"So basically PWM is just a digital way of turning a voltage like 12 volts into any voltage from "
Yes and no. PWM-DC really should be thought of as an AC form of voltage, since the waveform is quite variable and in most ways it can't be treated as "plain" DC at all.
Like, the radio interference problem, akin to AC not DC.
Like, not being able to accurately measure or meter it, akin to changing AC waveforms, not "plain" AC and not DC either.
" it's just the way that processors create a specific voltage from a higher voltage. "
Yes, but that's not critical. What's important about PWM is that it allows processors to work the OTHER WAY AROUND, boosting lower digital voltages to higher ones as well, and to change voltage WITHOUT DUMPING POWER. A plain DC regulator can reduce voltages just fine all by itself--but the PWM system does it without dumping power (net wattage), making it more efficient, if more expensive.
And, there's that effect on battery charging. Apparently well documented and confirmed by reputable parties--but someone forgot to tell us plain folks.
"Stereo systems could use PWM to create the voltages necessary to reproduce music on speakers, but it would sound like crap," Well, haven't you just described the CD player, MP3s and digital music? They all start with a digital signal, quite similar to PWM-DC with a uniform pulse width and only the rate varying. Matter of fact, that's almost identical to a classic automobile alternator putting out PWM-DC using a fixed pulse width, like a classic Delcotron. OK, it gets converted back to an analog signal before we hear it--but there are folks who still say it sounds like crap because of conversion issues.
I tried to get a look at the SolarBoost output on an oscilloscope, an older Tektronics model. If I really pushed things....I got something with a fairly regular waveform, but I have no idea how badly the battery was swamping things, or how that really could have changed once it got outside the bulk acceptance charge. It was a tall square wave with a sloppy bottom corner, which I assume was the result of an inductor "dying" in the end of a discharge cycle. One of those "yeah, but it really doesn't matter, it works just as well and is cheaper to build that way" things. Not worth speculating about.
Cam-
Although I was in the bulk charge phase...is it possible that I would have seen more amperage out of the controller IF the batteries had been discharged? Maybe it was giving me higher voltage and less amperage, because that's what the battery needed more in the existing charge state?
One more thing to test, next time the rain gods and the sun gods all conspire and the tornado warnings stop long enough for me to spend some quality time with a good book...and some electronics?
Last edited by hellosailor : 07-19-2007 at 08:13 PM.
HS...Thanks...but I am still confused about your revised statement which said: ""That would be...about 250 Watt-hours up here, based on four hours of full output power, which is what a full day is usually equal to, indicating 375Wh down there in sunnier climes. Or about 73 Amphours at 13.6V here for the four midday hours, and neglecting anything outside of them,"
Does that read clearer?
I read this as you saying that you would assume 250 watt hours where you are for the four midday hours combined...or about 75 watts on a perfect day vs. your measured 63 watts right?
Then you extrapolate this to 375 watt hours for the same 4 hours down south or about 90+ watts per hour. Correct so far???
If you take the 375 watt hours and divide it by 13.6V...that is 27 amp hours for the 4 hour peak period down south and less if you use the traditional bulk charging voltage of 14.4.
How do you come up with 73 amp hours ? I think that is a math error.
If I am correct then 8 hours of peak performance down south would result in 54 amp hours (2 x 27) and 12 hours would result in 81 but as you point out with your candlepower morning readings...there is really no possibility of getting 12 hours of full output. Do you agree with these numbers and that 80 amphours or more out of the panels per day is a dream?
**************** You thought Brian had not claimed excessive output from the panels themselves and thought it was someone else...but here is his direct quote: We bought 14 different brands of solar panels to determine which one was the most powerful, and after two years of testing, the BP350U was chosen. We were consistently able to exceed the STC rating of the panel in good conditions.
So he is saying that his panels will consistently exceed their 100 watt rating despite your measured 63 watts. Note that his ability to CLAIM output of OVER 100 watts is essential to his claim of 80-100 A/H's per day.
Just wanted to set the record straight that it IS Brian making these claims.
