Why are panels rated in 12 Volt units?

[Alaska Man]

Wouldn't that require another controller?

[vtmaps]

Wouldn't that require another controller?

Depends.  I'm confused as to what you have and what you want to do.  Is your system voltage 24 volts?  What is the wattage of your three panels?

If you have 3 panels and your system is 24 volts and you want to add a fourth panel, you do not need a second controller if you configure them as two parallel strings with two panels per string.

--vtMaps

[Alaska Man]

I have (3) 230W panels wired in series into a 20amp breaker and then into the MNClassic 150. The bank is wired in series and parallel at 12V. There is still another two breakers available in the combiner box. I have the Combiner Bar on the positive side of all three breakers and feed the controller off of the bar. I was told when I add another string to remove the combiner bar and feed the new MPPT Controller individually from the next breaker.

Exsisting panels:

VOC 36.7
Max Power Volt 29.7V
Current Max Power 7.74A
Max System Voltage 1000V/600V
Max series fuse rating is 15A

I'm not sure what the IRC is or how that effects adding another panel.

I'm also looking at adding another 4 panels 250w each on the west side of the house. When I do I'll go with the MN Classic 200.

[chris]

  I may be wrong, but is the Clasic 150 not rated for 80 amps?

4 X 230watt = 920 * .77 = 708.4 / 12 volts = 59 amps

and on a 12 volt system you don't need any of these panels in series.....unless you have a really long run to the controller.

[Alaska Man]

The 150 is rated for  80 - 96Amps  I believe. 

There are only 3 panels currently 230W X 3 =690 *.77 = 531.3 / 12 = 44.27 ampers

The run from the farthest panel to the combiner box is about 30' the combiner box is 8" from the MPPT Controller and the controler is about 4' from the battery bank.

My problem is that at 110V VOC for the string, I'm limited out for the 150 because of my location and the fact I could see -50°f


The 150 has a max VOC of 198 according to the PDF. Are we sure I can't get away with another..... say 130w panel?

[dgd]

The 150 is rated for  80 - 96Amps  I believe. 

There are only 3 panels currently 230W X 3 =690 *.77 = 531.3 / 12 = 44.27 ampers

The run from the farthest panel to the combiner box is about 30' the combiner box is 8" from the MPPT Controller and the controler is about 4' from the battery bank.

My problem is that at 110V VOC for the string, I'm limited out for the 150 because of my location and the fact I could see -50°f


The 150 has a max VOC of 198 according to the PDF. Are we sure I can't get away with another..... say 130w panel?

AM,
Where did the .77 come from in your wattage calculation?   In the right conditions the PVs could work near maximum spec so you get the full 690 watts.
Adding another panel in series may get the OCV too high and the Classic 150 can handle 150+12v maximum but this is in HyperVOC where I think it does not produce power
What about adding a 4th panel so that you have two parallel strings of two in series? (as vtmaps suggested above).
That would give you about 60v mpv which is still good for charging 12v battery, at about current of 65 to 75 amps.

Have you considered a 24v battery bank, your PV/Classic setup would work well at 24v

dgd

[Vic]

And Alaska,

The high HyperVOC limit for the Classic 150 is Battery nominal voltage plus 150 V.  The limit with a 12 V battery is 162 V MAX.

The Cl 150 with a 12 V battery has an upper limit for output current of about 96 Amps.  The higher string voltages,   like you have,  on a 12 V battery reduce the efficiency of your Charge Controller,  a bit.

Agree with vtmaps,  that if you added an additional PV,  but ran two strings of two PVs things would generally be a bit better.

Agree with dgd that if you could switch to a 24 V system,  things would generally be better ...  of course any inverter that you have would need to be changed to a 24 V model.

I do not quite understand your wiring.  It is important that you have a Breaker on the input of the CC,  and on the output for safety.

More later,   Vic

[vtmaps]

There is still another two breakers available in the combiner box. I have the Combiner Bar on the positive side of all three breakers and feed the controller off of the bar.  I was told when I add another string to remove the combiner bar and feed the new MPPT Controller individually from the next breaker.

