Current input limit

[asdex]

I see there are current input and output limits in the classic. Does this mean I can add more panels even though it would be over the maximum for one Classic? The idea is to collect more power in winter but in summer the input current from being over-panelled would not go above the Classics limit?
Thanks

[boB]

The input current limit was originally placed there (and by default, disabled at 99A) for some micro-hydro installations so it would not load the turbine so it would not run too slow. 

You could certainly use it for generic current limiting but it is not quite as accurate as the output current limit adjustment.

The Classic will also adjust its output current limit based on temperature.  So if you overload it for a while so that it gets too hot, the normal output current limit will "slide" down at a 5 amp step every minute or two and then come back up to the maximum set limit as it cools down.

Feel free to play with the current limits.  It won't let you adjust the output limit higher than it thinks is correct for the battery voltage and input voltage coming into it.

Remember that the Classic limits output current by raising the input voltage above the max power point voltage of the array.  Only up to the Voc open circuit voltage though which is technically, an open circuit and zero current and zero power.

[asdex]

Thanks for your reply. I'll see what extra panels I can get and plug the total figures into the panel calculator. I don't completely understand your answers but will start at the calculation I get and then apply it to your answer. I wouldn't want to run the system from an array producing too high a voltage.
Cheers

[asdex]

I have found what I think are suitable panels to add to my existing system.
I have six panels at the moment.
They are 320 watt each.
They are connected three strings of two panels in series paralleled together.
Voc 46.28v
Vmp 37.16v
Isc 8.92A
Imp 8.61A
72 cell

The new panels are 370w
Voc 41.5v
Vmp 38.1v
Isc 10.6A
Imp 9.73A

I would add 3 of these new panels
They would need to be three strings of three panels in series all connected in parallel.
I understand from the previous email if I limit the classic output to say 40Amps say, this will limit the current the classic handles in summer.
Is this correct?
Thanks,

[Vic]

Hi asdex,

Your proposed configuration seems to be OK,  with respect to PV matching.

BUT,  you will be running an STC  string voltage of around 112-ish V.   This is a high ratio of Vin,   down to the 24 V battery voltage.   This causes  more heating in the Classic,   than would be ideal.

Also,   is there a typo in the Voc,  noted for the proposed new PVs?   It seems a bit on the low side.

Please tell us the manufacturer and model numbers for each of the PV models that would be used together.

Later,   thanks for added info,   assume that your "Classic"  is a Classic 150 (?).   Vic

[asdex]

Hi, thanks for your reply. The brand of panel is Trina and the Voc is correct. My Classic is a 150.
Cheers,

[Vic]

Hi asdex,

OK,   am having trouble finding a Trina PV with the Vmp and/or Voc that you listed   â€¦

"Please tell us the manufacturer and model numbers for each of the PV models that would be used together"

Would like to look up the data sheet on each of the PVs.   OR,  do you have Links where the datasheets are listed  --  perhaps from your supplier?

The low-ish Voc of the 370 watt PV really seems too low,  vs the Vmp.   This makes one wonder about the compatibility twix the two,   or weather there might be a clerical,  somewhere.

Approximately how cold is your site on cold Winter days?

Thanks !!   Vic

[asdex]

Answer from supplier:
"Hi
These panels are manufactured by an independent manufacturer to our specifications and we source our cells directly from Trinasolar. Our model number is FSP370-72"

Maybe these panels are not so good?

[Vic]

Hi again asdex,

Thank you for the model number of that PV.

Searching for that model number,   CSUN does come up,   but with different numbers for the PV voltages and currents.

Many companies that actually manufacture Solar Cells save the best cells for their PVs,   and wholesale the cells that do not meet spec to other,  (often second-tier)  manufacturers.   This is not always the case,   though   ...

Depending on the coldest temperatures at your site,   and that you are using a Classic 150,   would recommend against strings of three Pvs,  on a 24 V system   â€¦   that's just me.

More later,   thanks again,   Vic

[asdex]

Thanks Vic, coldest here would be - 10decC. Sounds like it's a no go so I'll need to decide whether to buy another Classic or run the generator a bit more.
Will give it some thought.
Cheers,

[Vic]

Hi asdex,

Will try funning strings of 3X3 of your existing PVs,  with your -10 C coldest temps.

Your proposed setup will probably work on most days.   The Classic will run warmer than it would with the same amount of PV power verses strings of two of those PVs.

As you know,   when comparing PV power,   compared to more genset run time,  PVs almost always win.

It is never fun to rain on anyone's parade.

My system uses strings of three 72 cell PVs,   but these PV are 15 years old,   so the Vmp and Voc are lower,  and our climate is mild.

BUT,   the fans in the Classic run often,   even under light output loads,   due to the high Vin.   AND,   this is with the power room having priority A/C running on most days.

The Classic is a very tough CC,   and  this system has a Classic that went into service in early 2011.  The fan/s inside it make a bit of noise,   due to all of those hours of running,   but is still marches on,   without any complaints   â€¦

Will run strings  of 3X3 through the String Sizer tomorrow AM,  out time.

Later,   Vic

[Vic]

Hi asdex,

Did run the Classic String Sizer,   for 3 strings of 3 of  your existing PVs.   Results are attached below.

It shows that the Classic will stop working,  or not wake up (Hyper Voc),   at about 1 degree C,   outside temperature.

Realize that you probably would be using some different PVs.

FWIW,   more later, Vic

[Vic]

Should add,   that when running strings of 3X3 or the existing PVs through the Sizer,   used the Default Temperature Coefficient tor Voc.   If your existing PVs have a different value for this,  then the info on the temperature where the Classic enters  Hyper Voc will change.  In general,   most PVs  have a very similar number for this.  A few,  are very different   ...

If you have the manufacturer brand and model number those existing PVs (or a link),   would like to know the Temperature Coefficient of Voc,   or with the info on the PV,  may be able to find this data on-line.   Sometimes it can be a bit hard to locate this on the datasheet,   because   different manufacturers can have a different abbreviation for this.

Thanks, Vic

[asdex]

Think this has attached.

[Vic]

Thanks asdex for attaching that Datasheet.

Those existing PVs have the same Voc temperature coefficient as the Default in the Sizer.  So,   the Sizer's output on Hyper Voc  is correct.

More later,   thanks for the data,   Vic