MASSIVE Overpaneling -MPPT input current

[timselectric]

I'm not saying that overpaneling is efficient.
I'm just saying that it doesn't hurt anything.

 

[robot_zombie]

Mppt regulates the input by raising the voltage, if you look at the curves of any panel, past the maximum point the power drops off a cliff. By this method the controller isn't burning off power, it just isn't produced. Even the largest array can easily be reduced to essentially zero. Hence why you should design a little headroom to Voc and following limits here is very important.

 

[squowse]

Ahh I see what youre asking now. The SCC will see a short circuit when the panels short circuit. So technically if there’s never a short circuit I would assume everything would work fine and just clip the excess power above 20A. If you’re worried about damage to the SCC just add a 20A fuse before the controller to ensure you never exceed the limit of the SCC. I’m honestly not sure if the controller will see any damage otherwise, but I’d assume running it at 100% of its capability won’t help it last long.

controller will blow before the fuse does

 

[timselectric]

Mppt regulates the input by raising the voltage,

Actually it only controls the draw (amperage).
It raises the load (amperage) which pulls down the voltage.
There is a point where the draw pulls the voltage down enough to actually lower the output (wattage). At that point, it backs off on the draw (amperage).
It monitors the wattage, and tries to keep it at optimum output.
It's a constant balancing act.

 

[robot_zombie]

Actually it only controls the draw (amperage).
It raises the load (amperage) which pulls down the voltage.
There is a point where the draw pulls the voltage down enough to actually lower the output (wattage). At that point, it backs off on the draw (amperage).
It monitors the wattage, and tries to keep it at optimum output.
It's a constant balancing act.

ah yeah makes sense, as the draw falls close to zero the voltage rises up. I was just back to front hehe

 

[wpns]

We just had this discussion: https://diysolarforum.com/threads/voltage-limiting.82772/#post-1073877

TL;DR: Victron (and AFAICT only Victron) has (in addition to the reverse polarity issue) other edge cases where you can blow up the circuits if your Isc for the string exceeds the INPUT current maximum. So, just know that when you are designing the system, other than that they seem like fine SCC devices.

 

[SoakedUp]

controller will blow before the fuse does

Why would the controller blow before the fuse if the fuse is before the controller?

 

[wpns]

Why would the controller blow before the fuse if the fuse is before the controller?

It's a speed-of-damage thing. The fuse has to overheat and melt to open, while the electronics can just break down and short out and fail within milliseconds

 

[timselectric]

The SCC will never see short circuit current, unless it shorts internally.
Which means that the SCC has already failed.

 

[underdog5004]

I was doing research on my Outback FM 80 charge controllers and found that Outback recommends no more than 64 amps of solar coming into their 80 amp output charge controller. I forget the percentage I think it was 80% of output as input.

 

[Zsiger]

First, thank you for all replies!

Sorry guys but I still see some contradiction.
I'm not a professor so please forgive me if I miss something, but...

1. I = U / R. So if the huge 15kW array is fix 80V the current will change by the resistance. In simple: like the grid 230V AC output in your wall. You can connect 1W and 5000W load too. The current is based on the load (on it's resistance).

2. Based on the 1. point: power is DRAWN by the loads, not PUSHED by the source. Back to the previous example: the 230AC grid doesn't PUSHING power into your house and a simple cheap light bulb or a phone charger doesn't have to fight against that. They are safe to use.

3. Staying on the 230AC example: short circuit only occour by a mistake or a failure, never on purpose. That is why we have protection (fuse, breaker....).
When happens it in a solar system? Only when something bad happens? Bad wireing for example? I read something like:

"the limitation is a protection mode where, in order to stop power output from the panel, the MPPT will short circuit the PV input"

What? Short circuiting a solar array (or the 230AC grid) seems strange for me. That's a thing you never wanna do. Not?
It's not stopping the panels output, just stop the current flow into the MPPT. But for me, it not seem a safe mode. Short circuiting a big array means all it's power converted into heat in the panels, not?


4. What is the exact physical limit if all previous mentions are right? The MPPT's working method? The MPPT searching the arrays max potential even if it is way higher than the SCC's needs? The semiconductors somehow demaged when they are able to pull more power? What is the exact method of setting/controlling the input current?

Please keep in mind I'm interested in the physics, the ,,how?,, and the ,,why?,,.
In this specific topic I don't care about cost or is it worth or not.
Sorry for still writing, but still didn't get the answers I'm looking for.
Thanks for all the ,,never exceed the numbers in the manual,, comments, but (with respect) I can read too, and I always test, build everything by those rules or recommendations.
All I'm interested is the raw physical reasons, ,,whys?,, .
I am interested in why a SCC wants to pull 20kW of power if it doesn't need it for anything.

