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Author Topic: MPPT solar charge controllers: How do they match load?  (Read 7769 times)
KC2MMI
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« on: January 23, 2012, 03:57:26 PM »

The last word in power controllers for solar panels is MPPT controllers. These boxes work two kinds of magic in order to optimize the charging process, sometimes putting 20% more power into a battery bank than any conventional PWM or other type regulator.

On the battery side, they are using a fairly DC-to-DC converter and a microprocessor lookup table, so that they apply the full power wattage of the solar panels as "just enough voltage to charge" at "all the amps I can make". Instead of using the raw voltage from the panels, which would be wasted, they convert the total power output to optimize the amperage in the charge.

But the first half of their magic is that they present an optimum load to the solar panel, so that the solar panel will present a maximum power output. Solar panels put out a different amount of power depending on the load they are hooked up to, and supposedly an MPPT controller plays with the solar panel and actually varies the load on it, in order to coax out all the power the panel can provide at any given time.

OK, someone please. Tell me how you vary the load on a circuit (the solar panel) with no moving parts?? And no power source, except the circuit you are loading up? All I hear from the makers is "that's proprietary" and it isn't a myth, the MPPT controllers really do put out more power, and they all swear part of that is because they match the "Maximum Power Point" output for the panels.
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AA4HA
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« Reply #1 on: January 23, 2012, 04:03:42 PM »

Excellent questions. Some of the PWM's have a very high efficiency claim of almost 99% (not true) so if it is a really high percentage already how much more do you really gain and is the added cost worth it?

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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
K5LXP
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« Reply #2 on: January 24, 2012, 06:39:32 AM »

Tell me how you vary the load on a circuit (the solar panel) with no moving parts??

Typically the switching device is a FET.

The source is more or less coupled to the load by the power tracker.  In this context, the load is not just resistive, but typically a battery bank that is nonlinear with respect to applied voltage.  Indeed, if the supply is greater than the load and there's nowhere for the energy to go (light load/charged batteries), there's nothing for the power tracker to do (other than float the bank).  It's when you have the greatest mismatch (load exceeds supply) that the tracker has the most benefit.  At a system level a PPT doesn't provide a huge increase in overall efficiency, and whether or not their cost per gained watt is justified depends a lot on the installation.


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And no power source, except the circuit you are loading up?

A solar panel is a power supply, albeit relatively high impedance.  The tracker circuit itself requires very little power to operate.  Their increase in system efficiency "pays" for the power they use.


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  All I hear from the makers is "that's proprietary" and it isn't a myth, the MPPT controllers really do put out more power, and they all swear part of that is because they match the "Maximum Power Point" output for the panels.

Perhaps the algorithm they're using to determine the peak power point is proprietary, but there's no magic here.  The PPT is merely monitoring both voltage and current from the panels, and limiting the current via PWM or other method at the panel's maximum power point.  Since a panels' output is never constant, this point is always moving and the tracker "tracks" it.


Mark K5LXP
Albuquerque, NM


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KB1GMX
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« Reply #3 on: January 24, 2012, 03:22:17 PM »

First most solar panels are rated at their max power point, typically 17V for so called 12V panels.
So that means a "12V" 80W panel is really 4.65A at 17.2V and if loaded down to 13.8V that means you only get 64.2W of charge power.  The reason for this is even into a short circuit that panel only delivers 4.7A.  Solar panels are current limited and the best power point is where the Knee of the curve is.

So if you want to charge a battery you need to down convert 17.2V to about 13.8V (13.6 to 14.2 depending on battery type).  This is a watts to watts conversion (ignoring efficiency) so the output is 13.8V at 5.79A.

When your charging a battery with limited sunlight it all about Amps and time.  the more amps and the longer time you can deliver them the better.  Usually MPPT chargers will maximize even low output from cloudy days or low light (early or late day off axis sun).

