Classic 200 Troubleshooting

[f1engineering]

System:
(75) Panels, 250 Watts each, 18750W total, strung in groups of 3
(5) Classic 200 CC's, each has 15 panels, Voc=165VDC, configured as follow-me.
48 V Battery Bank, 3300AHr
(3) Outback Radian 8048 inverters.
Battery cables are #4/0. 15' run from battery to each inverter.
CC's are on bus bars with the battery cables at each inverter in Midnite Epanels.

Issue #1:
Batteries were fully charged, and allowed to absorb/float prior to starting inverters.
As inverters pulled power, CC's continued to Float, despite Vbatt falling to 46 Volts.
CC's started to fault, showing a "DEFCON 4" FET Drive Error at random intervals.
After manually restarting the master CC, all units switched to Bulk charging and have not produced the error again.

What is the trigger for restarting bulk charging?
Why did the CC's continue to float despite a low battery voltage?

[zoneblue]

System:
(75) Panels, 250 Watts each, 18750W total, strung in groups of 3
(5) Classic 200 CC's, each has 15 panels, Voc=165VDC, configured as follow-me.
48 V Battery Bank, 3300AHr
(3) Outback Radian 8048 inverters.
Battery cables are #4/0. 15' run from battery to each inverter.
CC's are on bus bars with the battery cables at each inverter in Midnite Epanels.

You get the large off grid install award. Is this commercial or residential?

Issue #1:
Batteries were fully charged, and allowed to absorb/float prior to starting inverters.
As inverters pulled power, CC's continued to Float, despite Vbatt falling to 46 Volts.
CC's started to fault, showing a "DEFCON 4" FET Drive Error at random intervals.
After manually restarting the master CC, all units switched to Bulk charging and have not produced the error again.

What is the trigger for restarting bulk charging?
Why did the CC's continue to float despite a low battery voltage?

Obviously the controllers will try their best to maintain float voltage, but if the inverter draw exceeds the classic throughput then yes the voltage will fall. The setting youre looking for there is called "rebulk". You set it to the voltage, that it drops below to intiate another bulk absorb cycle. However, in this case thats possibly not going to help as it appears that there isnt enough sun. BTW rebulk default setting is really low, so it doenst normally kick in at all. As for the fet error that has surfaced once or twice before and ill let bob address that.

[Westbranch]

do a search for DEFCON, there are only 5 hits for that search term, including this thread.  Happy reading...

[dgd]

I don't quite understand what is happening here.

When my battery bank is in Float and then a large AC load comes on, the battery voltage drops below the Float voltage setting and immediately the Classic changes mode into FLOAT MPPT and starts sending maximum PV power to the battery and brings it back up the Float voltage (or tries to). It does not go into BULK MPPT and take the battery up to Absorb voltage setting and repeat ABSORB.

My rebulk  is set to the default 8

dgd

[phxmark]

What is your Minimum Volts Limit set to on the Classic?

I have mine set at the Float Voltage.  Mine jumps to Bulk when it falls below the Minimum Volts Limit.

[Vic]

Hi F1e..,

We do not have enough information on the  specs of the PV modules that you are using ...   

BUT,  appears that each of these Classsic 200s are potentially full up --  right at maximum rated power,  and perhaps running into HyperVoc,  depending on your temperatures at the site.

Generally,  it is not a great idea to run solar battery chargers (CCs)  at full rated current,  as battery charging often takes a number of hours.

Have you run the Classic String Sizing Tool for your configuration?

As an aside,  having LONG inverter cables can cause instabilities in power systems,  and 15 feet is LONG in my book ...  Have not consulted the Radian manual,  but #4 AWG,  15 feet long  seems like trouble on 8 kW inverters,  IMO.
EDIT:  Sorry  my #4 AWG is a TYPO,  meant #4/0...

What are specs on the PVs in this system,  or what is the exact model number and manufacturer?

EDIT:  OH,  and on Rebulk,  as others have noted,  it ships set at 8 V,  which disables it.  Normally,  one would want to think about trying to start a second (or more) charge cycle on a given day.  Normally,  as was also noted previously,  the CCs,  when in Float,   will supply large amounts of current while maintaining Float voltage.   If Vfloat cannot be maintained,   the CC will supply all of the current that it can from the available PV power,  but the Vbat declines,  and the Classic will show ' Float MPPT',   showing that it is trying,  but cannot maintain Vbat.

