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Victron MPPT confusion

Rumbledethumps

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Aug 5, 2021
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Hi All,

I'm putting together my first proper system using Victron components and purchased the 100/50 MPPT smart charge controller to use with 3x200W panels wired in series. Following the purchase a couple of sources have made me question my choice so I wonder if you can give some clarification please...

My understanding was that as long as you check the Open Circuit Voltage (accounting for temperature coefficients) doesn't exceed the input voltage of the charge controller (leaving sufficient overhead), all should be well.

The specs shown on each panel are:

Max Power at STC (Pmax) 200W
Open Circuit Voltage (Voc) 27V
Short Circuit Current (Isc) 9.66A
Optimum Operating Voltage (Vmp) 22.6V
Optimum Operating Current (Imp) 8.85A
Temp Coefficient of Pmax -0.37%/C
Temp Coefficient of Voc - 0.28%/C
Temp Coefficient of Isc 0.048%/C

So 3x panels in series gives 81V Open circuit voltage and 9.66A Isc; ie well within the limits of the Victron 100/50 MPPT, or so I thought?

I was subsequently advised by a Victron products seller that the 100/50 may not be sufficient as when the input voltage is lowered within the controller to work with the battery, the amps could increase to around 60A, which could prove problematic?

I was under the impression that the amps output from the controller would be restricted to a max of 50A?

Also, to confuse me further when I input the specs of these 3 panels in series into the Victron MPPT suggestion site, it recommends the 150/45?

Please can someone clarify if the 100/50 is suitable for my 3 x 200W panels or do I need to return it and buy a larger charge controller? Please note that I have not yet purchased any other components, hence no info for those yet.

Thanks all.
 
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That MPPT will only deliver 50A at your systems charging voltage.
You don't mention it but that particular controller will be for a 12 or 24V system.
And it's not 12V or 24V strictly either, because it's actually the charging voltage of your system.

The worst-case scenario is the 12V system, but let's say you charge at 13.8V.
600W/13.8V =43.5A, which is < 50 Amps, so your controller is quite adequate.


A further point to mention is 600W will only be achieved in the best of conditions, ideal slope, good sun and ideal direction etc.
So it is likely that 95% of the time you won't have to deal with the full 600W anyway. Even if you did occasionally clip the current, so what.
Many people deliberately over-panel to clip slightly on the best days so that they still maximize production on the not-so-good days.

The next point I would like to make is these controllers can be paralleled, so there is no need to ever sell one and get a bigger one. You can just add another one and another one and so on.
 
You are correct that 3 of those panels give you a Voc of 81V. It would take temperatures below -58ºC/-73ºF to reach 100V so you should be fine there.

600W of panels at 12V can be 50A of charge current. When your batteries are closer to 13.5V then it will be more like 44A which is why Victron suggested the 45A model. But I see no reason for the 150V given your panels. Perhaps you entered a value incorrectly into the calculator.

From my calculations the 100/50 is just fine for your 3 panels in series.
 
I run 2x310w ... voltage around 46v per I think...
works great.. it has given me a high pv voltage twice when it was in the 20s
 
I just entered your panel specs into Victron's MPPT calculator and sure enough it seems to recommend the 150/45. But if you look at the calculations it shows the max Voc will be well under 100V so it makes no sense. I would call it a bug in their calculator.
 
he amps could increase to around 60A, which could prove problematic?

I was under the impression that the amps output from the controller would be restricted to a max of 50A?

Yes, output will be clamped at 50A. Here is my attempt to explain the concept, although I am some guy on the internet and not a Vic employee or EE.

It's been a while since I've read Vic's overpaneling recommendations, but I think they were 10%. That would explain the calculator's 45A recommendation.

Please can someone clarify if the 100/50 is suitable for my 3 x 200W panels or do I need to return it and buy a larger charge controller?

IMO 50A is generous for 600w. My previous setup was 570w on 40 and I think I saw it hit 40A and clamp exactly once. My present setup is 750w on 50A (non-Vic controller) and same kind of deal.
 
That MPPT will only deliver 50A at your systems charging voltage.
You don't mention it but that particular controller will be for a 12 or 24V system.
And it's not 12V or 24V strictly either, because it's actually the charging voltage of your system.

The worst-case scenario is the 12V system, but let's say you charge at 13.8V.
600W/13.8V =43.5A, which is < 50 Amps, so your controller is quite adequate.


A further point to mention is 600W will only be achieved in the best of conditions, ideal slope, good sun and ideal direction etc.
So it is likely that 95% of the time you won't have to deal with the full 600W anyway. Even if you did occasionally clip the current, so what.
Many people deliberately over-panel to clip slightly on the best days so that they still maximize production on the not-so-good days.

The next point I would like to make is these controllers can be paralleled, so there is no need to ever sell one and get a bigger one. You can just add another one and another one and so on.
Thanks Phil,

It's a 12V system so I'm assuming the calculation of 600W/13.8V = 43.5A is based on the output of the controller to a fully charged battery? I'm still in the process of choosing batteries so need to research this more....

This being the case I take it that it wouldn't ever be necessary to do the above calculation using VOCxIsc (810W)? Based on your comment about ideal conditions, I'm assuming that it wouldn't ever be possible for 600W of panels to output this kind of increased wattage?

Cheers for the tip on using controllers in parallel; good to know that's an option.
 
I just entered your panel specs into Victron's MPPT calculator and sure enough it seems to recommend the 150/45. But if you look at the calculations it shows the max Voc will be well under 100V so it makes no sense. I would call it a bug in their calculator.
Thank for checking this; I wasn't sure whether I'd input something incorrectly.
 
I run 2x310w ... voltage around 46v per I think...
works great.. it has given me a high pv voltage twice when it was in the 20s
Thanks, that's good to know; I'm definitely comfortably under on voltage with the 3 panels so it sounds like it should be fine.
 
Yes, output will be clamped at 50A. Here is my attempt to explain the concept, although I am some guy on the internet and not a Vic employee or EE.

It's been a while since I've read Vic's overpaneling recommendations, but I think they were 10%. That would explain the calculator's 45A recommendation.



IMO 50A is generous for 600w. My previous setup was 570w on 40 and I think I saw it hit 40A and clamp exactly once. My present setup is 750w on 50A (non-Vic controller) and same kind of deal.
Thanks for this; I'll check out the link. I'd rather err on the side of caution than risk damaging anything so it's good to know that 50A is generous.
 
This being the case I take it that it wouldn't ever be necessary to do the above calculation using VOCxIsc (810W)?
Isc and Voc are two mutually exclusive conditions.
When either condition exists there is no power produced by the panel.
 
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