Simple home made analog MPPT contoller

[outsider]

I have designed some pretty complicated control systems in my past ... all in analog. However, not in solar and not in power electronics.

I do think I already understand that the power curve at Vmp/Imp is pretty flat at the top. Actually, calculus demands it, namely, that the derivative of the power at the peak power point is zero, meaning, it doesn't vary with array voltage. And I think you would add to that, that this same curve doesn't even change that much with varying levels of insolation, so it's ok to just have a knob for "what input voltage do you want to track at" and set that once and leave it there, even though one might think it is crucial to efficiency to track Vmp to get every last drop of power out, a task that MPPTs are supposed to do.

 

[Warpspeed]

Yup.
You have it nailed.

 

[outsider]

I found another wall wart in my box of them, this one a higher-power 15 V 1.5 A unit, that runs off DC. It starts at a relatively low 65 V, and keeps going down to about 12 V, which means it must have a buck-boost or something going on inside. Also it starts to draw significant current at the lowest voltages near cutoff, even without any load.

Who found, or how did you find, that some line-powered switchers actually run off DC? I would not have thought to even try this.

 

[efficientPV]

I was sweeping up the shop and found one of these on the floor with some leads on it and a 260 ohm resistor on the 12V, 46ma. It actually started at 12.0V and drew 80ma, 20V at 37ma, 30V at 20ma, and 40V at 14ma. So it is only really happy once it gets well above 20V. But that is pretty impressive and it doesn't bump.

 

[Warpspeed]

Who found, or how did you find, that some line-powered switchers actually run off DC? I would not have thought to even try this.

In ancient times, if you needed 12v isolated dc from the 230v grid, you used a step down transformer and a bridge rectifier.
This has all kinds of disadvantages, including high no load idling current, and not working at 120v or less unless you fitted a different transformer to it.

What is now done, is the incoming ac voltage goes through a bridge rectifier first, to convert it to high voltage dc. A switching power supply then drives a very small high frequency transformer which then has an isolated secondary winding to produce a voltage regulated and isolated dc output voltage.

These work just as well from a dc input as an ac input, the bridge rectifier right at the input sorts all that out.
The switching power supply can be made to work over a very wide input voltage range. So its possible to build a universal wall pack that can operate in any part of the world, 50Hz or 60Hz or with dc input. Minimum supply voltage in Japan can go as low as 80v. Max supply voltage in Australia can go as high as 265v.

Its a very efficient way to do it, and its cheaper than using a transformer. In most countries now, its actually illegal to sell the old transformer wall packs, although there must still be millions of them out there that still work just fine.

Something that starts up at 65v might be fine for a 100v solar system, but obviously would not work with a 48v solar system.
Its not difficult to test a few different wall packs and find something that starts up at 30v or 40v or even a lot less.
Far cheaper than buying whole wall packs are the small circuit boards that go into these wall packs.
These can be bought for less than two dollars direct from China, and must be the bargain of the century.

They are usually specified to work down to 80v minimum ac voltage (for the Japanese market).
But they are usable down to much lower dc voltages if the output loading is kept very low.
We usually only need a very few milliamps anyway, so its an excellent way to get 12v or 5v for some small project at very low cost.

The only problem is, there is a bit of luck involved finding boards that will start up and run at very low dc input voltages.
But at less than two dollars each, its no problem to order several from several different suppliers, then order a whole bunch of them once you find something suitable. These obviously also work direct from 120/240v ac to power our projects.
But for solar it opens up quite a few interesting possibilities.

 

[JackNZ]

In ancient times, if you needed 12v isolated dc from the 230v grid, you used a step down transformer and a bridge rectifier.
This has all kinds of disadvantages, including high no load idling current, and not working at 120v or less unless you fitted a different transformer to it.

What is now done, is the incoming ac voltage goes through a bridge rectifier first, to convert it to high voltage dc. A switching power supply then drives a very small high frequency transformer which then has an isolated secondary winding to produce a voltage regulated and isolated dc output voltage.

These work just as well from a dc input as an ac input, the bridge rectifier right at the input sorts all that out.
The switching power supply can be made to work over a very wide input voltage range. So its possible to build a universal wall pack that can operate in any part of the world, 50Hz or 60Hz or with dc input. Minimum supply voltage in Japan can go as low as 80v. Max supply voltage in Australia can go as high as 265v.

Its a very efficient way to do it, and its cheaper than using a transformer. In most countries now, its actually illegal to sell the old transformer wall packs, although there must still be millions of them out there that still work just fine.

