Question on max input to CL 150

[elesaver]

I would like to add 4 additional panels to my system one set up.  The panels are nearly identical with the panels currently in place.  The Classic max input is 96A.   With max sun during this season of the year, I am seeing up to 65 A coming into the Classic.  Figuring that I want to add 50% more in panels, this would be getting to the max input.  I would prefer not to ruin the Classic!  How close is too close?  Suggestions and teaching are welcomed.

[Vic]

Hi elesaver,

There is an NEC Limit on the input current.

But for most of us,  we use the Classic String Sizer:
http://midnitesolar.com/sizingTool/displaySizing.php

It is a good idea to NOT run any CC near its output current Limit for long periods of time.

Your String Vmps are probably good for your 24 V battery  --  assuming that the PVs have Vmps of about 36.5-ish volts at STC.

FWIW,   Vic

[elesaver]

But for most of us,  we use the Classic String Sizer:
http://midnitesolar.com/sizingTool/displaySizing.php

Thanks, Vic.  Looks like it's "excessive" according to the stringsizer.   The way to accomplish this is to add another Classic, I guess. Strange, though...at least to my inexperienced mind.  I don't seem to have quite enough PV to bring my battery back to full charge after the overnight draw down.  The same load during the day as during the overnight is apparently too great to allow enough excess to go into the battery.  Since the DOD is around 20-22% overnight, I would've thought with full sun of at least 4 hours (probably 5 or 6 hours this time of year) would've been adequate.  When I look at the whizbang, jr. from time to time, I often see big numbers going into the battery....41.5 amps etc.  Is this the answer:  I would need constant 41.5 amps for 5 hours to replenish the battery?  Anyway, if you have time, help me understand this?

[Vic]

Hi elesaver,

YES,   adding four more 300 W PVs would be excessive on a 24 V system.

Just a couple of quick thoughts;
Charging Flooded batteries is not that efficient.  And there are inefficiencies in the PVs,  CC,  wiring etc (when looking at restoring AH removed from the battery).

On any reasonable day,  would expect the PVs to put out about 75% of STC ratings,  and extreme heat,   humidity,  panel dirt,  haze,  and so on could further-reduce PV output.

And,  as you noted,  daytime loads certainly subtract from battery charge current available to recharge the battery.

More later,   Vic

[elesaver]

OR...upgrading to 48V would be another option.  Seems like the only change would be to the inverter.  In the long run, that may be a better option?

[Vic]

elesaver,

Indeed,  if you knew of the future,  in the past,  you might have chosen to start at 48 V for this system.

Did not want to suggest 48 V,  as you have a very good inverter,  AND  a fairly stout 24 V battery,  which probably cannot be divided and connected in series for 48 V (ie,  there are not two parallel strings in the 24 V bank),   (assumed).

OR,  perhaps you were thinking about this present system becoming the shop system,  and buying a new inverter and battery for the main  )probably not).

FWIW,   Vic

[dgd]

I would like to add 4 additional panels to my system one set up.  The panels are nearly identical with the panels currently in place.  The Classic max input is 96A.   With max sun during this season of the year, I am seeing up to 65 A coming into the Classic.  Figuring that I want to add 50% more in panels, this would be getting to the max input.  I would prefer not to ruin the Classic!  How close is too close?  Suggestions and teaching are welcomed.

I assume you mean 65A coming out of the Classic?
Although you have 2400w of pvs which should be about 95a output, you see 65a because rarely will pvs produce nameplate power ouput. On good sunny clear days they will get quite hot reducing actual power to 70 to 80%. Then there are wiring and connector losses etc.
Attching more PVs can help increase the real power from the Classic and its very useful in boosting power on bad weather days. Over panelling is no issue for the Classic. It has protection built in and fans to assist cooling at high current output occasions.
You can assist keeping it cool by mounting on heat sinking material such as a section of plate aluminum.
So adding four more 300 watt pvs will take your nameplate power to 3600 watts and may get you closer to 90 amp output or even the max 96. If you get concerned about running the Classic, on good days, over 90a for many hours then I'd simply disconnect some pvs at the pv combiner box by turning off breaker(s)
These extra pvs should shorten the Bulkmppt phase, reaching absorb sooner. It may then be worthwhile looking at power diversion to water or space heating.
I have 2800w of pvs connected to a c150 charging a 24v 1025ah bank. I see 80A+ at near 29v quite often but the real benefit is better output in miserable weather
Dgd

[Jacotenente]

Ditto on what DgD said above. I got 2400w on one array into a CL150 (24v system w/ 1100aH). 70-75 amps max. The other two Classics are 1300w and 1200w. 40 amps max on those.

[elesaver]

Dgd and Chris, thanks for the input about maximizing the CL 150.  Yes, I did mean 65A OUT of the Classic, by the way. 

When you are talking about the CL having protection for over paneling, could you enlighten me?  The fan already comes on every day during the summer but is there another mechanism?  I just envisioned that it would seriously overheat and cause internal problems.

Also, if you have time, could you tell me more about "mounting on a heat sinking material such as plate aluminum?"  This sounds like something that I could do...that is, if I knew more about what that meant!

