Sizing Victron MPPT Controller

[Excalibur5]

Originally Posted by travellerw

Any chance you will head south?

My 15 year old panels have put out more power than they were rated for down here in the Caribbean (350W out of a 320W bank).

Personally I would size you controller %10-%15 over the maximum your panels can produce.

We will be. Mexico and the South Pacific in 2019-20. I assumed they would only produce up to their max rating only. If that is realistic the larger controller might be a good idea then.

[Excalibur5]

Originally Posted by noelex 77

The only other thing to consider is that the Victron units have a high start up voltage. Thus they are probably not a good choice for those 12v panels with lowish Voc, especially if you are in hot conditions. It is not clear if the practical effect of this limitation is significant. Some more detailed user reports would help. Certainly I am happier recommending the Victon units for high voltage panels, or at least 12v panels that have a Voc on the high, rather than the low side. Once again, details of your panels would help.

Noelex- our existing bank is (4) 75 watt Siemens panels, and (2) 90 watt Kyocera panels. They are in parallel, and yes, I know that isn’t optimal. Rewiring the panels could be really difficult though due to the wire run locations

Today, real world the small Victron 100/20 I have for my not yet installed bank (I temporarily hooked it up to check it out) said my panels were putting out between 17-19 volts, 100-190 watts depending on cloud cover.

Obviously this is late winter in Alaska so the sun is weak.

So it doesn’t look like I have any problem with enough voltage to start the controller.

[noelex 77]

Originally Posted by BjarneK

This is what the manual has to say about the 35A limit:

A higher short circuit current may damage the controller in case of reverse polarity connection of the PV array.

So it is probably not be that big of an issue if everything is wired correctly (I have never tried it myself).

Thanks for that BjarneK. If that is case, it less of a concern (providing it is wired correctly).

Interestingly, my controller handbook omits the qualification. The warning is: "A higher short circuit current may damage the controller".
Hopefully it is only during installation for all of the Victron range, but this needs some clarification.

[noelex 77]

Originally Posted by Excalibur5

Today, real world the small Victron 100/20 I have for my not yet installed bank (I temporarily hooked it up to check it out) said my panels were putting out between 17-19 volts, 100-190 watts depending on cloud cover.

That is a healthy Vmp. Cold temperatures really help and I doubt whether you will ever see any practical problems with the Victron controller not starting in these cold climates, but in Mexico or the South Pacific the voltages will be lower.

But the Vmp in the middle of the day is not really the number we are interested in. The solar panel voltage has to be 5v over the battery bank voltage first thing in the morning, when the sun will be low. The low sun angle reduces the energy and minor shadows will have more of an impact. Both of these factors will reduce the voltage from the 17-19v you are seeing when the sun is higher. The good news is the starting voltage that we are concerned with is Voc not the Vmp which the controller is reporting.

The best test is to test the solar panel voltage first thing in the morning when there is just enough brightness for the panels to start producing. If you do not have a charge source that may be running at night such as a wind generator, the highest voltage the batteries are likely to be is 12.6v. If we add 5v, the solar panel needs to be at 17.6v first thing in the morning for the Victron to start. A more realistic morning voltage might be 12.3v so adding 5v gives 17.3v. The high start up voltage becomes more of a problem with other charge sources.

If you are interested, it is also possible to calculate the likely drop in voltage you will see for different temperatures.

[chuckr]

Instead of asking here have you asked Victron? We have Blue Sky 3024i and 495w. I wanted to replace a 100w panel with a 165 for a total of 560w which is a bit more than the Blue Sky manual say. I wrote Blue Sky and had a conversation with them and they said it will handle it but no more period.


Ask Victron what they think.

[GTom]

I was wondering how well the Victron controllers can cope with a series connected array? In theory of course series should be better because of the higher voltage, but what happens in reality if one of the panels take the shadow of the boom/mast/seagull?

I am shopping for panels and there are many options on the table, the controller would like a huge high voltage panel or an unshaded array of smaller ones in series. The available real estate is quite limited, easiest would be to go with 5x80W panels, which individually (or parallel) most likely won't provide ideal voltage for MPPT but could shine in series.

[noelex 77]

Originally Posted by GTom

In theory of course series should be better because of the higher voltage, but what happens in reality if one of the panels take the shadow of the boom/mast/seagull?

MPPT is fine with "12v" panels. There is no advantages and some drawbacks connecting more than 36 cells in series (assuming a 12v battery system).

