MPPT Controller Explanation For Dummies

[goboatingnow]

Originally Posted by noelex 77

There are three types of solar controllers/regulators. From cheapest to best they are:

1. On/off.
2.PWM
3.MPPT (which are generally also PWM)

There are no suitable collective nouns to describe these regulators, but it is important to distinguish between them.
Calling PWM regulators On/off, or bang bang, is very confusing as it blurs the first two categories of regulators.

Yes but PWM charging as opposed to PWM switching , is just an on off variable duty cycle charger , a very cheap and nasty way that relies on PV panels being current sources. , an on off controller is just a PWM regulator operating at a fixed duty cycle.

Every time whether is PWM solar chargers , or on/off , the panel is ultimately connected to the battery directly and hence the PV operating point is pulled to the terminal voltage , this can introduce huge losses in efficiencies , especially if the the user is at the higher end of allowable panel voltages


Note mppt is NOT PWM , Mppt outputs pure DC after filtering , PWM chargers , as opposed to chargers that use switched mode pulse the battery , and are peculiar to PV charging.

People constantly mix up switch mode power conversion, ( which uses PWM , ) and PWM solar regulators , which just duty cycle the PV panel to the battery.
Dave

[goboatingnow]

Originally Posted by nimblemotors

This $100 SPV1020 controller board has no heat sink, has 97% efficiency.
In fact, if you read about them, it uses four small inductors, so it doesn't need a larger electrolic capacitor, which tend to have short lifetimes (1-3 years) in the heat.
I see both the circuit boards in the videos have electrolic caps.
Note however, it is JUST a MPPT controller that outputs a fixed voltage,
it is not a battery charger.

Actually that Evaluation board is a fully functional mppt battery charger ( just CV ) , but because the evaluation board doesn't have a buck converter onboard , the panel operating range has to lower then the battery voltage range !

To be useful , it would need a voltage down convertor, hence two switchers , that a common mppt design paradigm though.

Buck regulators are two a penny anyway.

I wonder what other integrated mppt solutions are out there.

Dave

[noelex 77]

Originally Posted by goboatingnow

Yes but PWM charging as opposed to PWM switching , is just an on off variable duty cycle charger , a very cheap and nasty way that relies on PV panels being current sources. , an on off controller is just a PWM regulator operating at a fixed duty cycle.

Every time whether is PWM solar chargers , or on/off , the panel is ultimately connected to the battery directly and hence the PV operating point is pulled to the terminal voltage , this can introduce huge losses in efficiencies , especially if the the user is at the higher end of allowable panel voltages


Note mppt is NOT PWM , Mppt outputs pure DC after filtering , PWM chargers , as opposed to chargers that use switched mode pulse the battery , and are peculiar to PV charging.

People constantly mix up switch mode power conversion, ( which uses PWM , ) and PWM solar regulators , which just duty cycle the PV panel to the battery.
Dave

The gain switching from PWM to MPPT is only modest. 5-15% is my estimate. This can be a useful, if boat is equipped with the maximum amount of solar, or if the installation costs of installing more panels is high.

I think describing PWM regulators with phrases like "huge losses in efficiencies" can be a bit misleading (unless you you are talking about using unsuitable panels for PWM) but as long as people understand the sort of gains to expect the semantics of the description is unimportant.

On/off regulators are very different, in practice, to PWM regulators. In many situations "huge losses in efficiencies" is apt. They also struggle to get the battery to high states of charge, which can have some detrimental effects on lead acid battery life.
It is very important consumers understand the difference between On/off regulators and PWM. The former are almost never a sensible buy. Where as the latter are often the best alternative and would be be the regulator of choice for many boat installations, superior to the cheap, unreliable MPPT regulators.

[goboatingnow]

For the technically minded the application note gives a good simple overview of mppt http://www.st.com/st-web-ui/static/a...DM00036523.pdf

Dave

[T1 Terry]

The parts that seem to be not fully understood is the difference between Li charging voltage and Pb charging voltages, and he fact that both respond well to pulse charging, just what PWM charging does.
A deeply discharged Pb battery could start it's charging down around the 11.8v mark, it will stay i the 12v area for quite a while before stepping up into the 13v and finally the 14v mark, we are talking about reasonable sized battery banks here.
With Li battery charging, 100% discharged is 12v, very little charge goes in before it's back to 13v, then the climb is slow between 13v and 14v, at 14v it's virtually fully charged. Between 13v and 14v is the perfect spot for hot 12v nom panels, MPPT isn't going to make that any better.
When an MPPT controller goes into current control to limit max voltage it does a sort of PWM control, but it also smooths the high voltage spikes through inductors and capacitors and other electronic bits (read buggered if I know) where a true PWM controller turns the panels on and off very quickly at first, then the off time extends as the full mark is approached. That pulsing involves high voltage down to terminal voltage before the mosfet switches off, then it is repeated, both lead acid and Li batteries respond very well to pulse charging, Li batteries can handle 20C pulse charging current, so you are never going to damage them, only rapid charge them, lead acid batteries shift accumulated sulphation crystals with a sudden and short high voltage spike repeated often, that's all the trick battery conditioners do, spike charge the battery.
MPPT works well when supplying a constant load, like feeding to the grid or driving an electrical load, they are crap at recharging batteries.

