Firmware Bug? Auto EQ then big amperage drop.

[danda]

true that.  I hadn't noticed the significance of that straight line before.  I was away at the time, so I didn't touch it until a couple hours later, near where the graph returns to normal.

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?

[danda]

ok, I just went out and checked.   The lowest string Vmp is 66 and the highest is 71.4.

Thank,

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

Vmp Vic

[danda]

FW update is on my todo list.  Already using P&O mode, thanks.

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

[danda]

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

correct.  forklift battery.

[Vic]

Thanks danda,

Am certain that if those are STC String Vmps,  that you do NOT have high enough Vin to run an MPPT CC very efficiently.

And,  am no expert on the BB,  and its data graphs,  But,  seems to me,  that you can see exactly what is happening  --  when the battery V got up to about 59,  or a smidge higher,  the Vmp was down to about 62.5 V.

There IS  a bit of a Tracking issue with Classics,  sometimes,  where the Vin gets dragged down to near Vbat,  and this could be part of the issue.  BUT,  the Voc of your string (well very lightly-load,  almost Voc)  was about 74 V with a few amps from the array.   MPPT CCs want an STC String Vmp of about 85 V or so to be able to work efficiently on warm/hot days,  especially with FLAs,  which DO require EQing.

Have you considered reconfiguring your PV array stringing?   Just to try to keep everything and body happy?

FWIW,   Vic

[danda]

I suppose that is in theory possible but in the past I've EQ'd it at 62v manually without problems and since then I lowered EQ voltage down to 60.

One thing I've noticed is that the PVin always seems to follow the output voltage pretty closely.

In fact, when I first got the classic, I was hearing an annoying chirping a lot and the PVin was often very close to the vOut.  Somewhere on this forum I found advice to raise the minimum voltage distance setting  ( I forget the exact setting name ).  I raised it to about 5v, and the chirping went away and I see what appears to be a larger mppt amperage boost.

...  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.

[danda]

Hi Vic.

That's new info for me, thanks.  I thought mppt could pretty much adjust voltage as necessary.  I guess it always has to be from significant higher to lower though, eh?

I'm not crazy about reconfiguring arrays due to:  1) physical constraints, 2) wiring hassles, and 3) I want to be able to pop in my old c40 charge controller in an emergency, so arrays should stay not too far from nominal voltage.

But at least now I'm aware of this constraint and can plan/test accordingly.

Further, if this is indeed the cause of the problem, then it would seem to me that the classic should notice an undervoltage situation, protect itself, and display some type of useful error message, rather than freaking out for approx 15 minutes and then putting out a few amps while supposedly in EQ mode.   ie, there's still a logic error to be fixed.

Thanks danda,

Am certain that if those are STC String Vmps,  that you do NOT have high enough Vin to run an MPPT CC very efficiently.

And,  am no expert on the BB,  and its data graphs,  But,  seems to me,  that you can see exactly what is happening  --  when the battery V got up to about 59,  or a smidge higher,  the Vmp was down to about 62.5 V.

There IS  a bit of a Tracking issue with Classics,  sometimes,  where the Vin gets dragged down to near Vbat,  and this could be part of the issue.  BUT,  the Voc of your string (well very lightly-load,  almost Voc)  was about 74 V with a few amps from the array.   MPPT CCs want an STC String Vmp of about 85 V or so to be able to work efficiently on warm/hot days,  especially with FLAs,  which DO require EQing.

Have you considered reconfiguring your PV array stringing?   Just to try to keep everything and body happy?

FWIW,   Vic

[Vic]

Hi danda,

Fine on all.   zoneblue wondered if the Classic had "crashed"  IIRC.   You Monitoring Whizzes are far ahead of me ...   so dunno about that.

BTW danda,  what IS the FW Version in the Classic?

Understand about not wanting to re-wire your present PVs,  but  perhaps you might want to consider doing it anyway,  and perhaps do a hack back to lower Vmp,  if you needed to revert to a PWM in an emergency.

Here,  on one system,  during the design process,  considered trying to run an early MPPT CC  (the OB MX-60)  with strings of two 35.4 Vmp PVs in series,  for a String Vmp  of about 71 volts ...  felt that  this was just too low,  and went with three PVs per String for a String Vmp of 106 V.  This is pushing the high end,  for most climates,  but the Classics seem happy.

Perhaps others will chime in,  but just my opinion that you need about 85 - 90-ish String STC Vmp.

FWIW,   Vic

[zoneblue]

The ever observant Vic is onto that Vmp issue. Vmp of 66V is cutting it too fine IMO. Remember that in hot weather the Vmp drops. When your PV amps are high the array home run cable drop is at max. Near the end of bulk, and the beginning of absorb  when the battery voltage and current demands are highest, this is where i would expect to see issues there. So the fact that your "accidental" EQ occured bang in the middle of the day, might be a clue.

[danda]

My two old c40 workhorses never had a problem with the voltage.  oh, and auto-EQ worked great from day 1.   :-D

This seems to be a downside to MPPT that I had not considered (for my system).  That said, I'm not yet fully convinced it was caused by the voltage given that I've manually EQ'd in warm weather before with the classic.  Even the previous day, which was auto-EQ try 1.   Next time I do a manual EQ, I'll pay closer attention.

For the sake of moving forward, let's say inadequate vmp was the underlying cause.   It still seems to me that this is a condition the classic should detect, protect against, and warn the user of.   And the observed behavior seems a serious bug.

I'm thankful for the diagnosis which definitely helps me plan and work around.   But I would also hope that midnite fix this erratic behavior.

[Vic]

Hi danda,

SO,  what is the Firmware version running on your Classic?

Thanks,  Vic

[zoneblue]

My two old c40 workhorses never had a problem with the voltage.  oh, and auto-EQ worked great from day 1.   :-D

PWM works best when the Vmp is around 17V per 12V of battery. That allows a few volts off for heat, cable and controller loss. In this situation you cant just swap in a MPPT. And 60 cell panels dont work well per 24V using any controller. There just isnt enough leeway, and the controller will ride teh IV curve leftwards and downwards where it settles on a reduced output. There is one guy who uses 60 cell panels with LFP and PWM, (LFP doesnt need quite as high voltage) but still he trades off a little reduced power at near full charge, to get a really high level of efficiency during the larger part of bulk, when you most need it. Obviously this needs careful tailoring of strings to achieve, you lose the flexibility of mppt. But in terms of total throughput effciency you cant beat PWM when you can manage to match the module Vmp to battery voltage.

With your strings varying in Vmp this also makes the controller choose a compromise of sorts, so that might be a factor here too.

Peoples experience with mppt varys. While the rule of thumb is to go one battery voltage higher for Vmp, the odd person has reported acceptable results using legacy mode, and o thers say that the Morningstar MPPT controllers can run closer to Vmp. I have no experience with either. Both Outback and Morningstar's have excellent power efficiency curves, which are worth a study on the matter.

As to the cause of your glitch im not real sure.