Hi, I'm building my first PV off-grid system and want to make sure I choose the right breakers between PV and charge controller, charge controller and battery bank and batteries and the inverter.
My system:
3 275W panels wired in series, each of which is 9.28A Isc and 38.6Voc (31.5 Vmp)
1 Midnight Solar Classic 200 chrg controller
24 V bat bank
Inverter: Samlex 2000W 24VDC (model: PST-2000-24 24 VDC- 120 VAC)
The PV array will be about 100ft from charge controller and I plan on using 10AWG (or bigger if necessary)
My questions:
1. Do I need a breaker right at the beginning of my 100ft wire to protect the wiring? I was thinking since I have a single array of panel in series with Isc of 9.28A and #10 wire has ampacity of at least 30 then I'm OK and won't need a breaker at the beginning of the wire. Please correct if I'm wrong.
2. What would be the correct breaker before connecting to PV+ in Classic? From my calculations: 9.28A Isc * 1.25 = 11.6A, 38.6 Voc *3 *1.2 = 138.96 VDC so - 10A 150 VDC Midnight Solar (continuous duty) breaker? Please correct if necessary.
3. What would be the correct breaker after coming out of BAT+ of the Classic? In table 12 of the Classic's manual (p. 84) - if I'm reading it correctly - it'll be 80A (or 90A) 150 VDC breaker? Please correct if necessary.
4. What would the correct breaker be from the positive battery lead before going to the inverter? The spec for the inverter is here: https://www.altestore.com/static/datafiles/Others/PST-2000W_specsheet.pdf (https://www.altestore.com/static/datafiles/Others/PST-2000W_specsheet.pdf)
So, there is this conversion table here https://www.altestore.com/howto/recommended-inverter-cables-sizing-and-breakers-or-fuses-a62/ (https://www.altestore.com/howto/recommended-inverter-cables-sizing-and-breakers-or-fuses-a62/) My inverter falls between the 1500 Watts and 2400 Watts. Would I choose 110A breaker or 175A breaker (with 2/0 wire)? And then what the VDC of the breaker should be?
Thank you for your patience and help in providing advice!
-Rich Rosiak
Your breaker is sized based on the wire size that you use. Of course you are sizing the wire size for the current and voltage drop. So you can go to a larger wire size than the current you are putting into the wire - you may need to do that in order to lower the voltage drop for a long run of wire. There are a lot of wire loss calculators on the web that can give you that info. If you go to the bigger wire size then you can put a larger breaker on up to the max that wire can handle.
If you have not looked at Midnite Mini DC box - take a look. You can get the one with the correct size breaker for your inverter. It will make your wiring so much easier. It also has the spots for breakers on the side of the box for PV IN to charge controller, Bat + from charge controller to battery , and some other slots you can use for another breaker for DC output to loads if you need that. The box also has the place to mount a shunt , and punch out holes to mount the charge controller on , and best of all a nice schematic showing where in the box all those wires go. It basically moves the battery terminals up to the box so you don't have a bunch off wires running all over the place. Look it up on the Midnite site where you can see a picture of the schematic too.
There are three Mini DC inverter breaker sizes available
http://www.midnitesolar.com/pdfs/mndc125_250_manual.pdf
Most setups would have a combiner box where the PV feeds in with a 15 amp breaker on each string . Since you have one string you could use 10 gauge with 20 amp breaker at the Mini DC . But for the PV in I think most people use 6 gauge wire in for that and a 60 amp breaker . That way you have low voltage drop and are all ready if you add more PV in the future. In that case you would need a 15 amp breaker at the place where the 10 gauge or 12 gauge from PV transitions to 6 gauge wire ( where combiner box is ) .
At the Mini DC box BAT + breaker there are two types of breaker you can use . The slots hold 5 of the skinnier type of breaker - forget what they are called but those have terminals on them that you insert wire into . The maximum current size on that is 60 amps. So if you need 80 amps then you need to use the other type of breaker which has 1/4 inch studs and you would put terminals on the end of your wire for those. And the Mini DC box has room for three of this type of breaker. On my setup I went with 100 amp breaker and the appropriate wire size. I think I did that because the maximum output of a Classic possible is 94 amps depending which battery voltage you are using.
What wire size and breaker does your inverter manual recommend ?
Schematic and Mini DC info ( on schematic skip the part where is shows field installed ground fault and a 60 and 5 amp breaker side by side )
Hope I explained that somewhat well if if I made any mistakes others will correct me !
Larry
I looked up your inverter manual and it says 120 amps is the maximum DC amps . So you could go with the 125 amp MiniDC box . The also say in the next column that minimum NEC ampicity cable being 150 amp . So I would go with 175 amp MiniDC and appropriate sized cables for that 2/0 from batteries to Mini DC inverter breaker - see schematic listed above.
