Global Current Limiting

[boB]

SEVEN Classics ??!?!

Well, this global current limit works easiest when there is just a couple of Classics and maybe another charger...

Then, the Classic with the WB Jr. on it can be the one that limits...  Assuming that one WB Jr. endowed
Classic is necessary to bring the charge current over the limit.

The software was designed to work with multiple Classics and multiple WB Jr's  BUT I haven't
tried it with THAT many Classics before !

Would like to hear how that works !

If it is a large battery bank, then maybe only a couple of the Classics need WB Jr's

boB

[Vic]

Hi boB,   Thanks for the reply.

My guesses are,   that one Classic needs a Shunt and WVjr to monitor all currents going into/out of the battery, and  three other Classics need Shunts and WBjrs,   allowing those three to have their battery charge current limited,  under somewhat unusual conditions.

More Later,   Vic

[Iboondock]

Hello, new to forum, I came across this thread looking for information on current limiting options on the Classics.

I'm working with a scenario similar to what Vic has, except 4 Classics instead of 7.

If more than one classic needs a shunt and a WBjr, what is the best way to accomplish that? You would want all of the Classics referencing the total charge current into the batteries, correct? Can you stack multiple WBjr's on one shunt? (I don't currently have one in hand to check this)  Or do you need to wire the shunts in series with one for each WBjr?

Thanks

[boB]

Yes, you should be able to add more WB Jr.s to one shunt.  Place them VERY close to the shunt itself
if at all possible.  Stacking them right on top of each other would be great.

Reason why is that if you connect a shunt (only one even) to a shunt with long-ish wires,
then the power draw of the WB. Jr. itself (the shunt is its negative lead) can corrupt the
WB. Jr. readings somewhat.

boB

[Iboondock]

Yes, you should be able to add more WB Jr.s to one shunt.  Place them VERY close to the shunt itself
if at all possible.  Stacking them right on top of each other would be great.

Reason why is that if you connect a shunt (only one even) to a shunt with long-ish wires,
then the power draw of the WB. Jr. itself (the shunt is its negative lead) can corrupt the
WB. Jr. readings somewhat.

boB

That's good to know. Without having one in hand, I wasn't sure if they could physically stack on the shunt.

Thanks!

[dgd]

Yes, you should be able to add more WB Jr.s to one shunt.  Place them VERY close to the shunt..

What about just sorting out the code so that up to four Classics share the WBjr readings from a master in the looped serial wiring. Same way the battery sensor temperature data is.

dgd

[boB]

Yes, you should be able to add more WB Jr.s to one shunt.  Place them VERY close to the shunt..

What about just sorting out the code so that up to four Classics share the WBjr readings from a master in the looped serial wiring. Same way the battery sensor temperature data is.

dgd

DGD, that is exactly what I wanted to do !  This is exactly what should be done !

Hopefully this will be done.

Unfortunately, we don't have the time to do that right at the moment.

Had to shoot the engineer and ship !

boB

[Vic]

dgd,  boB,

Yes that sounds like a great idea ...   but  for the target system,   stacking WBjrs  should be fine,   especially given the inve$tment made in the system,  to date.  A few WBjrs,   and  some SPDs  should do almost all that is needed.

boB and the MN Crew are doing wonderful things on the new product development side of things!   Thanks!

Of course,  we do hope that there will be time in the future to go back and add some additional functions to Classics  and KIDs,   etc.

73,   Thanks,   Vic

[boB]

Right Vic !

There's just way too much to do and so little time !

Now, if we only set our clocks back one hour every day we would have a 25 hour day !

boB

[harryn]

Hi,

It seems like the main problem is that your friend's large system was designed for a 24 volt battery pack rather than 48 volt, but that seems to be a done deal now.

As far as controlling current during "excessive production", this can easily be dealt with using a small PLC controller.  With panel prices at $1 / kW vs the old days of $10/kW, there isn't a need to count electrons, just keep things safe.

Any decent controls engineer can program a PLC to detect if things are running too hard and send an output to shut down 50% of the Classics in the system.  PLC's are pretty easy to program.  One of the electrical engineers that consults for me is a controls guy, feel free to pm me if you want some help.   He is fairly familiar with the Classic 150 (not an expert, but fairly familiar).

His normal rate is $80/ hr which isn't bad for an engineering consultant. (1/2 the price of a car repair shop)  I am guessing that he could do the project in 40 - 60 hours and then you would have the solution for any future projects as well.  Of course we all know how software projects go, so it can easily double. 

Harry



   

[Vic]

Hello Harry,   Thanks for this idea.

But,  just to me,  since this function is already in the later Classic Firmware versions,   with only the addition of three WBjrs (for this particular system),   at a cost of about U$D 150,   or even less,   this can be accomplished,   smoothly,  cleanly  and with little additional effort.

And,  again,  just to me,   this Limiting function could also be accomplished by adding a Diversion Load,   using the Diversion control function that is also already in the Classic Firmware.

But,   that is just my read on things.   Have done quite a bit of Microcontroller coding in the past,   but that just seems to be more than is required for this task  --  KISS  -- ...  IMO.

