How many solar panels can I use


New Member
Oct 15, 2020
Hello Solar guru's and enthusiast's alike. I can't seem to figure this out and need someone to try and makes sense out of it for me

I have a Magnum Energy PT-100 solar charge controller. My system is 12 V with 7200WH of Lithium batteries.
Spec's are
MAX PV INPUT 200VDC + battery voltage
PV operating Voltage (Vbat + 8V) to 187 VDC
MAX input current 100 ADC
Nominal Bat Voltage 12, 24, 48
Battery Charger output range 1 to 66 volts
Continuous Charger output Current 100 ADC
Max output power 6600 watts
Peak (and full power) efficiency >99% (98 typical)
Tare loss (nighttime power consumption) <4watts (fan off, dis[play/led off)

So I'm trying to get as much solar on this controller or very close. They have a PV array calculator, after using the calculator I'm under the impression that I can use a max of 1800 watts and still be within the parameters of this controller. Now the part that I'm unsure of .

So if 1800 / 14.4V = 125 Amps which is over the Max output of the controller. But the PV calculator says it's ok with a max output of 98.6 amps,
However if I divide 1650 / 14.4v =114.5 amps which is still over the max output. again the calculator shows it's fine with only 90 amps output.

So following that math I would only be able to use 1440 / 14.4v =100 amps. Again the calculator shows @79 Amps .I know that the panels are not putting out anywhere near 100 amps.

So I guess my question is which math is more correct? I don't want to burn out the controller by overpaneling it too far.

I looked at these panels
300 watt in a 3S/2P configuration
VOC 39.5
IMP 33.0
ISC 9.70
IMP 9.10

Here is a screen grab of the calculatorPV-Array-Calculator-for-the-Magnum-Energy-PT-100-Charge-Controller-Magnum-Dimensions.png



Participation Medalist
Nov 5, 2019
Silicon Valley
MAX PV INPUT 200VDC + battery voltage
300 watt in a 3S/2P configuration
VOC 39.5
Array output 120Voc and 19.4A

300W x 6 / 14.4 = 125A

So at 12.8V nominal battery, your SCC will only ever produce 100A charging current.
You will definitely be clipping the power when your panels are producing their maximum.

If you want to maximize your overall system, you can run more panels but have some facing east-ish
and some facing west-ish. This will spread your solar harvesting over a longer period by starting to charge earlier and finishing later.

Who much power do your NEED?


New Member
Oct 15, 2020
Hi, Thanks for the reply. I'm trying to get my 6 100ah batteries to recharge in 5 hours give or take.

6 X 1200 = 7200/5=1440W. Going by the calculator going with 1800W @25c. the anticipated output = 1440W @25c.
The anticipated output =1343 @40c.

Utilizing this information I figured that 1800W was the maximum Wattage I could use without doing any damage to the SCC,
all the voltages are within the parameters of the SCC.

I assume that since whoever designed their PV solar array calculator was using 80% output as a default. I have no knowledge of what the solar panels will actually produce in real time conditions.

If I'm wrong that's not a problem, as I'm just trying to get a better understanding of the SCC and how everything works together.
Attempting not to burn down my RV in the process. I know that 24V is a better option but since this is my first foray into the world
of Solar I felt it safer to stay with 12V until I get more knowledge about everything.


Retired Engineer Tech
Nov 26, 2020
Generally you can over panel and this helps with a series of rainy cloudy days. MPPT solar controllers tolerate it. Check your specs and ask the manufacturer about it.
Play with the calculater and add extra panels, watts, or strings. "Current Regulated to 100 amps" appears in Array Wattage?
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