See Section 8
http://www.samlexamerica.com/documents/manuals/11001-PST-1500-2000-12-24-0216_Web.pdf
Here is a photo of my setup when I was putting it together
Larry,
Thank you so much for both of the replies!
To confirm my understanding - your suggestion is:
15A breaker in combiner box
100ft of 6 AWG wire leading to 60A breaker (PV+ in)
80A on BAT+ out
175A between batteries + lead and inverter + input
Wiring: 6 AWG, except for bat bank and inverter connections - 2/0 AWG
But - what should the voltage be for those breakers? 125 VDC? 150 VDC? 200 VDC?
Thank you.
-Rich
Quote from: rosiakr on January 02, 2017, 01:50:07 PM
Larry,
Thank you so much for both of the replies!
To confirm my understanding - your suggestion is:
15A breaker in combiner box
100ft of 6 AWG wire leading to 60A breaker (PV+ in)
80A on BAT+ out
175A between batteries + lead and inverter + input
Wiring: 6 AWG, except for bat bank and inverter connections - 2/0 AWG
But - what should the voltage be for those breakers? 125 VDC? 150 VDC? 200 VDC?
Thank you.
-Rich
The smaller Din mount breakers that I used are rated 150v
Mini DC box holds five of those
https://www.solar-electric.com/mnepv.html
I see you are using Classic 200 volt model so you I guess you need to use different breakers rated for up to 300v on the PV section
Maybe someone else can weigh in on that
These are the Din mount
https://www.solar-electric.com/miso30dccibr.html
But if you are going with 80 or 100 amps you would want to use this kind with studs on back
Mini DC hold three of this panel mount type
https://www.solar-electric.com/pamodccibr.html
I am not sure how you would use both the Din Mount and panel mount type in the Mini DC box - you may want to call Midnite and ask or maybe someone else on here knows. There may be a way to modify the mount on the box to use both types of breaker.
From what you told me about yours system sounds like you have it all figured out pretty good - except for 24v you probably want to go with 90 or 100 amp instead of 80 to the batteries from controller ?
Maybe Vic or someone else will comment here - he is very experienced - I have only installed my own systems.
If you are doing it yourself get a good crimper for the lugs - I use the Harbor Freight hydraulic wire crimper with good success and it is relatively inexpensive.
Here is 200v combiner box for out by the panels
https://www.solar-electric.com/misomnsoarco.html
Why did you get the Classic 200v model - usually I think you get those if you have a really long wire run from PV to controller ? It doesn't look from your PV like you are up in that range .
Larry
Hi Rich, Larry,
Larry has given very good advice for your configuration, Rich.
It is very difficult to get 60-cell PVs cold enough to reach 150 VDC. We do not know Rich's location, but estimated the Imp for the 275 W PVs in the proposed system at 8.73 A, and ran Rich's PV data through the Classic String Sizer, using standard temperature coefficients for most PVs, and it says that with one string of three PVs in series on a Cl 150 that the CC enters HyperVoc at about --64 C, and reaches 137 V at --30C. Attached, is the file that the MN Sizer created.
So, IMO, the standard 150 V MNEPV breakers should be fine.
Regarding the size of the cable from the single string of PVs, if there is no plan to add to this PV array, #6 AWG might be a bit overkill, but would add a bit to the efficiency.
You could use #10 AWG Copper, and have a voltage drop of about 1.7 V.
Here is a good Voltage Drop Calculator:
http://www.calculator.net/voltage-drop-calculator.html
The distance on this calculator, is the one-way distance -- so enter 100 ft, and it will calculate the drop for the two conductors.
The breaker at the input of the Classic should be sized to the current rating of the cable (called Ampacity). So, if you choose to use a cable for that run to the Classic, you would want to use a smaller breaker. Suggest using an NEC Ampacity Table, and choose the 75 C column for the temperature rating of cable.
It is a good idea to use #4 AWG cable on 24 V (and 12 V) systems, so, an 80 A breaker on the output of the Classic would be fine with this size cable.
Most Solar boxes, busbars and breakers are designed for THHN type cable, which generally has 19 or fewer individual strands of wire inseide cable. Cable with fine strands generally requires lugs.
The MNEDC breakers with studs, also require lugs, which must really be crimped, as Larry mentioned.
More later, Vic
Agree with Larry, that it is quite convenient to have a breaker on each end of a long cable run, it is not absolutely necessary.
Larry, Vic,
Thank you for your help thus far, and patience - really appreciate it. To answer your questions:
1. Why Classic 200 - I am planning in the future to add 4th panel to my string, at which point the cumulative Voc would exceed 150 V. I realize I could have 2 strings of 2 panels in parallel, which would not exceed the limit of Classic 150, but the reasoning at the time was to keep all 4 panels in series in one string.