Now to do the whole job there are several regulators, Input voltage tracking to maintain the peak power point at the input, output tracking to manage the charge voltage and hence the charge current.  All of this is done using switch mode regulator in a down converter configuration and the two regulators are used to moderate the converter to assure the output voltage does not go too high (and remained fixed) and the input voltage does not go to low.  There are other circuits to protect the battery, panel and controller.

Since the technology is scaleable it allows the power to be managed at the few watts or thousands of watts level with good efficiency typically better than 95%.  That means a controller must be matched for the system size at the risk of risk poor efficiency or be undersized and burn out (or go off line due to internal protections). 

The controlling element is usually a switch mode power system using current tech that means power fets and inductors.  The control is pulse width or pulse rate based on regulator feedback.


That why and a brief overview of how.



Allison
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KC2MMI
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« Reply #4 on: January 24, 2012, 08:01:34 PM »

Mark, I've actually spent a day tracking the output from an MPPT controller and watching a battery bank charge from it, and I can tell you the increase in effective charging power is substantial. Plus, an engineer at the #1 or #2 battery maker in the US told me very definitely any type of PWM charger (the output from MPPT being PWM-DC) gains another 5-10 beyond that because the pulsed DC doesn't boil the electrolyte as intensely as pure DC would. He was very impressed with MPPT controllers, and the guy is a PhD working with batteries and charging day in and out. A paper from Morningstar, hosted on the Sandia Labs web site and accepted by Sandia, claims a 10-20% gain by using PWM on AGM batteries. No matter how you slice it, 10% is a nice extra.

As I was watching this particular controller, it was programmed for the battery type (V) and capacity (AH) and it constantly applied slightly more voltage than the battery was at. From memory...maybe a volt or two more, nowhere near what a "plain" bulk charge algorithm would have applied. The power was targeted at supplying more amps, at that lower voltage, and it kept readjusting every few minutes, keeping a little ahead of the battery voltage and maximizing amperage. from my own notes the panel output to an MPPT controller under test was 15.7 volts, with 13.6 being presented to the battery bank. An hour later, 15.42 from the panel, 13.37 to the bank, with 4.6A into the controller and 4.8A out to the bank. (Those are just two sets of numbers from a six hour long test session a while back.)

It really is fiddling around the volts and amps. Is it possible to fiddle both, just by varying the power into a DC-to-DC converter? How is it increasing the amperage out of the converter? There's something actively happening, or presenting the appearance of it, and I don't think it is simply the "dumb" reaction of the panels to the load being applied to them. Or maybe, the controller modulates the load based on the changing power it gets from the panels, in a feedback loop using the "AC"ish pulsed DC?

MPPT works. It isn't just pulsed DC or PWM. Without running the equipment and seeing the numbers from inline live metering, it can be hard to take on faith. But once it gets hands-on, it gives you religion. Now, I'd just like to understand what it is doing to the panels, or how it is reacting to them to "match" the MPP side of the system.
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ND6P
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« Reply #5 on: January 25, 2012, 06:28:19 AM »

I'm thinking that another way to go, if you have the grid available, is to use a MPPT grid tie inverter to feed the PV energy to the grid and use a battery charger that is plugged into the grid to keep your storage battery charged.  This way, any PV energy that is available after the battery is charged can be used elsewhere in the house. 

Then for power outages, switch the PVs to charge the battery directly via a charge controller.
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W6RMK
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« Reply #6 on: January 25, 2012, 06:50:40 AM »

Yes, you can fiddle with both the voltage and current.  The MPPT presents a variable impedance load to the solar panel to keep it operating at the optimum point.   Typically this is done with some sort of switcher to an intermediate DC bus.  Whether they use buck only or boost buck is up to the designer and the bus voltage (for instance, if you wanted 24V out, and the panel voltage is 10-30V, you need a boost buck).  The output current into the DC bus varies according to the power from the panel.

In a controller for a line connected application, the DC bus voltage is chosen so that you can PWM to a sine wave at line voltage to put power into the grid.