To me,   the MidNite Classic is really the Swiss Army Knife of Charge Controllers.   It has SO many useful functions already built in,   that allow SO many additional functions to be performed,   generally quite easily!

FWIW,   but thanks again for the ideas.     Vic

[Vic]

SEVEN Classics ??!?!

Well, this global current limit works easiest when there is just a couple of Classics and maybe another charger...

Then, the Classic with the WB Jr. on it can be the one that limits...  Assuming that one WB Jr. endowed
Classic is necessary to bring the charge current over the limit.

The software was designed to work with multiple Classics and multiple WB Jr's  BUT I haven't
tried it with THAT many Classics before !

Would like to hear how that works !

If it is a large battery bank, then maybe only a couple of the Classics need WB Jr's
boB

Hi boB,

Yes there are seven Classic 250s on a 24V 1060 Ah battery.   Yes,   this is not the best system design.   The  system evolved over time.   It IS a shame that the pre-existing 24 V SMA inverters drove the "decision"  to stay at 24 V.

Of course this is a far-too-common situation ...  "all I need to do is just replace this one item  ...   and I will be good to go   ...  ."

Just re-read your Post,  quoted above.   There will be four Classics with WBjrs.  One Master,   and three additional.   I DO hope that this does work,   well enough.

As an aside,   thought I would try to test this battery charge current limiting, on a single Classic system here,    and started to slew the Default value in Reg 4405 from its 30000 Default value.   But  there appears to be no higher slew rate,  with increased duration of the Down(or Up) arrow button press.   Would guess that this change in the register value might well take 15,  or so minutes to reach a test value of about 220.

Assume that this is a Modbus Register value,  and it IS nice that there is this register editing function built into the Classic FW ...   also assume that if this is Modbus,  that there is a Modbus R/W Utility that you Pros use.     However,   neither my friend,  nor I  are really computer HotShots  ...   what is the best way to try to expedite setting of reasonably small values in this target register?

Assume that the VMM for whatever reason  might possibly return any custom setting in Reg 4405 to its 30000 Default  value (?).

Know that you boB,   and all of your crew are quite busy right now.

The friend, Doug,   plans to buy the additional WBjrs  in the next week,   or so ...

73,   Thanks again,    Vic

[dgd]

Vic,

Why are there seven 250 Classics charging a 24v 1060ah battery bank?
This is close to my system with a 1025ah 24v bank yet all the charging is managed by one Classic 150 and one Classic 250.
It must be the inputs to the Classics, what are these?

Just my opinion but I would be seriously looking at the need for 7 Classics and how to get this reduced o just two or three.
Two Classic 250 should easily provide the c/10 106a this bank needs for max Absorb although even if you pushed each to 60A output that would not be detrimental to the bank.
Also with EA at 2% to 3% or thereabouts thats only 20A to 30A.
Then just think of all that $ from selling the spare 4 C250s, keep 1 as maintenance spare..

Also easy wiring just two CL, one with Wbjr and follow-me between them will keep the charge cycle running nicely.

dgd

[Vic]

Vic,

Why are there seven 250 Classics charging a 24v 1060ah battery bank?
This is close to my system with a 1025ah 24v bank yet all the charging is managed by one Classic 150 and one Classic 250.
It must be the inputs to the Classics, what are these?

Just my opinion but I would be seriously looking at the need for 7 Classics and how to get this reduced o just two or three.
Two Classic 250 should easily provide the c/10 106a this bank needs for max Absorb although even if you pushed each to 60A output that would not be detrimental to the bank.
Also with EA at 2% to 3% or thereabouts thats only 20A to 30A.
Then just think of all that $ from selling the spare 4 C250s, keep 1 as maintenance spare..

Also easy wiring just two CL, one with Wbjr and follow-me between them will keep the charge cycle running nicely.

dgd

Hi dgd,

Thanks for taking the time to think about this system,   and reply.

Attached is the Classic Sizer output for two strings of seven 180 W Pvs   ...   seems excessive to me.

This system has "evolved",   as noted before.

The roof of the building with the PVs on the roof,  had trusses reinforced,   was re-roofed (IIRC),   and the PROS came out to spend days racking,  wiring and running conduit for the hard-fixed array configuration of 7 PVs in series times 7 strings.   (this is a FIXED parameter).

SO,  OK,  Classic 250s (in place of the burned up AIMS CCs).

With this fixed String Vmp,   and power,   I would NOT run two parallel strings  of 7 PVs into a single Classic 250,   unless it was temporary  (and the CC output current  limited) ...   that's just me ...

I got kinna involved in this late in the process,  well after too many things were FIXED.  In retrospect,   these type systems always seem a bit difficult to understand,   but "at the time,   all made perfect sense".

Just my read on things,   73,   Thanks,   Vic

[dgd]

Ok, thanks for info, I now see what you are trying to deal with and the fixed config 7 by 7 array of 180watt PVs is the crazy part. About 9kW of PV charge potential seems way overkill for the battery bank capacity, it would ve interesting to see what one WBjr shows as total KWhr in and out per day

Dgd