2. My location - Florida, 27th latitude. The temps here are never below 32 deg F (0 deg C) during the day. They may drop that low during the night, only a few days of the year, but then climb back up quickly with the sunrise.
I've been looking closer at the recommended breaker sizes in the Classic manual (http://www.midnitesolar.com/pdfs/Classic_manual_REV_2056.pdf (http://www.midnitesolar.com/pdfs/Classic_manual_REV_2056.pdf)) - page 84. So, for Classic 200 and 24V system I see:
for input (before PV+ into the Classic I guess) - 50A 300VDC with 6AWG
for output (Bat+) - 80A 150 VDC and 4AWG wire
Am I reading this table correctly?
In the combiner box, where my #6 wire starts - wouldn't I also want to have 50A 300VDC breaker?
For inverter breaker - perhaps 175A 125 VDC and #2/0 wire
-Rich
Quote from: rosiakr on January 03, 2017, 12:49:43 AM
.....
2. My location - Florida, 27th latitude. The temps here are never below 32 deg F (0 deg C) during the day. They may drop that low during the night, only a few days of the year, but then climb back up quickly with the sunrise.
.....
Dawn, when it's the coldest, and before the panels have a chance to heat up, is when the Controller Fries. Hardly any amps, not even enough to wake it.
It takes very little light (ok, a bit more than a full moon) to "activate" a panel and have it produce voltage. The brighter the light, the more amps it produces. So the first breaking rays of dawn, activate the panel. The voltage rises to full voltage at that point, and the Controller either accepts it, goes to Hyper VOC or fries. Depends on the string voltage and ambient temps.
Also, don't forget how the Arabs made ice in the desert - set out shallow pans of water at night, and the IR radiation to the black night sky super chills the water to ice. Dark Blue PV panels, dark sky all night, they can get cold.
Quote from: rosiakr on January 03, 2017, 12:49:43 AM
Larry, Vic,
Thank you for your help thus far, and patience - really appreciate it. To answer your questions:
1. Why Classic 200 - I am planning in the future to add 4th panel to my string, at which point the cumulative Voc would exceed 150 V. I realize I could have 2 strings of 2 panels in parallel, which would not exceed the limit of Classic 150, but the reasoning at the time was to keep all 4 panels in series in one string.
2. My location - Florida, 27th latitude. The temps here are never below 32 deg F (0 deg C) during the day. They may drop that low during the night, only a few days of the year, but then climb back up quickly with the sunrise.
I've been looking closer at the recommended breaker sizes in the Classic manual (http://www.midnitesolar.com/pdfs/Classic_manual_REV_2056.pdf (http://www.midnitesolar.com/pdfs/Classic_manual_REV_2056.pdf)) - page 84. So, for Classic 200 and 24V system I see:
for input (before PV+ into the Classic I guess) - 50A 300VDC with 6AWG
for output (Bat+) - 80A 150 VDC and 4AWG wire
Am I reading this table correctly?
In the combiner box, where my #6 wire starts - wouldn't I also want to have 50A 300VDC breaker?
For inverter breaker - perhaps 175A 125 VDC and #2/0 wire
-Rich
PV is inexpensive these days so I think it is better to use the full potential of your system and controller by adding as much PV as
possible. If you already have a combiner and the input wiring to handle the extra current you could consider adding 3 more panels like you current ones and have two strings . It would only require adding one more 15 amp breaker to the combiner box. You would need to run the numbers in the Midnite series calculator available on their website . Not sure where you are at with your project but maybe you could exchange the Classic 200 ?
You only need the 15 amp breaker at the combiner box for your 12 or 10 gauge pv series string wiring , then the larger 50 or 60 amp breaker at the Mini DC box for your 6 gauge pv input .
Hi Rich,
Thanks for the additional info.
Questions:
1. Do you already have the fourth PV?
2. Do you already have a Combiner?
3. How will the PVs be mounted?
4. Do you have the PV mounts?
5. Do you have the Classic 200?
If you are planning on adding the fourth PV, and do not have it, it might be a good idea to buy it now, as PV power ratings change, and finding a fourth PV that would work well with the existing ones could be difficult, depending on the time period what you might wait.
Larry asked if you had or could exchange the Classic 200, for a Cl 150 ... good question ... do you, and can you?
You may know that the higher voltage Classics, like the Classic 200, are a bit less efficient than is the Cl 150. This efficiency loss results in a bit more heat that the CC needs to get rid of, and, reduces power reduction a bit. Also, converting a fairly high string voltage to 24 V (verses 48 V), also adds additional losses, that reduce power production, and results in a bit more CC heating.
