Infini 3KW plus: Is it possible to break inverter by exceeding max MPPT input current?

[bluwater]

Hi,

I recently installed 12 Jinko panels of 320watt each along with Infini 3KW plus inverter.

I have two strings with 6 panels connected in series. And both strings are connected in parallel for a max VOC of 278V.

The short circuit current of each string is 9.05A Infini's MPPT charge controller is rated at 18amp. So if I were to combine two strings with a short circuit current of 9.05 each, the total current would go up to 18.1A. My question is.... Is it ok to combine two strings like this for a total current of 18.1A? From what I understand, current is pulled by the Inverter and it could never exceed 18amps since that is the max that the MPPT charge controller can draw.

But then when I look at the user manual there is an error code (11) for overcurrent on PV input. So that means it is possible for the MPPT to exceed 18amps which will throw the error code.

I would like to hear your thoughts on this.

[___]

3 hours ago, bluwater said:

But then when I look at the user manual there is an error code (11) for overcurrent on PV input. So that means it is possible for the MPPT to exceed 18amps which will throw the error code.

Speaking from a Victron perspective.If you think about how an MPPT works: It is essentially a buck converter, usually running a square wave somewhere between 40Khz and 150Khz, and it controls the effective series resistance (ie the impedance the PV panel sees) by adjusting the mark/space ratio of that square wave. By adjusting the ratio smoothly and slowly, it can generally stop short of the MPP (maximum power point) if moving up further would exceed the capacity of the device. And this is what most of them does.

However, it is possible that changing light conditions can push it over faster than it can pull back. Imagine you're getting 900W/square meter insolation, and a thin white cloud passes on the edge causing what is called cloud edge effect, and this jumps to 1100W/square meter, or by about 20%. An MPPT that was tracking the maximum point at 90% of its capacity will instantly find itself at 110% while essentially tracking precisely the same power point. When this happens, most chargers detect this event as an overcurrent event, and will generally switch off and start from the beginning. I've never seen it damage the charger.

This is however one reason why I don't advocate oversizing of more than about 20%. It is plain common sense that if you push this too far, something is going to blow.

In your case, I see no reason for concern. You are only very slightly oversized.

This again brings us into somewhat of a technical domain, and if this is boring, you can stop reading.

At least for the BlueSolar and SmartSolar devices, there are broadly two kinds of devices. Some have a software limiter. These include the smaller and/or older devices, like the 75/15, 100/15, 150/35, even some of the rev2 controllers. Some of these even have a user-replaceable fuse. If the overcurrent event is a bit too severe, it simply pops the fuse. They avoid overcurrent in software, and if such an event happens (and doesn't pop the fuse), it simply switches off and starts over.

Then there are some of the nicer newer controllers, such as the newer 100/30, and the 150/45 and 150/65 controllers. These have a hardware current clamp. They simply won't go more than their rating.

[bluwater]

Thanks for the detailed explanation. This puts my mind at ease.

[___]

I wanted to add last night that one has to remember that a fuse doesn't blow the moment you exceed the limit. It can survive at 110% for ten minutes usually. The MPPT itself will usually detect the overcurrent event within seconds though, so I have never even seen a controller blow a fuse. Of course I am speaking of a different brand here, but I would expect that any electronic engineer worth his salt (and who added an overcurrent event to the firmware!) would do the same thing.

[seant]

Like with the 150v 80A outback controller it will go over the max input rating ,( by how much I'm not sure) and clips the output current to a max of 80A. You can even set the max output amps lower if needed

[SilverNodashi]

2 hours ago, plonkster said:

I wanted to add last night that one has to remember that a fuse doesn't blow the moment you exceed the limit. It can survive at 110% for ten minutes usually. The MPPT itself will usually detect the overcurrent event within seconds though, so I have never even seen a controller blow a fuse. Of course I am speaking of a different brand here, but I would expect that any electronic engineer worth his salt (and who added an overcurrent event to the firmware!) would do the same thing.

I have seen MPPT's with blown fuses, though it is rare. Even on the Victron's I have seen it. 

[___]

16 minutes ago, SilverNodashi said:

I have seen MPPT's with blown fuses, though it is rare. Even on the Victron's I have seen it. 

With a very large array I could easily imagine it. I've run a 100/15 on a 150% sized array before and though it did not pop a fuse I was sort-of amazed that it didn't. It ran at around 14.3 ampere on a sunny day, I suspect it derated the current a bit because it was running so hot (they are rated at 40°C, above that it starts to back off). But sometimes fuses just blow even though the current was fine. It happens.

[SilverNodashi]

26 minutes ago, plonkster said:

With a very large array I could easily imagine it. I've run a 100/15 on a 150% sized array before and though it did not pop a fuse I was sort-of amazed that it didn't. It ran at around 14.3 ampere on a sunny day, I suspect it derated the current a bit because it was running so hot (they are rated at 40°C, above that it starts to back off). But sometimes fuses just blow even though the current was fine. It happens.

No, quite the opposite. I often see this when the PV ampere is very close to the fuse rating, and I guess it happens with cloud edge effect. So, I always prefer to use the next size fuse, if it's replaceable, or the next size MPPT. i.e. with a 8.36A PV I would use 12A fuses, and not 10A. 

[___]

16 minutes ago, SilverNodashi said:

So, I always prefer to use the next size fuse

The fuse I speak of is integral to the controller. The 20A one there on the left.

[SilverNodashi]

Just now, plonkster said:

The fuse I speak of is integral to the controller. The 20A one there on the left.

I know  That's exactly the one I am talking about. So with 2x 8.6A panels, it could go over the 20A limit. I replace them with 25A fuses when they blow, and so far no issues at all. 

[Guest]

7 minutes ago, SilverNodashi said:

I replace them with 25A fuses when they blow, and so far no issues at all. 

I thought that the fuse the manufacturer put in, was to protect the internal stuff? Upping the fuse does solve the problem nicely, but what is the other side of that?

 

Reminds me of the early days, I used car fuses on the solar panels, was early days and DC fuses where scarce and very expensive. So each time I walked past the system, I smelt hot plastic. Turns out the fuses I used ... don't use car fuses no. 

Used these:

[___]

3 minutes ago, The Terrible Triplett said:

I thought that the fuse the manufacturer put in, was to protect the internal stuff? Upping the fuse does solve the problem nicely, but what is the other side of that?

On a 15A controller, one that derates as it gets hot in any case, I would not swap the 20A fuse for a 25A. If you do that, it might take several minutes at 30A (double the rating) before a fuse blows. a 20A fuse already has some margin built in.

The other possibility is that you are simply using the wrong fuse. There are fast- and slow-blow models. Sometimes you are supposed to use the slow-blow one.

5 minutes ago, The Terrible Triplett said:

don't use car fuses

The bigger danger with automotive fuses is they are not rated for the voltage. Nothing more than 32V. And close to the rated capacity they will get hot, so don't cheap out on the holder. Mostly though... just get a 32A DIN mount holder, it's not that expensive.