Home brew Arduino MPPT controller

[HiTech]

Pretty cool project. Highly programmable. He does not list the amps it is capable of but I'm thinking 4-8 only based on the diode sizing.

There are some very sophisticated MPPT algorithms out there, but it seems like a lot of the typical commercial units use pretty simplistic hill climbimg logic or even simple closed loop circuits (bad for multiple peak voltage systems like you might get with a panel in the shade and another in the sun) or a 76% of Voc fixed ratio where the panels are taken off line to measure Voc and then voltage is just nailed to 76% of Voc (not horribly far off on average for a single panel, but IFF that panel is around 80% Voc for Mpp under most conditions).

The fancier code is used in solar race cars and more advanced systems and includes fuzzy logic, neural nets and more.

A platform like this would enable trying out lots of approaches.

MPPT Project

Jim

[mlts22]

The solar trailer might be an idea, or perhaps just a collapsible system that can take an hour or two to set up and take down when boondocking.

I have been kicking around that concept, which would be a PVC (or other solid pipe) frame, a row of panels, a MPPT controller, a battery bank of 2-3 pairs of 6 volt golf cart batteries (to appease Mr. Peukert), and a 3000 watt inverter to get the power from the jars to the RV.

The purpose of this would be the simple fact that it would allow me to keep the batteries topped off on my rig without having to fire up a generator. Generators are tolerated, but because it is a quiet area, even a quiet inverter one is quite loud. This would go a long way to offsetting the furnace's use. When the weather switches over from heat needed to A/C, I'd just bring a fridge that can go in a tent or pavilion, stock it full of drinks, and run that.

This would be for the quarter of a year where I boondock on weekends, so it would be left on site when I'm not there, and when the off season hits, I might stuff it in a trailer, or with permission, just leave it on site (the local groundskeeper won't object to free electricity.

However, there are a lot of decisions to be made. With a MPPT controller, panel voltage isn't that big an issue. Of course, there are a lot of calculations which need to be done, including if this would fit in a budget. It won't be cheap, but it would be very useful.

[mena661]

pianotuna wrote:

If you were going "all electric" then a large fuel cell might be the "way to go". It would power electric wheel motors.

Off topic but my dream rig would be all electric but not just all electric, all 120V electric where everything runs from an inverter with the battery bank being wired for 48V. I also toyed with the idea of a trailer with batteries and solar (and extra FW and GW tanks) but it would have to be enough to run the A/C from inverter to make it all worthwhile.

[HiTech]

KJINTF wrote:
Jim

To me that algorithm is the heart of the MPPT design and where the rubber meets the road easily differentiating the competitors. I used Blue Sky, Outback and Morningstar controllers with two K135 panels in series producing about 40Voc. For me the MS algorithm performance was easily the best of the three.
My MPPT 60 has two processors one for the tracking and one for external communications. MS has upgraded the tracking algorithm a few times over the past couple of years; their File History lets you know what's been changed.

X2. The algorithm as well as the sampling speed and range are critical, as well as the interval between sampling, and the loss of production when sampling.

There are a lot of very crude approaches out there which can result in finding a local max power point instead of the overall system max power point, or a just plain wrong one, both depending mostly on panel mix and characteristics.

Jim

[pianotuna]

Hi KJ,

I agree it is all about the algorithm. That's one reason Salvo's comments may be flawed. I believe his controller may be an early model that has a knob to "tweak" the controller.

My favorite choice for "large" solar is the Tristar MPPT 60 unit because it has three 20 amp controllers "stacked". As amps come in first one is active, then two, and finally all three.

I'll be most interested to see the Rogue 3048 when Marc finally gets it "out the door". That should be very soon now. I hope his next effort will be a 60 amp capable unit.

Concerning the rare earths, I was quoting from the Blue Sky website from about three years ago. I believe it was about the Solar Boost 50, which I see they now offer again.

I'm generator free and hoping like heck to stay that way. The siren song of the Magnum Hybrid inverters are making that hard to resist. A thousand watt genny and the existing solar would let me run the roof air. If someone made a small (reliable) electric start genny, I'd probably be unable to say no.

