adding a pair of panels to existing mppt controller

rosoha · January 2016

I bought four 315 watt Kyocera panels from you folks two years ago, and would like to add two more panels to the Midnight Solar 150 volt mppt controller. The 315's are wired in series/parallel.
How closely matched does the open circuit voltage of the added panels have to be to the 315 watt panels, which is 49.2 volts? Kyocera no longer makes this particular panel and the closest I can find is the 325 watt panel you have for sale, but its Voc is 49.7 (as I remember) Is that close enough or does it have to be exact? Also, will the controller handle two more panels if the Voc is close enough? thanks for any help....rosoha

vtmaps · January 2016

rosoha said:

I bought four 315 watt Kyocera panels from you folks two years ago, and would like to add two more panels to the Midnight Solar 150 volt mppt controller. The 315's are wired in series/parallel.
How closely matched does the open circuit voltage of the added panels have to be to the 315 watt panels, which is 49.2 volts? Kyocera no longer makes this particular panel and the closest I can find is the 325 watt panel you have for sale, but its Voc is 49.7 (as I remember) Is that close enough or does it have to be exact? Also, will the controller handle two more panels if the Voc is close enough? thanks for any help....rosoha

Welcome to the forum,

Not enough detail about your system to answer your questions...

Are you planning to make a third string with the two panels (in which case your string voltage stays about the same), or are you planning to add one panel to each of your existing two strings (in which case your string voltage will be nearly 150 volts)?

Do you have a combiner?

What is your battery voltage?

--vtMaps

rosoha · January 2016

Hi there...nice to be here...Just adding another string is what I had hoped to be able to do. I'm a 24 volt system with a trace 4024 inverter. Not really understanding how to figure 'head room' or safety margin with this (or any..ha!) controller. and my original question about Voc. Not sure exactly what you mean by combiner. Each pair of panels has its own breaker immediately behind the panels and then goes to Midnight Solar, if thats what you mean. Thanks for your help....rosoha

vtmaps · January 2016

The voltages are close enough... just add the third string.

A combiner box is where the three strings are made parallel. It is weatherproof and very near the panels. From the combiner box a single, combined cable runs to the Classic 150 charge controller. Each string of panels will have its own breaker in the combiner box. A combiner box is also a great place to put a lightning arrestor.

The reason I asked about the combiner box is that with only two strings you do not need breakers and a combiner box. With three strings it is a safety requirement to have a combiner.

--vtMaps

rosoha · January 2016

Thanks very much for your help...one more question...can the new set of panels be in a somewhat different location with their own breaker and then sent to the controller where they are paralleled with the other panels?...rosoha

westbranch · January 2016

As long as they have the proper CB to prevent backfeeding , which is what damages them (PVs), YES.
The breakers do not have to be in the same location but them where will you place the combiner? ( the most convenient place to protect and combine, is in one fixture.)
They can also be in a different orientation (E vs W) than the others as well, like in a virtual array.

rosoha · January 2016

I was under the impression that the Midnight Solar 150 charge controller I'm using had a built in protection against back feeding. Am I mistaken in this assumption?

vtmaps · January 2016

rosoha said:

I was under the impression that the Midnight Solar 150 charge controller I'm using had a built in protection against back feeding. Am I mistaken in this assumption?

The charge controller will prevent backfeeding from the battery to the array.

Westbranch was referring to two strings of panels backfeeding into a third (defective) string. That's why if you have 3 or more strings in parallel you must have breakers on each string. When you have only 2 strings you do not need breakers because the current from one string can be handled by the other (defective) string.

--vtMaps

rosoha · January 2016

OK, cool....everybody gets a breaker...I do have a large diode on my old but trusty Jacobs wind machine to keep it from motoring when there is no wind...but thats another story...thanks to all...rosoha

vtmaps · January 2016

rosoha said:

OK, cool....everybody gets a breaker...I do have a large diode on my old but trusty Jacobs wind machine to keep it from motoring when there is no wind...but thats another story...thanks to all...rosoha

Of course your breakers are DC rated. Are they polarized?
(some DC breakers have a line (pos) side and a load (neg) side).

If they are polarized, which way will you wire them?

--vtMaps

rosoha · January 2016

HA! I think they are polarized and the one between the controller and the batteries I got backasswards and couldn't figure out why it was heating up so much (although the kind folks at NAWS said it should not have made such a difference or got so darn hot). After I melted it down they replaced it for me...(I recommend theses folks). This stuff happens at seat of the pants DIY places like mine....on the bright side, nothing has burned down (yet)...you folks are great..its like going to school...much obliged, as they say in these parts....rosoha

BB. · February 2016

DC breakers (current/old style) are generally polarized. They "expect" the current to flow one way through them. And many breakers have a magnet inside of them--The magnet literally "blows" the arc into the arc chute to extinguish the arc. If the current flows "backwards", then the reverse current flow+magnet polarity would "suck" the arc into the interior of the breaker and can cause damage/failure.

So--The next question... you put a breaker in between the solar charge controller and the battery bank. Current normally flows from charge controller to battery (negative ground system). However, the chance for high current flow is a dead short in the wiring/charge controller, and the high current source is the Battery Bank. So, the "+" terminal (may be called Line) should point to the battery bank,a nd the "-" terminal (Load) should point to the charge controller.

