MPPT Controller Explanation For Dummies

[sww914]

I didn't have any more room for panels and the cheap Chinese $30.00 PWM controller wasn't getting it done. I bought a Blue Seas and gained 25%.
Keep in mind, that's going from ebay's worst to one of the best.

[sailinglegend]

Originally Posted by Mystic38

....and in sunny conditions, batteries are easily to 100% by 2pm.....

So how do you know they are at 100% by 2pm?

Does the Morningstar tell you?
Has it dropped down to float so you assume they are 100%?
Does a battery monitor tell you 100%?
Do you use a digital Voltmeter?
Do you measure current going into the battery?

My Morningstar MPPT tells me the batteries are "nearly full" when my BEP battery monitor and a Smartguage tell me they are only at about 80%.

[goboatingnow]

Hey Dave. "It's cam provide anything uptp 25% boost" Sure, the magic weasel words "up to". As a consumer I don't want to know what it might be able to do it the best possible situation, I want a number I can be sure of hitting. And from what I've seen in casual testing, and heard from different makers, "up to 25%" translates into "10% or better" and that's why I say 10%. Because you can pretty much expect a 10% gain from MPPT alone. Now according to one battery maker you can add another 5%+ gain just by switching from pure DC battery charging (which is what naked solar cells do) to any type of PWM charging (which is what MPPT controllers do) so perhaps that 10% should be restated as "15% gain over pure DC chargers or 10% gain over PWM chargers". Numbers can be deceiving, installations will vary. If folks expect a ten percent gain over whatever else they had, in the worst case they'll be pleasantly surprised.

I don't know how many times I have to kill this lie. Mppt does not means PWM charging , switched mode power conversion does not mean PWM charging

PWM charging is used almost exclusively in cheaper solar regulators cause of the ability of solar panels to be connected directly to the battery , as its a current source , unlike other voltage sources

There is no evidence that PWM or pulse charging is any better , and many LA manufacturers don't recommend it. Pure DC is by far the most common method. ( ie the output of mppt or switched mode convertor)


I gave upto 25% because its a variable figure. Its not difficult folks to estimate for a given panel, look up the panels characteristic curves , estimate the Vmp and compare with battery Vo.

In real life its more difficult but with a well depleted battery , yiu could do direct comparisons between mppt and PWM ( bang bang ) types.


Dave

[goboatingnow]

Originally Posted by foggysail

My comment on PWM does apply to solar power regulation. Suggest that you look at the MorningStar ProStar PS-30 PWM.

And sure, on the cheapy side of regulation one can configure a plain old power mosfet as a switch giving the same function as a piece of wire until the load voltage reaches the desired voltage. At that time the mosfet can be modulated or simply left as an open circuit. Very crude!

MorningStar uses the buck instead. I installed one last year on my boat. No clue how others achieve so called PWM.

Foggy

I read through the data sheet , no where does it suggest it has a buck convertor. Its does PWM charge regulation , like all such controllers , ie in absorption the panel is switched in and out of the circuit.

I'm not doubting you, but I see no indication of what you say from a literature inspection

Dave

[foggysail]

Originally Posted by goboatingnow

I read through the data sheet , no where does it suggest it has a buck convertor. Its does PWM charge regulation , like all such controllers , ie in absorption the panel is switched in and out of the circuit.

I'm not doubting you, but I see no indication of what you say from a literature inspection

Dave

Dave-- you're right, Morningstar makes no mention of how regulation is performed other than to mention PWM. I got my info from a report/contest? done in 2011 at the University of Waterloo by students who did an analysis of the MP30. I did download the report which was in Microsoft Word and it is someplace in my computer. The students even summarized the results on Utube. VERY POPULAR ON UTUBE!!! YUP, there have been about 48 views! Now maybe if it was about "girls on campus" there would be 48,000,000+ views.

I will continue to see if I can locate it in my computer but the report is long. If I can find the URL I will post it. If I have a chance tomorrow or early next week I will call Morningstar to get something from them.

