Something wrong voltage drop not getting full watts

Started by Worldsworstfish, August 03, 2019, 04:38:20 PM

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Worldsworstfish

I added a second panel array and charge controller, thanks to everyone here for that help.

New issue though. 

Prior to adding second charge controller I would get 5000 watts out of my 1st array.

Now each array will max out at 3500 watts

On the wattage coming from the panels, I seem to max out at 3500 watts from each string at around 64.5 amps this is at around 77 Volts this is at bulk charge with 42 amp load on system.  Each charge controller is showing about the same.  The BMK on the magnum rtr is showing +18 amps dc going to battery. This is the max load that I can put on the system.  This is full sun.

If I drop the load to 6 amps I have one controller running 3500 watts 60 amps 83 volts second controller showing 2500 watts at 43.4 amps 89 volts  and the bmk is showing +88 amps going to the battery. 

If I shut down the breaker to the charge controller my voltage reading coming from the panels is 100 volts.  As soon as I turn on charge controller it drops to the 77 volts. 

I have #2 copper coming from my combiner box a run of around 45 feet. 

The second controller is warmer and the fan noise is a lot louder than the original.   

Even if I shut down the power to and from the second controller I am still limited to 3500 watts from the first controller. 

The total wattage of each array should be 5000 watts. 





boB

Quote from: Worldsworstfish on August 03, 2019, 04:38:20 PM

If I shut down the breaker to the charge controller my voltage reading coming from the panels is 100 volts.  As soon as I turn on charge controller it drops to the 77 volts. 


This sentence tells me that the charge controller is most likely tracking correctly at least.   Voc = 100V and Vmp = 77V which is 77% of Voc.

( What is your battery voltage ? )


Without any partial shading of the PV array, this would be very close to the normal percentage of open circuit voltage.

So, what that means (usually) is that you are getting the maximum amount of power from the PV array at that time.

If your batteries get full and go to Absorb OR the CC current limits, then the controller will reduce the power by raising the PV input voltage for that purpose.

What I would do is to take a close look at your re-wiring of the new PV arrangement.   The  MPPT will try to find the input voltage that gives you the most power, even if the strings of panels are mis-matched somehow.

If you had 2 or 3 strings of PV modules, had the same number of similar  panels in series on each string and then added one module to just one string, you would lose quite a bit of power because of that.

Anyhow, just give it a good look. Also make sure that all of the panels are good and none of them are shorted somehow or something like that.



K7IQ 🌛  He/She/Me

Worldsworstfish

#2
Bob

Thanks for reply.

The times I am talking about are during bulk mppt charging. 

Battery voltage is 48 volts, 1028 amp hours.

The second array is identical to the first array.

1 SOLAR PV MODULES ASTRONERGY CHSM6610P-260
PMAX VMPP VOC IMPP ISC
260 WATTS    31.05 VDC 38.53 VDC 8.39 ADC 8.72 ADC

PV STRINGS 3 MODULES
PMAX               VMPP              VOC.                IMPP                ISC
780 WATTS       93.15 VDC.    115.59 VDC        8.39 ADC      8.72 ADC

From manual what I figure is

116 V * .8 = 92.8 volts   I look at the chart and I should be above the the max 88 amps.

Is that right or am I missing something.



3 SUB ARRAY TOTAL 6 STRINGS
PMAX VMPP VOC IMPP ISC
4,680 WATTS 93.15 VDC 115.59 VDC
50.34 ADC 52.32 ADC



Checked wiring everything looks good. 

I shut each string down at combiner box and measured before each breaker all showing same voltage around 100 volts, this was at 9am so not quite direct sun yet. 

What is concerning me is that with a single controller I was seeing around 5000 watts coming in when the battery was charging with a load.  Now with a load and battery charging I am only getting 3500 watts on each string.  Even if I shut the second controller down I am not getting the watts I used to out of the first string.  I am only getting around 64 amps from each controller.  Shouldn’t I be up to the 88 amps max?  This is with perfect sun when I am checking no shading. 