KJINTF wrote:
Jim

I did a few simple tests a couple of years back on the "Magic" tracking algorithms used in MPPT controllers. To me that algorithm is the heart of the MPPT design and where the rubber meets the road easily differentiating the competitors. I used Blue Sky, Outback and Morningstar controllers with two K135 panels in series producing about 40Voc. For me the MS algorithm performance was easily the best of the three.
My MPPT 60 has two processors one for the tracking and one for external communications. MS has upgraded the tracking algorithm a few times over the past couple of years; their File History lets you know what's been changed.

PT

I was not aware of the use of any Rare Earth materials - please tell me more

[KJINTF]

Jim

I did a few simple tests a couple of years back on the "Magic" tracking algorithms used in MPPT controllers. To me that algorithm is the heart of the MPPT design and where the rubber meets the road easily differentiating the competitors. I used Blue Sky, Outback and Morningstar controllers with two K135 panels in series producing about 40Voc. For me the MS algorithm performance was easily the best of the three.
My MPPT 60 has two processors one for the tracking and one for external communications. MS has upgraded the tracking algorithm a few times over the past couple of years; their File History lets you know what's been changed.

PT

I was not aware of the use of any Rare Earth materials - please tell me more

[pianotuna]

Hi,

My understanding is that MPPT requires the use of rare earths materials. That boosts costs. I think that has been part of the "hold up" for Marc (Rogue controller developer). It was also one of the reasons Blue Sky stopped making their 50 amp model.

If you are in a self propelled RV, look at building a "solar trailer".

Do an energy audit and provide for 2 to 5 days of storage. Between the roof of the RV and such a trailer it should be easy to get to say 1500 watts of panels. (1000 on the trailer and 500 on the roof of the RV).

If you are willing to burn propane, then the solar requirements drop dramatically. But I was aiming at 100% electric other than motive power.

mlts22 wrote:


What I wonder about is why that we have PWM controllers at all. MPPT is better in every single way, and gets rid of a lot of headaches. If mass produced, economies of scale would make MPPT controllers the same price as PWM ones.



I'm itching to try building a collapsable, free-standing solar frame that can either stay at the boondocking festival site I'm at indefinitely, or be taken down and slid into a cargo trailer or truck bed. Time to look up costs, but if done right, it would provide enough power to my rig to counteract the drain from the furnace, so I never have to fire up the generator unless I am running the microwave or A/C. It would have its own battery bank and use a PSW inverter. That way, while I'm gone on weekdays, it can charge the batteries up, then I can plug it in, let the RV charger go from there.

[pianotuna]

Hi,

If you were going "all electric" then a large fuel cell might be the "way to go". It would power electric wheel motors.

I'd love to have panels that were double layered, with the bottom layer panels extending out once I've reached my destination for the day.

Another idea is a solar "trailer" that has lots of large 2 volt cells with a solar panel roof. When not traveling it would be easy to tilt the roof at an appropriate angle. I'd aim at a 48 volt system with a nice big pure sine wave inverter. That could provide up to about 40 kwh of power storage. Another potential battery might be one that is no longer suitable for a BEV car. With 100,000 bev's on the road, sooner or later used banks may be available.

For weekend trips I'm already able to be fully electric. For week long trips where I'm traveling significant distances each day, I again am nearly 100% electric. It is only when I'm in one location for more than two days that I have a power short fall. That is solved by moving the fridge to propane.

I've just ordered external and internal window covers from my local seamstress. I have pillows for the vents and home brew pillows for the sky lights. The external cover that will be the hardest is for the windshield. The "package" will also have a way to block off the cab area to cut down on the area to be cooled and heated.

The cheapest route for me to have more charging capacity without a generator would be to add a second alternator

[mlts22]

I like the voltage scanning aspect of their offerings, which is why Morningstar's product is on the top of my list if/when I built a RV solar array.

What I wonder about is why that we have PWM controllers at all. MPPT is better in every single way, and gets rid of a lot of headaches. If mass produced, economies of scale would make MPPT controllers the same price as PWM ones.

One Youtube person I follow (techman2015) upgraded controllers a few months ago, and it did a significant improvement in his amperage gain, especially because he could attach another panel and not force 17+ volts through a PWM controller that can at best just lop off the voltages coming in.

I'm itching to try building a collapsable, free-standing solar frame that can either stay at the boondocking festival site I'm at indefinitely, or be taken down and slid into a cargo trailer or truck bed. Time to look up costs, but if done right, it would provide enough power to my rig to counteract the drain from the furnace, so I never have to fire up the generator unless I am running the microwave or A/C. It would have its own battery bank and use a PSW inverter. That way, while I'm gone on weekdays, it can charge the batteries up, then I can plug it in, let the RV charger go from there.