Something that starts up at 65v might be fine for a 100v solar system, but obviously would not work with a 48v solar system.
Its not difficult to test a few different wall packs and find something that starts up at 30v or 40v or even a lot less.
Far cheaper than buying whole wall packs are the small circuit boards that go into these wall packs.
These can be bought for less than two dollars direct from China, and must be the bargain of the century.

They are usually specified to work down to 80v minimum ac voltage (for the Japanese market).
But they are usable down to much lower dc voltages if the output loading is kept very low.
We usually only need a very few milliamps anyway, so its an excellent way to get 12v or 5v for some small project at very low cost.

The only problem is, there is a bit of luck involved finding boards that will start up and run at very low dc input voltages.
But at less than two dollars each, its no problem to order several from several different suppliers, then order a whole bunch of them once you find something suitable. These obviously also work direct from 120/240v ac to power our projects.
But for solar it opens up quite a few interesting possibilities.

In ancient times, if you needed 12v isolated dc from the 230v grid, you used a step down transformer and a bridge rectifier.
This has all kinds of disadvantages, including high no load idling current, and not working at 120v or less unless you fitted a different transformer to it.

What is now done, is the incoming ac voltage goes through a bridge rectifier first, to convert it to high voltage dc. A switching power supply then drives a very small high frequency transformer which then has an isolated secondary winding to produce a voltage regulated and isolated dc output voltage.

These work just as well from a dc input as an ac input, the bridge rectifier right at the input sorts all that out.
The switching power supply can be made to work over a very wide input voltage range. So its possible to build a universal wall pack that can operate in any part of the world, 50Hz or 60Hz or with dc input. Minimum supply voltage in Japan can go as low as 80v. Max supply voltage in Australia can go as high as 265v.

Its a very efficient way to do it, and its cheaper than using a transformer. In most countries now, its actually illegal to sell the old transformer wall packs, although there must still be millions of them out there that still work just fine.

Something that starts up at 65v might be fine for a 100v solar system, but obviously would not work with a 48v solar system.
Its not difficult to test a few different wall packs and find something that starts up at 30v or 40v or even a lot less.
Far cheaper than buying whole wall packs are the small circuit boards that go into these wall packs.
These can be bought for less than two dollars direct from China, and must be the bargain of the century.

They are usually specified to work down to 80v minimum ac voltage (for the Japanese market).
But they are usable down to much lower dc voltages if the output loading is kept very low.
We usually only need a very few milliamps anyway, so its an excellent way to get 12v or 5v for some small project at very low cost.

The only problem is, there is a bit of luck involved finding boards that will start up and run at very low dc input voltages.
But at less than two dollars each, its no problem to order several from several different suppliers, then order a whole bunch of them once you find something suitable. These obviously also work direct from 120/240v ac to power our projects.
But for solar it opens up quite a few interesting possibilities.

My laptop powersupply has been running fine on about 80 to 120 volts for about 8 years.
Do you think a stator from a smart drive washing machine could be used as an inductor at a lower frequency than 10 khz or is that a silly idea?

 

[Warpspeed]

Do you think a stator from a smart drive washing machine could be used as an inductor at a lower frequency than 10 khz or is that a silly idea?

The inductor is a key component for efficient power transfer.
Too much resistance and it runs hot.
Not enough inductance, and the peak current then becomes very high, placing more stress and higher losses into your mosfet(s).
Almost anything can work "in a fashion", but for best results, try to find a decent suitably rated choke.

 

[jorby]

The inductor is a key component for efficient power transfer.
Too much resistance and it runs hot.
Not enough inductance, and the peak current then becomes very high, placing more stress and higher losses into your mosfet(s).
Almost anything can work "in a fashion", but for best results, try to find a decent suitably rated choke.

What would happen If i connected the output to a 16 ohm load as a dump when my other mppt lets array voltage to rise as the battery fills up?

 

[Warpspeed]

What would happen If i connected the output to a 16 ohm load as a dump when my other mppt lets array voltage to rise as the battery fills up?

It depends on the circumstances, number of panels in series, available sun, number of parallel strings and such.......

The sudden application of a 16 ohm load will definitely pull power from the solar panels.
How much current that is, depends on the available solar voltage, could be a little or a lot depending on how much total power is available from the solar panels. But it will definitely pull down the available solar voltage.

It might pull the solar voltage down so far that its then below the battery voltage, and the solar controller is unable to function at all.

If its only a 12v system, the one amp or so supplied to a 16 ohm load might have almost no effect at all.

Without a lot more information its not really possible to give a meaningful answer to your question.

 

[jorby]

It depends on the circumstances, number of panels in series, available sun, number of parallel strings and such.......

