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Outback charge controller not using all of the arrays volts
#1
Could use some help figuring this out. I have an fm60. It’s supplying 3200w max sustained, array is new panels 3660w, 99.9vmp, 120voc, 36amps I observe the input voltage not going higher than 80ish volts most of the time when it should be capable of 99v. It does show 99v and higher input on the screen rarely but I think this is only when input amps are low. Also I do rarely see 3600w but it’s only for a few seconds. When solar should be at it peak-highest production I can’t get anymore than 3200w sustained from the array.
My thoughts are that maybe the chargecontroller combines the battery voltage (16s 65.6v max) with array voltage, and will not let the input volts from array be higher than the difference between 150v (max allowable array input voltage for charge controller) and the batteries present voltage? Is this how it’s done by the charge controller? If it is, that could be why I’m not seeing closer to the voltage that should be available from panels.. I hope this isn’t correct,, 66v (2 panels in series) wasn’t enough volts to charge 16s battery so I needed 3 panels in series for 99v but if I can’t use all the arrays power that would be a huge bummer. 99v from array and 65.6v from battery would be 164.6v which might be why input array volts is being lowered-not accepted? When the battery is at 58ish volts then I also see higher input voltages around 100v.
#2
Interesting.   I have Midnite Classic 150s, been operating for over 2 years now with 24 and now 45 panels (285w each) and see the same things.   Mine are 3s and I'm guessing yours are too.    Not sure what you expect voltage wise as the point of MPPT is to maximize power (e.g. watts), not voltage.    Lower voltage is simply higher amps and vice versa.    My Midnite Classics MPPT voltage is typically around 83-88v as you describe and (anecdotally) around 90% of rated PV power per what the controllers report when things are 100% clear/sunny all day.  

I *rarely* get 100% of rated panel output and (as you describe) only for short periods.  I have gotten as much as 110% for short bursts.    There are many factors - the time of day, weather, angle of panels (both vertical and horizontal), and *temperature*.   I actually get less power (5-10% less) in the heat of summer (90-100F ambient high) as compared to cooler spring and fall (60-70F ambient high) on similar 100% clear/sunny days and the days are a little longer. 

I use the PVWatts website - https://pvwatts.nrel.gov/pvwatts.php - to see what I should expect and so far, I've been well matched with this website predictions - weather is quite variable so it can't be exact.   So I've come to believe that expecting 100% of your rated array was never reasonable except for a few peaks here and there as you describe.

You might try PVWatts or similar to see what you should expect for your location, angle, etc - and view it more as a monthly/yearly metric.  

Midnite Classic's offer 2 different 'main' MPPT tracking algorithms - maybe Outback does too? If so you might try some alternatives to see if it makes any difference.

Overall - I'd say your system is working in the range of 'as it should'..  but that's just an anecdotal comment based on my own experience and I'll look forward to other comments on this Smile
Doin it and Ampster like this post
#3
A couple of possible factors you're missing:
* You're measuring V-PV at the controller, whereas Vmax is at the panels. Ie you might be losing voltage in the PV cabling. The higher the current (~=power), the higher the V loss.
* May 31st, the sun is at the highest point now. If your panels are inclined towards the south (or north), they're kinda pointing in the wrong direction this time of year, thus the panels will not reach Pmax
* If you're in the north, it's probably getting hot. PV panels lose Pmax at around 0.5%/C
* Summer and little rain... panels dirty from dust, pollen, bird poo, etc?
Doin it likes this post
Modular PowerShelf using 3D printed packs.  60kWh and growing.
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#4
Very good-knowledgeable comments, thanks!
So does from roughly 460w to 560w under max sound reasonable for what I would consider a full sunny day at peak sun, 70f degrees, two strings 40ft each of 10gauge wire supplying 19amps each?
Panels aren’t dirty, they are cleaned often and the 3200w max I’m seeing is year round
Panels are facing south (I live in Tennessee) and on a 6/12 pitch roof 26 degrees
As for what voltages I expect,, I’m thinking that when panels are capable of full amp output and full voltage output then I should see closer to max (3660w) from array..
can any of u verify that the combined battery voltage and input voltage on charge controllers screen from array is higher than 150v on a 150v charge controller?
How would I try a different mppt tracking algorithm? The outback has something called U-pick mppt.