In the battery charger application the DC bus is run through another switcher to be a battery charger.


If it's going to be ONLY used for battery charging, AND the panel voltage is sufficiently high, even at the low operating point, you can probably combine the two switchers into one.  Some sort of regulator changes the bus voltage set point on the first switcher.
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K5LXP
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« Reply #7 on: January 25, 2012, 09:16:01 AM »

I can tell you the increase in effective charging power is substantial.

"Substantial" isn't possible.  If you look at the panel output in terms of watts into a fixed voltage load vs at the peak power point, there's not that much difference to be gained.  A PPT allows you to recover this small difference, but at a price.  In many cases, it's cheaper to add another panel than it is to install a PPT.  If panel throughput is your primary goal, then the first thing to do is use a panel tracker before a power tracker.

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any type of PWM charger (the output from MPPT being PWM-DC) gains another 5-10 beyond that

Percent?  Of current?  Power?  Net into the bank?  Or at a system level with all losses factored?  It's important to gauge this at the system level, due to efficiencies of conversion.  The only Wh's that count are the ones that make it to the load.

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the pulsed DC doesn't boil the electrolyte as intensely as pure DC would.

I wouldn't dispute that but if you're boiling electrolyte you're at 100% SOC, so the PWM current from a PPT isn't doing anything for you other than boiling your batteries more effectively.  It could be extended with less gassing, water use would be reduced resulting in less maintenance but if you're floating your bank that often, not only do you not need a PPT but you could probably get away with fewer panels and a smaller battery bank.  I get your point though that "any gain is a good gain" but that gain comes at a cost of dollars and complexity/points of failure.  A PPT will cost some number of dollars to net some number percent gain of throughput. I would lay odds you could buy the same dollars worth of additional panels instead and get an even greater net increase.

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He was very impressed with MPPT controllers, and the guy is a PhD working with batteries and charging day in and out. A paper from Morningstar, hosted on the Sandia Labs web site and accepted by Sandia, claims a 10-20% gain by using PWM on AGM batteries. No matter how you slice it, 10% is a nice extra.

I knew one of the engineers from Sandia that participated in some of those studies and I have some (all?) of the white papers (I know a number of folks there).  What I take from all of these various studies is certain charging profiles and methods may result in increases in efficiency or cycle life, but under very specific controlled conditions.  You mention AGM's specifically - how many solar systems use AGM's?  It would take a lot more than a 10% gain to offset the battery cost and BMS you'd need for such a system (over a more conventional flooded system).  Additionally, put it out in the real world where the loads are dynamic, charge cycles inconsistent, then throw in environmental variables and a lot of these improvements get lost in the noise. 

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it was programmed for the battery type (V) and capacity (AH) and it constantly applied slightly more voltage than the battery was at.

The charge voltage for any battery is always higher than its resting voltage.

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From memory...maybe a volt or two more, nowhere near what a "plain" bulk charge algorithm would have applied.

Were you observing this with an RMS meter?  I would bet you were seeing an average of the modulated voltage.  In any event, in bulk phase the voltage rise you see is directly proportional to charge current, the battery impedance and inherent interconnect drop.

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The power was targeted at supplying more amps, at that lower voltage, and it kept readjusting every few minutes,

You must've had a pretty steady power state from the panel. 

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the panel output to an MPPT controller under test was 15.7 volts, with 13.6 being presented to the battery bank. An hour later, 15.42 from the panel, 13.37 to the bank, with 4.6A into the controller and 4.8A out to the bank.

If the PPT is keeping a panel at its peak number of watts, you will get the same watts out (minus inefficiencies) on the battery side.  If the volts are lower than the PPT input on the battery side, the amps will be higher.  That's ohm's law for power:

P= I*E

Panel - 15.42 * 4.6 = 70.9W
Battery - 13.37 * 4.8 = 64.2W
~90.5% efficient.