Here is the link to his full exposition: http://archives.sailboatowners.com/p...07096173139.65
Based on your review of how the ACTUAL performance of the unit can easily be misinterperted by the product owner given what they see...and Brian's own statement that he is not scientist...I am not accusing him of lying about the panels. Indeed...the fact that he gave them to you to test indicates that he believes in them. I think he is merely mis-informed about their real output just like the people that have bought them.
I would hope that he either refutes your tested findings in a scientific manner or stops making claims that you have refuted with testing.
You are obviously impressed with the quality and performance of the product he has put together and it should be able to find its niche with cruisers without needing to resort to marketing hype.
I hope you can get a measurement of wattage in direct sun on a perfect day before you turn 'em back in so we can really end this debate...but you deserve major kudos for the work you have done on behalf of your fellow sailors!
Let me know if there is anything you disagree with in what I have said as I don't want to spin your results.
The military tests everything hey use before spending many of our dimes.
Perchance, is any of that for public comsumption?
Oh, thanks so much for putting this thing thru its paces. I DO think it could be a viable product, IF it can be nailed down as to what it really does on a consistant basis.
__________________
We are not primarily on earth to see through one another, but to see one another through
Some people are like slinkies: not really good for anything... but you can't help laughing when you push them down the stairs
Cam-
"I read this as you saying that ... Correct so far???"
Yes.
"If you take the 375 watt hours and divide it by 13.6V...that is 27 amp hours for the 4 hour peak period down south and less if you use the traditional bulk charging voltage of 14.4.
How do you come up with 73 amp hours ? I think that is a math error. "
OK, now I'm getting confused, too many notes and quotes in too many places. I see where I said "about 250 Watt-hours up here, indicating 375Wh down there in sunnier climes. Or about 73 Amphours at 13.6V here,". Let me try to figure out what I was thinking. 250 WH divided by 13.6V would be about 18 Ah. I think I *ed that up and multiplied out by four (hours) again!
And yes, I was reading/seeing the bulk/acceptance charge happening at 13.6 volts, not 14.4 volts, for what that's worth. Whether that's the charging algorithm, or a deception of reading PWM as DC, or whether that's really all the voltage you need to do this...Dunno.
"If I am correct..." And I think you are, "... then 8 hours of peak performance down south would result in 54 amp hours (2 x 27) and 12 hours would result in 81 but as you point out with your candlepower morning readings...there is really no possibility of getting 12 hours of full output. Do you agree with these numbers and that 80 amphours or more out of the panels per day is a dream?" At this point, and without complete testing, YES, I agree. I can't see any way to get 80AH, even 80AH at 13.6V, out of a 100W panel array.
80AH x 13.6V = 1088 WH, yes?
So given ten hours of screaming daylight and a panel set putting out 100W...it would still be a stretch. I don't think that's possible.
"You thought Brian had not claimed excessive output from the panels themselves and thought it was someone else...but here is his direct quote:...We were consistently able to exceed the STC rating of the panel in good conditions. "
"...it IS Brian making these claims.
Here is the link to his full exposition:
http://archives.sailboatowners.com/p...07096173139.65"
He does seem awfully optimistic about ouput, but then again he also says flat out "But given optimal conditions, 70-80 amp hours is a fair representation of the daily power output for the marine market." and I have to wonder, did he make the same mistake of double-converting that I did?? Or did he just make the mistake of confusing amps and watts? There's obviously SOMEthing wrong with the claims--which if you remember is how I got sucked into this.
I don't think it is hard to exceed the STC ratings of the panel IF (IIRC) you consider that the STC ratings are for flat panels, not tracking the sun. By tracking the sun, sure, you can pick up extra power. Whether that power can be effectively gained 1/2 hour before sunset...I don't know, it can't be gained around here. BUT, I also "read" that kind of power that late in the day, when I was just using a voltmeter and no load. I don't know if Brian is electrically astute enough to realize that when the panels are loaded (plugged into a charger) that bonus power can't actually be sucked out of them, the voltage plummets.
"I think he is merely mis-informed about their real output just like the people that have bought them."
One thing that he made clear is that he is not a techie. I'm no EE but I'm more astute about volts and amps than the average idiot, and I still found this "exploration" to be full of surprises. He does have an incredibly robust mounting system, and some technology that is "as good as it gets" for squeezing the power out of the solar panels though. (Unless there's another brand of MPPT controller that squeezes even harder.)