I really appreciate any help. 




boB


Well, the nameplate voltage ratings are probably STC or "Standard Test Conditions" which means that the PV modules are measured at 25 degrees C.

When they are in the sun, they heat up and the voltages come down at around 1.1% per 25 degrees C of module solar cell temperature.  I think that is why you are seeing 100V open circuit and more like 80V and not 90V Vmp at maximum power point (77V was close enough for solar work).  The power output would be lower as well of course...    At 9 AM, the Voc would be about the same or  even higher than later in the day when they are hotter.

That is all well and good BUT you say you are not getting as much power out as you were before with just one Classic.

I am not quite understanding which array and which output current you are getting on each individual Classic.

>>>>" I am only getting around 64 amps from each controller."
Wouldn't that be 64A + 64A = 128 amps total ?  64A at say, 50V would be 3.2kW...  What is the battery voltage when you see the 64 amps 50V ?  55V ? etc...

Are you getting 64A out of each Classic or is just one Classic and array not quite pulling its fair share ? 

Also, is there ANY partial shading at all ?




K7IQ 🌛  He/She/Me

Worldsworstfish

Thanks Bob.

I am getting more power out of two than I was the one.  Just seems that when I had one I was showing 5000 watts at times.  I don’t see much over 3500 watts now.


During heavy loads, 42 amps AC load.  The battery bank monitor is showing +18 amps going to the battery.

Classic 1 is putting out 64 amps at around 77 volts 3500 watts

Classic 2 (new) is also putting out 64 amps at around 77 volts 3500 watts



Then drop the load to 6 amps AC.

Classic 1 is putting out 60 amps at 83 volts 3500 watts

Classic 2 is putting out 43 amps at 89 volts 2500 watts

The battery bank monitor is showing + 88 amps going to the battery.

I am just wondering if during heavy loads if I should be getting higher if during the heavy load situation if I should be getting more than 18 amps to the battery.

There is no issue with shading on either bank unless a cloud comes over


I am getting more power out of the two together than I was the one.  It just seems that Classic 1 I was seeing multiple times where I was seeing 5000 watts.  I wasn’t paying attention to everything else during the time that I was running just one.  I added a bunch of loads when I added Classic 2 so that is why I am paying so much more attention. 

ClassicCrazy

I think you need to consider the batteries internal resistance - or how close they are to full because they just might not accept more power.  Also not sure when you did your observations but the battery temperature could be doing some limiting because of temperature compensation ?   Do you have those two systems in Follow Me ?   

Larry
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

boB


Thanks Larry.   Follow Me will help sharing if one Classic goes to Float but not from bulk to absorb.
Oh, yes, then also back to bulk/absorb from float IF that happens...

>>>Then drop the load to 6 amps AC.
>>>Classic 1 is putting out 60 amps at 83 volts 3500 watts
>>>Classic 2 is putting out 43 amps at 89 volts 2500 watts

Did you happen to notice if one or both Classics went from bulk to absorb after the AC load was dropped ?  That would definitely raise the PV input voltage and reduce the output current and they would not share 100%...   

Classic 2 had lower output current than Classic 1 and their PV input voltages kind of leads me to think that it is possible that they could have come out of bulk MPPT and into absorb voltage regulation mode until a big load comes back on.

There is a lot that can be inferred from Voc and Vmp as far as MPPT tracking and mode is concerned..... In general

I'm not 100% sure of course because of all the tolerances and temperatures and efficiencies and stuff.

boB


K7IQ 🌛  He/She/Me

Worldsworstfish

When I removed the load it was still in bulk charging.  It’s just that the current going to the battery went from +18 amps to +88 amps, according to the battery bank monitor.  Follow me is on.

bee88man

You doubled production but still same battery, correct?

Battery still has it's same resistance value...hard to fool ohms law...not to say there no improvement, but maybe not where you're looking.

Double the battery and it's resistance along with doubling the production and it wil be a whole new result...loads/resistance is what changes totals

Worldsworstfish

Bee man

Thanks.  The rub is that even if I shut down the new controller I am still getting the same, new lower output from the original controller.  I would see 5000 watts on the original controller prior to installing new controller.  Now it maxes at at 3500.  Same thing happens if I shut down the original controller my max output is 3500 on the new controller. 


boB

OK, try this...

