Photovoltaic charge regulator

As best I can tell, a photovoltaic "12 volt" "15 watt" panel is about 19 volts open circuit in full sun and 13.4 volts at rated current of an amp or so. If this is so, it can be described as a "hard" voltage source of 13.4 volts in series with about 5 ohms.

To minimize I^2*R loss, it seems that a switching regulator designed for an input voltage of 16-19 volts and an output voltage of 13.4 volts at 1.3 amps would maximize the efficiency of the system.

Of course, theory bows to practice every time. Comments appreciated.

Jim

Reply to
RST Engineering (jw)
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Congratulations, you've just invented the MPPT charge controller (well, you missed a detail or two, but nevermind that). Unfortunately for your bank account, others beat you to it. Fortunately for if you don't feel like building one, others beat you to it, and you can rush out and buy one. Or you can build one if you prefer to.

MPPT = maximum power point tracking.

Next...

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Reply to
Ecnerwal

I've reinvented so many things, I assume that if I can't find a reference to something new I've done it's 'cause I'm not looking back into history far enough.

There may be new things under the sun, but they don't seem to be coming out of _my_ brain.

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

Hi Tim,

Not necessarily....the mppt products tend to be expensive, so there is always room for another product made better and cheaper!

Larry

Reply to
lgreenwood

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design note 1012 by john shannon

martin

Reply to
martin griffith

Hi I heard about many differents technologies for Mppt. But some of them are certainly less expensive. I think that some of them are scanning with a processor the caracteristic I=f(U) of the PV cells and fixes the not operation. But heard that a new way is to find it with an analogic scan, finding differents slopes of the caracteristic I=f(U) . Jo

Reply to
jo

No, your calculation is not right, but apart from that it is a *current source* with the short circuit current and 30 or 31 silicon diodes in parallel (count them). Well, that is pretty much what it is. And the current is proportional to light intensity in W/m^2 and usually specified for

1000W/m^2 and 25C. Both together is hard to obtain. There might be also a small R in series with the output, but much smaller than your 5 ohms.

Also wrong, that would be 17.4W for a 100% efficient converter and be sure the manufacturer would claim that.

You should brush up your theory as well.

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ciao Ban
Apricale, Italy
Reply to
Ban

Actually most silicon PV panels have 36 cells.

Actually they are usually in series.

Did that, and all of mine have 36 cells. Ok, I have one "6 volt" panel that has 18.

Duane

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Reply to
Duane C. Johnson

Well, since nearly all "12 volt" panels have 36 cells, not 30 or 31, perhaps you should take your own advice.

Reply to
Windsun

Lead acid charging voltage is the maximum power point for solar panels, its why theyre made with the number of cells they are. Maximum power point _tracking_ means the mppt will be tracked as it varies with varying light levels.

NT

Reply to
meow2222

I looked at my Siemens M55W and it has indeed 36 cells. The equivalent spice circuit would then be: ___ .--------+-|___|-o + | | /|\\ Is V | - | | / \\ V ( I ) - \\_/ | | V | - | | | V | - | | | 36 diodes | | | | V | - | | +--------+-------o - | === GND (created by AACircuit v1.28 beta 10/06/04

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ciao Ban
Apricale, Italy
Reply to
Ban

There was no calculation done, merely a postulation. If your knowledge is superior to mine (which I'm starting to doubt) then give what you think to be the correct topology.

but apart from that it is a *current

YOU count them. 36 cells in a 12 volt panel.

If your postulation of a current source is correct, then it wouldn't matter if it were a short circuit or high impedance load, the current would be constant. At that, it would put out an amp into a short circuit or a 19 ohm load, giving 19 watts max. That means the switcher would be 92% efficient, which my freshman engineering students can design in a heartbeat.

My sense is that you are wrong on the current source topology.

You should take it and stuff it in your ear.

Jim

Reply to
RST Engineering (jw)

Thank you , I also `*appreciate* comments on my power supply theory, come on. I wouldn't mind, if you give it a try. Don't get angry, else your "students" laugh at you.

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ciao Ban
Apricale, Italy
Reply to
Ban

Utter nonsense.

PV panels are made with 36 cells because when they get hot their voltage drops. If a nominal 12v panel has 36 cells it can drop 5v and still produce some charging current. If it only had 33 cells (a once common alternative) then when it got hot the battery wouldn't charge.

PV voltage and max power point varies depending on temperature. I live in a mild 4-season climate, and nominally 12v panel's peak voltage goes well over 20v in the winter and down to barely over 15v in summer heat.

Battery voltage varies depending on temperature and state of charge.

To get maximum power from the PV panel, you need to operate the PV at its max power point voltage regardless of the battery voltage.

sdb

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Reply to
sylvan butler

If you crosspost to S.E.D. and write something which is wrong and even invite commentaries, you should also accept when someone points out the mistake. It doesn't have to do with superiority.

What you thought to have measured would be an ideal voltage source with 19V in series with a resistor of 5.6 ohms. Anyway that would be as well equivalent to an ideal current source of 3.39A with a resistor of 5.6 ohms in parallel. I do not need to tell you that.

I admit there are mostly 36 diodes in a panel, and this string lies in parallel with the current source. I didn't explicitly state the string, but it should have been obvious.

The diodes are slowly shorting the current source, so the output voltage can not rise any higher. And the available output current goes to zero. Now unfortunately diodes are not linear and thus it will be impossible to express them in an equivalent circuit with a voltage source, at least not with known components.

BTW tell us more about you, your students seem to be rather smart.

You see, that is not a theory, it is only an idea, which has some truth in it. The step to a theory would be to study the behaviour, get an equivalent circuit that meets this behaviour and then have it peer reviewed. Like Shockley with his diode theory, which certainly will be familiar to you.

Well should I praise you for what you said? I leave that to the google posters.

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ciao Ban
Apricale, Italy
Reply to
Ban

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