Which Breaker for combiner box should I go with?

hmong2017 · June 2019

Solar Panel:
Brand: GCL SOLR Model P6/72335
Maximum Power (PMax) 335W(0~+5W)
Maximum Power Voltage(Vmp) 38.00V
Maximum Power Current(Imp) 8.82A
Open Circut Voltage(Voc) 46.40V
Short Circut Current(Isc) 9.41A
Maximum Series Fuse 15A
Maximum Temperature 85C
Maximum System Voltage 1000VDC

Combiner Box:
Brand: Midnite MNPV6

Will 20A 150Vdc be able to handle or is it right for the solar panels?
I will parallel 2 panels into one breaker.
Please advise. Thank you.

I try to avoid Fuse.

BB. · June 2019

Are you going to 2x in series (double Voc/Vmp) or 2x in parallel (2* Isc/Imp)?

In general, for a "correct install", you need a fuse/breaker per series string. Paralleling two strings into one breaker is not usually done (i.e, instead of 3x or more 15 amp series string into 3x or more 15 amp OCPD, you would have 2x 15 amp strings in parallel into a single 30 amp OCPD (over current protective device).

-Bill

hmong2017 · June 2019

BB. said:

Are you going to 2x in series (double Voc/Vmp) or 2x in parallel (2* Isc/Imp)?

In general, for a "correct install", you need a fuse/breaker per series string. Paralleling two strings into one breaker is not usually done (i.e, instead of 3x or more 15 amp series string into 3x or more 15 amp OCPD, you would have 2x 15 amp strings in parallel into a single 30 amp OCPD (over current protective device).

-Bill

I am doing 2x in parallel. So two solar panel positive with positive, negative with negative in a Y Split MC4 connector into one breaker. So will the 15A 150VDC hold these two solar panels? I have 12 of these panels, and two of them are parallel into one wire into one breaker, so total I will have 6 breakers. But I need to know if these breakers will be able to handle the two solar panels.

Tecnodave · June 2019

Hmong2017,

First I'd like to know what type of charge controller you will be using and at what battery voltage. Please specify if charge controller is PWM or MPPT type and what type of battery, number of batteries, and voltage of battery set.
You may well be better off using a series panel arraignment.

BB. · June 2019

If your array is two panels in parallel--Then there is no requirement for DC series fusing/breaker. For your panels, if you want to install a DC Breaker (very nice to turn on/off the array when working on the system):

8.82 amps * 1.25 NEC continuous current derating * 2 parallel panels = 22 amps minimum (round up to 25 amps)
15 amp series fuse rating * 2 parallel panels = 30 Amp nominal breaker rating

In either case, the breaker should never break in normal operation... It would take a lightning strike or cross with battery DC Bus wiring to trip.

-Bill

hmong2017 · June 2019

BB. said:

If your array is two panels in parallel--Then there is no requirement for DC series fusing/breaker. For your panels, if you want to install a DC Breaker (very nice to turn on/off the array when working on the system):
8.82 amps * 1.25 NEC continuous current derating * 2 parallel panels = 22 amps minimum (round up to 25 amps)
15 amp series fuse rating * 2 parallel panels = 30 Amp nominal breaker rating
In either case, the breaker should never break in normal operation... It would take a lightning strike or cross with battery DC Bus wiring to trip.

-Bill

So I should use a 30A breaker then? how about the VDC? would that matter?

BB. · June 2019

Voc~46.40 volts... So, any breaker (or switch) rated for >=50 VDC minimum should be fine (note that VDC vs VAC ratings are usually very different, wth VDC and IDC ratings significantly lower than the VAC/IAC ratings... And many DC breakers have polarity ratings--Wiring backwards can cause internal arcing/failure of the breaker).

Are you planning to ever increase your Array/system capacity? If you have 3 or more strings in parallel, you will need a 15 amp breaker per string. And if you put upwards of 2-3 panels in series, you will need 150 VDC rated breakers).

-Bill

hmong2017 · June 2019

BB. said:

Voc~46.40 volts... So, any breaker (or switch) rated for >=50 VDC minimum should be fine (note that VDC vs VAC ratings are usually very different, wth VDC and IDC ratings significantly lower than the VAC/IAC ratings... And many DC breakers have polarity ratings--Wiring backwards can cause internal arcing/failure of the breaker).

Are you planning to ever increase your Array/system capacity? If you have 3 or more strings in parallel, you will need a 15 amp breaker per string. And if you put upwards of 2-3 panels in series, you will need 150 VDC rated breakers).