The profile you need to run is into a battery that's at various stages of SOC, both with and without the PPT in circuit. Plot that out and you can directly see what your PPT is doing in your system.

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It really is fiddling around the volts and amps.

Yes it is.

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Is it possible to fiddle both, just by varying the power into a DC-to-DC converter?

The power out of a converter is never more than what's going in.  It will always have less out than in, due to losses.  Depending on the topology the efficiency can be anywhere from 70% to over 95%.  With most converters, they will draw whatever power is necessary to keep the output within regulation, within the power limits of the design.

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How is it increasing the amperage out of the converter?

It's power conversion.  The input power at a given voltage and current is converted to a different voltage and current.  We're back to ohm's law for power.  If your load is drawing 10 amps at 10 volts, that's 100W.  A converter can supply that with any combination of input voltage and current it's designed to do.  That could be 100V at 1 amp, or 5 volts at 20 amps.  Watts is watts.

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There's something actively happening, or presenting the appearance of it, and I don't think it is simply the "dumb" reaction of the panels to the load being applied to them.  Or maybe, the controller modulates the load based on the changing power it gets from the panels, in a feedback loop using the "AC"ish pulsed DC?

The PPT is merely regulating to the battery bank the power it gets from the panels, as determined by where it has measured the peak power (voltage and current) for the panels connected to it.  Secondarily, it also monitors the battery voltage to keep from overcharging them.  How the PPT determines the peak power is done numerous ways, from incrementally adjusting the load and observing the power, to "bumping" the panels with an increased load and noting the power shift, to just keeping the panels at a fixed (presumably optimum) voltage point.  From a proprietary standpoint you might apply some mix of all three of these.

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MPPT works.

Yes, it does.  But it costs money and adds a point of failure.

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It isn't just pulsed DC or PWM.

Right, that's the current limiting method but of course there's the peak tracking smarts that goes with it.

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Without running the equipment and seeing the numbers from inline live metering, it can be hard to take on faith. But once it gets hands-on, it gives you religion.

I've been playing the battery, solar and power conversion game a long time, and while there's no disputing a PPT can net a power increase there is more to it than a few extra watts out of a panel.  The cost vs benefit needs to be run to see if there is a real benefit to adding a PPT to a system.  It all comes down to dollars per *delivered* watt hour over a given timespan (what enviroweenies and politicians don't usually understand). I get that some folks don't care about the numbers, they just want peak performance with what they have.  That's fine, I get that too.  But a PPT is just a tool in the toolbox.  They have their place but they have to be considered for what they do at the system, and not just the unit level.  System cost, output, reliability, lost opportunity and maintenance all factor into the equation.  It's one thing if you're playing around at home with a few panels and experimenting with optimizing a system.  It's another thing entirely if you're running a tens of thousands of dollar system to power a house or a remote site on a mountaintop somewhere.  It's not black and white unless time and money aren't part of the equation.

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Now, I'd just like to understand what it is doing to the panels, or how it is reacting to them to "match" the MPP side of the system.

Google is your friend.  Lots of sites dedicated to solar systems and PPT theory/application.


Mark K5LXP
Albuquerque, NM
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K9FV
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« Reply #8 on: January 25, 2012, 09:40:14 AM »

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The power out of a converter is never more than what's going in.  It will always have less out than in, due to losses.

That was always my thinking also on any type of charge controller/regulator. I used solar and wind for charging batteries on a boat for over 20 yrs and never felt the need for any type of charge controller/regulator.  Solar never created more engery than needed to keep batteries topped off, but when in trades the wind would provide more power, so the kids just watched a movies to use the extra power. 

I only had a small system using 4 golf cart batteries charged by 200 watts of solar, and a single wind generator.  It was hard to track the sun while swinging on anchor or traveling, and the wind didn't always blow - but they did help.

I understand my case was different than the typical home installation where the battery bank is not providing the mail source of power.

