I've seen modules rated at 12V, 24V etc. Yet they all put out somewhere around 36.7VOC. So there is really no such thing as a 12v OR 24v Module Correct?
Another head scratcher, as the Volts the MN classics are rated for go up the Amps go down. i.e. 150 rated for 98A the 200 rated for 79A, 250 rated for 63A. If I add more panels to my array, my VOC and Max power current will both go up not down.
Quote from: Alaska Man on May 07, 2014, 06:10:04 PM
I've seen modules rated at 12V, 24V etc. Yet they all put out somewhere around 36.7VOC. So there is really no such thing as a 12v OR 24v Module Correct?
Voc occurs when there is no load on a panel. Vmp is the panels voltage when it is producing power.
The so called "12 volt" and "24 volt" panels have a Vmp of about 17 (or 34) volts. Corresponding Voc is a bit over 20 (or 40) volts. If you have such a panel, you can use a cheap PWM controller to charge your battery.
The panels you are looking at are 60-cell 'grid-tie' panels. Their Vmp is about 30 volts and they will NOT reliable charge a 24 volt battery. These 'grid-tie' panels are much cheaper than the so called "12 volt" and "24 volt" panels. BUT in order to use them effectively you need to use an expensive MPPT controller.
Quote from: Alaska Man on May 07, 2014, 06:10:04 PM
If I add more panels to my array, my VOC and Max power current will both go up not down.
That depends entirely on how you have your panels configured (how many panels per string, and how many strings).
Have you tried out Midnite's string sizing tool?
--vtMaps
I did I bought the 150 MPPT, but I maxed it out at 110V input from my panels. Since we regulary get -40F up here in the winter and it can get down -60°F I hesitate to add another panel to the three I have in series now.
HyperVOC and all that.
I'm adding a second string (4) 250W Canadian Black on Black modules for 73amps of Power (1040w). I plan on using the Classic 200 this time.
Wish I had went with the 200 on the first string................ Live and learn.
I still don't understand why the Classic Line Rating for AMPs goes down at its Rating for Volts goes up.
Quote from: Alaska Man on May 07, 2014, 08:44:46 PM
I still don't understand why the Classic Line Rating for AMPs goes down at its Rating for Volts goes up.
Simple... All the classics become less efficient as the ratio of voltage in to voltage out becomes greater. In other words, the more down conversion of voltage that the classic has to perform, the less efficient it is.
Less efficiency means more heat production in the Classic. More heat production means lower ratings.
btw, the rating of the classic 150 is not 96 amps at all input and output voltages.
--vtMaps
Quote from: vtmaps on May 07, 2014, 08:59:37 PM
Quote from: Alaska Man on May 07, 2014, 08:44:46 PM
I still don't understand why the Classic Line Rating for AMPs goes down at its Rating for Volts goes up.
Simple... All the classics become less efficient as the ratio of voltage in to voltage out becomes greater. In other words, the more down conversion of voltage that the classic has to perform, the less efficient it is.
Less efficiency means more heat production in the Classic. More heat production means lower ratings.
btw, the rating of the classic 150 is not 96 amps at all input and output voltages.
--vtMaps
I'm not actually sure that this is really a significant issue. What are we talking about? perhaps a variation in efficiency of under a half percent with input voltage to battery voltage rations of 1.5:1 up to 4:1
When I increased the pv voltage from my arrays from about 54v (3 by 18v mpv panels) to 90v (5 by 18v mpv) where the pv array was about 35metres from the controller, I
never noticed any Classic temp increase or loss of efficiency.
I did notice a slight improvement when I went from tin 6mm cable to twin 4G cable when it was at the 54v. (24v battery system)
I also see absolutely no loss of efficieny in rewiring my array of 20 pvs into two series strings of 10 pvs giving 180v mpv into my Classic 250 and charging the same 24v battery bank. Problem with 250 was it current limited at 63A with this jnput.
Logic would indicate that what you say is true, but I don't think MN has ever produced an efficiency table showing different input voltages vs %efficient for any of the Classic controllers. The nearest I remember is the table that was in the docs for the MX60 and even then the range of efficiency variation was really really low.