-Bill

I'm a bit confused. Let's put it as a Yes or No. If I parallel two of these panels using a Y MC4 Split connector into the breaker, will it overload or be too much for the breaker. The breaker is 20A 150VDC.

BB. · June 2019

Paralleling the two panels with Imp=8.82 Amps / Isc=9.41 amps means

2 * 8.82 Amps = 17.64 Amps current flow at Imp
2 * 9.41 Amps = 18.8 Amps Isc (short circuit current)
17.64 Amps paralleled current Imp * 1.25 NEC derating for continuous current = 22.05 Amps minimum Branch Circuit wiring+fuse rating

For typical US Fuses and Breakers and NEC, breakers and fuses will generally never open at 80% of rated current. And at 100% of rated current, the will open (could be minutes to hours).

Running 17.64 Amps through a 15 amp NEC rated breaker or fuse, the breaker will probably trip (minutes to many minutes) on a bright/clear day.

Running 17.64 amps through a 20 amp Breaker, it may or may not trip over time (like anything, running near rated capacity, things get hot and age--It may not trip tomorrow, but it may trip 10 years from now--and start tripping every few weeks after).

Breakers and fuses have a fairly wide trip range. This link goes into some detail and specification sheets about the details:

http://forum.solar-electric.com/discussion/353232/oversized-wire-and-breaker

For two panels in parallel, there is no reason to have a breaker (or fuse)--The panels, with 30 amp rated wiring (typically 10 AWG or larger for 30 amp circuit), will never trip (or really protect anything--Other than a lightning strike or cross wiring with battery bus). You could just use a good size On/Off switch--If you wanted.

If you were going to add more panels in parallel in the future, then 3 strings or more in parallel, you would need a 15 amp breaker (or fuse) in series with each string of panels. And where the wiring goes together, the wires from the combiner box would need to be rated for the total current rating of the array.

There other options, if you have an MPPT controller--You can put several panels in series (higher Vmp-array) --- And keep the current lower, and the wiring+parallel breaker costs down).

Remember that Power = Voltage * Current ... If you put three panels in parallel:

P-array = Vmp * 3 * Imp (three panels in parallel)

And if you put 3 panels in series:

P-array = 3 * Vmp * Imp (three panels in series)

The power in either case is the same... Higher Vmp-array means less current and smaller wires--Great for upgrading an existing array and not pulling new cable from array to charge controller---Or for long wire runs of 100 feet or more. High Vmp-array and low Imp-array means low current and low voltage drop on smaller AWG/cheaper cable.

Sorry to be so confusing--I am not sure how you are asking the question and if I and answering what you need.

-Bill

Estragon · June 2019

To be unconfusing "maximum series fuse 15A" means exactly that. So as a yes or no, the simple answer is no.

BB. · June 2019

Estragon, trying to unconfuse the poor reader of my posts? How dare you.

Just to be clear and confusing:

15 amps per solar string, if you have 3 or more solar panels (or strings of panels) in parallel. That is the maximum series fuse rating for your solar panels (1x breaker for 1x string).

If you have 1 or 2 parallel strings of solar panels, you really don't need any breakers on the input side (array side) of the solar charge controller. You can use a simple on/off switch... (one 30 amp rated switch, or 2x 15 amp rated switches--one for each string).

However, if you have 2x panel strings in parallel, that would require a 25-30 amp breaker to avoid "false trips". A 15 amp breaker fed with two strings, will probably, someday, have one or more false trips (and not make your system "any safer".

The reason I am confusing is that you, HMong, are asking for a "non-standard" configuration that really just uses a breaker like a switch (you could use a 100 Amp breaker in this particular setup, and it would not change the "safety" of the system).

-Bill

hmong2017 · June 2019

Okay, Maybe I wasn't clear on my setup. I am starting to understand.
I have 12 of these solar panels at the same rating. I need to combine all of them into the combiner box before it goes into my Charge Controller. I was asking if I use 6 of 20A 150VDC breaker at 2x panels for one breaker, will it work? If not, what rating breaker should I use for every 2x panels inside the combiner box.
If it helps, my charge controller is Renogy 100A MPPT Charge Controller.

BB. said:

Estragon, trying to unconfuse the poor reader of my posts? How dare you.

Just to be clear and confusing:

15 amps per solar string, if you have 3 or more solar panels (or strings of panels) in parallel. That is the maximum series fuse rating for your solar panels (1x breaker for 1x string).

If you have 1 or 2 parallel strings of solar panels, you really don't need any breakers on the input side (array side) of the solar charge controller. You can use a simple on/off switch... (one 30 amp rated switch, or 2x 15 amp rated switches--one for each string).