Thanks!

 

[ricardocello]

What? Short circuiting a solar array (or the 230AC grid) seems strange for me. That's a thing you never wanna do. Not?
It's not stopping the panels output, just stop the current flow into the MPPT. But for me, it not seem a safe mode. Short circuiting a big array means all it's power converted into heat in the panels, not?

When solar arrays are shorted , they are supplying 0W. Because the voltage drops to 0 and power = volts* amps
Only some minor heating in the panels will occur.

 

[sunsurfer]

When the 100/20 SCC (Solar Controller) @ 48V is limited to
100VDC, 1160W MAX input and 20A.
Exceed the PV Voltage & Max Amps it will fry the fuse hopefully before the SCC. Victron does NOT have HyperVOC capability which does allow for slight over panelling. But it isn't much.

Hmmm, thats the charge controller I want to use. I am wanting to use 300w panels in a 2P 2S. Panel VOC is 39volts and ISC is 9.8amps. I wonder if its to much on a good cold sunny day?

 

[pollenface]

Things happen. And when they do, I like my expensive equipment to have a chance at surviving.

I know right

I nearly burnt a motorbike to the ground because i wired a charging cable wrong. Positive and negative. Red and black. Who'd have thought that would be so easy to mess up?

 

[wpns]

First, thank you for all replies!

Sorry guys but I still see some contradiction.
I'm not a professor so please forgive me if I miss something, but...

1. I = U / R. So if the huge 15kW array is fix 80V the current will change by the resistance. In simple: like the grid 230V AC output in your wall. You can connect 1W and 5000W load too. The current is based on the load (on it's resistance).

2. Based on the 1. point: power is DRAWN by the loads, not PUSHED by the source. Back to the previous example: the 230AC grid doesn't PUSHING power into your house and a simple cheap light bulb or a phone charger doesn't have to fight against that. They are safe to use.

3. Staying on the 230AC example: short circuit only occour by a mistake or a failure, never on purpose. That is why we have protection (fuse, breaker....).
When happens it in a solar system? Only when something bad happens? Bad wireing for example? I read something like:

What? Short circuiting a solar array (or the 230AC grid) seems strange for me. That's a thing you never wanna do. Not?
It's not stopping the panels output, just stop the current flow into the MPPT. But for me, it not seem a safe mode. Short circuiting a big array means all it's power converted into heat in the panels, not?


4. What is the exact physical limit if all previous mentions are right? The MPPT's working method? The MPPT searching the arrays max potential even if it is way higher than the SCC's needs? The semiconductors somehow demaged when they are able to pull more power? What is the exact method of setting/controlling the input current?

Please keep in mind I'm interested in the physics, the ,,how?,, and the ,,why?,,.
In this specific topic I don't care about cost or is it worth or not.
Sorry for still writing, but still didn't get the answers I'm looking for.
Thanks for all the ,,never exceed the numbers in the manual,, comments, but (with respect) I can read too, and I always test, build everything by those rules or recommendations.
All I'm interested is the raw physical reasons, ,,whys?,, .
I am interested in why a SCC wants to pull 20kW of power if it doesn't need it for anything.

Thanks!

Solar panels aren’t a normal power source. Think of them as a voltage source (Voc) with a built-in current limiter (Isc).

Yes, most MPPT inputs will just draw less current and allow the voltage to rise, but Victron for some reason works differently.

 

[timselectric]

but Victron for some reason works differently.

I used to think this, too.
But actually they are the same. (Just more paranoid)

 

[wpns]

For some reason I wasn’t invited to their engineering review meetings, so all I can do is go by their published specs and warnings and forum posts.

 

[Vigo]

My basic understanding of this is that anything that PWMs to control ‘average’ current actually flows far more during its ‘on pulses’ and if the math works out that your source vs your load would equal a damaging amount of current, the control has no way to implement a reaction to that without letting it flow at least one time. If that one time is all it takes to smoke the components, the current limiting strategy never had a chance.

May be complete BS.. Its what my car mechanic brain can muster with current education level.

 

[timselectric]

I don't know enough about PWM controllers to comment comfortably.
But I can definitely see how overpaneling could be a problem for them.
Their ability to switch on and off the current is limited by what the parts they are made of can handle.

 

[rogerdw]

2. Based on the 1. point: power is DRAWN by the loads, not PUSHED by the source.

My basic understanding of this is that anything that PWMs to control ‘average’ current actually flows far more during its ‘on pulses’

I don't know the answer to the OP but I see an MPPT as "ALLOWING" power through ... not DRAWING it ... or having it PUSHED.

If that is the case, then the analogy of a load plugged into a normal AC outlet should apply. As long as the voltage max is not exceeded.

Anyone wanna experiment and try out their favourite SCC?