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Roman Le Houelleur avatar image

SmartSolar Maximum input current

Hello there, the smartsolar 100/30 datasheet says:

1a) If more PV power is connected, the controller will limitinput power

2) A PV array with a higher short circuit current may damage the controller

Am i the only to see a contradiction here ? Maybe 1a) holds for high voltage and current within limit (serial connection) ? My understanding of 2) is that several PV in parallel will damage the controller. Or maybe that's me begin stupid this morning ... Anyone cares to clarify ? thanks !


MPPT - Solar Charge Controllerinput current
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I have always learnt that when it comes to input on the Victron MPPT controllers, what is important is to NOT exceed the maximum voltage, in your case 100V.


But that you can put as many PV in parallell as you want, because the controller will then just limit the current.


I hope someone from Victron can clarify this here, because I agree with you, there seems to be a contradiction in the datasheet...

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Mark avatar image

Max power, max voltage and max current are 3 different things, even though P=VxI.

The MPPT has contol over how much power to draw from the PV array - so there is no problem with having a PV array that has a higher max 'power' then the MPPT can use.

The MPPT can easily control power by reducing the charge current delivered the battery, as a result the PV voltage will increase closer to the open circuit voltage and the solar panels will operate at a less efficient point on their power curve.

When assessing the suitability of a solar array for a particular MPPT, the primary specification to check is the maximum PV voltage limit. Ensure that the PV array Voc (open circuit voltage) rating is at least 5 to 10% below the MPPT limit. This is to protect for a scenario with very cold temperature combined with very high irradiance - as the PV Voc rating can be exceeded in the right conditions.

The other specification to check is the maximum PV current limit. Also ensure that the PV array Isc (short circuit current) rating is below the MPPT limit.

Providing these 2 criteria are satisfied, then you can basically install as much 'theoretical' PV power as you want. More PV power is great for overcast days, as you can still have decent solar yield when the solar conditions are unfavorable. Under good conditions the extra power just won't be utilized.

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Ruben avatar image

Hi Guys, I am new on this forum, but I would love to hook on into this topic, because it concerns me as well and I find it as confusing as @Roman Le Houelleur finds it as well.

And most important, I did not find a proper answer till know, with a clear explanation WHY/ HOW the MPPT is limiting currents... To be clear, we All know and accept that the Voltage limit (Voc) shall never be higher than the MPPT allows...

I just summarize here the raised question by Roman and some answers 'he' got till now:

"1a) If more PV power is connected, the controller will limitinput power

2) A PV array with a higher short circuit current may damage the controller"

I just downloaded version 06 (september2, 2019) of following Manual https://www.victronenergy.nl/upload/documents/Manual-BlueSolar-charge-controller-MPPT-75-10-75-15--100-15-EN-NL-FR-DE-ES-SE.pdf:

this manual tells the same as @Klim8Skeptic found, which sounds for me quite clear and logic (but please confirm) --> I undestand it as: The MPPT is able to regulate PV Voltage/ Currents in order to find best performance... however, in case of a bright summer day in combination with more PV power installed then the rated PV-Power of the charge-controller, the MPPT needs to limit its current to the maximum (e.g. 15 Amps for the MPPT 75/15) and the voltage might climb to Voc voltages, resulting in a fixed/ limited maximum output POWER which is again limited by the used charge-controller in combination with a certain battery-bank voltage.


BUT, when I download the Datasheet of the same MPPT (No publication date mentioned, Datasheet-Blue-Solar-Charge-Controller-MPPT-75-10,-75-15-&-MPPT-100-15-EN.pdf), the explanation to foot-note 2, is limited to which makes it confusing again (Maybe Victron thought to keep it short and simple for the spec. sheet and therefore left out some important details?!)So, @Lucian Popescu (Victron Energy Staff), are your sure about your comment "Hi, input current is also very important, don't go above the specified value because you will blow the mosfets from the MPPT", please confirm internally, or could you explain in more detail, why the MPPT would not be able to limit it's PV-current to the alowable max. value? , because I do not believe (up till now) that it will blow its MOSFETS.... (I could change my mind, but need better clarification about this matter :) !)

I Also partly agree on @Marks explaination about fullfilling 2 criterias (especially on Voltage part), but regarding the Current limit I do not believe that is is needed to stay below that limit (as the MPPT should be clever enough to limit it to it's max. value... But, okay we should not install the PV-with reversed polarity,...(what you should never do of coarse :) )

@Mark wrote: "The other specification to check is the maximum PV current limit. Also ensure that the PV array Isc (short circuit current) rating is below the MPPT limit. Providing these 2 criteria are satisfied, then you can basically install as much 'theoretical' PV power as you want. More PV power is great for overcast days, as you can still have decent solar yield when the solar conditions are unfavorable. Under good conditions the extra power just won't be utilized." --> But again, Why do you mark believe that we may not overdesign Isc? How would it harm the controller (not talking about reverse polarities), how would the MPPT drain higher PV currents than its own limit? It is a MPPT though, regulating the Voltage and Current right?, maybe a PWM could be damaged in such a case (please confirm)?



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Wingphil avatar image

Personally I don’t think it’s confusing. Power and current are only related by voltage.

You double power by doubling voltage for a given current, yes increasing current at the same voltage also increases power, and at a greater rate. But it’s voltage and current that relate to power not either one on its own. A Combined relationship the national grid are totally dependent on.

And that is how I read the spec sheets as someone new to pv power systems

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You double power by doubling voltage for a given current, yes increasing current at the same voltage also increases power, and at a greater rate.