However, if you have 2x panel strings in parallel, that would require a 25-30 amp breaker to avoid "false trips". A 15 amp breaker fed with two strings, will probably, someday, have one or more false trips (and not make your system "any safer".

The reason I am confusing is that you, HMong, are asking for a "non-standard" configuration that really just uses a breaker like a switch (you could use a 100 Amp breaker in this particular setup, and it would not change the "safety" of the system).

-Bill

hmong2017 · June 2019

Bill, Thank you so much for answering my questions nicely and with extra info. It helps a lot. I am not adding or upgrading the system anytime soon. If I do, it would be by professionals for a bigger system. For now, it is just a DIY for my offgrid use at this time. Another question now. Does the VDC on the breaker mean anything? and if I parallel two panel into one of those breaker, will I overload the VDC since the panel spec says Maximum system voltage is 1000VDC. But the Breaker is only 150VDC?????
Am I best to go with a 30A breaker? But it would Still be a 150VDC too.... does it matter?

BB. · June 2019

Is this the controller?:

https://www.renogy.com/rover-li-100-amp-mppt-solar-charge-controller/

Its maximum panel input voltage is around 150 VDC to 140 VDC, depending on temperature.

Depending on how cold it gets where you are at, very roughly, Vmp-array maximum is around 100 VDC... You should be able to put 2x 38 volt Vmp panels in series (cold region). It looks like 3x panels in series is too high unless you are in a Caribbean island where it is >70F all year round.

So, your array would probably 2x panels in series by 6 parallel strings. Each string would require a 15 amp breaker (6x). This is to protect a single shorted panel from being fed current from the other 5 parallel connected string (this would trip the 15 amp series fuse/breaker).

The array would be (2x38v Vmp=) 74 VDC. And (6x8.82a Imp=) 52.92 Amps Imp -- So your wiring from the combiner would need to support:

52.92 Amps * 1.25 NEC = 66.15 Amps Branch Circuit rating

You could have a ~70+ single breaker as an On/Off switch to the input of the charge controller--But this is really just for a convenient on/off switch. The "protection" is from the 6x 15 breakers in the combiner).

This 2x series x 6x parallel should work fine for a 12 volt or 24 volt battery bank (1,300 Watt max @ 12 volt; 2,600 Watt max @ 24 volt battery bank). The array voltage of 2x series (76 volts Vmp-array) is probably to low to be optimal for a 48 volt battery bank.

This is starting to make more sense... Do you have a reason you would want to put all 12 panels in parallel (other than a 12 breaker combiner box)? A single panel (Vmp-array 38 volts) is probably more efficient for a 12 volt battery bank--But usually not a big difference for the MPPT controller.

-Bill

hmong2017 · June 2019

BB. said:

Is this the controller?:

https://www.renogy.com/rover-li-100-amp-mppt-solar-charge-controller/

Its maximum panel input voltage is around 150 VDC to 140 VDC, depending on temperature.

Depending on how cold it gets where you are at, very roughly, Vmp-array maximum is around 100 VDC... You should be able to put 2x 38 volt Vmp panels in series (cold region). It looks like 3x panels in series is too high unless you are in a Caribbean island where it is >70F all year round.

So, your array would probably 2x panels in series by 6 parallel strings. Each string would require a 15 amp breaker (6x). This is to protect a single shorted panel from being fed current from the other 5 parallel connected string (this would trip the 15 amp series fuse/breaker).

The array would be (2x38v Vmp=) 74 VDC. And (6x8.82a Imp=) 52.92 Amps Imp -- So your wiring from the combiner would need to support:
52.92 Amps * 1.25 NEC = 66.15 Amps Branch Circuit rating
You could have a ~70+ single breaker as an On/Off switch to the input of the charge controller--But this is really just for a convenient on/off switch. The "protection" is from the 6x 15 breakers in the combiner).

This 2x series x 6x parallel should work fine for a 12 volt or 24 volt battery bank (1,300 Watt max @ 12 volt; 2,600 Watt max @ 24 volt battery bank). The array voltage of 2x series (76 volts Vmp-array) is probably to low to be optimal for a 48 volt battery bank.

This is starting to make more sense... Do you have a reason you would want to put all 12 panels in parallel (other than a 12 breaker combiner box)? A single panel (Vmp-array 38 volts) is probably more efficient for a 12 volt battery bank--But usually not a big difference for the MPPT controller.