I also found a report from Scandia Labs on Morningstar's Sunsaver. Now that regulator DOES NOT use a buck.

http://www.energymatters.com.au/imag.../SS-Sandia.pdf

Scandia goes on to list the benefits of an inexpensive regulator that comes close to walking on water by pulse charging the batteries. Take you pick I guess.

I believe the marketiers have created too many buzzwords such as PWM which many associate with some form of regulation without a clue that PWM simply is an abbreviation for pulse width modulation. That in itself is NOT regulation, it is one of the means from which regulation can be achieved with additional circuitry.

Foggy

EDIT: Dave-- try this URL

http://www.google.com/url?sa=t&rct=j...YV9AbrbXUCdmZg

[goboatingnow]

Hi Foggy,

Read through the paper, what the students are evaluating is comparing the Morningstar controller with the Open source Free charge controller, which is a mppt/buck unit Free Charge Controller - Free Charge Controller. The characteristics they describe relate to that and not the PS-30!

As I said the PS-30 is a simple PWM charge controller. ie, uptill the preset absorption voltage it merely connects the panel to the battery, at the cutoff voltage it PWMs the panel to the battery ( this is to ensure that the battery voltage isnt pushed higher by the panel, leading to gassing, its a very crude technique).

BTW that free charge controller circuit is now based on Tim Nolans, Arduino project heres a graph of a directly connected panel and a mppt connected panel from Tims MPPT project



You can see that when teh panel has a load big enough to demand its full power , quite good gains can be made, ie 30W compared to 22-23W, this is typically in bulk mode and is exacerbated by the lower battery voltage and hence differences in Vo( Vbat) compared to Vmp, and the differences become smaller as the battery needs less current and Vmp no longer is attainable as the panel isnt anywhere near Imp

dave

[foggysail]

Its been awhile since I first read the report. After rereading it is clear that the buck was associated with the Li-Ion charger to provide voltage source charging vs averaging that is fine with the lead acid.

Your graphs are impressive! The bulk mode performance is significantly better with MPPT. Last year when I installed a pair of 140 watt panels I weighed the cost difference between MTTP and that of an additional panel. Because I had the real estate to mount an additional panel, it was overall more economical to just add the panel for almost a 100% improvement. The panel cost from Amazon was around $320 delivered pair. The cost was so reasonable I purchased a second pair that is still in my garage waiting for me to install them.

MTTP prices are going to become better competitive to panel cost. I see this especially true now that governments both here in the States and Europe are penalizing lower cost Chinese panels with tariffs.

Final comment--Arduino!!!! Those products have made so many low cost circuit boards accessible to hobbyists! They have really opened the door to inexpensive projects. I have not caught on to their software because I have concentrated on Microchip's C18 (now being phased out) and the I2C bus.

Foggy

[endoftheroad]

WOW....
This thread is loaded with intense technical information.

Most of It I can't understand but I understand this;

[btrayfors]

Originally Posted by endoftheroad

WOW....
This thread is loaded with intense technical information.

Most of It I can't understand but I understand this;

Yeah, but don't always believe it....sometimes they lie :-)

Bill

[Mystic38]

I use a battery monitor... simple, effective and very accurate...oh, and a clock

Originally Posted by sailinglegend

So how do you know they are at 100% by 2pm?

Does the Morningstar tell you?
Has it dropped down to float so you assume they are 100%?
Does a battery monitor tell you 100%?
Do you use a digital Voltmeter?
Do you measure current going into the battery?

My Morningstar MPPT tells me the batteries are "nearly full" when my BEP battery monitor and a Smartguage tell me they are only at about 80%.

[T1 Terry]

The battery monitors that don't read past 100% can be very misleading as you have no idea if the monitor is still in sync with the batteries, a monitor that displays past 100% gives an instant signal that it’s accuracy has drifted and needs to be reset.
A true test for any battery monitor would be to check the current still flowing in when the monitor claims the batteries are at the displayed 100% SOC, it should be down around 1 to 2 amps, if it's still 10 amps or more the monitor is out of calibration compared to the actual condition of the battery bank. A battery bank has not reach a 100% SOC till no more Ah can be pumped in.
It requires a greater number of Ah in than Ah out to get a lead acid battery back to 100%, if this is not accounted for the error becomes accumulative and the battery monitor could be well off the mark after a mth or so of deep cycling.
An instrument is only a guide and that guide is only accurate if a program of verifying the displayed results is part of a regular routine.