T1 Terry

[goboatingnow]

And here's a complete TI solution 9A , upto 50v input , full smart charger implemented on board


150 bucks , and needs a few external bits ( case etc ) http://www.digikey.com/product-detai...OPB-ND/2636677

Lego for electronic engineers !!!

Dave

[noelex 77]

Originally Posted by T1 Terry

With Li battery charging, 100% discharged is 12v, very little charge goes in before it's back to 13v, then the climb is slow between 13v and 14v, at 14v it's virtually fully charged. Between 13v and 14v is the perfect spot for hot 12v nom panels, MPPT isn't going to make that any better.

The greater the difference between the solar panel voltage (Vmp) and the battery voltage the higher the gain MPPT regulators will have over Non MPPT regulators.
Average voltages under charge for LI are lower than with lead acid.

Vmp of nominally 12v panels is typically around 18v under STC. This needs to be derated for real world conditions, particularly higher temperatures, but there is still plenty of leeway for modest gains when charging voltages used for lithium batteries, which typically will be a maximum of 13.8v.

[T1 Terry]

Originally Posted by noelex 77

The greater the difference between the solar panel voltage (Vmp) and the battery voltage the higher the gain MPPT regulators will have over Non MPPT regulators.
Average voltages under charge for LI are lower than with lead acid.

Vmp of nominally 12v panels is typically around 18v under STC. This needs to be derated for real world conditions, particularly higher temperatures, but there is still plenty of leeway for modest gains when charging voltages used for lithium batteries, which typically will be a maximum of 13.8v.

Try it, I have with quite a number of different controllers, the theory is good, but the reality is some what different. A simpe 3 way battery switch on the solar, a shunt at the battery terminal end, switch between the 2 controllers and read the amps going into the battery, the MPPT is slightly ahead with Pb batteries, but behind with Li batteries.

T1 Terry

[noelex 77]

Originally Posted by T1 Terry

Try it, I have with quite a number of different controllers, the theory is good, but the reality is some what different. A simpe 3 way battery switch on the solar, a shunt at the battery terminal end, switch between the 2 controllers and read the amps going into the battery, the MPPT is slightly ahead with Pb batteries, but behind with Li batteries.

T1 Terry

The solar panels, or controller does not know the battery chemistry it is connected too. The only variable is the battery voltage.
The charging battery voltage must have been lower for the lead acid batteries than for the lithium batteries to produce this result.

This is not what would be found most of time (whilst charging) in a boat system.

Many of the low cost MPPT controllers are poor and outputs less than a simple PWM regulator are not unusual. What controller was it?

It would be great if could outline some other details of your experiment. There are few controlled tests especially on boat (rather than household) solar systems.

[Maine Sail]

Originally Posted by goboatingnow

What do you mean PWM versus on off , the PWMsokar regulators are an on off charger design.

Dave

PWM is a fast on/off. Many of the shunters or "on/off" controllers hit a voltage of say 14.2V then immediately turn off and wait for the battery surface charge to naturally decay back down to 13.0V before they turn back on and charge to 14.2V again only turn off and wait for the batts to decay to 13.0V again. Lots of the day is wasted in the OFF mode waiting for the battery voltage to fall back to the "on" voltage... Getting that last bit of charge into the batteries can take a long time with this type of controller....

[s/v Jedi]

And all those without MPPT controllers will tell us they have negative efficiency (!!! means batteries get discharged when you use them lol), are crap for charging batteries, are a waste of money, PWM is better, MPPT is only (!!!) 10-15% better, etc. etc.

And all who switched to MPPT see huge jumps in power output, with 25% or better reported everytime. And all panel manufacturers confirm this. And all our MPPT controllers and volt meters show panel voltages much higher than battery voltage, while this is impossible according to the naysayers because the heat has reduced voltage output to the point that they hardly charge the battery anymore, and they ignore or dismiss reported results. How can those who spent a little extra money be right!?