The exception is possibly with the popular Victron controllers. The unusual start up criterion of the Victron controllers creates the possibility of these controllers not starting up at the optimum time in some conditions.

These controllers are reasonably new and it unclear if this concern is theoretical, or if it is a significant practical effect.

Complicating the picture is that the best high efficiency panels are only available (with a few exceptions) as high voltage panels with more than 36 cells. As these panels have significant advantages on the number of watts per area this is often the overwhelming factor dictating solar panel choice.

[conachair]

Originally Posted by GTom

I was wondering how well the Victron controllers can cope with a series connected array? In theory of course series should be better because of the higher voltage, but what happens in reality if one of the panels take the shadow of the boom/mast/seagull?

https://www.youtube.com/watch?v=ofo1HQyGG8s

Also, a day of fiddling and I've got my victron talking signalk so should be able to graph various tests to see what goes on.

[GTom]

The outcome probably also depends on the number of bypass diodes installed. Here is another interesting bit from a fellow CF'er:

Originally Posted by wiekeith

I really can't agree with this, at least not for my panels.

I connected my 3x80watt panels in series as, living in the UK, I thought the higher voltage on poor-light days would give the the MPPT controller a fighting chance.

I was, however, concerned about all the reports on the forum warning against such a configuration, so whilst I was on a swinging mooring with a cloudless blue sky (and no mast shadowing on panels) one day last May, I though I'd find out for myself.

I firstly turned off the fridge, radio etc as I didn't want them kicking-in half was through the test. The remote display of my MPPT controller was indicating it was providing 8A at 14.2V. I then covered one of the panels with a dark green bath towel. The output current from the controller dropped drastically, then after 30 seconds or so it reconfigured itself (MPPT doing it's stuff I guess) and the controller output was providing 5.8A at 13.6V.

So, the shading dropped the power output from 113.6w to 78.9w (interestingly only a 30% reduction), but absolutely did not cripple the whole bank.

I know not where the opinion that 'series panels are killed by shading' comes from, maybe before the days of bypass diodes? But I suspect it no longer applies with modern panels, not that I'm an expert on this. It would be useful if others could try it and see what results they get.

Anyway, I'll sure test my kit in both parallel and series once I have all the components.

[john61ct]

Originally Posted by Excalibur5

Understood on everything, except what you mean by the last line. By 1:1 ratio are you referring to breaking up my 6 panels to more than one controller to help with shading decreases? Could you please clarify?

Again,

Originally Posted by john61ct

one 75/15 per panel will give greater total output when one is shaded

[travellerw]

Originally Posted by john61ct

Again,

That would be a pretty expensive way to configure his panels (6 times 75/15 controllers is about $550 off Amazon). Sure it would eliminate shading issues, but I don't think its worth it.

I think a good compromise would be 2 banks of 3 panels or 3 banks of 2 panels (I would prefer this). If there is limited shading, then I would put the panels in series. The tests I did with one of my banks showed an %8-14 increase in overall production when I wired in series. Plus with series, you can use smaller guage wire and save some costs/weight.

P.S. If you do decide on one controller per panel then the Victron 75/10 probably makes more sense and would save you $10 per controller.

[Bleemus]

John,
My Victron 100/50 doesnt have a battery temp sensor and didn't think the 30 did either. (It's only shortcoming IMHO) How do you set this up?

Cheers.

[travellerw]

Originally Posted by Bleemus

John,
My Victron 100/50 doesnt have a battery temp sensor and didn't think the 30 did either. (It's only shortcoming IMHO) How do you set this up?

Cheers.

The temperature sensor is built into the controller. This is why its best to have the controllers mounted close to the batteries. I agree this is a shortcoming of the Victron MPPT controllers. Its best to read the battery temperature from a lug on the battery.

If however, you do want a remote sensor, they do make one. I'm guessing its eyewateringly expensive.
https://www.victronenergy.com/access...-battery-sense

[basssears]

Originally Posted by Excalibur5

We will be. Mexico and the South Pacific in 2019-20. I assumed they would only produce up to their max rating only. If that is realistic the larger controller might be a good idea then.

Others have the tech side going here so I won't comment on that (I have a much smaller array), but more to the "what might happen" side of things, were you planning on puddle jumping with your "around 10 years old" panels?

Seems when that date gets close you might be tempted by newer, more efficient panels, in which case it would be a shame to be just barely undersized on the controller.

Just a thought

[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.