"but you deserve major kudos" Thank you, all deposits to the First National Bank of Karma graciously accepted. I'll tell you, it would be both easier and harder to sit all day in the sun and test that thing, if there was an iced marguerita dispenser built into it!
And you deserve major credit for proofreading me and catching the errors! Maybe if the wx holds for this Sunday...I'll get a chance to make new math errors.
CPaul-
I have no idea what the military has available in testing. Bear in mind that Sandia Labs, which has a lot of photovoltaic testing up for public access, is also one of those places where you can get on wrong end of an M16 if you go in the wrong places. Sometimes, when the military needs a light bulb, they just send someone down the store to buy one. If it lights up, they buy more of 'em.
I used to go to Sandia quite a bit. (and Fort Huachuca...) as well as "An Agency of the Federal Government based in Langley Virginia" (Honest enjun, thats how we billed 'em)
They do some real spooky stuff at all of those places. I'm glad I'm retired.
A friend I went to HS ith worked for T.I. Over an adult beverage one evening many years ago, he says "I have to go home early, I leave for Utah in the morning"
Really, I ask, whatcha gonna do in Utah?
"testing" was the reply
Whatcha gonna test?
"just some testing, thats all"
25 years later, that SOB still won't say what he was blowing up or tracking down.
__________________
We are not primarily on earth to see through one another, but to see one another through
Some people are like slinkies: not really good for anything... but you can't help laughing when you push them down the stairs
Thanks HS...one note...you said:
I don't think it is hard to exceed the STC ratings of the panel IF (IIRC) you consider that the STC ratings are for flat panels, not tracking the sun.
The STC ratings are actually with sun overhead and not accumulated ratings...just output ratings and even done at nearly a mile high altitude so there is less atmosphere blockage so the STC ratings tend to be quite unrealistic on the high side vs. actual use. The California ratings measure off angle rays so tend to be more conservative and realistic for fixed panels but probably too conservative for adjustable ones. The right answer is probably somewhere between the two numbers but he main point is that you don't get more than 100 watts out of the panels...and you are lucky if you get close to 100 on a bright sunlit day with a still cool breeze blowing.
I hate my computer. Every once in a while I compose a reply, go out to check a web site, come back, and everything is gone because some damned link closed the window where I was posting the reply. sigh.
G-
What Lewis Armstrong thing? Whadda talking about?
Cam-
While looking for solar output /vs/ temp, I found http://userwww.sfsu.edu/~ozer/engr300-solar1N.pdf
Where some engineering students were measuring output versus angle to the sun. They made the SAME MISTAKE I DID, and others have, of measuring the panle output under no-load conditions. So bear in mind--when they show output voltage from the panels, they are probably WAY WRONG and the voltage probabyl drops WAY SOONER. Dunno, I didn't see any link to check with them or their professor.
But check it out, they do show how both voltage and current plummet as the panel faces away from the sun, if as I've noticed it drops much faster under load--they are way over-optimistic and panel orientation makes a much bigger difference.
Also found [IMG]http://www.locoengineering.com/images/Current_vs_Time.gif
[/IMG] a graph which lives at http://www.locoengineering.com/Solar%20Info.htm
and gives a display of output-vs-time-of-day, for fixed panels. Do some calculus for me, how does their output from 10-2 compare to the entire day's output? (Nothing radical or new there, just the first nice graphs I've seen for that.) They're showing surprisingly good output at 6AM/PM, and again that's with "fixed" panels...if I were more enterprising I could combine that data with the angle-of-incidence bit from the first site to get some numbers for us, on how much gain can be gotten from angling the panels between 6AM-10AM and 2PM-6PM. Without doing the math...I suspect it's more than 20% power gain during those hours?? Take a look.
I am glad that ConchyJoe isn't allowed on this board any longer... he'd be attacking you for telling what you're seeing—regardless of whether it is realistic and honest or not.
Thanks for the update... When you get some hard numbers, can you post a table or something with the actual output and some sense of the conditions it was under, and how often the panels were adjusted, and how much adjusting the panels really affects actual output??
__________________
Sailingdog Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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