The sudden application of a 16 ohm load will definitely pull power from the solar panels.
How much current that is, depends on the available solar voltage, could be a little or a lot depending on how much total power is available from the solar panels. But it will definitely pull down the available solar voltage.

It might pull the solar voltage down so far that its then below the battery voltage, and the solar controller is unable to function at all.

If its only a 12v system, the one amp or so supplied to a 16 ohm load might have almost no effect at all.

Without a lot more information its not really possible to give a meaningful answer to your question.

I must apologize for leaving out all the details that you could not possibly know....duh....

I have 3 400+v strings running to an EG18kpv inverter. I only want to connect to one of the strings which runs around 400v mppt. It can do 22 amps max. The 16 ohms is my bottom element in the water heater. This circuit controls the output voltage as well as the input voltage. The panels are over rated for this load. I assume that the circuit would stop if the input is below the 400v I would set for the input and limit loading of the panels at the 220v output I would set to protect the element. Am I missing something here. I don't care what the output voltage is as long as it does not burn out my heater.

 

[Warpspeed]

That should work.
If your panels peak out at 400v max power point (found by your EG18pv MPPT software) that is where its going to bulk charge.
The solar voltage will sit there, until the battery voltage rises to the point where it goes into absorb, and the battery charging current begins to slowly taper back to zero. There will then be excess solar available.

The solar voltage will begin to rise, and if your constant voltage solar controller is set to a voltage a bit higher than 400v, any excess solar power will then be diverted into the heating element.
If the heating element voltage reaches the maximum output voltage set point, presumably 220v, then the power to the heating element will be held at that, and increase no further.
So I expect it should do exactly what you want it to do.

Its then just a case of setting the appropriate voltages for both input and output.
Perhaps 420v and 220v.

 

[jorby]

That should work.
If your panels peak out at 400v max power point (found by your EG18pv MPPT software) that is where its going to bulk charge.
The solar voltage will sit there, until the battery voltage rises to the point where it goes into absorb, and the battery charging current begins to slowly taper back to zero. There will then be excess solar available.

The solar voltage will begin to rise, and if your constant voltage solar controller is set to a voltage a bit higher than 400v, any excess solar power will then be diverted into the heating element.
If the heating element voltage reaches the maximum output voltage set point, presumably 220v, then the power to the heating element will be held at that, and increase no further.
So I expect it should do exactly what you want it to do.

Its then just a case of setting the appropriate voltages for both input and output.
Perhaps 420v and 220v.

Thank you very much! That is exactly what I need. I am surprised that such a device is not available on the market already. (Edit: device that works at 400volts vs battery voltage) I think the approach is much better than just switching on a big load all at once based on reaching a set battery voltage or after finally reaching float status. A lot of power can be wasted during that time. I wish I had enough battery to never let any available power go to waste but I also need the battery to get full for cell balancing. I am not going to get involved with pushing it to the grid. The hassle here is not worth it.

 

[Warpspeed]

I am surprised that such a device is not available on the market already.

All it will take is for a few pioneers to blaze the trail, and get some really good results, and the Chinese will soon be selling them cheaper than you could make one yourself.
They are always slow to invent and innovate, but they are the supreme experts at copying ideas that are demonstrated to work.
And they do read the Forums....

 

[Ray Clout]

All it will take is for a few pioneers to blaze the trail, and get some really good results, and the Chinese will soon be selling them cheaper than you could make one yourself.
They are always slow to invent and innovate, but they are the supreme experts at copying ideas that are demonstrated to work.
And they do read the Forums....

G'day Viewers
I've been following this post and decided to build one of this design.
A few changes here and there but mostly components that are or are becoming obsolete....not recommended for new designs.
For example. The mosfet is discontinued and its replacement has superior parameters....600V...50A
Also, I refuse to use the plug type multi screw connectors for the high power components. The pictures attached show a far better method of terminating power cables.
You can also see in the pics, that I use copper planes for high current areas rather than thick tracks. The pcb will be 2oz copper as well...bottom and top layers
Thanks to the OP

 

[Warpspeed]

A really excellent result there Ray
Let us know the final results.

The original design was the result of a quick rummage through my junk box one rainy Sunday afternoon.
Whatever turned up was tossed together as my very first proof of concept experiment.
Its by no means an optimum final design, never was intended to be.
But it did work beyond my wildest hopes !!
Which is really all that mattered at the time.

Its not a complex circuit, and its wide open to all kinds of improvements.
But the constant voltage concept definitely works, and its something for others to improve upon in its implementation.

 

[solar8484]

Also, I refuse to use the plug type multi screw connectors for the high power components. The pictures attached show a far better method of terminating power cables.