If your are seeing Defcon,  it usually means that the CC is being severely stressed,  although,  have never seen this warning message.

My opinions,   FWIW,     Vic

[f1engineering]

Responses:

This is for an orphanage/guest house in Haiti, so probably would classify it as "commercial".

The cables are #4/0, not #4. They are pushing the limit on length, but are within recommended usage. That still may be the problem, but I'm not certain on that, still searching out issues.

The PV strings are wires up in series of 5, with a Voc of about 165V. Temperatures are in the 30-40C range, so we shouldn't be hitting a hyperVOC condition.
Each controller has 3 strings in parallel feeding it. Each string is Isc of 9.09A.

Ran the sizing tool. We're spot on the money for a 200. Shouldn't hit hyperVOC until freezing, and since we're in Haiti, that's a safe bet.

Updates:
Today, the DEFCON 4: FET Drive Errors are still occurring sporadically, maybe 15-20 minutes, and scattered across the charge controllers. No noticeable pattern to it.

The CC's are in Bulk mode, so it is unrelated to the Float MPPT mode that I thought was a trigger last night.

I did find the rebulk voltage settings and have changed that, but my problem still remains.

I have not seen the controllers push more than 2300 Watts each, so it doesn't seem like we should be overstressing them, as they are rated for 3750 in this setup.

[Vic]

Hi f1engineering,

First,  sorry for my TYPO on the 4/0 inverter cables ...  but seemed that 4/0 was probably beyond a limit for 8 KVA inverters.

The Classics will limit their temperature by limiting current.  Believe that the MAXIMUM rated current is at about 25 C,  and will be reduced as the Classic gets warm/hot.  You might set the Mode in one Classic to Off,  and wait for about ten minutes,  and then switch the Mode back to Solar,  and see if the output current is considerably higher when first turned on,  and then is reduced as the Classic gets warm/hot.

High ambient temperatures will reduce the amount of power that the Classic can produce.

What are the FET and PCB Temps (in the Temp menu) when you are getting the Defcon warning?

More Later,  Good Luck,   Vic

[f1engineering]

response:
fet and pcb are hovering around 60C +/- about 3 degrees.
anyone know what the temp derating on the FET outputs is?

i want to try to isolate the battery cable problem, but i don't have a ton of spare cable to work with since i'm here in Haiti. So, I have 2 questions:

-Would it help to move the PV- line? It currently runs from the combiner box directly to the CC. Would it be better to run to the DC Negative bus in the Epanel box?
-Would running a #2/0 directly to the battery bus from the CC be helpful? Essentially, I would move the CC+ line from the Batt+ bus in one of the Epanels to the battery banks, but leave the inverter on its original #4/0 line. Is this sufficient, or woud I need to run a DC- line as well for it to be effective.

update: (EDITED 10:55 EST)
we have 5 classic 200's running identical strings of panels.
all of of them sporadically drop out the voltage.
watching the controller, it will be producing well (~130VDC, 2600W out, then we can watch the voltage drop on the input, until it hits 57, at which the unit resets and jumps back up to Voc (160VDC), then restarts the cycle.
there does not seem to be a correlation to inverter output levels or shading of the panels.

[Westbranch]

How long does it take for the V to drop before a reset occurs? 
What are the FET temps when the drop starts and when the reset occurs?
How are those 4/0 cables downsized to the #4 ga (I believe) that connects to the Classic?
Just curious as it seems to be working OK...

Most of the time planning to run the CC's and inverters at > 80% causes hiccups...  too close to the edge since the equipments built-in defenses start to come into play... so they don't self destruct..

[Vic]

f1,

Do not know the exact derating.  The label on each Classic states that Nominal operation is 25 C,  derated above 40 C.  The derating will be based on the temepratures of the Classics 60 C for FET and PCB is HOT.