73 de Ken H>
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KC2MMI
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« Reply #9 on: January 25, 2012, 02:02:23 PM »

Mark-
 Maybe you can always add an extra panel, but in mobile and marine applications that's frequently impossible because there is no place to put it. Making a 10% gain from the charging system SUBSTANTIAL.
 " if you're boiling electrolyte you're at 100% SOC," Nope. Not at all. During normal charging your are boiling electrolyte at the micro level. The electrolyte that is in immediate contact with the surface of the plate normally IS boiling, that is why batteries normally outgas during charging. I'm not talking about churning all the electrolyte like a cauldron of soup. The folks who make 'em, say that the electrolyte normally is boiling and outgassing at the micro level at the plate surfaces, and those gas bubbles are enough to slow down the charge acceptance and waste power. Seen from the micro perspective, pulsed charging does not heat the electrolyte as much, so it does not boiul and outgas as much, and you wind up putting more of the power back into the plates instead of wasting it making tiny bubbles.

 I know Google is my friend, I've researched it. But if you try to find out how MPPT "controls" or matches the max power point of the panels--you get either zilch or information overload.

 And while all the incidental talk of grids, sine waves, etc. is nice...that's not the question. I really only want to know, if the MPPT controller is "matching" hte peak power point of a solar panel, and by doing so somehow "extracting" more power than other controllers do, how is it doing that? By varying the load it presents to the panel, by varying the pulse width it charges the DC-to-DC converter with? By doing a dual conversion somehow?

 I don't remember the details last time I looked inside one, but I recall only one toroidal coil, and all the rest being the usual mix of components, nothing moving, no other signs of transformers, etc. I don't intend to build one but I'd hoped someone knew how they "matched" to the power point. Sounds more like they aren't really matching anything, they're just looking for what speed/rate they can operate the converter at, which sees the maximum power obtained.
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K5LXP
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« Reply #10 on: January 25, 2012, 08:30:36 PM »

in mobile and marine applications that's frequently impossible because there is no place to put it.

That would be a valid system level justification.

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" if you're boiling electrolyte you're at 100% SOC," Nope. Not at all. During normal charging your are boiling electrolyte at the micro level.

This is one of those "in the noise" factors.  Gassing is present at some level any time the battery is above 0% SOC, and yes it does reduce the effective surface area by an incremental amount.  And there's nothing you're going to do about it.

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pulsed charging does not heat the electrolyte as much,

The electrolyte isn't heated in the first place.  The "boiling" isn't from temperature, it's dissolution of water.  The bubbles are hydrogen and oxygen, and they're present during discharge as well as charge, even when a charged battery is idle.  The idea that pulse charging is "better" for a battery is nothing new and I'm here to tell you that pulsed charged batteries gas pretty well too.  The amount of gas created is a direct function of time, current and state of charge.  Gassing promotes circulation of electrolyte.  Lacking this incurs stratification which is a significant problem with stationary batteries, more so than an inconsequential decrease in plate surface area from trapped gas (which doesn't stay trapped for long).

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you wind up putting more of the power back into the plates instead of wasting it making tiny bubbles.

I think you're buying into some sales hype.  Believe what you like, there's nothing I'm going to say that will dissuade you. 

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I really only want to know, if the MPPT controller is "matching" hte peak power point of a solar panel, and by doing so somehow "extracting" more power than other controllers do, how is it doing that?   By varying the load it presents to the panel, by varying the pulse width it charges the DC-to-DC converter with?

Yes!  That's it exactly.

The tracker empirically tests the voltage and current coming out of a panel on an ongoing basis.  By regulating the output of the converter circuit using a PWM switch, the tracker can limit the current coming out of the panel by just the right amount to keep the panel voltage at the precise point it determined the peak power to be, no matter what the impedance of the load is and across variations of light input.  Solar panels are fairly high impedance, and a battery is a very low impedance so just connecting them together will pull the panel down to the charging voltage of the battery and below the peak power point of the panel.  While the tracker has switching losses itself, the energy it gains by keeping the panel at maximum output is greater than what it uses.