You might want to review/edit the last 5 words.....

Fideri avatar image

Thanks all. I see now that I’m going to wire some PVs in a series, which is not the most efficient way for my roof. That will ensure that I don’t exceed the Wp, ISC and VOC capacity of the 250/100-Tr chargers.

@klim8skeptic, I was planning 4 parallel strings of 10 PVs each, which would give me 3200Wp, 46.4 PV volts and 56.2 batt bank + 5 volts. In my mind, that would work. I now know better as the ISC would be 90.5A, way above the charger’s ISC limit of 70A.

Fideri

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Fideri avatar image

Thanks Matthias for the reply.
My panels are Jinko, 320 Watts each. I have 20, with intentions of buying 20 more. I already have two 250/100 and was planning to get two more for 48 volt batt bank.
I can certainly wire some of them in a series. That wasn’t the plan because of the layout of my roof and other issues. Back to the drawing board.
My humble request is that Victron makes this limitation clear, like the voltage limitation.
Fideri

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You are going to have to wire your panels at least 2 series, to be able to charge a 48v battery.

If you extend the maximum Voc or Isc you can/will damage the controller.
As long as you below these values you can connect as much panels/power as you want, the MPPT will give you a maximum of 100A charging current.

Fideri avatar image

Sorry to resurrect an old question. The comments here and official documentation is still contradictory.
To summarize, my Victron Installer says my 250/100-Tr Charger doesn’t care how I wire my pv panels provided the array voltage and my batt voltage + 5 volts is less than the 250 volts my charger allows. All good so far as the documents downloaded on the Victron website and most of the comments here say the same thing. But according to Mark (accepted answer) and Lucian of Victron, I should also look at the charger’s “PV Max Current” which for the 250/100-Tr is 70A. Who is right? The official documentation certainly gives the (wrong?) impression that the pv current doesn’t matter to the charger while pv and batt voltages matter.
My pvs have 46.4 volts or VOC and 9.05A ISC or short circuit current. That means I can’t wire 10 of them in parallel (46.4 voltage and theoretically up to 90.5A ISC) as I was planning to.
To a common man, it is wrong to say both that the charger will limit the input “power” and that the charger might be damaged if an array goes beyond the charger’s current rating, as identified by Roman. They both can’t be correct. The public manuals on the Victron public website still say that.
As a side note, under what circumstances may I take advantage of my Charger’s 100A charge current?

Fideri


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@Fideri

What panels do you have exactly?
Depending on the V temp. coeff and the lowest temperature at you place, you can connect 4 or 5 panels in series and 7 strings in parallel.

e.g. you have 300Wp panels 4S 7P -> 8400Wp PV-power -> the MPPT will limit the charging power to about 5800W.

https://www.victronenergy.com/mppt-calculator

One reason for the limitation is a protection mode where, in order to stop power output from the panel, the MPPT will short circuit the PV input. It's likely via the MOSFETs which have to handle the resulting current from the panels.


This mode can be triggered by battery voltage anomalies but there are probably other reasons.



klim8skeptic avatar image

Always check the latest manual. https://www.victronenergy.com/upload/documents/Manual-SmartSolar-charge-controller-MPPT-100-30---100-50-EN-NL-FR-DE-ES-SE.pdf

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



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Good catch klim8 ! This certainly adds to the confusion .... is Lucian Popescu right in his comment below with mosfets or is it only in case when reversed polarity ? Hopefully Mark & Victron team will understand the need for a clarification & correction of manuals/datasheets.

Lucian Popescu (Victron Energy Staff) avatar image

Hi, input current is also very important, don't go above the specified value because you will blow the mosfets from the MPPT

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Roman Le Houelleur avatar image

Thank you Mark for taking the time to answer, unfortunately that was not the question. I believe that either 1a) or 2) in the datasheet is not correct. Exemple: let's say I have 10 benq sunforte 330 connected in parallel at the input of a smartsolar 100/50. This is potentially more PV power than the controller can accept but from "1a)" I can expect the controller to limit power input. However the total Isc is about 65A, well above the 50A limit of the controller, and according to "2)" that may damage the controller.

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Hi Roman,

It may seem 'unusual' to you but there is no contradiction.

The MPPT short circuit current limit is also an independent rating and only applies to the input/PV side of the MPPT.

If you take a look at all the Victron MPPT data sheets you will find that it is sometimes lower, equal or higher than the MPPT max charge current.

For the 100/50 model the Isc limit is 60A according to the data sheet.

So for this particular MPPT it's perfectly fine to connect a PV array with a Isc of upto 60A, more than 60A is NOT permitted and can cause damage to the MPPT hardware.

But realistically, even if you had such a setup (with PV Isc somewhere between 50 to 60A) the PV array will almost never provide such a high current (over 50A) during operation. This is because it's also a function of the MPPT output/charge current and because the PV array voltage must always be higher than the battery voltage.

With most setups the MPPT Isc limit is normally well above the Isc of the PV array, this is because its good practice for the PV array to have a Vmp/Voc well above the battery voltage (>2x). Therefore for the same PV power the PV current is far lower.

Mark, thank you but talking about good practices doesn't help and makes your answer difficult to read.

If you read the datasheet like "the input limitation is 1a) AND 2)", then it's ok, no contradiction. But as an educated user I am telling you that the way it is written is confusing.

My proposal is to modify 1a) to something like: "If more PV power is connected, and total Isc is lower than PV short circuit current, the controller will limit input power"

Also, rather than "PV short circuit current" I would simply talk about "max input current"

But that is my humble opinion. cheers