Do not know which e-panels you are running,  and just how the CC positive outputs are collected,  but assume that inside one of the e-panels,  that perhaps all of the CC to battery connections are on one very large buss,  and from that buss there is a large cable connecting to the inverter positive buss ...   This is a very large system,  and the details of how the battery cables connect to the inverters and the CCs needs to be carefully considered.

There must be a very large battery negative buss in a DC conduit box/e-panel,  and this negative buss probably has a very large Shunt.   Usually the CC negative connections are all to this large neg buss.  If you are using Ground Fault Protection,   the way these negative connections are handled is important.

Regarding the Classics Sweeping the PV input voltage down to near the battery voltage,  this has been seen with earlier versions of the Firmware.  The latest Production Firmware for the Classics  seems to have helped this issue.

Please confirm that you are using the latest FW for each of the Classics:
http://www.midnitesolar.com/firmware.php?firmwareProduct_ID=1

More later,   Vic

[dgd]

update: (EDITED 10:55 EST)
we have 5 classic 200's running identical strings of panels.
all of of them sporadically drop out the voltage.
watching the controller, it will be producing well (~130VDC, 2600W out, then we can watch the voltage drop on the input, until it hits 57, at which the unit resets and jumps back up to Voc (160VDC), then restarts the cycle.
there does not seem to be a correlation to inverter output levels or shading of the panels.

So they are running in SOLAR mode? 
You could try changing to Legacy P&O and see if this works better.
It should not do the input voltage dropping to just above battery voltage thing in P&O

Dgd

[f1engineering]

Responses:

We're using the Epanels made for Outback Radian inverters.

We have (3) parallel setups with the Epanels.

Each Epanel has 1 Outback Radian and 2 Classic 200's.
The Battery + Bus bar is bolted to the (2) 175A DC breakers that disconnect the inverter.
The CC outputs run on #4, through an 80A GFDI breaker, to this bus bas.
The batteries run on #4/0 to this bus bar as well. (1) #4/0 positive cable into each Epanel.

For the negative side.
The inverter is connected straight to the DC negative bus bar.
Each CC runs across a shunt to the DC negative bus bar, again as #4 wire.
The shunt are currently not monitored by anything. We have disabled the one Whizbang that we had on the system to make sure it wasn't contributing to our problems.
The battery negative connection also runs on (1) #4/0 negative cable for each Epanel.

We are also on firmware 1849 already, so it shouldn't be a firmware issue.
Yes, they are in SOLAR mode right now.

The FET Drive Error even occurs with a FET temp of 45C.
What is the expected range of FET temps?

UPDATE:
We're testing some different configurations right now.
CC 1, remains wired the same, but SPD has been disconnected.
CC 2, we have moved the #6 PV- line. It WAS direct from the combiner box to the CC. Now it goes to the DC Negative bus. SPD is also disconnected.
CC 3, is our control. No changes at all.
CC 4, our CC+ output is now connected directly (well, #4 out to dual mechanical lug to #4/0 directly to the battery bank)
CC5, is now set to "Legacy P&O"

[f1engineering]

Nothing seems to have changed.

If anything, the cycles seem to be occurring faster now.
All of them continue to do the dropping voltage issue.
I was hoping that #4 and #5 might show improvements, but so far, nothing has changed.
I'm not sure what else to try.

[Vic]

Hi f1,

Thanks for the added info on your configuration ...   am still trying to process all of your info ...

Well,  Legacy P&O  'should'  help with the PV input being dragged down to Vbat.

Regarding the FET temp ranges;   Here,  with Cl 150s and string Vmps in the 93 to 106 V range,  running about 40  Amps out,  or so,  and ambient temps around 22 C,  the FET temps are in the range of 45 - 55 C,  and PCB temps a bit lower than FETs.    But   have NO experience with Cl 200s or 250s.   IMO,  your string Vmps are at the very high end of the expected operating range for the Cl 200.  This would make the Classic run hot at any current above 50% or rating for your string Vmp,  IMO.

45 C for FETs is surprisingly low,  and may be the result of the Vin being dragged all the way down to/near Vbat,  or perhaps the FET Drive warning is a component.

Am busy laying pipe in trenches,  but will try to think more about the way the negative CC connections are cabled,  and all of the differing configurations that you have tried for the CCs.

Good that you have 1849  FW.   Later,  good luck,   Vic