Sizing Victron MPPT Controller

[mitiempo]

Originally Posted by moseriw

PLEASE DISCUSS THIS WITH A GOOD ELECTRICIAN:

mine threw out the MPPT and replaced it with 2 PWM's
for a good reason. The charge improved from 8 Amps max to 18 Amps.

Could you explain that result?

[john61ct]

Originally Posted by moseriw

PLEASE DISCUSS THIS WITH A GOOD ELECTRICIAN:

mine threw out the MPPT and replaced it with 2 PWM's
for a good reason. The charge improved from 8 Amps max to 18 Amps.

I haven't met an "electrician" yet that's really up to speed on solar, except for a very few very rare specialists.

And I can't think of many scenarios where that result would make sense, certainly not as a result of PWM being "better" than MPPT.

[basssears]

Originally Posted by john61ct

I haven't met an "electrician" yet that's really up to speed on solar, except for a very few very rare specialists.

I wholeheartedly agree...

Originally Posted by john61ct

And I can't think of many scenarios where that result would make sense, certainly not as a result of PWM being "better" than MPPT.

Wild ass guess here, but I would imagine the improvement had a lot more to do with there being two controllers instead of one and therefore overcoming some potential shading issues?

Other possibility is I've heard you don't realize as much of the gains from MPPT if you run 12v panels, if you are running higher voltage (either native higher voltage panels or putting some in serial) it seems you get to use more of the advantages of the MPPT controller.

-- Bass

[GTom]

Originally Posted by moseriw

PLEASE DISCUSS THIS WITH A GOOD ELECTRICIAN:

mine threw out the MPPT and replaced it with 2 PWM's
for a good reason. The charge improved from 8 Amps max to 18 Amps.

Wow, that one will beg for an explanation. My guess is something similar as Bass explained above: one panel regularly gets partially shaded and they were wired in series. This killed the output in the first case because of the one single controller (regardless MTTP or PWM). Two controllers help a lot in such a situation.

[Davidhoy]

Originally Posted by Suijin

Since they are already wired in parallel another option is to get two smaller Victron controllers and separate it into two banks. This might give you better overall performance if you have any shading issues or the panels are not all oriented on the same plane.

This! Multiple MPPT controllers gives you many advantages.
1. Redundancy
2. Parallel panels reduce effects of shading
3. Locate the controllers close to the batteries, and you can run smaller gauge wires from the panels to the controllers.
4. Redundancy ;-)

I personally have two SmartSolar MPPT 100/30 controllers, but I have two big 350 watt panels, so I do have one per panel.

-David

[wrwakefield]

We were able to fit 2- 165W and 1- 125W panels on our ketch. We decided to go with a separate Victron 75-15 controller [with built-in BlueTooth (BT)- no dongle needed] for each panel to optimize gain in shaded situations and for hardware redundancy [we frequent remote locations...]

One Victron controller replaced a BlueSky 2512i MPPT controller on the legacy 125W panel- mainly for the wireless [BT] reporting capability of the Victron. [The BlueSky will replace an existing PMW controller on the 200W camper solar array....] The other two Victron controllers are in use with the 2 new 165W panels.

Outputs seem to be optimized in this configuration as sun-shade-sun-shade cycles throughout the day between 57° and 62°N [our current cruising grounds...]

Note my mention that the Victron controllers we purchased are now available with built-in BlueTooth- no dongle necessary.

Best wishes working out what is best for your set-up.

Cheers! Bill

[basssears]

Originally Posted by wrwakefield

Note my mention that the Victron controllers we purchased are now available with built-in BlueTooth- no dongle necessary.

Love the Bluetooth functionality, always thought not having it built in was cheap, nice to see they have it all as one now.

Cheaper at PKYS though ($118):
Victron Energy MPPT 75/15 Smart Solar Charge Controller with built-in Bluetooth

-- Bass

[Emouchet]

If panel output voltage is 18v or under, MPPT will,not bring much more compared to PWM.


MPPT is useful when output voltage for the panels is much higher than battery charge bulk voltage.


MPPT will "convert" higher voltage to lower suitable bulk voltage and increase driving current.


PWM is simply operating as an on/off switch, so that average voltage is equivalent to bulk voltage.


So if panel output voltage is close to battery bulk voltage, MPPT does not bring much gain.

[Suijin]

Originally Posted by Emouchet

If panel output voltage is 18v or under, MPPT will,not bring much more compared to PWM.


MPPT is useful when output voltage for the panels is much higher than battery charge bulk voltage.

Correct. For my information on choosing PWM vs. MPPT controllers based on your panels and the environment in which you sail, check out this white paper from Victron. This is the summary, a link to the full white paper is at the end of the summary (which is probably all you want/need to know anyway).

https://www.victronenergy.com/blog/2...r-pwm-or-mppt/

I love the bluetooth functionality of the Victrons. That said, it's not as easy as just looking at a panel readout. The real value of them is the historical data and some of the configuration options.

