Charge Controller PV Input Limits

[haycord]

I have seriously researched this but still cant get it. I do understand the obvious Max Voc limit for a Controller but I can't understand the 'why' behind the Max PV Input power limit. I must be wrong when I look at the Controller as any other normal 'electrical load' in that it would only pull the required current for the load regardless of a grossly oversized supply.
Take the Epever Tracer 40A for example: the Voc is 100V and the Max Input is 1040W/24V. I'm hung up on why an Array exceeding the 1040W would be a problem. My (apparently wrong) thinking is even if the Array was sized to 1400W the Controller would never pull more than the 1040W so nothing gets damaged. Please help me understand.

 

[sunshine_eggo]

IIRC in the older manuals, they allowed a 150-200% over-paneling allowance. I don't see it in the current manual.

 

[Suijkerbuijk]

If the watts go up means the amps go up to.
A solar panel will try to set that to the mppt.
The mppt can not handel this and will burn out by over heating .

That is told by epever on the email
Wy i ask them is that my epever can handel 260watts on 12 volt battery and i use 300watts solar pannel.
Now are my panels flat on the boat so i never will have that max of 260 watts
Max what i have from them is about 225watts.
So i'm in the specs of the charger.

 

[Texas-Mark]

A solar panel will try to set that to the mppt.
The mppt can not handel this and will burn out by over heating .

The controller should only "draw" what it can handle. A solar panel can not "push" more amps than that.

 

[timselectric]

I have seriously researched this but still cant get it. I do understand the obvious Max Voc limit for a Controller but I can't understand the 'why' behind the Max PV Input power limit. I must be wrong when I look at the Controller as any other normal 'electrical load' in that it would only pull the required current for the load regardless of a grossly oversized supply.
Take the Epever Tracer 40A for example: the Voc is 100V and the Max Input is 1040W/24V. I'm hung up on why an Array exceeding the 1040W would be a problem. My (apparently wrong) thinking is even if the Array was sized to 1400W the Controller would never pull more than the 1040W so nothing gets damaged. Please help me understand.

The amperage rating is based on the limits of reverse polarity protection.
As long as you don't connect the PV circuit in reverse polarity. You can make as much as you want available.
But if that maximum is exceeded, and connected in reverse polarity, damage can occur.

 

[haycord]

The controller should only "draw" what it can handle. A solar panel can not "push" more amps than that.

That is exactly my assumption as well but even listening to Will's YT videos he seems to be saying to respect the power limit as well as the Voc. Maybe I am misunderstanding though.

 

[Suijkerbuijk]

The controller should only "draw" what it can handle. A solar panel can not "push" more amps than that.

A solar panel go up and down .
So its never the same pull from the mppt.

 

[haycord]

That is exactly my assumption as well but even listening to Will's YT videos he seems to be saying to respect the power limit as well as the Voc. Maybe I am misunderstanding though.

BTW if the PV Array was 'pushing current' into the Controller and there was no load on the batteries, the Controller would have a lot of heat to dissipate.

 

[Texas-Mark]

A solar panel go up and down .
So its never the same pull from the mppt.

???
I said the controller should not "draw" more than it's rated output regardless of input. In other words if the controller draws 15 amps at the solar input when it is maxing out it's rated output, putting more panels will not "force" more then 15 amps into it.

As noted, there are other reasons for limiting the input, but panels can't push more than what is being drawn.

 

[timselectric]

Voltage is pushed. (Respect the limits)
Current (amps) must be drawn. You can make as much available as you want.
But at some point it becomes wasteful.

 

[marsingbob]

I also do not understand this. 98% of the time the PV is sending or making available a lot of amps, while the battery is fully charged or almost fully charged. No one seems to see a problem with the SCC not accepting the amps from the PV. Why does it matter whether the SCC has available more or less amps than it can send to the battery when the battery is fully charged, but not when the battery will accept all of the amps the SCC can send?

Maybe the seller of the SCC has optimistically rated the SCC to deliver more amps that it can sustain for a few hours?

 

[Texas-Mark]

I also do not understand this. 98% of the time the PV is sending or making available a lot of amps, while the battery is fully charged or almost fully charged. No one seems to see a problem with the SCC not accepting the amps from the PV.