[HiTech]

It looks like Morningstar avoids most of the pitfalls of simplistic MPPT tracking in their Trackstar approach (details in sidebar on right).

Using voltage as a trigger to rescan seems like a pretty good strategy. I actually considered if using a tiny "sense" solar panel would not be a good approach to see if a rescan was needed to avoid taking the main array out of optimum settings.

The only thing really missing is them disclosing how quickly it will rescan if needed. Other than that, a nice to have would be being able to limit the scan voltage to a smaller range than 0-150v if you know your array does not need the full range.

Really the technique used DOES matter and all MPPT approaches are not created equal.

Jim

[HiTech]

I've had similar thoughts. A retrofit to an existing Motorhome could be a little trailer with regen braking built in, proportional acceleration assist, of course a nice battery bank, and various forms of power generation.

One easy advantage to any RV with regen braking is amazingly rapid battery recharging if you set up that mode. Driving between stops could fully recharge your banks instead of just giving a bit of a boost.

Jim

[mlts22]

Taking all this to its logical conclusion, having a completely electric RV, even the motor (or perhaps have each wheel be its own independent motor) would be interesting. The gas engine can be completely chucked and a high wattage, variable RPM, inverter generator with common-rail fuel injection be put in its place. The batteries can be merged into something like the packs on the Prius/Volt/Tesla/Leaf, with a high wattage inverter used for all subsystems (dash A/C, overhead A/C, etc.) On shore power, it would not just be ready for boondocking, but ready for the road.

Now add some electric grid smarts, and when it is in storage, it slowly charges from shore power. If there is a blackout, and the electric company gives the signal, it would have the ability to backfeed, perhaps running the generator (assuming the owner gave permission) to help keep parts of the grid online for a good long while (well, until the gas gets to 1/4 tank or so.)

[HiTech]

See if you are doing that, then it's time too to synch controller+inverter with the other sources as well, with hybrid car type strategies like use as much battery as possible first vs as little as possible/charge battery...etc. Really a hybrid car control strategy model coupled to a genset instead of wheels has a lot of the right capability.

[mlts22]

I like the supercap because it can suck in large amounts of electricity. No worries about pulsing or the right tenths of a volt, just shove the juice in the cap at or below its ratings. Then, on the other side of the cap, a smart charger can take its own sweet time charging, desulfating, balancing, and other battery tasks, even when the sun is down, as the cap would still have plenty of juice left.

I also wouldn't mind seeing a smart meta-controller. That way, you can have an EFOY fuel cell, solar, wind, shore power, generator, and engine alternator, and the controller can deal with all those power sources at once to ensure the batteries are charged as optimally as possible.

Maybe even have an RFID chip on the batteries with some sensors built in, so the controller would know the age, type, amount of acid (if flooded), plate status, etc. I know that modern BMWs do something like this, where if the car battery is pulled, the vehicle won't start until the dealer re-inputs these parameters into the car's computer, so the vehicle knows exactly what voltage the battery will make and its expected life.

Then, the last piece of the puzzle would be a smart EMS. If the batteries go below 50%, shed everything but vital circuits. If below 25%, shed everything but the e-brakes. Better the EMS cutting off current than having a dead fridge or furnace due to undervoltage burnouts.

Of course with all these controllers come cool tricks, such as turning on the fuel cell when the solar cells stop giving enough useful energy, turning the generator on if batteries are rapidly discharging, allowing the A/C or microwave to take its locked rotor amps from the batteries, then firing up the generator to handle the constant load, etc.

[HiTech]

Me too so it could still adjust the voltage up and down on the solar panels to maximize watts out. Really the cap could just be on a 3rd set of terminals as well doing an energy buffer function.

You could make a poor man's version with a medium sized battery as well. Either the cap or a secondary battery would let you continue trickle charging until sun up the next morning. If MPPT were one of the few with boost AND buck converter functionality built in, you could use a single (below 80% capacity, old mostly used up) 6v golf cart battery as the buffer.

Actually this could be the basis of a smart controller like that by adding a bit of circuitry to be able to switch around where the charge goes to, and where it comes from...

Jim