Newer breakers (and new NEC/NRTL standards) and defining circuit breakers as "non-polarized" designs, so that they do not have the problem with arc quenching with bi-directional DC current flow.

-Bill

vtmaps · February 2016

BB. said:
Newer breakers (and new NEC/NRTL standards) and defining circuit breakers as "non-polarized" designs, so that they do not have the problem with arc quenching with bi-directional DC current flow.

However DC breakers (polarized or not) may be sensitive to their position. Midnite's non-polarized Panel Mount DC breakers cannot be installed "on their backs", but they can be installed on their sides. I haven't a clue what might happen to those breakers in zero gravity.

--vtMaps

rosoha · February 2016

Yeah...zero gravity...you'd have a tough time 'floating' in it methinks....thanks for all the info....and I think BB nailed it, as I had the + line pointed the wrong way, since when I 'flipped' the replacement breaker things have been hunky dory ever since. While we're at it still, I never did get an answer to my original question which was how close does the Voc of another pair of panels have to be to those you are currently running to the mppt controller...curious if there is actually a percentage or number (like 'within 3 volts or something)...just wondering....

vtmaps · February 2016

rosoha said:

While we're at it still, I never did get an answer to my original question which was how close does the Voc of another pair of panels have to be to those you are currently running to the mppt controller...curious if there is actually a percentage or number (like 'within 3 volts or something)...just wondering....

If they are very far apart all sorts of bad things can happen. If they are within a few percent, you may lose a few percent of the total nameplate power. The difference between Voc 49.7 and 49.2 probably means that there is about 0.4 volts difference between the Vmp of those panels.... less than a percent difference. Just do it. I would draw the line at 5%. Others would draw it somewhat higher.

What is the Imp of the old and new panels? ... if (and only if) it's much closer than the voltages, here's what I suggest...
Make up your three strings with one of the new panels in each of two strings. Thus your Voc of the three strings would be:
49.2 + 49.2 = 98.4
49.2 + 49.7 = 98.9
49.2 + 49.7 = 98.9

rosoha said:

and I think BB nailed it, as I had the + line pointed the wrong way, since when I 'flipped' the replacement breaker things have been hunky dory ever since.

You mentioned that the first breaker was oveheating because it was in backwards. That doesn't sound right, unless there was an overcurrent condition. When the current is above the breaker's rating, the breaker is supposed to trip and break the current. If it's in backwards it may fail to do its job.

But if there was no overcurrent, then (for all the breakers I know about) it doesn't matter which way the current is flowing. The breaker was defective or had a loose connection if it was heating up at less than its rated current. The most common examples are the breaker between the inverter/charger and the battery... the current goes one way through the breaker when charging, and the other way when discharging.

--vtMaps

rosoha · February 2016

Thanks: I am going to do it..I was just curious about the numbers....as far as the breaker stuff goes, NAWS would agree with you that even wired backwards it should never have melted down like it did, that maybe it was just defective (they gave me a new one in any case)...anyway thanks for your valuable time in all this...its snowing, I think I should walk the dog...he likes the snow...someday I may ask you about batteries....rosoha

BB. · February 2016

Look closely at the wires, wire ends, and breaker terminals... I would be with vtMaps on this. There is a reason the breaker melted down, and loose/corroded connections and/or miss-sized wiring would be my first guess.

Secondary issues can include water following the wires into the main panel/breaker ends--And causing internal/bus bar connection corroding. Conduit is really good at carrying water to the electrical panels if you have a leak/no drip loops on exterior wiring entering the conduit/boxes.

-Bill

rosoha · February 2016

I understand what you are saying, and fortunately, there has been no problem since the breaker was replaced...same wires, box, distance, everything. A new breaker (midnite solar MNEPV-63 amp) ,same as the other, inverted, solved whatever the problem was. I have learned more about breakers here than I thought there was possible to know about them...I will certainly ask questions about any that I install in the future...thanks...rosoha

rosoha · February 2016

Well, after all the sound and fury, NAWS tells me the Kyocera 325's are no longer available...at least not now or for many months to come...sigh...at least I learned a lot from you folks....rosoha

arby · February 2016

rosoha-- I have a 48 volt system that started out with 4X125 watt 12 volt Kyoceras. To this I added 4X 270 watt 24 volt Sun Techs. I changed the wiring to 72 volts which put the 4 X125 watt panels together with one Sun Tech. I wired the other 3 sun techs in series for another 72 volt feed. Routed all of this through a combiner box and fed it to the CC. So far it works just fine. I have in a package, 6 more 280 watt Sun Techs, which I am going to install this summer and will put all of this at 72 volts nominal through 4 breakers of a 6 breaker combiner box.
IMO, the CC only knows what it is getting and doesn't ask questions or look for ID's.

rosoha · February 2016

OK, thanks....thats a great idea...just find panels to wire in series close to what I currently have...I'm laughing a bit since it never occurred to me that the 325's were not available (they were on the web site when I started this thread)....my wind generator (an old 2500 watt 32volt 400 lb. monster) is much less fussy about all this stuff....(Mr Jacobs must be smiling) just hook that machine up to any battery voltage up to 48 (thats all I've done), and it happily charges without complaint...older style tech, of course...still, the simplicity is endearing....thanks for your idea...rosoha

adding a pair of panels to existing mppt controller

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