Too much amps for Victron Bluesolar 150/85

dekoekemoer

I have designed a 6x300W panel mobile system and the MPPT 150/70 works nicely, giving me 61Amps on a nice sunny day in Africa. I can however upgrade to a 9x300W panel system which should give me 91Amps, but the biggest MPPT available is the 150/85.

Will I get away with pushing 6 more amps, or will it damage the unit/batteries? The MPPT should have a overload protection or something, but I don't want to take chances with expensive equipment and I can't find any information regarding this.

I was thinking of using six panels on the 150/70 and three on the 150/35, but I don't know if its possible or what implications it will have on charging the same set of battery banks.

I am open to any suggestions

BB.

stA typical (good quality) MPPT charge controller can be "over paneled"--And the MPPT controller will be limited to its rated output. However, that will also limit the maximum output current from the array to the battery bank (some lost harvest).

Assuming you are in a relatively warm climate--Arrays, at warmer temperatures, output less than rated Vmp--And MPPT controllers will have less power (Pmp=Vmp*Imp) to convert. In general, I use 0.77 as a typical derating for controller+solar panels:

• 70 Amps * 29 volts charging * 1/0.77 panel+controller derating = 2,637 Watt array "cost effective maximum" array

So--It is justifiable to use a near 2,700 Watt array on a 70 Amp MPPT charge controller.

However--MPPT controllers do waste some heat (around 5%)--So, running one near/at its rated output can cause the controller to run hot (especially in a hot climate)--So running a second controller (charging the same battery bank) would help the controller run cooler--And heat is a real killer for electronics (as is thermal cycling).

Now--Back to some other questions. First, what are the Vmp and Imp ratings for your present and new panels? Most large format solar panels have Vmp~30 volts. That is too low of voltage to optimally charge a 24 volt battery bank. There are some Vmp~36 volt panels--And running that to a MPPT (or PWM) controller will work OK on a 24 volt battery bank.

You have an odd number of panels--So if you are running them in series--9 panels can only run as 1x9 or 3x3 array (3 in series, by 3 series strings). MPPT controllers have a maximum array input voltage... If your contoller has a 140-150 VDC max array input voltage (Voc-cold--Voltage open circuit cold) rating, roughly around Vmp-array of ~100 volts maximum is probably recommended--Depending on how cold it gets where you live (cold array, high Voc and Vmp voltages which could damage your controllers).

-Bill

BB.

Can you also tell us your AH rating of your 24 volt battery bank? About the minimum battery bank capacity recommended for your 2,700 Watt array would be ~539 AH @ 24 volts (that would be a 13% rate of charge) unless you have a lot of daytime loads. Too large of array can cause charging issues with your battery bank.

-Bill

Dave Angelini

Too large of an array can cause over amping issues for the battery unless your controller has the ability to limit battery charging amps. The Schneider and Outback systems do. They still produce max power but limit amps for battery charging.

dekoekemoer

Thanks for all the comments. To answer all the questions in general.

My charging capacity of 1800W goes out the MPPT at 24V and 61Amps. By using your 0.77 factor the math is out a little bit, but the panels were clean and it was the first time we switched the system on. I will definitely use the 0.77 equation in future, thanks. I still however think I am not going to get past the output current of over 85W for one single MPPT.

I use the Yingli YGE 72 cell series with Vmp of 35.8V and Imp of 8.37Amps. I am currently running my six panels on three in series and the two in parallel and I am pleased with the YGE 72 cell panels. The 9 panel system will then be three in series and three in parallel.

We have a 800 AH battery bank on 32V and control the charge with a battery management system.

When I had a look at the Solar panel spec I saw there is a new version that can go up to 325W. With how the efficiencies of the panels are increasing these days I might as well use two MPPT's from the start and just upgrade the panels as the efficiencies increase.

vtmaps

dekoekemoer said:

I was thinking of using six panels on the 150/70 and three on the 150/35, but I don't know if its possible or what implications it will have on charging the same set of battery banks.

Controllers usually have no problem sharing a battery.  They cannot share an array.   Your plan to put six panels on the 150/70 and three on the 150/35 makes sense and is a good way to upgrade.  

To repeat Bill and Dave's warning:  Watch out that you don't overheat your batteries with too high a charging current... I imagine that your batteries, being in Africa, can get pretty warm.  Do you have a battery temperature sensor?

--vtMaps

dekoekemoer

Awesome, thanks.

I have three temperature sensors in the battery enclosure and one in the electrical enclosure where the MPPT and all the comms are. The Victron temp sensor is one of the three in the battery enclosure and the other two and the one in the electrical enclosure is required by the BMS.

I have a ventilation system that switches on when one of the sensors picks up a temp higher that 32 degC and is controlled by the BMS. So during the summer in the Kalahari it runs almost 24/7, but have had no trouble yet with our lithium-ion batteries.

BB.

Li Ion batteries do change the math (minimum/maximum charging current and such)--The biggest issue is to make sure you are not over charging the batteries or taking to "dead"--Li Ion chemistry responds very badly to that.

-Bill

dekoekemoer

Yes, I only charge it to 98% capacity and never let it deplete less than 40%. This is where the BMS is champion.

Dave Angelini

dekoekemoer  are you using the samsung cells please?

dekoekemoer

No, we import our own.

South Africa

Dekoekemoer, dis so lekker om te sien ander manne van SA kom ook hier en vrae die meesters hier, hulle is goed hoor (!), en die huiswerk was reeds reg gedoen.  

BB.

"Dekoekemoer, it's so nice to see other guys SA also come here and question the masters here, they are good to hear (!), And the homework had been done right."

-Bill

Dave Angelini

dekoekemoer said:

No, we import our own.

From where? Who makes them is my question? or are you saying you make them?
I am glad that you get it Bill, but I certainly don't

dekoekemoer

Toe ek die raakloop was ek verbaas met hoe vêr agter SA eintlik is met hierdie goed. Vir nou moet 'n man maar kos op die tafel sit.

I can't answer your question yet, Dave. We are busy working on something from our side, so nothing personal haha.

South Africa

BB. said:

"Dekoekemoer, it's so nice to see other guys SA also come here and question the masters here, they are good to hear (!), And the homework had been done right."

-Bill

I am impressed Bill. 

The above would be more like this in English, typed slower:  
DeKoekemoer, it is so nice to see other SA guys seeking the assistance and advises from the solar masters here (whom are exceptionally good), especially after they have done their own homework.


DeKoekemoer, yes, these guys are unmatched from all the sites I have been to. Bill's, and others, patience is phenomenal!

Yes, back here in SA, the amount of new solar installers are creating a rather interesting problem due to inexperience.

When you learn here from experienced solar people living off-grid, batteries lasting 10+ years, applying their maths seeing the results are as close as damn to the real life output of a system, that when you speak to a solar company realizing they are missing a few rather salient key points like i.e. losses that are going to result in premature battery failure, unbeknownst to their owner, it makes one concerned.

And when the client is told about the flaw, needing to spend even more to fix it, it gets really sad.

BB.

Google Translate usually works pretty well these days.

Thank you for the kind words. We try our best here.
-Bill

Dave Angelini

Less than 1% live offgrid for more than a few years. So, yes it has always been hard to find people that know more than installing equipment. I am not taking it personal so ha ha ha yourself.
 Recently looking at the Samsung cells for a client and one of the bad things with them is you can's store them for more than 6 months. After that they are HazMat.

South Africa

Dave, from what I have read on your posts. respect.