Exceed the nominal wattage ratings of SS-MPPT-15L

[awillfor]

Hello experts!

What is the maximum input power someone in this forum has connnected to a Morningstar SS-MPPT-15?

I have connected two 140W panels in series to my 12V setup. This exceeds the nominal input (200W) by 80W (at perfect conditions)
Voc 21,85V x 2 = 43.7V, and maximum input voltage is 75V, so that is no issue.

Reading the document http://www.morningstarcorp.com/en/su...PT-Primer2.pdf
Morningstar are saying:
-You can size Morningstar’s MPPT controllers well above the Maximum Nominal Solar PV Input rating without damaging the controller and without the charging current exceeding the maximum output current rating. The controller can limit output current and will run at 100% of rated current output and not higher. The controller was designed with this powershaving capability and when oversized it does not void the warranty.

-Morningstar’s MPPT controllers can operate with an oversized array that is several times larger than the maximum Nominal Solar PV ratings, while still limiting the maximum battery current to the controller’s maximum current rating.


The question is if it is safe to have these panels connected to this controller. (Lets not discuss why I let so many Ah go to waste by limiting the output to 15A)

When I asked Morningstar support, their answer was:
-Maximum input voltage is 75 volts and maximum power in is 200 watts for 12v system.
-It is not recommended to operate our controller with over sized arrays even though our controllers are designed to limit maximum current allowed to be passed to battery. This causes excessive stress on electronic circuits and warranty can be voided.

[inetdog]

Hello experts!

What is the maximum input power someone in this forum has connnected to a Morningstar SS-MPPT-15?

I have connected two 140W panels in series to my 12V setup. This exceeds the nominal input (200W) by 80W (at perfect conditions)
Voc 21,85V x 2 = 43.7V, and maximum input voltage is 75V, so that is no issue.

Reading the document http://www.morningstarcorp.com/en/su...PT-Primer2.pdf
Morningstar are saying:
-You can size Morningstar’s MPPT controllers well above the Maximum Nominal Solar PV Input rating without damaging the controller and without the charging current exceeding the maximum output current rating. The controller can limit output current and will run at 100% of rated current output and not higher. The controller was designed with this powershaving capability and when oversized it does not void the warranty.

-Morningstar’s MPPT controllers can operate with an oversized array that is several times larger than the maximum Nominal Solar PV ratings, while still limiting the maximum battery current to the controller’s maximum current rating.


The question is if it is safe to have these panels connected to this controller. (Lets not discuss why I let so many Ah go to waste by limiting the output to 15A)

When I asked Morningstar support, their answer was:
-Maximum input voltage is 75 volts and maximum power in is 200 watts for 12v system.
-It is not recommended to operate our controller with over sized arrays even though our controllers are designed to limit maximum current allowed to be passed to battery. This causes excessive stress on electronic circuits and warranty can be voided.

Since Morningstar's support does not agree with their printed documentation, it is hard to tell just who to believe.
But on general physical and electronic purposes, I do not see any good reason to think that putting the 280W array on the input will cause any problems.

For a PWM (non-MPPT) CC, there could well be excess power dissipation when an oversized array is connected, but that should not happen to the same extent with an MPPT design.
A PWM controller will, at any given moment, have its switching elements either on or off, and the ration between the two states will determine the amount of current whiich will flow and the resulting battery voltage. If you have too large (high current) a panel array, the current during the on part of the cycle will be too great and could cause excessive heating in the transistors, leading to shutdown or failure.

A 15A CC could theoretically deliver up to ~220W to the battery if that current were maintained at a terminal voltage of just under 15V. For an MPPT controller to be damaged by just an extra 60W does not seem likely to me. Caution: I cannot guarantee this, and of course take no responsibility for any bad outcomes.

[Sunking]

The power will be clipped off.

[FloridaSun]

The power will be clipped off.

Understood how the clipping would take effect but how much stress that would cause the SS-MPPT-15 I don't understand... as in possibly overheating on a daily basis. Seems the same would happen using the SS-MPPT-15 to charge a 12V battery from a 24V bank which I understand is possible but I've seen little performance/longevity stats from actual users. Hope this thread brings more to light on this subject. Would be nice if Morningstar would actually give more statistics instead of contradictions.

[Sunking]

Understood how the clipping would take effect but how much stress that would cause the SS-MPPT-15 I don't understand... as in possibly overheating on a daily basis. Seems the same would happen using the SS-MPPT-15 to charge a 12V battery from a 24V bank which I understand is possible but I've seen little performance/longevity stats from actual users. Hope this thread brings more to light on this subject. Would be nice if Morningstar would actually give more statistics instead of contradictions.

It has to do with the IR curve of a panel and at which point the MPPT controller sets the tracking point. When power is clipped, it is going to track on the higher voltage curve above the knee, and thus lower the current. In other words the voltage is going to be between Vmp and Voc range where the panel becomes a voltage source rather than a current source.

[FloridaSun]

It has to do with the IR curve of a panel and at which point the MPPT controller sets the tracking point. When power is clipped, it is going to track on the higher voltage curve above the knee, and thus lower the current. In other words the voltage is going to be between Vmp and Voc range where the panel becomes a voltage source rather than a current source.

awillfor's reply from Morningstar support,
"-It is not recommended to operate our controller with over sized arrays even though our controllers are designed to limit maximum current allowed to be passed to battery. This causes excessive stress on electronic circuits and warranty can be voided."
is in direct conflict with their statement,
"You can size Morningstar’s MPPT controllers well above the Maximum Nominal Solar PV Input rating without damaging the controller and without the charging current exceeding the maximum output current rating. The controller can limit output current and will run at 100% of rated current output and not higher. The controller was designed with this power-shaving capability and when oversized it does not void the warranty." at http://www.morningstarcorp.com/en/su...PT-Primer2.pdf

On that same page it also says, "• Also, to avoid unnecessary stress on the controller’s electronic components, it is recommended that when the controller is installed in a sustained warm temperature climate, the controller not operate at full power, close to its maximum ambient temperature, for prolonged periods of time."
According to the SS-MPPT-15 manual, "Ambient Temperature Range -40°C to +60°C" would make all well as long as 140*F is not exceeded.... yes?
hahaha, and why do I ask these questions here instead of writing morningstar? Seems that I have more faith in the common sense of solarpaneltalk pros than I do some canned response from some flunky at a manufacturer.

[Mike90250]

I would not worry about the extra wattage, unless your controller is in a hot location, keep the electronics cool.
I've been running mine on a 205 w panel for years.