Vic and dgd gave you good advice.  Is your combiner box a Midnite product?  If so, you have the breakers wired improperly.  In the Midnite combiners the Positive side of the breaker goes to the Positive form the PV string, and the negative side of the breaker goes to the combiner bar.

btw, the usual way to use a combiner is to put it very near the panels and then run a single larger cable (with the combined output of the array) to the controller.  If you put a second array in another location, put in a second combiner for that array. 

btw, you really should consider going to 24 volts.  you mentioned that your battery is a series/parallel bank... if you have two strings in parallel, you could reconfigure them to a single string at 24 volts.  You could have 8 of your panels on a single Classic if you go to a 24 volt system.  You are in a 12 volt hole... stop digging yourself in deeper.

--vtMaps

[RossW]

btw, the usual way to use a combiner is to put it very near the panels and then run a single larger cable (with the combined output of the array) to the controller.  If you put a second array in another location, put in a second combiner for that array. 

I agree this is the common way, but "why"?
Perhaps my situation is unique, or I'm just strange (both are equally likely!) - but I have 36 modules. They are arranged as 6 series strings of 6 modules each. They range in distance from about 9 to 30 metres (30 to 100 feet) from my batteries.
I specifically ran each array via its own (thinner) cable - mostly 4 sq mm (about 11AWG).
Each goes through its own double-pole breaker.
Each then goes through an isolating diode and ammeter.
They are combined AFTER the isolation diode and ammeter, then a single larger wire feeds the Charge Controller.

Obvious downsides: additional expense in extra breakers; extra meters etc.
Obvious upsides: ability to easily isolate an individual array while seeing what's going on inside; ability to monitor each array.

What else am I missing?

[vtmaps]

Obvious downsides: additional expense in extra breakers; extra meters etc.
Obvious upsides: ability to easily isolate an individual array while seeing what's going on inside; ability to monitor each array.

What else am I missing?

One reason to have the combiner near the panels is for lightning protection.  I like to take the combined array and put a SPD on it.   I don't want my combiner and SPD indoors... I don't want to bring lightning indoors.

I guess you could put an SPD on each PV string outdoors.

--vtMaps

[Alaska Man]

Appreciate all the advice, but I just spent $3,500, less than three years ago, on the inverter/charger. A little bit to early in my journey to jump on the 24V boat.

I wired the Midnight Combiner box just like the picture. Positive wire from the array goes into the bottom of the 20A breaker. The negative from the array goes the to negative ground bar. 
The positive wire for the controller comes off the top of the breaker while the negative for the Controller is grounded at the negative bar.

Right now the other breakers sit unused.

After the controller is a 63A single breaker before the battery bank.

The combiner box is mounted exterior to the house.

[Alaska Man]

I'll try and get a picture loaded.


This is not showing the feed from the array, but like I said, I ran the positive to the bottom of the breaker and terminated the negative on the negative bar.

[Alaska Man]

My thinking was to add another array I just feed the next breaker and the breakers feed the controller. This was before I realized the Classic 150 was too small for another array.

It appears the combiner box was  a waist of money. I could have gotten away with just adding breakers as I added more PVs. Since it looks like another controller will be necassary.

[Alaska Man]

Panels are mounted above the Combiner Box:

As you can see this arrangement is crying out for another panel. It would be nice to balance the look at the front of the house.

[vtmaps]

This is not showing the feed from the array, but like I said, I ran the positive to the bottom of the breaker and terminated the negative on the negative bar.

You picture shows you did it correctly.  Previously you wrote:  "I have the Combiner Bar on the positive side of all three breakers and feed the controller off of the bar."

That's not what I see in the picture.  The combiner bar is that bar at the top that the negative side of the breakers attach to.

As far as adding another panel.  As I mentioned earlier, you can do that by configuring the 4 panels as series/parallel.

--vtMaps