Appreciate the pvwatts link.. I believe that it’s showing me the possible amount my array can produce if I was using all of the power. For this month pvwatts said 518kwh,,, my monitoring system tells me I only used 378kwh from array this month. Ofcourse this is due to my battery bank (once full) being to small to store all of the potential panels power
#5
The key point is mostly likely the specs for the panels (eg Vmp & Imp) are measured under test conditions & there's generally two of these test conditions:
- The lab special: STC "Standard Test Conditions" where the panel is at 25degC, with 1,000W/sqm light & measured quickly before the cells start to warm up.
- The more like reality: NOCT "Normal Operating Cell Temperature" where the ambient is 20degC, there's 1m/s wind & only 800W/sqm light & measured when the cells have warmed up to typically 45degC or so.
Bottom line: you typically see output from your panels of the NOCT values when the sun is at 90 degrees to the panels.
It can burst above this eg if the sun pops out from clouds in a cold clear day.
Combined with the other factors the guys above have mentioned, you get less into the controller accordingly, typical best being about 80% or so of the STC max power specs.

EDIT: I checked the specs for the FM60 here:
http://www.outbackpower.com/downloads/do...csheet.pdf
It says "NEC Recommended Solar Maximum Array STC Nameplate" for 48V battery systems is 3000W & 60V 3750W
So it's possible depending on your battery voltage (somewhere between 48 & 60V?) you're maxing out the FM60?
Running off solar, DIY & electronics fan :-)
#6
My array is 3660w. I charge my battery to 65.6. I’m under the 3750w and only getting 3200w sustained
Most likely it’s that I’m getting all I can from the array due to everything mentioned above.
I would still like to know if anyone sees higher than 150v on the outbacks screen, combining battery and array input voltage.

heres an example, the combined voltage is 151.4 (86.1 + 65.3) and as battery voltage drops then the input voltage from array rises on charge controllers screen, but still not going over roughly 150v combined.
I’m saying that the array at time of the pic was only capable of supplying 30amps, which is reasonable for the time of day,, but I’m fairly certain at the time of the pic that the array is capable of supplying higher voltage..
Is the mppt not capable of allowing more than 86.1v in from array because it cannot lower voltage that is any higher than 86.1 down to 65.3?

This pic is showing a higher amount of volts input from panels, amps are lower because loads are lower. But just a min ago when loads were higher and more amps were needed then the volts were like the first pic
#7
Re adding the input & output voltages together, far as I know, that's not a done thing by the manufacturers :-)
As long as each voltage (separately) is in spec, then it's fine.
It's input V x input A = Vmp x Imp from the panels, &
output V x output A = power into the batteries, which you already know.
With those 10AWG cables at 19A your voltage drop should only be about 0.4V so not too much.
https://www.rapidtables.com/calc/wire/vo...lator.html

Did you look up the NOCT values for your panels?
Mine (larger 72 cell panels) are quite different from the STC values:
STC Vmp: 37.2V
NOCT Vmp: 34.5V so about 92% IF the conditions at my place match the NOCT ones, so note if it's hotter &/or less wind = worse (lower Vmp & Imp)....

