Classic 150 Power Rating

[Vic]

All,

Have been studing the Power Curves.  I am planning to use a single Classic 150 for a new off-grid install.

Eight strings of three SW-245 panels,  Vmp per string 92.4ish Volts.  Array total power is 5880 Watts STC.  This is pushing the current max of the CL 150,  and when the 1280 AH 48 volt battery is a bit discharged,  the CC will be running near its max current rating for an extended period.  Am I expecting too much out of a single Classic ?  Know that on cold windy days,  the CC will need to limit charge current a bit.  Am willing to put up with this smallish loss.

Did not use the built-in Classic String Calculator,  but rather,  another company's on-line SSTool.

Am leaving space for an additional Classic.  Whatta you MN folks think ... Limits were meant to be pushed,  right?
Thanks  Vic

[keyturbocars]

Vic,

I know that you want the opinion from the experts and I'm sure they will chime in, but just giving my opinion... sounds like a lot of power for any single charge controller to handle!  At 5880W, that would put you around 118A if battery bank voltage got down to 50V.  That's way over the current limits that I've seen for a Classic 150 (especially considering the 48V battery bank).  From what I can see on the power curves, it looks like you would be able to handle about 80A on a sustained basis with a PV voltage near 100V.

http://www.midnitesolar.com/images/classicFrontPage/graphs.php

If you ran a couple Classic 200's, you could run 6 strings of 4 panels to boost your voltage and save some on the copper wiring (or at least have lower voltage drop with your existing wiring plans).

Edward

[Halfcrazy]

I would say that you will spend a fair amount of time current limiting and the unit will run hard and hot when the battery's are low. If there is any distance between the array and the battery's the pair of Classic 200's as Edward suggested may be a nice option other wise I would seriously consider 2 150's. You could start with one and see how much it is limiting but I truly think you will be giving up enough production to warrant the second controller.

[Vic]

OK,  thanks Gents,

Well,  5880 watts IS the STC rating.  So using the bit high 80% of that is so that is about 4700 watts nominal.  At 50 volts battery V, there is some current limiting.  The roof and panel tilt is 30 degrees,  so not ideal for either Summer or winter at 37.5 degrees N Lat.

Will go back to look at PV Watts.  Part of my rationale is that significant battery charging occurs at low sun angles.  Such that when the sun is at optimum angle,  often the CC would be in Asorb.

Amd have not been really fair,  am starting in the middle of my consideration process,  and no description of the system.

The average one-way distance from from Combiner to CC is about 25 feet.

It is possible that when in Float,  my water heater diversion load might really tax the Max current capability of the CC.

But,  was really wondering about running the CC at/near its max rating of 83ish amps (for a 48 V  bank,  and sub 100 V PV in) for an extended period.

And, 1/2,  yes that was my plan,  to see how happy thing were with one CL 150,  and add a second as required.  As a strategy,  think at this power level,  two CCs is a nice approach.  Redundancy.

Do have an X SCC (** not my favorite), and the great MX-60,  which could perhaps take some of the load.

OK,  Thanks,  Vic

[keyturbocars]

Vic,

I am not a solar expert (which is probably obvious  ), but if the STC rating on those panels is 5880W, then couldn't the power output be higher than STC under certain winter conditions?  Perhaps you live in an area that doesn't get very cold winters. 

Edward

[Vic]

Hi Edward,

YES,  it is my expectation that on the cold windy days that the array will be putting out more power,  prob not up to STC,  in our moderate NorCal weather.  There is little/no opportunity for snow reflection,  as this system is on a ridge top,  and is looking downslope to the south.

Some have said that some CCs, when run at their at their current limit,  can break due to lag-times in the current limiting loop,  with large battery load current. changes and so on.

The correct answer is two CCs,  which am sure will implement at some point,  probably not from the beginning,  unless MN councils otherwise.  The original plan was for PV in to be 123 V nominal,  just to be cute,  but the CC is less efficient and has less current available with this high V,  and might need a load on the PV to drag the CC out of HyperVOC when the array is cool/cold.  As cute as that was,  did toss that concept (have often run the PV on the high side of ratings).

