Programming deltas

[krementz]

I have 2 Classics connected to SMA inverters.

I want to identify when Classic1 is producing more power than Classic2 and then give me a signal I can use to trigger energy consuming devices, like hot water heaters.

IF Classic1 - Classic2 > 500 watts, DO this1
IF Classic1 - Classic2 > 100 watts, DO this2

Any suggestions on how to do this? I am using z-wave Vera controllers to talk to the heaters. This1 and This2 are scenes on the Vera controllers. I already have

If Absorb = TRUE, DO this1

However, I notice on cloudy days I may be in absorption phase, yet Classic1 - Classic2 < 100 watts, eg, not enough energy to be worthwhile.

[ClassicCrazy]

Seems like you could use any number of options to control via the AUX contacts.
Are your two Classics in Follow Me ?

Larry

[Vic]

I have 2 Classics connected to SMA inverters.

I want to identify when Classic1 is producing more power than Classic2 and then give me a signal I can use to trigger energy consuming devices, like hot water heaters.

IF Classic1 - Classic2 > 500 watts, DO this1
IF Classic1 - Classic2 > 100 watts, DO this2

Any suggestions on how to do this? I am using z-wave Vera controllers to talk to the heaters. This1 and This2 are scenes on the Vera controllers. I already have

If Absorb = TRUE, DO this1

However, I notice on cloudy days I may be in absorption phase, yet Classic1 - Classic2 < 100 watts, eg, not enough energy to be worthwhile.

Hi Krementz,

To me,   looks like you are expecting an imbalance in power delivery to try to infer that there might be excess power available (?).

As you know,   when in any CC stage that shows -MPPT,   there is no excess power available.

So,  when in a voltage-regulated stage,  like Absorb (Float,  and even perhaps EQ),   there can be a large amount of excess power available,   with only a small difference between the two Classics

So  as Larry was alluding to,   you could use  a "  Waste Not  "  function available on an Aux output of the Classic.

You could start by looking in the latest Classic Manual version to get started.   And using ' waste not '  as a Search term on the main Index page of this Forum should show  many Threads on the details of this function.

Some users of this function seem to see better results by using excess power from the battery,  or inverters,   rather than the PV input to the Classics (IMO).

Perhaps I do not really understand just what/why you were looking at output power differentials between two Classics.

It is very common for multiple charge sources on a single battery bank to not share battery charge currents too well when in a voltage-regulated stage,   but,   this really matters not,   as long as the regulated voltage can be maintained.

FWIW,    Vic

[bee88man]

I switch loads on and off by adjustable threshold inputs to relays sensing current levels through current transformers.
Relay (24vac) is pilot duty to heavier mercury relay/switch.

[krementz]

I have noticed very consistently that my Classic1 will be the controller with maximum output, and Classic2 will be reduced depending on the state on electricity demand.

When in Absorb or Float modes on sunny days, Classic 2 is always much lower, often zero watts. If I add some heavy loads, Classic1 will try to power it, and if insufficient power is available, only then will Classic2 raise its output. I have about a year of graphs comparing the to output, and there is no question that is how my system is working.

I have never seen both Classics producing matching low levels of power on sunny days.

If I get to Absorb mode on a cloudy day, both Classics are putting out maximum (identical) watts. Adding extra load would then reduces the battery charging.

I am not trying to "Waste Not" and power a DC load directly from the controllers. I just want a trigger/relay that I can sense/measure and then communicate to the Vera Z-wave controller, which will then add the heavy AC loads. It seems most (all?) of the threads I have read are talking about diverting DC power directly, not telling an AC load to be active. I do not have any DC loads except charging the battery bank itself.

"Heavy loads" include heat pump hot water heater (c. 900 W), hot tub heating system (in steps up to 4500 W), and "emergency hot water" 3500 W).

Does this clarify my question?

[Vic]

Hi krementz,

Thanks  for the added context.

NO,   this does not really clarify  your question (for me,  at least).

Each of your Classics  may have PV arrays of different sizes,  or oriented at differing Azimuths.

There may be significant differences in voltage drops on the output side of each Classic,   so even if the PV arrays on each Classic are identical,   and at identical azimuth angles,  this could contribute to each Classic producing differing amounts of power.

You might have set an Offset voltage in one or both Classics  that might account for some of this difference.

SO,   it does not seem that your Classics are very well balanced,   but only if the PV arrays are essentially identical  with very close PV elevation angles and Azimuths would the system  be very balanced throughout a day.

AND,   have never heard of that "vera .....  ..." controller.

So,   in summary,   I can not be of much help on this,   but with that large amount of graphic data,  you should be in a good position to determine just what will work best for your system as it has been performing in the past.

All, FWIW.   Good Luck,   Vic

[dgd]

I want to identify when Classic1 is producing more power than Classic2 and then give me a signal I can use to trigger energy consuming devices, like hot water heaters.
IF Classic1 - Classic2 > 500 watts, DO this1
IF Classic1 - Classic2 > 100 watts, DO this2

There is no way in the Classic firmware to achieve communications between two or more CLassics to achieve what you are wanting.
There has been some discussion previously about input power balancing or input power ratios between Classics, load balancing between Classics and diversion control from multiple Classics but nothing has ever progressed with these because of the significant firmware reprogramming necessary and MN are concentrating on other higher priority projects.

