Two Classics not agreeing on absorb time

[Eric L]

I'm noticing that my two Classic 200s are finishing absorb at very different times. I'm not always around to monitor them, but this weekend I noticed that one is finishing absorb over an hour before the other (one is still trying to complete an absorb this afternoon; it probably won't be able to finish before dusk).

All the settings that I can think of are identical. Each Classic absorb time is set for a 1 hour minimum and 3 hour max, per battery manufacturer's instructions. I have tweaked the two Classics' voltages to be as close as I can get them (one was tweaked down .2 to get a match). The batt. temp sensors from each are right  next to each other on a battery. They are each connected to pv arrays that are very similarly situated, although of course they don't get identical light. They do seem to turn on within a few minutes of each other in the morning though. Not sure why this is happening.

The early finisher is connected as 'master' and has a larger pv array connected to it, FWIW. The laggard is the slave.

A sometimes complicating factor is that I run an irrigation pump as an opportunity load. It's a fairly large intermittent draw, and once the early-finishing Classic goes to resting mode, the 'laggard' Classic struggles to lift the voltage back to absorb when the pump pulls the voltage down (there are other loads on the system too, so by this time it's working hard and running pretty hot as well). However, while the cycling caused by the pump has probably been drawing the absorb time out, it does not explain the whole absorb time problem, since I turned the pump off early this afternoon, and the laggard Classic is still trying to finish the absorb an hour later (and holding the absorb voltage o.k. for an hour after the pump was turned off). With the pump on, the battery bank bounces between about 52.4 and 58.8 volts once the first Classic finishes absorb. I'm not sure whether this is harmful, but I guess I'd rather not have it happen; if both Classics are working together, there's enough power from the panels that it doesn't happen.

Anyway, thanks for any ideas.

Edit: It occurred to me after I posted this that I could go back and check the float times on each Classic to get an idea how much this is happening. About 3 days out of 5, they are showing float times within 10 or so minutes of each other, suggesting that on those days they are finishing absorb at roughly the same time. The remaining days, one Classic (not always the same one) is never going into float, even though the other spends 2-4 hours there. This suggests the absorb cycle is never finishing on that Classic (and I'm probably over-charging my batteries  )

[Vic]

Hi Eric,

Have been thinking about your post,  and just now saw your edit.

I am unaware of any ability of Classic CCs to network,  so I do not understand the Master/Slave references.  Did look at the manual,  but see nothing there either.

I had wondered about a situation like this for non-networked CCs,  where one CC finishes Asorb,  and another is unable to maintain Asorb voltage,  but tries for hours,  perhaps overcharging batts.

Do wonder about you setting the calibration of the Voltage of the CC with the larger array to one tenth volt below the other CC,  such that the other might be a bit more dominant.  Doubt that this would have a detrimental impact on the behavior during Float,  but dunno.  Sounds like you do not customarily spend a lot of time in Float (guessing,  given opportunity loads etc)>

Have been unable to get my two CCs to terminate Asorb together,  or close to it.  Have been overcharging my bank while trying to get a fixed Asorb time dialed in.

Average  DOD on this system  is small,  as the site is still under constructionj,  altho on some days the consumption can increase by a factor or 3-5X.  Variable DOD requires a variable Asorb time.  End Amps cannot work for me,  as know of no method for the CCs to sum EA,  and use that to end Asorb.

Am adding nothing to your wonderment.

Are your Classics Networked and able to share charge information?   Or just what is the Master/Slave function that you noted?

Thanks,   and Good Luck,    Vic

[niel]

vic, try page 15 and 16 of the current classic manual.

[boB]

Networking will fix this issue.  We're working on that right now.
You will also only need one battery temp sensor then.

Aside from looking at what Niel mentioned, you might try changing
the Absorb time (MAX absorb time I should say) to a low amount
of time on one of the controllers.

boB

[Vic]

Hi niel,

Thanks for the info,  have seen the ref in the manual,   and the Master and Slave on the PCB legend of the Classics  ...   BUT,  for now,  think that this will allow FUTURE firmware to communicate between multiple Classics.  Have been unable to find any reference about any current benefits/functions that can now be shared between the CCs.

In my situation,  have switched one CC off,  and let one do the job,  with one of the two arrays.   Am considering bussing both PV arrays together into a single Classic,   with the current limit on that CC set to about 70 Amps max.   Then, may run several incandescant lamps 24/7 to increase the average power consumption -- do not spend enough time above the "ideal" End Amp setting (16 A) to allow that to terminate Asorb.

>> Thread Hijack = End<<

None of this is a big deal.  The construction of this new site is just behind schedule.  Since day one,  the off-grid power system has been on-line.  This is a real treat for construction -- almost NO gen run time.  But  the little details of often using too little power comes into play on most days.

Thanks again for the help,  and good luck,  Eric.    Vic

[Eric L]

Thanks for the replies. boB, that's a good short-term solution (lowering the max time on one cc); I look forward to the updates.

Vic:

Are your Classics Networked and able to share charge information?   Or just what is the Master/Slave function that you noted?

I don't know much about the master/slave relation apart from what I read about it in Hegel years ago.    On the Classic, It doesn't seem to do much now, although it might do something (I'm not sure).

[boB]

At the moment, all the networking does is allow two (2) Classics to be read or controlled by one MNGP remote.

That does verify the Master/Slave connection and the networking but that's about all.  Coming soon !
(sooner the better in my book !)

boB

[Vic]

Thanks boB,

Would love to see Networking of CCs,  but,  really,  do not need two CC here right now.  A/C will be the thing that pushes my system over that hurdle,  and a real A/C sysetem may be two months away.  May hack a window A/C into the power room as a temp solution to help keep all things there cool - hate to see batts and electronics with tounges hanging out.

Thanks for the info on the current Networking functionality.

Oh,  and Eric,  i did get the joke,    He  He.  Thanks,  good luck,  Vic.

[Westbranch]

or as Hegel might say... OK which one of you is or isn't it?