standard desktop mouse but larger than the itty bitty things.

You can get anti-glare filters, but aint cheap.

Sometimes I've had to move a bit avoid the glare. Wearing a dark colored shirt helps too.

Enjoy your new toy.
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Old 06-09-2007, 07:46 AM   #16
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Per...[b]why the heck do you need a scanner, anyway?? Don't tell me you are shooting and scanning slides or negative film, are you? Yah, you may be old but you can't be THAT old!

Oh, wait, I get it. When you're out there deep the Oregon woods and you finish a roll of Velvia or Kodacolor 100 you just run over to the nearest drug store for processing, wait half an hour, then take your film back to the Burro so you can scan it. Ahhh-ha-ha-ha-hoo-hah!
You don't have to be very old to have a closet full of 35mm slides and a desk drawer full of prints. Some of us switched to digital soon as possible, but now what do we do with all those slides. Mine number close to 5,000.

When people make comments indicating the Oregon might be a bit behind the East Coast I have to remind them where Intel (Oregon) and Microsoft (Washington State) are. And there are places with names like Silicon Valley (California) and Silicon Forest (Oregon).

If you've ever been in Oregon you'd know that there are places where it's a long ways to the nearest drug store, and they wouldn't have 1 hour photo processor either.
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Old 06-09-2007, 08:19 AM   #17
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The issue with square wave vs sine wave vs modified sine wave inverters really comes up when using certain switching power supplies as well as inductive devices...

There are a couple of ways to convert high voltage AC to low voltage DC. One is to use a 'linear supply' which is basically a rectifier (2 diodes to convert the positive/negative swinging sine wave to a lumpy but all positive level), a transformer to squish the level down to where you want it, and capacitors to smooth things out. This sort of supply is relatively indifferent to a square wave.

The other way is to use a switching supply which is more complicated but more efficient and uses a lot less copper and easier to make tolerable of AC levels and frequencies (110-240 50-60hz for example). Modern laptop supplies use switchers. If your "wall wart" doesn't feel heavy, there's probably a switcher in it. Some poor quality switchers are highly intolerant of square wave AC. They will work but you'll hear an annoying and high pitched whine, the supply will get really hot, and could simply overheat and die. I'd be surprised if any current (last 2 to 3 years) laptops have switchers that are intolerant to cheap inverters... I think manufacturers understand that there are cheap inverters out there and that people are likely to use them.

The other problem with cheap square wave inverters is with an inductive load. Basically, anything with an AC motor (a drill, skil saw, blender, food processor, personal massager). The way these motors are wound, they pretty much require a nice true sine wave. With a square wave, they may turn slowly or lock up and hum loudly... They will get hot and in short order, you will probably smell magic smoke as the windings burn off their lacquer.

Probably more technical than people want, but I figured it was important to understand when you might want to invest more in an inverter.. A good dietary source of relatively decent quality inverters that people may not consider but has done me in good stead in the past, is old computer UPSes. People tend to throw these away when the batteries die but often, they can be coaxed to take 12V via another means. I have a 1kva inverter that takes 4 12v gel cells and which produces an absolutely beautiful sine wave. Sadly, it weighs 60lbs without batteries.
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Old 06-09-2007, 04:07 PM   #18
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Thanks, Herb.
They are the light-weight variety, but only the one for the HD is a 110-240 version. I mentioned this to my son, thinking he'd know nothing about it. Big mistake, wouldn't you know it. He agreed they both are switchers, but started talking about a water-bucket analogy, EU compliance markers, and PFC circuits. No EU marks on them, not a good thing.
I might search Waeco for possible replacements if needed, should be possible. Sine-wave inverters are spendy.

Myron: don't get me started. Byron and Donna have it: a lifetime of slides and negatives stashed away, and family pictures and negatives going back as far a 130 years. Before the software became completely impossible I rescued and digitized quite a few, fixing scratched, soiled and otherwise damaged items with Photoshop. Now it appears I'm back on track.
I, like Byron, may be a little sensitive about our deep woods environment here, but we try. Yes, I use a 8 pigamexel Canon DSLR and some Image Stabilizer lenses to keep my shaking hands from transferring to the images, but I hedge my bet with a Canon FTb system I've kept as insurance.
After scanning I send my files downstairs to a RAID system which unfortunately only has about 650 Gigabytes left in memory. Time for an upgrade. New Jersey!?
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Old 06-09-2007, 08:24 PM   #19
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Herb,

Maybe you could explain what would cause a switching power supply to get hot when powered with a square wave, or dirty power source. After looking a couple schematics and thinking about it I can't think any reason for a large loss of efficiency.

