question

drrob avatar image
drrob asked

Help me understand the MPPT Calculator results

Hi,

Why does the MPPT Sizing Calculator recommend an MPPT 150/45 here when an MPPT 100/50 ought to be sufficient? Is it that the calculator doesn't know about that model? I wish it explained its choices a bit more. Maybe there's another limit of the 100/50 that I'm not aware of.

https://mppt.victronenergy.com#djE7Y3VzdG9tLDIsMSwzNiwtMTAsNzAsMTIsOS41NCwwLjA2LDEwLjA4LDI5NSwzMC45MywtMC4zLDM3LjE4LDEwLDY=

Thanks,
Rob.

MPPT Controllerssolar sizing
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4 Answers
Alexandra avatar image
Alexandra answered ·

@DrRob

Not sure exactly what your system voltage is - there are two totally different figures on your linked page. If it is 12 you will be fine.

That being said the 100/50 does not do 36V system so that is most likely why it is not listed there. At least mine does not.


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1633699835029.png (11.2 KiB)
3 comments
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Hi Alexandra, thanks for your reply.

I don't know what that Battery Float voltage box means, but 36 is the lowest value it will accept, or else it turns red. The pop-up info for that input item says, "Used only for RS controllers" but I don't know what that means.

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Ah right. (Insert face slap emojie) It has been a while since i have used the online calculator.

Try this downloadable one and see if the graphs go out of range for the mppt of choice with your panels.

You should be fine on a 100/50 on a 12v system.

(2x295w) ÷ 12v = 49A this is at 25°C you will probably hit power limiting at low temps.

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The 100/50 mppt does appear in some configs, so from that side it is all ok.

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1633715334438.png (123.7 KiB)
drrob avatar image
drrob answered ·

Interesting... at 338W (x2 in series) it recommends the 100/50, but at 337W (x2 in series) it recommends the 150/45, which is a much more expensive model. ¯\_(ツ)_/¯

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JohnC avatar image
JohnC answered ·

Hi @DrRob

The calculator doesn't consider cost, it's technical only, and will derive the the lowest Amp output unit it considers suitable. If you can find more Amps cheaper, then good. But then you need to watch Volts if you choose more A and less V.

The RS units are for long pv strings (<450V) and 48V batteries only.

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drrob avatar image
drrob answered ·

Thanks for explaining. It's a shame the calculator doesn't list all suitable units rather than the lowest amp output ones.

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