T1 Terry

[sailinglegend]

Originally Posted by T1 Terry

A true test for any battery monitor would be to check the current still flowing in when the monitor claims the batteries are at the displayed 100% SOC, it should be down around 1 to 2 amps.........

There is a “Reset Gotchya” with Battery monitors and solar panels because the manufacturers reset voltage and current values can easily be met by the charge controller because of shade or cloud, or just too small a solar array, so the BM gets reset when the battery maybe at only 80%.

Ideally the proper values should be set so that the current is about 0.5 % of the battery capacity C at the battery absorption voltage of about 14.4 volts. But this voltage/current is impossible to achieve as most regulators may reset to a float voltage much lower than this long before the current has reduced to 0.5% of C. To test for 100% charge, as soon as the regulator drops to float it needs to be forced back on by some means (a switch or remove the fuse), this forces the float voltage back to the absorption voltage. If the current flowing into the batteries in absorption mode is much higher than in float mode then the batteries are not near 100%. On my 1000 AH bank my alternator regulator went from 15A to 60A when absorption mode was switched back on!!!

Many people say their batteries are fully charged by lunchtime. I suggest they force the regulators back on and see how much the charge current rises.

Regulators are designed to recharge batteries not overcharge them. As they don't measure the current into batteries, or know what size the bank is, they may switch of prematurely.

[noelex 77]

Originally Posted by sailinglegend

Regulators are designed to recharge batteries not overcharge them. As they don't measure the current into batteries, or know what size the bank is, they may switch of prematurely.

Some systems do, but its a pity this feature is only available on a small number of controllers.

For the majority of boat owners if you monitor a few typical cycles and adjust the adsorption time so the criterion is met you will achieve a reasonable compromise, especially with flooded batteries.

Personally I think 0.5% is a bit aggressive for a battery return current. There is some debate about this, but I think 1% is a better number, particularly when relying on absorption time where the criterion will be exceeded for some cycles.

[T1 Terry]

Personally I think 0.5% is a bit aggressive for a battery return current. There is some debate about this, but I think 1% is a better number, particularly when relying on absorption time where the criterion will be exceeded for some cycles.

1 amp per 100Ah capacity at what voltage? Even at a 13.8v float that would be close to 95% SOC for a lead acid battery, I doubt those believing their batteries are at 100% SOC by lunch time have a charge current that has dropped that low. Most people seem to think that because the regulator has dropped to float voltage the batteries are fully charged, yet they have no idea what the criteria is for their regulator to drop into float. The most common method is a timed function after boost voltage is achieved, rare for a min current flow to be measured as a criteria, a load of any type would negate the controller ever dropping into float.

T1 Terry

[noelex 77]

Originally Posted by T1 Terry

[COLOR=black][FONT=Verdana]1 amp per 100Ah capacity at what voltage?

The generally accepted criterion is 0.2v below absorption voltage (or greater). Often a short delay is incorporated to minimise the effects of surface charge.

Originally Posted by T1 Terry

The most common method is a timed function after boost voltage is achieved, rare for a min current flow to be measured as a criteria, a load of any type would negate the controller ever dropping into float.

Some systems do measure battery return amps independently of load ( like mine), but it is not common. Most days in summer we reach 1-1.5% (my general criterion for switching to float) by lunchtime. With typically another 5 or 6hours on (a slightly aggressive) float, the batteries are reaching almost 100% on most days.


In winter the settings are much more critical. The batteries can go many weeks before reaching 100%. I tend to make the settings a bit more aggressive during this season. The damage from slight overcharging is better than leaving the batteries at a lower SOC.