Firmware Bug? Auto EQ then big amperage drop.

[danda]

So I seem to have run into some sort of classic bug today.

I'm not running latest firmware yet.  This incident gives me more incentive to upgrade.

Lately I've been running some opportunity loads and I also had the absorb time set to 4 hours which is pretty long.  The combination meant that for the past week I haven't quite made it to float, and so the auto EQ kicked in yesterday.  ( This behavior is due to known issue where auto EQ daily counter gets reset if float is reached -- supposed to be fixed in latest firmware )   Yesterday it did not quite finish EQ and so it tries again today. 

Right about when it reached the EQ voltage, the amps dropped from approx 50 down to about 2. 

Fortunately I went out there to turn off EQ and adjust the timings and so I discovered the issue within about 2 hours.  I first checked for any popped breakers on the input side... nothing amiss.

So then I tried to disable the EQ.  I tried stopping and starting it manually several times.   No matter what I did, the status screen kept displaying the mode as "EQ MPPT".  I tried turning off the PV input and the mode changed to "Resting" after about 2 minutes.  Then I turned the PV back on, and guess what...  mode returns to "EQ MPPT" and amperage stays between 1 and 3 amps.  lame.

I was getting worried I might need to reset the thing and lose all my settings.

Finally hunting around I found "Force Bulk" under the tweaks menu.   After turning that on, the amperage returned to normal, and all was well.

I'm attaching a graph from blackbox that clearly shows the event.

One other anomaly I noticed is that my solarvisor script that polls blackbox each minute for battery voltage was unable to retrieve valid voltage info during the event.  Yet blackbox's graph code was clearly getting it via modbus somehow.   I haven't looked into that any deeper yet.

[ClassicCrazy]

Why not update the firmware ?

Larry

[ClassicCrazy]

Your graph does not show the battery voltage during that event so hard to tell what is going on exactly .

Larry

[danda]

Why not update the firmware ?

Larry

I'm planning to.  mostly just curious if anyone else has encountered this.   It is distinct/separate from the auto-eq daily counter issue.

I wonder if it:

a) is just a one-time freak thing.
b) occurs every time auto-EQ try 2 is reached.
c) occurred due to some sort of overload.
d) is actually fixed by the latest firmware or not.

[danda]

Your graph does not show the battery voltage during that event so hard to tell what is going on exactly .

Larry

Battery voltage just dropped down to normal levels when there is little or no charging and moderate load, ie 52v .. 51.6v.   as would be expected.  In EQ mode, the amps should have stayed much higher to keep the voltage up/constant.

Edit:  oh and actually the graph does show "output voltage" which in my experience is always the same as battery voltage.  It is the light green line.

[Vic]

Hi danda,

Just looked at your Graph ...

Is there any Scale Factor on that graph for battery voltage,  or other items,  or,  are the legends to scale?

Please tell us more about your system.  PV STC String voltage,  battery voltage and type,  etc.

Thanks,  Vic

[danda]

@vic everything to scale.   nothing funny in the graph.

Normal peak output on a sunny day is 3-3.5 kw.  About 50-60 amps at approx 58v.

During the event voltage dropped to around 51.5 and amperage to between 1 and 3 amps.  I confirmed this on the classic itself, which was not even operating the fan.

[Vic]

Hi danda,

Fine,  thanks for that info.

However,  please;
What is the String Vmp,  or,  how are your PV strings arranged  (PVs in series and how many strings),  and what is the manufacturer and model number for the PVs?

Assume that you are running Flooded Lead Acid batteries,  correct?

Thanks,   Vic

[danda]

Hi danda,
Please tell us more about your system.  PV STC String voltage,  battery voltage and type,  etc.

System uses mixed panels but I matched them pretty well to have similar voltages.   Open circuit voltage is around 86.

Battery voltage is 48.  forklift battery.  750 amp hour at 6 hour rate.

[Vic]

OK,  thanks again danda,

But,  what IS the String Vmp,  based on the STC Vmp of each PV in one series string?   We could guess,  but especially with a mix of PVs,  could you give the manufacturer and model number of each PV?

From the Graph,  it looks like you ran out of Vin when doing that EQ.

TIA,  Vic

[zoneblue]

Also note that your BB curves seem to have no data between about 1245 and 1300. (Its not ideal but BB presently just skips missing data with a straight line.) Wonder if the controller just crashed, a freak surge or something, then it WDT reset after a period? Or did you power it down for a bit?

[Vic]

 ...  It looks like the battery V was at about 59 V,  and the PVin was about 64 V.  This is NOT enough headroom for MPPT CCs to find a good Vmp and operate well ...   IMO,  the Classic might well have given up on doing the EQ,  as the battery V rose too close to Vin.

How long after the Classis's output went to a few amps,  did you ReBulk?

Vic

[danda]

also: 2 arrays on separate breakers.

array 1: 6 strings.  mix of 200 watt and 75 watt panels.
array 2: 6 strings.  mix of 175 watt and 65 watt panels.

each individual string uses identical panels and open circuit voltage is at or near 86.

[Vic]

Thank,

BUT,  what is the String Vmp?   The CC does its work,  and makes power from Vmp,  NOT Voc.

Vmp Vic

[Vic]

And, danda,

A FW Update would not hurt,  tracking has gotten better with later revs,  believe.

Also,  you might try Legacy P&O Mode to see if that helps ...   Vic