I think the biggest objection to square wave or modified wave inverter output would be interference caused to radios and maybe some audio and video devices. Big old inductors, like motors will intergrate the square wave. Maybe a capacitive start motor could have trouble starting?

A switcher works the same way as a linear supply only the transformer and filtering elements can be much smaller because of the "switching". The linear part operates at a much higher frequency than a standard linear. The input still goes through an inductor which intergrates the square wave to some extent. Then into a bridge with filtering before the swiching circuit.
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Old 06-09-2007, 09:52 PM   #20
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Per, you're kidding, right? When my hands shake I upgrade to a tripod. When my dedicated slide scanner died I switched to an Epson 2450 flatbed to scan the 6 zillion-plus slides I have shot. Never thought to take that work with me to the woods, though. Maybe now, I will. (...Nah.)

Actually, Byron, I am familiar with Oregon. After breaking my heart my first love ran off to Klamath Falls with the other guy. Oh, and I saw Oregon on the horizon from 60 thousand feet, coming back over the Pacific, once.

Put down yer guns, fellas. Ain't no call for no defensive posturing. Be glad for the deep woods. To me, you are the envy of the world. Canít go a hundred yards in some eastern parts of the "...cough...Garden State" without running into a gas station, drug store, paved parking lot, ek-setter-ah. Anybody shows you pictures of Jersey farmland... remain skeptical. Unlike in the great northwest, probably done with Photoshop.

You're AC with me, Herb. You're right, Donna. Never make assumptions because when you do, you.....
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Old 06-10-2007, 12:28 AM   #21
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Well, Myron, they don't call it "Orygun" fer nothing.
Yep, I'm kidding. Actually my hands do not shake hardly at all, but my tripod weighs half a ton, so I don't use it as I should. Should get a carbon-foam one I guess.

My "other" scanner is an E. 2450 also, and it has done fine service, especially on medium format and some of the totally off the wall negative sizes from about a century ago. Other than that, I really ought to replace the Rolleiflex I dropped decades ago, nothing quite like it.

Then there is Eastern Oregon, a whole 'nuther world which I like just about as much but for different reasons. Fabulous stuff.
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Old 06-10-2007, 07:00 AM   #22
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Maybe you could explain what would cause a switching power supply to get hot when powered with a square wave, or dirty power source. After looking a couple schematics and thinking about it I can't think any reason for a large loss of efficiency.

I think the biggest objection to square wave or modified wave inverter output would be interference caused to radios and maybe some audio and video devices. Big old inductors, like motors will intergrate the square wave. Maybe a capacitive start motor could have trouble starting?

A switcher works the same way as a linear supply only the transformer and filtering elements can be much smaller because of the "switching". The linear part operates at a much higher frequency than a standard linear. The input still goes through an inductor which intergrates the square wave to some extent. Then into a bridge with filtering before the swiching circuit.
I can't explain because I'm not a designer. I'm always happy to be proven wrong.. In this case, back in about 1992, I was in charge of a bunch of Apollo workstations which had switching supplies... Some of them were in a part of the building where the main UPS wouldn't reach so we bought UPSes for them... The first time we lost power and they switched over to battery, the supplies started squealing real bad. By the time I got there, the back of the supply was hot. We took a scope to the UPSes and discovered they were basically crap, so we replaced them with these big-azz units that put out an almost perfect sine wave (a little teeny glitch on the trailing edge) and our problems went away...

Also, I've tried running a skil saw and a black&decker corded drill off cheap inverters. The drill just hummed, the drill bit sort of vibrated back and forth but didn't turn. On the skil saw, the motor hummed really bad and the blade turned slowly but that 'hot smell' came out of it almost right away...
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Old 06-10-2007, 11:59 AM   #23
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Maybe you could explain what would cause a switching power supply to get hot when powered with a square wave, or dirty power source. After looking a couple schematics and thinking about it I can't think any reason for a large loss of efficiency.
I'm not sure either, Byron, but since "cheap" usually means cutting corners I suspect a cheap switcher would probably use cheap capacitors.

Pumping joules into a lightly charged capacitor as the voltage rose above the rated voltage of the capacitor for a breif time wouldn't result in arcing across the dielectric until the dielectric is substantially energized. If one assumes a standard sine wave, perhaps you could take advantage of that and use a capacitor with a voltage rating below what you'd expect from a 115v RMS input source, and everything would work just fine until you hooked it up to a cheap inverter? If this were true the square sine wave of the inverter would spend more net time at the rms value from the input source, provide more time to pump more joules into the dielectric, allow it to reach a substantial charge level at which point the capacitor would be much more likely to leak across the plates.

Not an expert opinion . . . just a thought.

