question

MPPT Sizing calculator

I am using the mppt sizing calculator and have some questions about the results. Here are my inputs using a custom module:

Wp: 305

1 series 3 parallel

Voc: 45.6

Isc: 9.05

Vmpp: 37.4

Impp: 8.16

System voltage 12.

With these inputs in recommends the BlueSolar MPPT 150/60 Tr but not the SmartSolar Mppt 150/60 Tr. As near as I can tell they have the same specs. Is there a limiting factor?

Also, given the input, what would the outputted amps be from the charge controller given the best case scenario? I am not sure how to calculate the conversion.

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The Bluesolar and Smartsolar will handle the same array power each. The Smartsolar's only difference is that it has a bluetooth module installed within.

Your battery amps will depend upon the battery Voltage at any point in time. At 12V with absolutely ideal environmental conditions the amps will be Max PV Power / Battery Volts (915 / 12 = 76.25A). As you battery gets full (915 /14.8 = 62A).

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For the best case calculate the input power Pin = Impp x Vmpp or 8.16A x 37.4V = 305W

Maximum stated efficiency is 98% per the data sheet.

Most of the recharge cycle is spent in Bulk/Absorption so assume an output voltage of 13.8VDC.

Taking into account the efficiency and since Pout = 0.98 x Pin

Pout = 0.98 x 305W =299W

Iout = Pout/Vout; Iout = 299W/13.8VDC = 21.7A

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Hello @dlong20,

The Bluesolar and Smartsolar charge controllers are identical, except for the build-in Bluetooth of the Smartsolar. The Bluesolar has no build-in Bluetooth. But for the electrical part, they are the same.

The outputted amps would be: 305 Watt (Vmpp: 37.4 times Impp: 8.16) diveded by your system voltage of 12 volt, so that makes a maximum of 25,4 amps output to the battery, per 1 solar panel. (Only with an empty battery will you charge with a low voltage of 12 volt. Normally the voltage will be higher, all the way up to 14,4 volt, and then the amps will be lower. (21,2 amps with 14,4 volts)) So total for 3 panels will be max. 75 amps, or 63 amps with a full battery. So you can use a charge controller with around 60 amps limit. Don't worry that you go over the limit sometimes, it won't break, the power output will just be a little bit limited.

If the 150/60 controller is suitable, depends on the characteristics (V temp coeff), on the minimum temperature in which the solar panels will operate and the way the panels are connected. If the V temp coeff is 0,33 %/degree C then the minimum temperature should not drop below -4 degrees Celsius, because if it does, the voltage (with the 3 panels in series) will raise above 150 volts and will kill the controller. You could put the panels in parallel, but this is bit less efficient, but safer for your controller with low temperatures.

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The calculation from @WKirby is the only correct one - the other 2 neglect to consider that there is power being provided by 3 panels.

Only increasing the battery system voltage would allow a MPPT with a signigicantly smaller current output to be used.

If you run those 3 panels in series with a 150v max MPPT you should properly determine/calculate Voc in worst case cold conditions as it may be a little over the limit.

Please also note that the MPPT will limit output current to its limit - so it's OK to be 'theoretically' over the output current in ideal conditions.

Conversely if PV is too far 'oversized' then it can be a bit of a waste...

You just need to ensure you comply with the individual MPPT Isc & Voc limits & consider the whole PV array when you check.

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MPPT 150/60 up to 250/70 Manual