The only solution would be to use an external processor that reads register info from each Classic then does the logic operations you want and then writes, if required, new values to registers in each Classic to control the various input and output.
If you look in the Arduino area you can see the efforts taken there to control water heating when dealing with multiple Classics. And its pretty complicated

The charging behaviour you see where one CLassic charges and the other drops off to zero is perfactly normal behaviour since there is no charge output balancing.  The reason one takes over is because its impossible for the two Classics to be electronically identical and the slight measured differences in input voltages will slew the charging priority to one Classic. You cannot change this. Although some have fiddled with set point voltages its not and exact solution.

dgd

[mike90045]

I use the Local App to fine tune the voltage setpoints (not the internal voltmeter) in real time while watching both controllers and I can get good load sharing between two brands (Midnight & Morningstar)
Set both Bulk and Absorb

[krementz]

Reading various responses, I guess I have not been clear.

I am not trying to control my Classics. There is no issue "balancing" the two Classics. They are working fine, and I do not want to change their behaviour.

All I am trying to do is identify when there is a significant, say over 500 or 1000 watts, difference between the two Classics. I do not care if one is 100 watts different.

The two Classic 150s are attached to identical 2550 watt panel arrays (same azimuth, same elevation, same brand, same installation date, etc., with no shading issues).  When in bulk mode, both Classics show nearly identical readings, eg, within 50 watts.

Depending on the weather, SOC, absorption status, and daytime loads, the arrays may produce more power than can be used. Therefore, the output of Classic2 drops, while Classic1 remains at full power. At the end of a cycle, with no extra loads, Classic2 will be zero and Classic1 at a low output. I want to be able to automatically increase my AC demand when there is a significant difference.

Now, I manually look at the outputs, then manually switch on high wattage loads. There must be a better way.

[Vic]

Reading various responses, I guess I have not been clear.

I am not trying to control my Classics. There is no issue "balancing" the two Classics. They are working fine, and I do not want to change their behaviour.

All I am trying to do is identify when there is a significant, say over 500 or 1000 watts, difference between the two Classics. I do not care if one is 100 watts different.

The two Classic 150s are attached to identical 2550 watt panel arrays (same azimuth, same elevation, same brand, same installation date, etc., with no shading issues).  When in bulk mode, both Classics show nearly identical readings, eg, within 50 watts.

Depending on the weather, SOC, absorption status, and daytime loads, the arrays may produce more power than can be used. Therefore, the output of Classic2 drops, while Classic1 remains at full power. At the end of a cycle, with no extra loads, Classic2 will be zero and Classic1 at a low output. I want to be able to automatically increase my AC demand when there is a significant difference.

Now, I manually look at the outputs, then manually switch on high wattage loads. There must be a better way.

Krementz,

First,   do you have the latest Classic Manual?:
http://www.midnitesolar.com/documents.php?productCat_ID=21&productCatName=Charge+Controllers+-+Classics&model=CLASSIC 150&product_ID=256&act=

If not, scroll down the above-linked page to ' Manuals ',   and choose the one with the highest number  --  2056 -- at this moment.

Starting on pp 37,   the Aux 1 and Aux 2 functions that are built-into the Classic FirmWare are described.

PLEASE study the " Waste Not "  and Diversion portions to this manual section.

Your Classics DO behave a bit differently that any that I have installed/used/or seen,   and many/most of us might well try to get the best balance between the two Classics ...

It is just me,  BUT,   I would try to get the Classics BALANCED as well as possible,   such that each carries close to 50% of the loads in Bulk,   AND,   as much as possible in Absorb/Float.   You DO have a different perspective on this.

Trying to infer the amount of power that might be available  is never an exact science,   as there are a number of variables.

You might need to momentarily connect some heater/heating element on the AC outputs of the inverters just to SEE  how much excess power might be available   ...   

BTW,  the moment Absorb begins,   there is NO excess power available,   but as Absorb progresses there usually is more and more excess power available,   depending solar conditions as Absorb progresses (as you probably know),   SO,  knowing when the CC/s are in Absorb is not really a good indicator of the availability of excess PV power.

On this Forum,  you will see the common ways that some users use the Waste Not,  and Diversion functions on the Aux outputs.   BUT  these examples are not the only ways to use these functions.

You should be able to come up with ways to use these on the AC output side of your inverters,   rather than on the DC side  ...   it is up to you (primarily)  to figure this out,  given the nature of your Opportunity Loads.

AND,  since YOU DO have all of that historic data,  you can see the effect of turning on a/some Opportunity loads on the behavior of the CCs,   and their ability to power these loads under varying conditions.

EDT:  Also,   to the extent that you might need a smallish control system to do some simple processing,   there has been quite a lot effort devoted to the " Black Box Project ":
http://midniteftp.com/forum/index.php?board=47.0

This,  essentially,   is a cooperative project that could accumulate data,   process it and then control external devices,   based upon an individual's system and needs ...   FWIW <.

Wish you well in this.   Good Luck,   Vic

[bee88man]

Older thread, but...
Was a solution found for this situation?

This being a "Off Grid" system seems to make it more difficult to sense a surplus being available..