OK, Back to the layout puzzle.

Thanks for the input,  Vic

[nigel]

Hi Vic long time no chat,

I have no doubt that you already considered that anything run at its maximum capacity even with current limiting features makes everything work harder and hotter, thats why we choose items that stay in there optimum comfort zone, why we choose low rpm generator over hi rpm, better fuel economy, longer life, sizing inverters that spend most there time cruising and occasionally meeting there peaks,but I know where your coming from, Ive just gone from 24v to 48v on my system and seeing my FM80 only pushing out 30 amps is annoying, my flexmax 60 on the tracked array idling  all day long around 18 amps,even more annoying   makes me want to save up for more panels.  

Nigel

[Vic]

Nigel !!

Have wondered about you a number of times.  Very nice to see you here.  Hope all is well with you,  there.

Well,  I am trying to wait a bit longer to get an additional Classic CC.  Generally,  do not cycle the bank very deeply,  so think that much of the bank charging will happen when the PV is the limiting factor.

However,  this light cycling could change,  plus the chance that adding an electric water heater that could run the CC @ or near Max current for a period of perhaps one hour, or even a bit longer made me wonder.

Yes,   you are correct about running systems at or near limits,  and have avoided it here for the most part.  The ultimate plan is to use a second CL 150,  but wanted to wait about six months.

OK,  have prob wasted enough bandwidth on this topic.  The system is currently set up for two CCs.  The MX-60 is on-line with only 1050 STC watts of panels charging the batts and running this internet conntction.

Thanks again,  Nigel,  and all, for the wisdom. 
Take care,  hope you are still installing systems there.  The pix of your Villa shows that you do some very nice work.  C U,  Vic

[boB]

When the Classic is running up against the current limit, it limits that current by raising its input voltage.  So it will have max output current in addition to the higher input voltage which ~should~ limit the output current even more.

The Classic 150 is pretty tough, so you might be OK.

I guess you will just have to be our test case, Vic !

boB

[Vic]

OK,  boB,

You caught me on that one ... forgot that the rated Vmp is only that low at rated Imp.  The curves are fairly flat,  but ...

Guess that will use the venerable MX-60 to share the load.,  altho this might make it fairly difficult to terminate Asorb at some End Amp setting,  as the currents will be divided (in some fashion) twix the two different CCs.  Can set Max charger current in each,  but that is only the MAX.  Have never used two different types of MPPT CCs for simultaneous charge of sinble bank.

Do you feel that the MX and CL 150 will play well enough together?  There is another Classic in the future for this system,  but was hoping to delay a number of months before ordering it.

Thanks,  Vic

[boB]

OK,  boB,

Do you feel that the MX and CL 150 will play well enough together?  There is another Classic in the future for this system,  but was hoping to delay a number of months before ordering it.

Thanks,  Vic

Yes, they should play well together.  Same precautions apply to almost any two MPPT charge controllers on one single bank.   Make sure
they both read close in battery voltage is about it.   They basically work the same as far as Absorb timing I believe, unless big changes
were made to the FM series.  I don't that part changed though.

Maybe some day the two will even be able to communicate and follow each other.  I would think that the Classic could do this with
other modbus CCs fairly easily.  Tall Girl is working on some communications software that may just help to get this going  soon as
we don't have time right now to implement communications with other CC's.

If done right, I could see everybody's CCs playing well with each other.

Stop the unnecessary fighting and let's be civil about this battery charging stuff !!  

boB

[Vic]

Ok,  thanks boB for the added info,

I do like to terminate Asorb based upon charge current rather than time,  as the DOD varies quite a bit here,  and that had a farily large effect on required Asorb time.  And short of haveing your to-be-finished Battery Monitor/Charge Terminator,  guess that there is no absolute way for each CC to equally share the currents such that each could terminate charging at the same time   Will split the array into two halves,  each to its own CC,  but still,  think that it is uncertain how the charging will be shared at any point time.

Just musing ... 73.  Thanks for getting this great new CC into production, and the great support as well.   Thanks Edward and HC as well.  Vic