Weird production for 6 panel array

[ABarbarian]

I have 6 matching panels wired up as shown in attached image, but am getting wierd production into the charge controller.

- Each pair of panels in serial should be producing about 400 watts
- When everything is hooked up expected production should be 1200 watts, I am getting 800 watts
- If I turn off 'dc breaker A' I produce 400 watts, as expected
- If I turn off 'dc breaker B' I produce 800 watts, as expected
- If I break point 1 I get 800 watts, as expected
- If I break point 2 I get 800 watts, as expected
- If I break point 3 I get 800 watts, as expected

.. but when it is all wired up, only 800 watts

Probably something simple, I can't work it out.

 

[rodrick]

What is the system voltage?
how many amp is the charge controller?
what type of battery bank do you have?
it could be the scc is clipping excess or batteries are near full

 

[MisterSandals]

That should work, its 2S3P from what i figure.

.. but when it is all wired up, only 800 watts

How are you measuring watts?

 

[rodrick]

That should work, its 2S3P from what i figure.

How are you measuring watts?

Well you had me thinking hard trying to understand that curve ball

 

[ABarbarian]

What is the system voltage?
how many amp is the charge controller?
what type of battery bank do you have?
it could be the scc is clipping excess or batteries are near full

- Controller feeds into a 48V inverter
- Controller: Battery Rated Voltage: 48V
- Each pair of panels gives out about 84 volts
- LifePo4 48V battery pack

Panel Specs:
- 455W MONO Genius GS-455WM/HC
- Half Cut cells
- Open Circuit Voltage: 55.25 V
- Short Circuit Current: 10.9 A
- Voltage at Pmax: 44.61 V
- Max Series Fuse Rating: 20A
- Voc temp coefficient: 0.36%/celsius

You may be right about the Controller clipping because the batteries are basically full, I will check it over the next few days.

It's probably that simple, for some reason I thought the Controller would show 0 and cut off supply when full, I have a weird (cheap and strong) Thai made controller where I had to set the floating voltage to use as a cut off voltage to control over charge into the BMS/LifePo4 batteries

 

[MisterSandals]

Well you had me thinking hard trying to understand that curve ball

Are you referring to the idiotic post i first wrote and then deleted? :*)

 

[ABarbarian]

That should work, its 2S3P from what i figure.

How are you measuring watts?

2S3P is correct.

Measuring from the Controller, it shows input voltage, output volt/amp/watts.

@rodrick may be correct about it showing clipped watt output from the Controller, not the full input watts from the panels.

 

[MisterSandals]

Thai made controller where I had to set the floating voltage to use as a cut off voltage to control over charge into the BMS/LifePo4 batteries

If the SCC has a user defined battery type you can setup a charge profile better than most LiFePO4 specific profiles.

 

[MisterSandals]

800W / 56V charging = 14.28A

Is your SCC rated at 15A by chance?

 

[rodrick]

Are you referring to the idiotic post i first wrote and then deleted? :*)

yes you had me working hard to figure it out?

 

[ABarbarian]

800W / 56V charging = 14.28A

Is your SCC rated at 15A by chance?

Nah, it goes up to 60A (at least that is the Max Charge Current setting)

I recently moved this setup and it regularly worked at the higher watts, sometimes when I first eg turn on 'dc breaker A' the watts will jump up to 1200W then come down to the lower values.

 

[ABarbarian]

After a days testing it does appear to be the same as @rodrick said, when the batteries are low I see the full production/watts passing the Controller, as the batteries become fully charged the watts reduce down.

Thanks for the replies

 

[JBertok]

If your MPPT displays input voltage, a telltale sign it's throttling back is that the PV input voltage will begin rise past n*Vmp. So, for example, a 2S string of 24V-nominal panels with a Vmp of 37V will be around 74V at peak MPPT. The way MPPT controllers throttle back is by allowing the PV input voltage to rise toward PV Voc. Voltage rise beyond the Vmp rating has a corresponding drop in available output current until Voc where Voltage reaches the highest value possible but available current is 0 Amps. Maximum Power Point Tracking controllers utilize the PV Voltage/Current curve by manipulating their harvest voltage from the PV to achieve their output target.
Full current through a charge controller may only be achieved in Bulk mode. Absorption and Float modes are each trying to hold and not exceed a specific DC bus voltage, and will throttle back PV if abundant.