In time, I wouldn't mind buying another Classic.  I've watched the video and the hook-up to the follow me looks pretty simple.  Am I to figure that the battery and inverter hookups all remain as they are?  It is just that the two (or multiple) classics are dividing up the incoming current...kinda' like two people carrying the same load?  The video doesn't mention any need to wire anything to the second classic.

Anyway, I'm still thinking about this.  Thanks for the input.

[elesaver]

Another concern that just popped into my head...wire size from combiner box then to dc-disconnect and then to the Classic.  I have a distance of about 50'.  To carry 90+ amps, I would need some pretty hefty wire...AWG 2 probably?  I don't think that size wiring works with the Classic or maybe not even the combiner box.  How do you get past that problem? 

[elesaver]

Sorry for thinking out loud.  I checked the specs on the combiner box and output wire size is as large as 1/0, so that problem is solved.  I do not see wiring specs for the mini dc disconnect other than 6 AWG.  I know the Classic will accept up to 6 AWG.

It must be that 6 AWG is adequate or larger wire size would have been listed.

Thanks again.

[Vic]

Another concern that just popped into my head...wire size from combiner box then to dc-disconnect and then to the Classic.  I have a distance of about 50'.  To carry 90+ amps, I would need some pretty hefty wire...AWG 2 probably?  I don't think that size wiring works with the Classic or maybe not even the combiner box.  How do you get past that problem?

Hi elesaver,

On the INPUT to the CC,  the current will be lower than will the output current from the MPPT Classic.

You will probably not see more than about 50 A on a sustained basis.

The Classic terminal block will accept #4 AWG 19 strand cable (like the customary THHN building wire).  For the cable from the CC could be # 4 AWG,  and then from the output of the breaker,  to the battery,  you could use larger cable.

We all have opinions.   Have had opportunities in designing systems with Classics,  to consider over PVing the system.   But after several minutes of reflection,  decided to divide the work between two Classics.

There can be Fault events,  where current Limiting in CCs can be delayed.   There can often be cloud edge effects,  where PV currents rise quickly,  often at of above STC values for a few moments ...

The Classic uses several output limiting functions.  One is limiting current to  the set value,  in the Limits menu.   It will also limit output current based on its operating temperature.   A Classic in a warm/hot environment,  may well limit output current below either its maximum Limit setting as a way to help control its operating temperature.   This reduces power production,  to help protect it from excessive heating.

It's just me,  but,  would never operate any power electronics at its maximum for extended periods,  let alone beyond its maximum.

Some MPPT CCs have a stated Max limit on Isc totals for the PVs connected to the input.    Think that this is a NEC requirement,  at least in the "states".

Over PVing is more common,  when PVs have different azimuth orientations.   This helps limit the maximum available current at any given time of day.

FWIW.   Just opinions,   Vic

[elesaver]

Thanks, Vic.  My thinking is more in line with yours after I have had time to mull a bit.  I never run my lawn mower or other power tools at max...at least not for long.   Nor can I run at full speed for long!  So, rather than chance a problem why not prevent the chance of the problem in the first place.  Solar power is addictive and since I've become an addict, I may as well do it right!  You never go wrong when you do the right thing.  Thanks for the reminders.

[Jacotenente]

Sorry for thinking out loud.  I checked the specs on the combiner box and output wire size is as large as 1/0, so that problem is solved.  I do not see wiring specs for the mini dc disconnect other than 6 AWG.  I know the Classic will accept up to 6 AWG.

It must be that 6 AWG is adequate or larger wire size would have been listed.

Thanks again.

FWIW - My wiring/cabling is as follows:
Solar panels to Classics/Baby Big Boxes - 10 AWG PV feeder cable. Panels are stringed in series for high volts (~105) and low current (125' runs from the backyard to the garage)
Midnite Solar Baby Big Boxes to/from Classics - 4 AWG TEMCo welding cable with fine strands
Baby Big Boxes to Blue Sea Systems Maxibus (250-amp) Busbars - 4 AWG TEMCo welding cable
Busbars to the three strings of batteries - 2/0 TEMCo welding cable
Battery stringing - 2/0 TEMCo welding cable
Inverter to busbars (to include the circuit breaker and WBJr shunt) - 4/0 TEMCo welding cable

So, yes, I use fine stranded and flexible(ish) welding cable everywhere. I also construct all my cable using a hydraulic crimping tool, quality lugs, and industrial strength adhesive heat shrink. All these cables are oversized for the amount of current that will ever go through them. I figure, rough guess, I only run them at 50% capacity. However, like Vic says, there will be times when the current will spike up (like when the air conditioner or fridges kick on). Works dam good...but, to each their own. I equate it like this: If you are thirsty and go to 7-11 and buy a Big Gulp with a straw...yeh, that will work. But, if you are really thirsty, take that same Big Gulp and drink it with a garden hose...you get more flow into your mouth and everyone is happy...the flow of soda pope through the garden hose just flooooows nicely.

Chris
My Youtube Channel is Chris DIYer if you want to see my stuff

[elesaver]

I purchased 4 AWG welding cable to go from mini dc disconnect battery breaker to Classic and from the shunt for the negative battery cable to Classic but had a whale of a time to get it into the Classic blue terminal box.  I was ready to pull my hair out!  I don't have specialized tools but is there some kind of process to make this easier?