And our voltmeters are wrong and dreams busted. And the Outback controllers are bad because they are big and heavy. And you're much better of with just buying a cheap PWM controller and extra panels (which suggests MPPT is better). And the absorption phase from MPPT controllers is fake because what we see is just a surface charge. And cheaper is better, and and and... all the naysayers can't stand to see a guy having spent some dough for better gear than they have and loving the kick-ass results. So instead of being happy for the guy, they can't stand it and tryto put him down. Except the guy knows what he has and is having a ball anyway haha

[goboatingnow]

Originally Posted by T1 Terry

Try it, I have with quite a number of different controllers, the theory is good, but the reality is some what different. A simpe 3 way battery switch on the solar, a shunt at the battery terminal end, switch between the 2 controllers and read the amps going into the battery, the MPPT is slightly ahead with Pb batteries, but behind with Li batteries.

T1 Terry

Terry that makes no sense.

A PV panel is effectively a diode , ie a variable current for a basically fixed voltage ( upto a point )

If the Vmp happens to coincide with the battery operating point , great , no need for mppt tracking

But battery voltages move, less so in Li . So unless you pick your panel very carefully , the Vo of the panel will be Vbat and that could be along way from the optimum Vmp, especially if the user has picked a panel with higher or lower Voc then the battery.

Take a 22v panel , lets say it outputs 10A at a Vmp of 20 V , if I connect that to a discharged battery , the Vo will be pulled to say 12v , at that point I now have turned a technically 200watt panel into a 120 watt , one , hence 80 W of potential solar energy is being lost.

This is irrespective of Li LA or anything.

If I implement DC DC conversion , at regulate on input voltage , I can restore the basic panels efficiency. That's even leaving out mpp tracking and just manually setting the tracking point

Its even worse , if the battery voltage drags the Vo past Vmp and down the curve , now the panel efficiency tanks.

So using PV panels close to their Vmp always results in gains , except in the case where " you happen " to match the Vmp against the battery voltage

So yes , your right, in a very narrow sense, sourcing a panel with a Vmp close to the Li cell voltage means that the panel will work at its Vmp anytime its called on , as Li voltage doesn't change much the panel will not move that far away from the Vmp.

However add in temperature changes in Vmp and movement due to shading and the situation is not as good

For LA is obviously worse

People get confused , they buy PV panels that say 200W , ( at a stated Vmp) which is often a good bit away from their operating point , then they don't realise that you don't get much current at a lower operating voltage , hence they are throwing away power generation.

Operating your panel at Vmp , IRRESPECTIVE, of any other factors , is always the correct way. ( leaving tracking the mppt aside )

Dave

[noelex 77]

Originally Posted by s/v Jedi

And all those without MPPT controllers will tell us they have negative efficiency (!!! means batteries get discharged when you use them lol), are crap for charging batteries, are a waste of money, PWM is better, MPPT is only (!!!) 10-15% better, etc. etc.

And all who switched to MPPT see huge jumps in power output, with 25% or better reported everytime. And all panel manufacturers confirm this. And all our MPPT controllers and volt meters show panel voltages much higher than battery voltage, while this is impossible according to the naysayers because the heat has reduced voltage output to the point that they hardly charge the battery anymore, and they ignore or dismiss reported results. How can those who spent a little extra money be right!?

And our voltmeters are wrong and dreams busted. And the Outback controllers are bad because they are big and heavy. And you're much better of with just buying a cheap PWM controller and extra panels (which suggests MPPT is better). And the absorption phase from MPPT controllers is fake because what we see is just a surface charge. And cheaper is better, and and and... all the naysayers can't stand to see a guy having spent some dough for better gear than they have and loving the kick-ass results. So instead of being happy for the guy, they can't stand it and tryto put him down. Except the guy knows what he has and is having a ball anyway haha

For the record I do have an MPPT controller.

[goboatingnow]

Originally Posted by Maine Sail

PWM is a fast on/off. Many of the shunters or "on/off" controllers hit a voltage of say 14.2V then immediately turn off and wait for the battery surface charge to naturally decay back down to 13.0V before they turn back on and charge to 14.2V again only turn off and wait for the batts to decay to 13.0V again. Lots of the day is wasted in the OFF mode waiting for the battery voltage to fall back to the "on" voltage... Getting that last bit of charge into the batteries can take a long time with this type of controller....

Yes but both types connect the panel to the battery directly. , that moves Vo to the Vbat , which could be away from Vmp , with a big enough mismatch , you could loose 50% or more of the panels power with these controllers.

I mean I've seen them advertised with 30-40 V operating input voltage ranges. , unsuspecting citizen joe , connect up a 25 V panel , ( with a Vmp of say 23v) , every time the PWM switch connects the panel in , its Vo is pulled miles away from Vmp, resulting in huge looses in power generation.


Unless the panel is so small that you don't care about loosing 30-50% of say 20W , or your lucky in sourcing a panel with a Vmp close to your charging point , not doing DC DC conversion on solar , is throwing away power generation.

Dave

[endoftheroad]

I read 100% of this thread, I understood about 10% before reading, now I'm at about 30% undertanding.

For me that's good!