The two screens above look like normal & expected operation to me?
It's normal that as the controller reaches your "battery full" voltage, it backs off the current to the batteries which in turn unloads the panels so the volts there rise.
The MPPT algorithm will search for the max power point & do it's best to get the most from the panels (if not close to battery full).
Running off solar, DIY & electronics fan :-)
#8
Red, I understand that it’s normal for the amps to lower when battery is full. I don’t understand why the charge controller cant use 100v from array. Shouldn’t the controller be able to use 100v if at the time the panels are capable of 100v?,, regardless of the amps being used from the array.. Is there a maximum amount of volts that the mppt can use depending on what battery voltage is? Even tho I’m well under the 150v the controller can accept?
Something’s telling me that it’s not a coincidence that my battery voltage and array input voltage (on charge controllers screen) never go over roughly 150v, unless the charge controller isn’t having to create more amps, then it’ll use over 150v combined like the second pic
#9
(06-01-2020, 01:12 AM)Doin it Wrote: Red, I understand that it’s normal for the amps to lower when battery is full. I don’t understand why the charge controller can use 100v from array when the amps the controller is charging with are lower. Shouldn’t the controller be able to use 100v if at the time the panels are capable of 100v?,, regardless of the amps being used from the array..  Is there a maximum amount of volts that the mppt can use depending on what battery voltage is? Even tho I’m well under the 150v the controller 
It sounds like you're focusing on voltage - but voltage, by itself, is not the issue.   The issue is *power* = e.g. watts.   Note that 100v * 30a = 3000w  and  90v * 35a = 3150w.  In this example, 90v is giving more power than 100v.   The Outback MPPT algorithm is raising and lowering the voltage (and correspondingly raising and lowering the amps) every few seconds to find the maximum power point - e.g. the combination of voltage * amps that brings in the most power.      A lower voltage (than panel max) will result in greater amps / power - you can trust the Outback to find the sweet spot on this.

I've seen videos explaining the 'maximum power point curve' concept - but don't remember the details.  You might want to search one out to get more info.   But the idea is that there is a curve of volts/amps that determine max power (max watts from panels) that changes from moment to moment as the panel output changes from moment to moment due to clouds, temp, sun strength etc.  

As a side issue - as the battery fills and it goes into absorb/float, the Outback will limit the output current to the battery..  because its in CV (constant voltage / declining amps) mode as the battery fills.  This in turn will cause the Outback to accept less input power or shunt aside excess power - because its the output that is the overriding issue - e.g. to avoid overcharging the battery.    Ultimately, if the battery reaches 100% full, the output will go to 0 and the input power will go to 0 as well...   even thought the panels are still producing power.    
Example from my own system on output affecting PV input power:
Midnite Classics let you set the max output amps and I had to set mine to down to 80a because at 86a (the max the controller supports) my 80a circuit breakers trip.  This actually happened and I was going crazy trying to figure out what happened.  This means my input power is limited to 80a * battery-voltage which means that when my battery is low (say 50v), I can actually loose some PV input power because the input cannot exceed the 80a * 50v = 4000w output whereas my array can produce 4275 watts at 100%.    As soon as my battery reaches 53.5v then 53.5 * 80 = 4280watts and I'm good to go.     


This is all 'as is should be' and why you buy an expensive controller like Outback or Midnite Classic (or others) because they are quire sophisticated in getting every bit of power (e.g. watts) that it can and constantly check for the best solution.
Wolf likes this post
#10
.. I’m thinking this is the issue.. the charge controller dropping my array from 100v down to roughly 86v when it’s trying toget max output from my array,, problem with that is my array is 100vmp and 36amps for 3660w and when the charge controller mppts the voltage at 86v (instead of 100w) and arrays producing close to it’s max input amps at 36amps, then charge controllers only allowing 3100w. I could understand if the controller was dropping my volts to make more amps but that’s not what’s happening. It’s like controller will not accept voltage from the array higher than 85ish, unless battery voltage is lowered, which allows the input voltage to raise the same amount that the battery voltage drops. Or over 85v is seen in pic 2 when the controller doesn’t have to create more amps than what’s being input by array.

I’m starting to think that the controller is only capable of raising the amps to a certain amount above what the array is inputting and it will only allow array to input enough voltage to enable the controller to raise the amps to the max amount above the input amps that the controller is capable of. The controller is capable of 60amps but it can only raise the amps by a certain amount higher than what’s being input by array. This could be why I can’t get closer to the 3660w I should be seeing from the array.

So basically I’m thinking my array should have been closer to 90 volts instead of 100v so I’m not losing the top 10ish volts from my array. 10 volts at 36 amps is 360w which is close to the 460w I’m not getting from array that I should be.
Basically I’d see no way to change anything in the settings to make the controller mppt at a higher voltage because the controller can only use the amount of volts needed to raise the amps by the amount it can raise the amps to.. I’m saying if input amps are 30amps then the controller can’t make that into 60amps, it can only use the amount of voltage needed to raise the amps by the amount it can raise the amps


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