It seems to me that the buck conversion in the Classic is pretty darn efficient. No complaints here ;)
Anyway just IMHO
dgd
Quote from: dgd on May 07, 2014, 10:08:10 PM
I'm not actually sure that this is really a significant issue. What are we talking about? perhaps a variation in efficiency of under a half percent with input voltage to battery voltage rations of 1.5:1 up to 4:1
The OP asked about the Classic's ratings. The ratings ARE the limits. And when you're at the limit, there is no capacity to handle extra heat production.
When you are handling 1000s of watts, a half percent (or more) extra heat production does matter if you are already at the limit.
--vtMaps
Vtmaps,
Yes you are correct. The current limits are just that.
However, I was just not sure with the concept of trying to make input voltage closer to output voltage, or at least at a level to let mppt work. I was also not sure that the greater the input voltage then the hotter the Classic runs. Hasn't been my experience or its so minimal that its not that noticeable.
dgd
The reason that each classic has the limit that it does has entirely to do with how hot the components get.
Usually either the FETs or the inductors. In the last 10 to 15 years or so, inductors have pretty much
been the limiting factor.
Given a set output current and input voltage along with a higher input voltage specified controller,
(150 --> 200 --> 250) the efficiency must be lower but not a lot
Just a few extra watts of dissipation means you have to reduce the output current if
it is already at the temperature limit.
So when in my head I'm thinking, "Okay I Wired 3 "12 volt" panels is series for an input voltage of 36V" is just not right.
What I actually did was wired 3 modules with a VMP @ 29.7V in series for what is really 89V coming into the MN Controller?
So then these are really "24V" panels is this correct?
Hi Alaska..,
NO, 29 - 31 Vmp PVs are NOT 24 Volt PVs.
Real 24 V PVs have a Vmp of about 35.4 Volts, or a bit more. This is because a 24 volt battery is seldom 24 volts. A fully charged Flooded 24 V battery at 77 degrees F (25C), which has had NO charge or discharge for 3 -8 hours (Rested) is about 25.4 V. On charge, this voltage must be higher. Often the Absorption voltage is about 28.8 to about 30 volts, depending on the exact battery construction. A 30-ish Vmp PV cannot fully charge this battery, due to the voltage drops in cable and the CC, plus temperature effects on the Vmp of the PV, etc.
The majority of the PVs being sold these days are for Grid-Tied systems, and have 60-cells -- 30-ish Vmp. Recently, as the power output levels of large PVs have risen, there are some PVs available with a 36 or so Vmp. These could be referred to as a real 24 V PV.
When using MPPT CCs, like the MN Classic and KID, the distinction of weather a PV is 12 or 24 V, etc has little meaning, as these controllers allow converting string voltages higher than the nominal 12 V multiples efficiently. It is common to see two or three 30-ish V PVs per string on 24 and 48 volt system respectively.
When using PWM CCs, it is important to match the nominal PV Vmp to the system battery voltage for efficiency. MPPT CCs allow a much wider difference between string Vmp and battery voltage.
Vic
Ah............. Okay, I get it. Thanks
just out of curiosity and i should point out i have no intention of trying what i am about to ask.
Theoretically any Midnite classic 150...200...250....250ks can put out a larger amount of amps if inductors are kept cool.....within operating temperature range ?
Quote from: mahendra on May 08, 2014, 08:23:55 PM
just out of curiosity and i should point out i have no intention of trying what i am about to ask.
Theoretically any Midnite classic 150...200...250....250ks can put out a larger amount of amps if inductors are kept cool.....within operating temperature range ?
Yep. That's where heat sinks and fans come in.
With a VOC of 36.7 per panel and 3 panels in series producing 110.1V into the MN Classic 150. How many more volts do you think the 150 could handle before I got in HYPERVOC trouble?
I'd really like to add one more PV to the string, even if it's a small one.
Quote from: Alaska Man on May 09, 2014, 03:00:16 PM
With a VOC of 36.7 per panel and 3 panels in series producing 110.1V into the MN Classic 150. How many more volts do you think the 150 could handle before I got in HYPERVOC trouble?
I'd really like to add one more PV to the string, even if it's a small one.
With the low temps you get in the winter, you're at the max. btw, if you were to add a "small" panel to the string, you must be sure that its Isc is the same as the other panels in the string.
If you have a 24 volt system, why not buy a fourth panel and configure them as two parallel strings with two panels per string?
--vtMaps
Wouldn't that require another controller?
Quote from: Alaska Man on May 09, 2014, 03:49:56 PM
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
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.