What don't you understand? That is how it works. The panels can not "push" amps that are not needed. The statement below was just confirming that. That if the panels could somehow "push" current, it would have to go somewhere, and it would have to dissipate it somehow (i.e. as heat).

BTW if the PV Array was 'pushing current' into the Controller and there was no load on the batteries, the Controller would have a lot of heat to dissipate.

 

[Suijkerbuijk]

???
I said the controller should not "draw" more than it's rated output regardless of input. In other words if the controller draws 15 amps at the solar input when it is maxing out it's rated output, putting more panels will not "force" more then 15 amps into it.

As noted, there are other reasons for limiting the input, but panels can't push more than what is being drawn.

Well it have te be test than
Somting for will to do for his YouTube

Using a watt/amp meter between the solar panel and mppt .
With a over power solar panels .
And than see if it true or not.
I think there are spikes to the volt pump up and down and that you spikes on the amps by pulling on the solar panels.

 

[Old Solar Guy]

Some charge controllers can handle oversized solar arrays and some cannot. The MPPT in most of them will pull the greatest power they can from the solar array up to the maximum output current limit of the charge controller. When the max output current is reached or the battery is full and the charge controller needs to limit the output current, it must push the array voltage up so the the current is reduced. This produces heat in the charge controller that it must dissipate. There is always a limit to that heat dissipation so the maximum array size will vary from one unit to another depending on that ability. Simplified description of course.

Old Solar Guy

 

[timselectric]

It's actually the opposite.
The panels provide their VOC.
And when current is drawn, the voltage is pulled down to a lower level.
If no load is applied, the panels return to VOC.
When no current flows, there's no heat created. (Nothing to dissipate)

 

[sunshine_eggo]

Well it have te be test than
Somting for will to do for his YouTube

Using a watt/amp meter between the solar panel and mppt .
With a over power solar panels .
And than see if it true or not.
I think there are spikes to the volt pump up and down and that you spikes on the amps by pulling on the solar panels.

I'm guessing you've never used those little power meters and discovered how horribly inaccurate they can be.

 

[haycord]

BTW if the PV Array was 'pushing current' into the Controller and there was no load on the batteries, the Controller would have a lot of heat to dissipate.

I'm going to take a stab and say this:

Overpaneling (exceeding the CC PV Input Power Limit) will allow the Array to provide more power during low-light conditions. During times of maximum Array output - the CC will limit its output to that specified (ie: 40A) regardless of any excess current available at the Array. Obviously when the CC limits its output it naturally limits its input demand.

If my statement is correct, I am curious why that is not made clear in the manufactures documentation considering the significant advantages in design.

 

[Texas-Mark]

When no current flows, there's no heat created. (Nothing to dissipate)

Yes that is correct. The heat dissipation example was used to describe what would have to happen if the panels could somehow force current into the controller when there was no load on it. But of course that is not how it actually works. The panels can not push current that is not already being drawn.

 

[Texas-Mark]

If my statement is correct, I am curious why that is not made clear in the manufactures documentation considering the significant advantages in design.

I suppose if one over-paneled too much it could cause the controller to be outputting it's max for a longer period of time and thus could shorten it's life. Especially if it's cooling system is not great.

 

[Suijkerbuijk]

Some charge controllers can handle oversized solar arrays and some cannot. The MPPT in most of them will pull the greatest power they can from the solar array up to the maximum output current limit of the charge controller. When the max output current is reached or the battery is full and the charge controller needs to limit the output current, it must push the array voltage up so the the current is reduced. This produces heat in the charge controller that it must dissipate. There is always a limit to that heat dissipation so the maximum array size will vary from one unit to another depending on that ability. Simplified description of course.

Old Solar Guy

My portable powerpack have a warning on it.
Max solar panel 80watts 24 volt on the mppt .
Strange the same connection is use to set a carlighter plug on it and than i charge with 10amps .
It draw 120watts on that moment.

So one mppt is not the same like a other.

My epever solar charger warning is that max 260watt by a 12 volt battery .
Do not go over it , it can damage the controller.
Its a 20amp model
In the Manuel.

On the victron 75/15 it tell max 220watt solar panel.
If its connect with more it will not use it but no damage.