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I don't remember the details last time I looked inside one, but I recall only one toroidal coil, and all the rest being the usual mix of components, nothing moving, no other signs of transformers, etc.

Because the conversion step is nearly always from a higher voltage to a lower voltage, what's called a buck converter is employed.  You could research that as a separate topic.  If it's the type of tracker that just keeps the panel at a fixed voltage, the circuitry for the panel sense and the converter can be very simple.

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Sounds more like they aren't really matching anything,

You can say it's matching the high Z of a panel to the low Z of the load.  Technically when the impedance of a source matches the load, that's the point of maximum power transfer.  The tracker is always the right Z to the panel, and can efficiently transfer the power to the low Z load.


Mark K5LXP
Albuquerque, NM
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KC2MMI
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« Reply #11 on: January 30, 2012, 07:37:36 PM »

Mark-
 "I think you're buying into some sales hype."
Nope. I'm questioning and verifying everything, which is how I got turned on to MPPT in the first place. Bear in mind, the guy (PhD & top tech at a battery maker who doesn't sell any charging equipment and has no iron in that fire) who said he's found PWM charges more effectively, faster, is telling folks how to care for his batteries. He doesn't get a penny from the sales of any charging equipment.

I suppose it would be interesting to compare plain PWM, MPPT-solar, and pure DC with all sorts of sophisticated equipment that measured "real" power transfers but I lack the lab and the PhD-level knowledge to make that happen. Since a guy who does have it says PWM works better because it causes less micro-gassing (call it boiling or electrolysis or whatyouwill) I don't think it is unreasonable to believe him.

"there's nothing I'm going to say that will dissuade you." Hey, I may be a skeptic but I'm not a zealot. I'm open to theory and demonstration, bearing in mind a DMM is about the limit of my ability to measure what's happening.

" By varying the load it presents to the panel, by varying the pulse width it charges the DC-to-DC converter with?"...
..."Yes!  That's it exactly."

So they are cutting off the saturation of a coil (the toroid that is usually in an MPPT) or the connection to a capacitor, one way or another "throttling" an inductive load and not actually matching the load but, but doing a sort of "saturation pulse modulation" in the way that PWM-DC fakes being a constant real DC voltage? I hope that reads how I meant it, because it sounds horrid, I'm sure there is a better way to phrase it.

That would be an interesting wrinkle, since anything that is actually only rapidly taking pulses OUT of the panel, instead of sucking smoothly on it, might then also be subject to losses simply because it wasn't taking power out 100% of the time. Implying there is a power output lost between those "pulses" feeding the inductive load?

Unless you alternated feeding two "charge banks" from the panel, so there was only switching overhead, rather than unused power from the panel. I feel a light bulb turning on, THAT would seem quite logical, wouldn't it?

Coming back against the potential gain by using pulsed DC to more effectively adjust power/voltage applied to the battery. If that was more effective, that would still make MPPT a possible better way to go--even if the "matching" PPT side of it was bogus, no?
« Last Edit: January 30, 2012, 07:40:01 PM by KC2MMI » Logged
K5LXP
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« Reply #12 on: February 01, 2012, 09:53:55 AM »

I suppose it would be interesting to compare plain PWM, MPPT-solar, and pure DC with all sorts of sophisticated equipment that measured "real" power transfers but I lack the lab and the PhD-level knowledge to make that happen.

In my opinion, if it takes a critically controlled environment and racks full of test equipment to discern an effect, we're back to my "lost in the noise" premise.  And indeed, in my experience with this stuff over the years no one has been able to usefully increase capacity and cycle life except under carefully controlled environmental, charge and discharge conditions. 

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Since a guy who does have it says PWM works better because it causes less micro-gassing (call it boiling or electrolysis or whatyouwill) I don't think it is unreasonable to believe him.