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.
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?
Quote from: Alaska Man on May 09, 2014, 05:36:18 PM
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
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
Quote from: Alaska Man on May 09, 2014, 05:20:34 PM
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
Quote from: vtmaps on May 09, 2014, 08:29:44 PM
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?
Quote from: RossW on May 09, 2014, 09:03:39 PM
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
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.
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.
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.
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.
Quote from: Alaska Man on May 12, 2014, 02:16:27 PM
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
So if I add another panel, I make the one array into two Arrays wired in series I get.
Where does the parallel come into play and what what am I losing over all?
Quote from: Alaska Man on May 12, 2014, 02:52:23 PM
So if I add another panel, I make the one array into two Arrays wired in series I get.
Where does the parallel come into play and what what am I losing over all?
You put two panels in series (called a 'string' of panels) and connect it to a breaker in your combiner. You take the other two panels and also put them in series and connect them to a different breaker. You now have two strings of panels (two panels per string) that are in parallel (the parallel connection is made by the combiner).
Your classic will work more efficiently with the lower input voltage of only two panels in series (rather than three panels in series which you currently have).
--vtMaps
A M,
As vtmaps has said twice;
You CAN add an additional 230 watt PV, identical or very similar in specs to what you now have.
ALL that you need to do is to run two 230 W PVs in each string. There will be two of these strings of two 230 W PVs, four in total.
You will need to add an additional pair of wires from this new string to your Combiner or Charge Controller, and make sure that the added current from this new PV will not overload the cables from your Combiner to the CC.
The Classic should be able to accept this additional power, and convert it to added current to your batteries.
This new configuration to TWO Strings of two PVs each, will allow the Classic to run cooler, and therefore will be more efficient (will waste less power).
You will not really need separate breakers in the Combiner with only two strings, but might be handy.
BUT, the MAXIMUM breaker or fuse size is 15 Amps. Think that there is only one 15 A breaker in that mockup of the Combiner. You may have additional 15 A breakers available.
You appear to be off to a good start on the Combiner -- just needs some more cable connections. But with one or two strings of these PVs that you speced, a Combiner is not absolutely required.
Just make certain that all of the circuit breakers are not too large for the wire that connects to them, as breakers and fuses are really there to protect the wiring from overheating, and causing a FIRE risk.
Good Luck, Vic
I replied don't know where that one went. I'll try again.
I get the two arrays and I can do this no problem.
Please forgive my ignorance, but if two arrays are feeding one controller isn't that the same thing. I would still be pushing 73.4VOC from number one array and 73.4VOC from array number two. All of which are combined (146.8VOC) and then fed through the top mounted bus bar on top of the breakers and into the controller?
I realize I must be missing something here.
Nope, when the voltage and amperage goes into the combiner in parallel, the voltage does not add as in series, BUT the amperage does add in the combiner...
I went over to the string sizing tool and according to it, I can do 3 strings of (2 Panels in series) and still use the 150.
Now we're talking.......... Wire is cheaper than another controller by a long shot.
Thanks the light just went on............ I get it now.
AM,
Just looking at the house pic you posted, I see you have space for another panel that would, as you say, balance the look. If you had the battery bank at 24v then you could probably get another two of those panels installed to make six in total - 3 strings of two. You certainly have enough breakers and connections in the breaker box for 3 strings. :)
There seems to be enough space to have 3 panels each side of the windows mounted horizontally instead of vertical as you now have them.
Perhaps two beside each other with a third on top of one nearest window. Looks like they would still fit below that shadow line your roof overhang is casting
dgd
Thanks again everyone for the schooling.
The house faces due South on that end and with one more panel it will be just about right for my 880Ah battery bank. Right now the three panels can keep up in full sun, but a bit more juice would be nice.
However, the sun shines on the western side (side to left of pic) for even longer. The panels on the west side would get sunlight from 5:00 pm until well after midnight. Although the sun is not as bright during the night, I'm thinking the next (2) strings would go on that side. The Black on Black panels that are designed for lower light situations would be ideal, I think?
In the winter the sun hits that left corner so that low winter sun would get a crack at the front and the side. Granted it's only for about 3 hours, but still every bit helps during late Dec-early Feb. If I had the sense god gave geese I would spend those months in Kauai. Which, truth be told is the eventual plan.