[GTom]

Originally Posted by Suijin

Correct. For my information on choosing PWM vs. MPPT controllers based on your panels and the environment in which you sail, check out this white paper from Victron. This is the summary, a link to the full white paper is at the end of the summary (which is probably all you want/need to know anyway).

https://www.victronenergy.com/blog/2...r-pwm-or-mppt/

I love the bluetooth functionality of the Victrons. That said, it's not as easy as just looking at a panel readout. The real value of them is the historical data and some of the configuration options.

Maybe I am looking at the wrong place but I can't find a specific graph for each Victron controllers on their efficiency vs input voltage? E.g. how much would a 75/15 model profit from a 24V (Vmpp=36V) panel vs a 12V (Vmpp=18.5V) one?

[noelex 77]

Originally Posted by Emouchet

If panel output voltage is 18v or under, MPPT will,not bring much more compared to PWM.

18v is a higher Vmp than will commonly be seen in practice with "12v" panels, but at this voltage conversion to 14.2v would produce a 27% improvement. The real improvement will be a little less than this for complicated reasons, but there is still a healthy margin.

If you have "12v" panels, connecting more panels in series to produce a higher voltage will, I think, be counterproductive on a boat. There is some question mark over the ability of the Victron units to start up correctly with "12v" panels, which is perhaps why they are encouraging the higher voltages, but this limitation does not apply to most controllers.

Of course, if you have higher voltage panels there is no choice but to use MPPT controllers. They will not work very well at all without the voltage conversion inherent in MPPT controllers.

[noelex 77]

Originally Posted by GTom

Maybe I am looking at the wrong place but I can't find a specific graph for each Victron controllers on their efficiency vs input voltage? E.g. how much would a 75/15 model profit from a 24V (Vmpp=36V) panel vs a 12V (Vmpp=18.5V) one?

A simple way to look at this problem is if you had two "12v" 36 cell panels with a MPPT controller, would you be better connecting them in series or in parallel. I think the overwhelming evidence (although more comparisons would be helpful ) is that on a boat parallel connection is better.

There is more of question mark over the Victron controllers. It would be nice to see some independent reports comparing series and parallel connection with 12v panels. I suspect parallel connection would still win but this is subject to a few qualifications.

Of course high voltage panels are electrical identical to multiple "12v" panels connected in series.

[GTom]

Originally Posted by noelex 77

A simple way to look at this problem is if you had two "12v" 36 cell panels with a MPPT controller, would you be better connecting them in series or in parallel. I think the overwhelming evidence (although more comparisons would be helpful ) is that on a boat parallel connection is better.

Isn't that more dependent on the number and quality of the bypass diodes?

There is more of question mark over the Victron controllers. It would be nice to see some independent reports comparing series and parallel connection with 12v panels. I suspect parallel connection would still win but this is subject to a few qualifications.

I am with you on this and once I got my kit I'll do some testing @controlled conditions (it seems it'll be 4x100W panels, the 100/30 controller already arrived - I ordered that one first and until now I was devoted to a single large panel).

Of course high voltage panels are electrical identical to multiple "12v" panels connected in series.

Exactly, a single solar cell produces 5-600mV open circuit, one can do the math how many are in series in a certain panel. Actually I am surprised to see 100W panels with 42V oc. voltage.

[noelex 77]

Originally Posted by GTom

Isn't that more dependent on the number and quality of the bypass diodes?

The number of bypass diodes influences the performance when the panels are connected in series, but even if you use panels with a high number of bypass diodes and install additional bypass diodes between the panels (as you should do in series connection), the results still stongly favour parallel connection.

The internal bypass diodes are primarily installed to protect the cells from overheating. Due to changes in the way solar panels are constructed, the number of internal bypass diodes is reducing. For example, some of the old Kyocera panels had eight bypass diodes, even on 50w panels. Modern Sunpower panels have three bypass diodes, even on their large 360w panels.

[travellerw]

Originally Posted by noelex 77

A simple way to look at this problem is if you had two "12v" 36 cell panels with a MPPT controller, would you be better connecting them in series or in parallel. I think the overwhelming evidence (although more comparisons would be helpful ) is that on a boat parallel connection is better.

We have a small bank (200W) of cheap Chinese panels (HQST brand). They have a VMP of 16V so essentially 12V panels. They are connected to a Victron 75/15

After reading numerous posts here (and watching the Wynns video), I decided to try them connected both ways. My experience has been about an %8 increase when the panels were connected in series. However, that was only over a 1 month period and the increase could be due to weather of course. However the series test was done in January and the parallel test was done in Feb, so you would think parallel should have had the advantage.

One thing I did notice straight away is when connected in series, the panels were able to achieve their rated output at times. When connected in parallel, they never achieved their full rated output (200W) even once in the month.

The other thing I noticed was my panels do not act anything like the panels in the Wynns video. Although there is power loss when shading occurs it was MUCH less dramatic then the video showed when connected in series. Maybe its because I watched real life shade (e.g. the mast shadow) and didn't artificially try to create shade. I just let my boat naturally provide the shade, while I watched the Victron app to see the impact.

Not sure how definitive these results are, but choose to switch everything back to series.