Nice but you can be sure the Chinese copying the design won't be using those or anything else from Wurth

 

[Warpspeed]

The plug in screw terminal connectors are especially convenient for experimental prototyping.
The whole circuit board is quickly removable and much easier to work on when unplugged from all the larger power components.

Removing a mosfet for checking, or replacement, or doing some back to back testing, only takes seconds, when no soldering is required.
Testing prototypes, is a very different thing to designing for low cost mass production.

Been doing this for years, and making things that are very easy to test, repair, and modify sure makes the whole process more pleasant during development. Especially if there are a few blow ups
The connectors themselves are big clunky and expensive, but they are easily removable and re usable.

 

[Jose Sol]

Estuve leyendo la mayoría de los comentarios de este hilo ya que mi propósito en este form es aprender todo lo posible y me parecen interesantes las propuestas que han dando muchos de los miembros a solucionar de una forma u otra un regulador mppt lo más económico y fiable posible, en mi caso acá en Cuba se hace difícil comprarlo por que no se venden directamente en ninguna tienda y se hace difícil importarlo además de su valor en dólares es bastante dinero en acá por lo que busco una solución económica de construcción de un regulador ya sea mppt o pmw ...Si pudiesen ayudarme algunos de los miembros con algunos diagramas de construcción económico se les voy agradecer. Saludos

 

[Warpspeed]

Sorry Jose, I only can read English.

 

[DPC]

Sorry Jose, I only can read English.

from Google translate


I have been reading most of the comments in this thread since my purpose in this form is to learn as much as possible and I find interesting the proposals that many of the members have given to solve in one way or another an mppt regulator as economically and reliably as possible, in my case here in Cuba it is difficult to buy it because they are not sold directly in any store and it is difficult to import it in addition to its value in dollars is quite a lot of money here so I am looking for an economical solution to build a regulator either mppt or pmw ... If some of the members could help me with some economical construction diagrams I would be grateful. Greetings

We got to help this guy out!

 

[jorby]

That should work.
If your panels peak out at 400v max power point (found by your EG18pv MPPT software) that is where its going to bulk charge.
The solar voltage will sit there, until the battery voltage rises to the point where it goes into absorb, and the battery charging current begins to slowly taper back to zero. There will then be excess solar available.

The solar voltage will begin to rise, and if your constant voltage solar controller is set to a voltage a bit higher than 400v, any excess solar power will then be diverted into the heating element.
If the heating element voltage reaches the maximum output voltage set point, presumably 220v, then the power to the heating element will be held at that, and increase no further.
So I expect it should do exactly what you want it to do.

Its then just a case of setting the appropriate voltages for both input and output.
Perhaps 420v and 220v.

I have noticed that when it is overcast and sprinkling outside (current weather situation), MPPT runs around 425v. Seems I will need a more sophisticated decision making process for enabling this thing. I would not want it running today! Of course I have to build it first.........

 

[Warpspeed]

We got to help this guy out!

Yes I agree, but how best to go about it ?
Can he order components through the internet, order circuit boards from China, I have no idea.
The language barrier is a bit of a problem too.....

 

[Warpspeed]

I have noticed that when it is overcast and sprinkling outside (current weather situation), MPPT runs around 425v. Seems I will need a more sophisticated decision making process for enabling this thing. I would not want it running today! Of course I have to build it first.........

When you finally have it all going, you will discover that tweaking the solar voltage up and down between 400v and 425v will make zero measurable difference to the bulk charging current.

The important thing is that the controller throttles the loading on the panels right back when its grey and cloudy and horrible, allowing the panel voltage to remain up in the 400 volt region with very little loading where they are still most efficient.
When there is plenty of sun in a clear blue sky, the controller will really pull serious current from the panels, again keeping the panel voltage up in the maximum power 400 volt region.

That is what makes this all work so very well, its the extremely wide available change in loading on the panels that is vitally important.
The exact voltage to which the controller is set is is not in the least bit critical.
This will all become much clearer once you have a working controller to play with.

 

[DPC]

Yes I agree, but how best to go about it ?
Can he order components through the internet, order circuit boards from China, I have no idea.
The language barrier is a bit of a problem too.....

Your Americans speak Spanish...

Aliexpress will deliver components to Cuba.

Considering the power problems in the workers paradise of a simple mppt can be made int a kit form thats something a a lot of people around the world could use too.

 

[AntronX]

a simple mppt can be made int a kit form thats something a a lot of people around the world could use too.

I like this idea of dirt cheap solar electronics for poor countries. Working on something similar right now (PWM water heater controller). But he is not going to build reliable MPPT without skills and access to test equipment. Best he could do is voltage controlled switch to prevent batteries overcharging.