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chrisgla avatar image
chrisgla asked

MPPT Online calculator different result to spreadsheet?

I'm looking for MPPT (either separate or Easysolar II GX 250/70) to use with 6 off JA Solar JAM60S10 -340/PR. I have an existing 6mm cable limiting me to 39 amps.

The online calculator gives me a result of MPPT 250/60 for 6 in series, or MPPT 150/35 for 3S2P.

But spreadsheet I added a custom module which is then not accepted and neither the Max PV V or current makes sense to me unless temperature is the impact (I'd expect 248.16V and 10.46A for serial?):-



Are 6 off these panels ok in series and any idea why spreadsheet fails?


Thanks!

MPPT Controllers
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5 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

The value for V temp coeff. must be negative and with only 2 decimal digits.

If I enter a value higher 0 or with more than 2 decimal digits I get this (with Firefox):


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klim8skeptic avatar image
klim8skeptic answered ·

The spreadsheet is correct! 273.226v @ -10c.


The online tool is broken.


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Lasse avatar image
Lasse answered ·

@M.Lange is correct, the system should have given an error when you tried to add a positive value to the V. temp. coeff. [%/C] apparently this is was not the case. It is a problem that occurs with Chrome, not with Firefox, this will be fixed in the next release.

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JohnC avatar image JohnC ♦ commented ·

It happens with FF too. I tested this earlier, but by the time I nailed it down the question was already answered.

A little thin red line around that box under certain circumstances, but it happily shows the incorrect result.

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klim8skeptic avatar image klim8skeptic ♦ commented ·

"the system should have given an error when you tried to add a positive value to the V. temp. coeff. [%/C] "

To further this, temps below STC will have a positive temp coefficient effect on the Voc. It should not matter if you add a - #, or a number greater than zero.

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Bob (Victron Energy Staff) avatar image Bob (Victron Energy Staff) ♦♦ klim8skeptic ♦ commented ·

Dear klim8skeptic,

the temperature coeff. of the voltage of a solar panel should be a negative value, mr. Lange answered this already. This will affect the voltage automatically and increases the solar panel voltage when the cell temp. is going down.

The problem would be if you insert a positive coeff. in the calculator, it would calculate a lower solar panel voltage @ lower temperatures. Which is in real life not the case.

Regards,

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klim8skeptic avatar image klim8skeptic ♦ Bob (Victron Energy Staff) ♦♦ commented ·

"the temperature coeff. of the voltage of a solar panel should be a negative value"

Unfortunately the app has not been set up to apply those rules, at least in this instance.

Just a green tick.

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Lasse avatar image Lasse ♦♦ klim8skeptic ♦ commented ·

Dear @klim8skeptic the field validation did know that the value was incorrect but due to the different browser implementations of showing errors, this was not visible. Yesterday this has been fixed and pushed to production.

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chrisgla avatar image
chrisgla answered ·

Thank you for fixing this, both the online and spreadsheet tools are really useful tools!

Looking forward to receiving my Multiplus ii 5k, Cerberus and CAN MPPT. I work in Smart Grid and the Modbus functionality with Victron quality and support will let me try a few innovative ideas....

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Warwick Bruce Chapman avatar image
Warwick Bruce Chapman answered ·

I have been able to reproduce this.

For Canadian 365's, web suggests a 150/60 is fine but Excel says current will be limited:

Another example for Canadian 415's, web suggests 150/45 is fine but Excel says current will be limited:


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