--Peter
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Old 06-10-2007, 04:09 PM   #24
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I don't want to push this much deeper into the theory which makes eyes glaze over in normal people....

--- electrical theory starts here ---

but there's one detail to clarify:
A transformer with a sine wave input will have a sine wave output. One fed a square wave will not make a nice sine wave out of it; instead, it produces a wild-looking series of spikes. The rate of change of current (and thus the rate of change of magnetic field) on the input side determines the output, so those steps in the square wave produce the spikes, and the constant-voltage spaces between them do zip. The current does not immediately follow the square wave voltage, due to the inductance of the input windings, so the output is a spike which decays as the current wanes and the field collapses. The key is that the time-derivative of a sine wave is another sine-wave; not so for square waves.

--- electrical theory ends here ---

Those interested in running motors from inverters should consider whether they are real AC motors (synchronous or induction), or "universal" motors with commutators. Small tools generally have universal motors, which don't care about frequency - heck, they run happily on DC. I don't know what bizarre things happen when square-wave power, capacitor starters, and various inductive bits get together in a specific appliance. I do know smoke coming out is bad, because we all know it's the smoke inside which makes things work (well, they stop working when the smoke comes out...)

I think that the old UPS as inverter source is an inspired reuse idea.
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Old 06-10-2007, 05:32 PM   #25
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I can't explain because I'm not a designer. I'm always happy to be proven wrong.. In this case, back in about 1992, I was in charge of a bunch of Apollo workstations which had switching supplies... Some of them were in a part of the building where the main UPS wouldn't reach so we bought UPSes for them... The first time we lost power and they switched over to battery, the supplies started squealing real bad. By the time I got there, the back of the supply was hot. We took a scope to the UPSes and discovered they were basically crap, so we replaced them with these big-azz units that put out an almost perfect sine wave (a little teeny glitch on the trailing edge) and our problems went away...

Also, I've tried running a skil saw and a black&decker corded drill off cheap inverters. The drill just hummed, the drill bit sort of vibrated back and forth but didn't turn. On the skil saw, the motor hummed really bad and the blade turned slowly but that 'hot smell' came out of it almost right away...

I wasn't doubting your experience, I was just trying to get an understanding. Thanks for responding. I talk to a co-worker tomorrow and see if he has any insite.
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Old 06-10-2007, 06:04 PM   #26
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Wow... there is some SERIOUS beanie propeller spinning in THIS thread!

We just got back from a camping weekend. In preparation for our trip to Australia this summer, I bought a 12" ultra-transportable Compaq/HP nc4010 laptop with all the goodies off eBay for the princely sum of $300. I also have a bluetooth GPS antenna and Microsoft and DeLorme maps. We used the whole shebang this weekend while we navigated from our house to Moraine View State Park in LeRoy IL on Friday night. It was a God send. I mention it here because I use a five or six year old 12v DC/120AC inverter to power the brick to power the laptop for a time significantly longer than it's 2 hour battery. It works like a champ, regardless of the shape of the juice.

Roger
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Old 06-11-2007, 09:44 AM   #27
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I discussed the heating problem with a square wave output inverter with a co-worker. The conclusion is that it's quite possible. How much is dependent on the input circuit of the switcher.

It seems to me it might be wise to stay away from square wave output inverters.
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Old 06-23-2007, 06:08 PM   #28
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There is a bit of "closure" (don't like that word much) on this subject for me.
When my wife can't answer my questions she tells me to "Google" it, which is what I did. A number of answers, some conflicting, but a pattern eventually emerged, and with the answers given here it started to make a little sense.

One site gave a list of items which would either not work or could be damaged by modified sine wave inverters. In it was "speed-controlled sewing machines" and I remembered that I was supposed to take the quilter's machine in for service, because it didn't run, or actually stuttered only at full speed off the inverter. Finally got the gears in my head turning.

I posed the question about this to the head geek at our local computer store, and he offered that as far as laptops go the battery is the item which will suffer the most (didn't make much sense to me). Some other items are questionable or won't work well at all. Then the opening: he said truckers use sine-wave inverters all the time with their laptops. Whether this was a lemming phenomenon or not I don't know, but they may be on to something.

His advice was to check for the "Samlex" brand, also sold by donrowe.com out of Monroe, OR. It turns out that they offer these things at far lower prices than through the RV stores and marine outlets.

Got a 300w model, installed it, ran the sewing machine. It was smooth, ran beautifully at even the lowest speed and acted as if it was on clean grid power. The net result is that it no longer matters what I connect up to this inverter: if it runs at home it will run just as well on this one.My wife is looking forward to using the quilter on camping trips when appropriate. It is her only addiction, so the problem could not be ignored. Thanks, all!
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