I wouldn't deny it either, but unless you can deploy it into the world it's a lab curiosity or a boundary condition that only select applications can take advantage of.  Sure, you can make incremental increases in efficiencies but that's all you're going to get.   There's only so much electrochemical energy in a bunch of lead in a pot of acid.

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I'm open to theory and demonstration, bearing in mind a DMM is about the limit of my ability to measure what's happening.

Does your DMM have a serial port?  If you can perform automated simple (volts, amps) measurements over time (even over just a single charge or discharge cycle) you can do some pretty useful characterizations.  My first setup was a radio shack DMM hooked up to a DOS laptop saving data to floppy.  Anymore, basic DAQ equipment can be cobbled together very economically.

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So they are cutting off the saturation of a coil (the toroid that is usually in an MPPT) or the connection to a capacitor, one way or another "throttling" an inductive load and not actually matching the load but, but doing a sort of "saturation pulse modulation" in the way that PWM-DC fakes being a constant real DC voltage? I hope that reads how I meant it, because it sounds horrid, I'm sure there is a better way to phrase it.

That would be an interesting wrinkle, since anything that is actually only rapidly taking pulses OUT of the panel, instead of sucking smoothly on it, might then also be subject to losses simply because it wasn't taking power out 100% of the time. Implying there is a power output lost between those "pulses" feeding the inductive load?

With proper control/feedback, and a correctly proportioned switching network the source will not merely be pulsed into the load.  In the case of a buck converter with a series L, the starting impedance is high when the switch is closed, and with the right mix of inductance and switching frequency it will resemble more of a resistance than a pulsed low Z load.  It of course depends on the exact topology of the circuit (some being more elegant than others).  It's anything but a coarse chopping of the current as you'd find in some simpler charge controllers.

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Unless you alternated feeding two "charge banks" from the panel, so there was only switching overhead, rather than unused power from the panel. I feel a light bulb turning on, THAT would seem quite logical, wouldn't it?

That assumes there is power lost "between pulses", but that's not the case.  If you could lay your hands on a scope and watch the thing work, you would gain some good insight how it works.

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Coming back against the potential gain by using pulsed DC to more effectively adjust power/voltage applied to the battery. If that was more effective, that would still make MPPT a possible better way to go--even if the "matching" PPT side of it was bogus, no?

The PPT is a net gain (of power) itself.  So yeah, if there's a secondary gain as a result of its output waveform as well, so much the better.  Overall it still needs to be factored in at the system level unless you don't care about cost and overhead.


Mark K5LXP
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KC2MMI
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« Reply #13 on: February 01, 2012, 09:08:36 PM »

Mark-
 "Does your DMM have a serial port?  If you can perform automated simple (volts, amps) measurements over time"
 No, but I'll suggest one to Santa. Bear in mind that my good impression of MPPTs comes from having spent more than six hours going back and forth every 15 minutes to observe panel output versus MPPT output, on a system with multiple meters/displays installed.

"With proper control/feedback, ... it will resemble more of a resistance than a pulsed low Z load. "
 So properly (cleverly) feeding even the one toroid typically found in an MPPT controller, could present varying matched loads to the panel even while it optimised output to the battery. Or at least in theory, which is probably why they are so concerned about proprietary issues.

"That assumes there is power lost "between pulses", but that's not the case.  If you could lay your hands on a scope and watch the thing work, you would gain some good insight how it works." Not in the immediate future, but maybe later in the year. I'll file that under the "oneathesedays" file for now and suspect a digital scope with a log file to look at would actually be the better way to go on that. I'd expect a meter with serial output to be too slow?


"Overall it still needs to be factored in at the system level unless you don't care about cost and overhead."

Which is why I'm asking, not just spending. Thanks for the insights.
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K5LXP
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« Reply #14 on: February 02, 2012, 06:02:35 AM »

No problemo, I think you're well on your way.

73,

Mark K5LXP
Albuquerque, NM
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