MPPT vs PWM cotrollers?

[CatNewBee]

MPPT vs. PWM: MPPT makes only sense if you have enough over-voltage from the panels. On 32cell or 36 Cell panels you would practically not see any difference in the output current. So if you are going to use those, you can just drop in cheep PWM per panel and off you go.

If you go the more sophisticated way with MPPT, use panels with many cells and high voltage output instead of wiring in series. They are more efficient.
If you wire more than 2 panels in parallel it is a good advice to use blocking diodes or at least string fuses just in case one panel becomes a short
cut and the other panels fire it up...

I personally will install 5 high-power / high voltage panels with 339Wp / 96 cells each in parallel with a single MPPT controller. It's expensive, yes - and no redundancy. But also easier to monitor and program with the BMS of the lithium bank. The more controller you use the more wire you need and the more potential failures may occur during usage. I was thinking to split the solar array to 2 smaller MPPT controller, but finally made the decision to go for one large, it was simply much cheaper and the controller has more capabilities built in (bluetooth, display, remote switch).

There will be just 2 wires coming in through the deck with up to 30A current and up to 60V what yields up to 100A charging current at 13.8V.

[conachair]

Originally Posted by CatNewBee

On 32cell or 36 Cell panels you would practically not see any difference in the output current.

When switching between direct/mppt I see significant increase in current with 36 cell 20.5v panels when the MPPT finds its target and stabilizes after a little while. . Can't remember the exact figures but enough to make it well worth the while fitting.

[john61ct]

Originally Posted by missourisailor

when you start to charge, the battery will drag the voltage down to...whatever. Until the current starts to drop. Then the voltage will began to rise.

More specifically

1. High current low voltage (Bulk/CC), as SoC climbs voltage always rises and current may start to fall
2a Voltage reaches Absorb, not via the regulator but the current rate, battery & SoC determines when.
2b Voltage now limited by the regulator (Absorb/CV)
2c Important to maintain Absorb V until trailing amps spec shows bank is 100% Full
3 Only then drop to Float

2c and 3 is where nearly all charge sources fail out of the box.

Adjustability allows this to be corrected by a knowledgeable user with an accurate ammeter.

[john61ct]

Originally Posted by conachair

When switching between direct/mppt I see significant increase in current with 36 cell 20.5v panels when the MPPT finds its target and stabilizes after a little while. . Can't remember the exact figures but enough to make it well worth the while fitting.

Yes. But most MPPT show a much greater advantage with a greater V difference between panel and bank.

Barely any with 17-18Voc panels.

With PWM you want lower V, since any higher than the minimum is discarded.

A lot of modern MPPT advantage at those lower ranges is not from MPP function,

actually coming from DCDC buck conversion preserving watts by increasing amps as output voltage is reduced.

[conachair]

Originally Posted by john61ct

A lot of modern MPPT advantage at those lower ranges is not from MPP function,

actually coming from DCDC buck conversion preserving watts by increasing amps as output voltage is reduced.

So we could just get a cheap buck converter for each panel then set to 14 point whatever..

[Maine Sail]

I have conducted quite a bit of head to head testing & data logging on PWM vs. MPPT. I have yet to see a PWM controller beat an MPPT. The panels in the graph below are typical Kyocera 140W panels with a Vmp of 17.7V.. Over 7 days the MPPT controller provided a 20.8% gain over the PWM even on a rated Vmp of just 17.7V.

This is one test I did in 2014:

[john61ct]

Mr Hard Data, accept no substitute! 8-)

Great stuff. . .

[john61ct]

Originally Posted by conachair

So we could just get a cheap buck converter for each panel then set to 14 point whatever..

Except likely less efficient.

You also want the drop to float, adjustable Hold Absorb Time etc.

Saving pennies to buy headaches makes no sense to me.

[conachair]

Originally Posted by john61ct

Except likely less efficient.

You also want the drop to float, adjustable Hold Absorb Time etc.

Saving pennies to buy headaches makes no sense to me.

It was mostly in jest ..

Though for anyone living aboard float is quite possibly superfluous if you want to actually get to full charge.

Have you any data on the buck converters in mppt being that much more efficient than om ebay?

One day maybe I'll have a play and a measure if the sun ever shines again

[conachair]

Originally Posted by Maine Sail

I have conducted quite a bit of head to head testing & data logging on PWM vs. MPPT. I have yet to see a PWM controller beat an MPPT. The panels in the graph below are typical Kyocera 140W panels with a Vmp of 17.7V.. Over 7 days the MPPT controller provided a 20.8% gain over the PWM even on a rated Vmp of just 17.7V.

Great stuff
How many cells were the panels/Voc?

[GTom]

Perfect! How are the panels mounted? (=any issues with the occasional shade? Are they in series/parallel or one panel got the pwm the other the mppt controller?)

Also nice to see, that even in puring rain you get an amperage that can be useful for something.

Originally Posted by Maine Sail

I have conducted quite a bit of head to head testing & data logging on PWM vs. MPPT. I have yet to see a PWM controller beat an MPPT. The panels in the graph below are typical Kyocera 140W panels with a Vmp of 17.7V.. Over 7 days the MPPT controller provided a 20.8% gain over the PWM even on a rated Vmp of just 17.7V.

This is one test I did in 2014:

[conachair]

Originally Posted by conachair

Great stuff
How many cells were the panels/Voc?

Don't worry - found it in the article, thanks for sharing.

36 cell looks like from the data sheet.

https://marinehowto.com/mppt-vs-pwm-solar-controllers/

[noelex 77]

Originally Posted by missourisailor

Yeah, I don't understand your comments.
I realize that a "shaded panel" offers high resistance path to other current sources, but I'm getting the impression that you are stating to hook them up in parallel and forgo the blocking diodes.

Yes. I would not recommend adding blocking diodes in most installations.

[noelex 77]

Originally Posted by wiekeith

Let's say we have two panels with two controllers, A and B. A is in sunlight, B is in shade. A applies 14v, say, because of batteries low state of charge, B comes out of shade, sees battery voltage of 14v so just applies a float charge, hence 'wasting' the available charge from its panel.

The charge algorithm for most controllers is such that the controller starting will apply the absorption voltage (say 14.5v) for the absorption time (say 2 hours) even if it measures the initial battery voltage as the 14v given in your example.

Thus the controller coming out of shade will not be in float.

Two (or more) charge controllers do not generally cause any problems or conflicts. The only issue sometimes seen is slight overcharging caused by both controllers applying their full absorption time. With adjustable controllers setting the absorption time on the shorter side (say 1hr) is usually better if multiple controllers are used, especially with more sensitive battery chemistries such as gel cells.

[john61ct]

The opposite problem, premature infloatulation, is much more frequently a problem.

When all sources have gone to float, bring one online at Absorb and see if the bank accepts a rate higher than spec'd endAmps, say .005C.

If so the Hold Absorb Time settings should be increased not shortened.

In extreme cases solar Float set = Absorb, the sun does set every day so little risk of too muchovercharging.

But as usage patterns, weather etc changes, a human with an ammeter usually needs to keep an eye on things.