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lightguide avatar image
lightguide asked

MPPT 150/45 TR with 4 175W HQST Solar panels

I recently acquired a Smart Solar MPPT 150/45 TR. I used the Victron MPPT Calculator and the recommended settings based on Victron solar panels, was this model. My question is The following.

Based on the Nominal PV power @ 12V for the controller is 650W. My total PV array power with all PV cells in Series will be 700W. The Voc for each pannel is 24.3 and Vmp is 20.3, the current is Imp 8.62A and Isc 9.35A. If I used these 4 panels in this case I will be exceeding the recommended power in which I know is not good; But when I typed my numbers it appeared to be good for this model in the calculator as seen below:
Using other calculators and taking into consideration the temperature effects it will give me 60Amps which also exceeds the current parameter.

My battery is a Lifepo4 at 12Vdc or 14.4Vdc (400AH). If I do a manual calculation using the MPPT of 700W/14.4 it gives me 48.61A. (1) Should I drop 1 solar panel to reduce the wattage, to be on the safe side or (2) should I do a parallel series arrangement for this controller? On a similar note the PV array will be 40ft away from the solar controller, the MPPT Boost effect only occurs downstream meaning on the output of the solar charge controller or this MPPT boost effect occurs input and output of the controller. This is just to know how I will size my Input cables from the PV array and the output to the batteries. Thanks for your help in advance.




smart solar set-up help
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2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Serial or parallel doesn't matter the power of the panels is the same 700Wp.

You are not allowed to exceed the maximal PV voltage of 150Voc. But you can exceed the current without damage the MPPT.

So you can use the 150/45 but under certain conditions you may "lose" some power.

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lightguide avatar image
lightguide answered ·

Matthias thanks for your response. I understand the wattage remains the same for either of the configurations. I just stated it that way just to show how I was planning to wire the panels.


as for the current, then the controller will just limit the output to 45A max? if that is the case then I would not worry too much. I thought that the controller will be damage because the PV array was capable on supplying that amount of current.


Also, on the controller wattage; The maximum figure for the controller spec it states to be 650W for a 12v system.

Is it "ok" to exceed it by ~8% this figure even I'm not exceeding the voltage for the MPPT of the controller? The maximum voltage for this configuration in my case will be around ~122 Vdc.


I saw on the spec that the controller has a current input max of 50A from the PV array and a current batt output of 45A. With my current config I will not exceed this figure since the average current will be ~9.4 and max of 9.7. My question in this regard is on the wiring for the input and output.

Does the MPPT will effect the current at the input of the controller or is only the output that will always be higher in this case? meaning that the output will be a max of 45 and the input will remain always constant only dependent on the amount of current produced in my case of 9.7 max?


Thanks in advance!





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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

The spec sheet says:
"Nominal PV power, 12V 1a,b) 650W
1a) If more PV power is connected, the controller will limit input power.
1b) The PV voltage must exceed Vbat + 5V for the controller to start. Thereafter the minimum PV voltage is Vbat + 1V."

So it is ok to connect more power the MPPT output limit is 45A

"Max. PV short circuit current 2) 50A
2) A PV array with a higher short circuit current may damage the controller."

It is the short circuit current and it's only adding up in parallel, not in series.

The MPPT converts the PV voltage into the battery voltage -> with a smaller voltage the current must rise to deliver the same power.

P=U*I

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lightguide avatar image lightguide Matthias Lange - DE ♦ commented ·

Understood, Thanks! again


My final question:

Using nominal values for the expected currents on the input and output, what wire size would be recommended. Don't need an exact figure only an approximate to have an idea if my thoughts are correct.


PV Input

For the Wire size input from PV array -> to controller

Imp = 8.62A

Volts = 106

L =20m

wire size from PV to controller

using calculator

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=3.277&voltage=122&phase=dc&noofconductor=1&distance=20&distanceunit=meters&amperes=8.62&x=51&y=17

it gives me a 10AWG with 1.13% loss


Battery Output

For the Wire Size Output

Imp = 45

Volts = 14.4

L=1m


Wire size from controller to batt.


https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=1.296&voltage=14.4&phase=dc&noofconductor=1&distance=1&distanceunit=meters&amperes=45&x=58&y=24


it gives me a 6AWG with 0.12% loss


My assumptions for the wire size are correct?

Thanks in advance


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