Right after your turn off your big AC load and you see the PV input voltage rise up tho that high 80 volt value, press ENTER when in the main MNGP status screen. 
This should force the Classic, at least that classic, to do a new sweep of the PV array.

IF that does bring the Classic(s) up to high power, try changing the MODE from SOLAR to  LEGACY P&O and see if that makes a difference.

boB
K7IQ 🌛  He/She/Me

TimBandTech

Be sure you are in bulk mode and not in absorb mode(which would explain current limiting) .
Alren't there maximum current specs per CC? Possibly someone has set a current limit based on battery specs, which generally do spec a maximum charge current. In this case there is nothing wrong. Seems you are real close to a good configuration. As I recall 10kW of panel is about as much as a medium size battery bank can take respecting max charge current.

A bit of sulfation would have you out of bulk and into absorb mode. Isn't there some timing detail in there too?


Quote from: Worldsworstfish on August 04, 2019, 01:08:29 PM
Bob

Thanks for reply.

The times I am talking about are during bulk mppt charging. 

Battery voltage is 48 volts, 1028 amp hours.

The second array is identical to the first array.

1 SOLAR PV MODULES ASTRONERGY CHSM6610P-260
PMAX VMPP VOC IMPP ISC
260 WATTS    31.05 VDC 38.53 VDC 8.39 ADC 8.72 ADC

PV STRINGS 3 MODULES
PMAX               VMPP              VOC.                IMPP                ISC
780 WATTS       93.15 VDC.    115.59 VDC        8.39 ADC      8.72 ADC

From manual what I figure is

116 V * .8 = 92.8 volts   I look at the chart and I should be above the the max 88 amps.

Is that right or am I missing something.



3 SUB ARRAY TOTAL 6 STRINGS
PMAX VMPP VOC IMPP ISC
4,680 WATTS 93.15 VDC 115.59 VDC
50.34 ADC 52.32 ADC



Checked wiring everything looks good. 

I shut each string down at combiner box and measured before each breaker all showing same voltage around 100 volts, this was at 9am so not quite direct sun yet. 

What is concerning me is that with a single controller I was seeing around 5000 watts coming in when the battery was charging with a load.  Now with a load and battery charging I am only getting 3500 watts on each string.  Even if I shut the second controller down I am not getting the watts I used to out of the first string.  I am only getting around 64 amps from each controller.  Shouldn’t I be up to the 88 amps max?  This is with perfect sun when I am checking no shading. 

I really appreciate any help.
24 SURRETTE 2-KS-33PS 2V 2500AH @48VDC, 7kW STC PV  (three arrays) 3 Midnite Classics, one with Waste Not High diversion driving 3kW of heating element at 48VDC through three SSR circuits, Two 6kW XW inverters

Worldsworstfish

#12
Bob, 

I won’t be home til Monday, but will give that a shot.

Tim,

It is in Bulk mode, with the heavy load it is only putting 18 amps to the battery, so battery is not limiting in that case.  My limit is what is coming out of charge controller. Even shutting down one controller the power does not increase.

Thanks to all

mike90045

 After a couple hours of Absorb,  at your combiners, shut down all but 1 string of panels. Place a heavy load on the system and see what that string is sending to the battery (in amps) .  After a minute, switch in another string, then turn off the first.  You want to keep the controller active, not shutting off the solar, but adding a string, then removing a prior string. Cycle through all the strings, on all the controllers.   You find the bad string this way, under load, not by simply measuring the string voltage which is quite variable.
http://tinyurl.com/LMR-Solar

Classic 200| 2Kw PV, 160Voc | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph )| Listeroid 6/1, st5 gen head | XW6048 inverter/chgr | midnight ePanel & 4 SPDs | 48V, 800A NiFe battery bank | MS-TS-MPPT60 w/3Kw PV

Worldsworstfish

Mike,

I will do that when I get back, no idea why I hadn’t thought of that.   :-\

I don’t think I have a bad string but that will confirm it one way or another.