For longer cable runs between the PVs and the CC, can dictate using higher string voltages, to save on cable cost, as you have been thinking of doing.
But, if you do not plan to add considerably more PVs, and/or change to a 48 V system, do wonder about running a Classic 150, with two strings of two PVs, on your 24 V battery. The system will be more efficient, and the Classic will be a bit happier.
We do not know about your battery bank size, and type, but since you were already thinking about adding a fourth PV ...
You really do not need #6 AWG cable for the run from the PVs to the CC, #8 AWG should be fine, IMO. And, a Combiner is not an absolute necessity, even with 2 X 2 PVs, IMO.
But, using a Combiner does give you a great place to mount a Surge Protection Device (SPD), at the PVs, where is would do the most good. And, 150V MNEPV breakers would have more than enough voltage rating.
Just wanted to throw this out for your consideration
Did run the MidNite Classic String Sizer, for four 275 W PVs, 2 X 2, which is attached.
FWIW, my opinions, Vic
Vic,
Thank you for responding. My responses to your questions:
1. Do you already have the fourth PV?
No, not yet.
2. Do you already have a Combiner?
No, not yet, but will get one. Having the SPD is reason good enough for me to get it.
3. How will the PVs be mounted?
Pole mount (no roof mounting)
4. Do you have the PV mounts?
Not yet.
5. Do you have the Classic 200?
Yes
I spoke with the CC seller and I am not sure if the swap will be possible - it's been over a month since the purchase. They will review my case and notify me. If I can't swap - how critical is this heating problem? Would it be highly recommended I go to 48V bank? By the way - I don't have any batteries yet. The only items in my possession are the 3 panels and the Classic 200.
I don't mind paying for #6 wire - I was going to buy at HomeDepot, which has the THHN type wire.
QuoteAnd, 150V MNEPV breakers would have more than enough voltage rating.
Is that the voltage of breaker in combiner box? Or for PV+ in the Mini DC/E-panel box? And, for which Classic - 200 or 150?
-Rich
Hi Rich,
Thanks for those answers.
While there is not specific data that directly states the efficiency-loss between a Classic 200 verses a Classic 150, with a nominal STC Vmp of about 63 volts, there will be a reduction when using a Cl 200 vs the 150. This reduction will probably be in the range of 1 or 1.5 percentage points for the Cl 200. This is not huge, and if one has sufficient PV power available, it would seem relatively unimportant.
The small efficiency hit would just make the internal fans run a bit more, but on some of our systems, the fans run fairly often anyway. Heat is also a primary factor for longevity of electronic devices, but, again IMO, the difference would be relatively small.
Will ADD, that IMO, the efficiency that you will GAIN from reducing the PV string voltage into the Classic will be much larger, than the small reduction in running a Cl 200 vs a Cl 150.<
At the best, guess that the seller of the Classic would want you to pay shipping, each way ($30 - 50, depending), and they may want a re-stocking fee ...
There are few absolutes in this, just shades of grey.
Generally, demands on our battery-based systems do grow, but, still, you would probably also grow the amount of PV power to keep up with any demand growth.
It is often a bit difficult to try to offer specific answers to questions without knowing very much about the nature and purpose of a system. And, there seems to always be more questions that need to be asked.
But, guess that this is a small grid backup system, or, perhaps a remote off grid system ... or??
Fine on staying with #6 AWG cable for the run from the array to the CC. This will increase the power production somewhat, and if you later expand the system, this should still be fine (within reason).
For the Combiner, you will be running MNEPV DIN Rail breakers. 150 VDC rating would be fine for a string of three, or two strings of two of those PVs. Customarily, one would size the breaker at the Maximum Fuse Rating that is stated in the specs for, or on the label on the back of the PV. These days, this is often a 15 A rating.
In the Combiner you would use one breaker for each string, and it is convenient to use an additional breaker as a connection point for the MN SPD.
For the breakers near the CC, you could also use MNEPVs, or MNEDCs.
The current rating for the breaker at the input to the Classic should be sized for the Ampacity of the cable that runs from the PV array -- #6 AWG Copper, in your case. So, this breaker should not be larger than 60A, and 150 V is fine, unless/until you increase the string voltage that will be above 150 VDC under the worst-case conditions.
For the breaker that is between the Classic and the battery, again, the cable size dictates the maximum current rating of the breaker -- 60 A for #6, 80 A for #4 copper, generally.
If this system will be inspected, then there may be a few things that might need to be changed, depending upon the dictates of the Inspection Authority (call the AHJ).
Enough for now! Vic
Vic,
The store approved my return request, so I'll be getting Classic 150.
Thank you (and others) for guiding me in this processes.
With this new classic, the only thing that will change is BAT+ breaker (out of CC) to be MNEPV 100A (150VDC).