MPPT max power calculation

[New_Climber]

How far above the max power (current) can I push a MPPT charge controller?

I currently have 2- 185W, 36v panels and want to connect these into a charge controller to charge batteries. I am looking at the Morningstar MPPT-45, using a 12v battery system. I also want to purchase an additional panel and want to make sure my calculations are correct.

So is my calculation correct??

Current power:
185*2=370w

Charge controller specs:
45a*12v=540w max

Wanting to add:
an additional 190w panel

Total power would be 560w at 12v= 47A to charge controller.

I know that I will not get the full rated power from my panels, but how much can I figure into my calculation without hurting my charge controller... is 80% output allowed?....560*80%=448w….448w/12v=37A

At 37A that is well below the charge controller rating…

So is there a rule of thumb for calculation the needed capacity of the charge controller?

Any questions or help is much appreciated...thank you.

[Sunking]

Doesn't quite work that way. Close for estimation, but not exact. Morningstar uses 13.3 volts. With MPPT controllers the limit is panel wattage vs battery voltage. For your unit 600 watts @ 12 volt battery is the limit. To be honest INMO once you get above 500 watt panel wattage, it is time to move up from toy voltages of 12 volts to bigger boy toy voltage of 24 volts. Doing that with your controller is now good to 1200 watts.

[New_Climber]

Thanks much for the reply...

The main reason I am looking to stay at 12v (battery voltage) is due to the inverter on the other side to run my load(s). It seems that 24vDC inverters are much more expensive....My plan is to run some area lighting in the summer and if I have enough PV power in the winter (with reduced sun light time), is to run a pellet stove during the winter.

For what I am looking to do, it would seem that running a 12vDC inverter would work fine...but it sounds like to get more solar input, I either need to get a larger charge controller or get a 24v inventer...and using 24V battery system voltage.

Eitherway am I understanding your answer correctly...Don't go above the 45amp (540W) input limit of the charge controller?? Even keep it below 500w or approx 41amps

Am I understanding this correctly?

Thx again for the help

[New_Climber]

Sorry for the second post...but another question...

What do I then use for panel watt rating...I know the panels are not 100% efficent, so they will not put out the max power rated...

How do I fact this into my calculation?? Can I take 80% of the panel power rating to use in my CC calculation?

[Sunking]

Eitherway am I understanding your answer correctly...Don't go above the 45amp (540W) input limit of the charge controller?? Even keep it below 500w or approx 41amps

Am I understanding this correctly?

No Sir. Look at the user manual. 600 watts is the limit on your controller.

[New_Climber]

I understand...600w on 12v. Not sure why I keep saying 540w.

Back to my other question...do I just add up my panel rates....and use that number? Or am I able to account for panel efficiency?

Just want to make sure I understand this correctly.

[Sunking]

Just add up the panel spec wattage.

[Naptown]

I understand...600w on 12v. Not sure why I keep saying 540w.

Back to my other question...do I just add up my panel rates....and use that number? Or am I able to account for panel efficiency?

Just want to make sure I understand this correctly.

Add up the wattage of the panels (nameplate) Some loss of efficiency is already accounted for in the CC input #