-Bill

Starting to understand more now too. I wanted to go with just parallel because my very first solar setup was a small 12V 800Watt. It doesn't have a combine box and was all parallel directly to my controller. Had it for over 7 years until I decide to upgrade to this unit. Got stuck on the part to decide which breaker is appropriate for the panels in parallel by 2x, 2x, 2x, 2x, 2x, 2x into 6 breakers inside my combine box so I could get all of them into my controller. If Parallel works, then I would prefer to stick with parallel because it is easier to work with.
The setup for this confusing combine box question is a 24V battery bank system, Acid Sealed AGM batteries.
Since you're a pro at this, can you tell me if I go Parallel, What breaker Amp and VDC for Midnite brand should I use?
I have some 20A 150VDC that I have been mentioning about. Got them with the Combine box off Ebay. If these works for what I am talking about, then I'd like to just hook it up and start using it. If not, then I need to get the right breakers and replace it.
I didn't want to go with Fuse, because then I'll have to replace fuses when it blows.

BB. · June 2019

Breakers are very nice because they can be used for switches too (touch safe fuse holders cannot be popped out under load).

MPPT controller (real MPPT) are almost like magic. For a 24 volt battery bank they can take Vmp-array from ~40 volts or so to ~100 VDC Vmp-array. And other than 1 or 2% more losses at the higher array voltage, there is usually no "functional" difference as long as you are in the MPPT operating range.

And the proper way to reduce / combine panels to use fewer series breakers, in this case, is to put two panels in series by 6 parallel strings (6x 15 amp breakers total in the positive panel leads).

I am not the expert here... But you are looking for a box that holds 6 or more breaker and have bus bars for the + and - combined buses, and a connection for a +/- set of wiring (plus greenwire safety ground to local ground rod and back to the battery shed--If needed).

A starting point could be:

https://www.solar-electric.com/mnpv6.html (6x position breaker combiner box)
https://www.solar-electric.com/midnite-solar-mnepv-15-amps-circuit-breaker.html (Midnite 150 VDC 15 Amp breaker)

Combiner box information:

https://www.solar-electric.com/lib/wind-sun/PVcombiners-explained.pdf

There are people who much more than I--And/or you can contact NAWS (our host) or your local solar supplier for details/confirmation on needed parts.

-Bill

hmong2017 · June 2019

BB. said:

Breakers are very nice because they can be used for switches too (touch safe fuse holders cannot be popped out under load).

MPPT controller (real MPPT) are almost like magic. For a 24 volt battery bank they can take Vmp-array from ~40 volts or so to ~100 VDC Vmp-array. And other than 1 or 2% more losses at the higher array voltage, there is usually no "functional" difference as long as you are in the MPPT operating range.

And the proper way to reduce / combine panels to use fewer series breakers, in this case, is to put two panels in series by 6 parallel strings (6x 15 amp breakers total in the positive panel leads).

I am not the expert here... But you are looking for a box that holds 6 or more breaker and have bus bars for the + and - combined buses, and a connection for a +/- set of wiring (plus greenwire safety ground to local ground rod and back to the battery shed--If needed).

A starting point could be:

https://www.solar-electric.com/mnpv6.html (6x position breaker combiner box)
https://www.solar-electric.com/midnite-solar-mnepv-15-amps-circuit-breaker.html (Midnite 150 VDC 15 Amp breaker)

Combiner box information:

https://www.solar-electric.com/lib/wind-sun/PVcombiners-explained.pdf

There are people who much more than I--And/or you can contact NAWS (our host) or your local solar supplier for details/confirmation on needed parts.

-Bill

Thanks for the information. I want to clarify one thing. When you say series two panel into one breaker, you mean using two panels and connect positive and negative together. Then the other Positive goes into the breaker 15A, and the negative will go right into the negative bus bar right?

What about my 20A breakers now? Can I not connect two panels using a Y Split MC4 to make it into one line into the 20A breaker and negative bus? The Y split is like this one: https://www.google.com/search?tbm=isch&source=hp&biw=1920&bih=969&ei=rUr_XJG5EYPQ0PEP_56_6AU&q=mc4+split+Y&oq=mc4+split+Y&gs_l=img.3...871.3300..3603...0.0..0.230.1569.5j5j2......0....1..gws-wiz-img.....0..35i39j0j0i8i30j0i24._kw-wCINUxU#imgrc=di87A_83etHJyM:

BB. · June 2019

Yep, that is a series connected pair of solar panels.

Just like stacking two D Cell batteries end to end (negative bus to negative Batt A, positive from Batt A to negative Batt B, positive Batt B to positive bus).

Nice explanation:

https://www.solarreviews.com/blog/do-you-wire-solar-panels-series-or-parallel

Two panels in series Is one negative wire in and one positive wire out through the 15 amp breaker. No need for Y connectors.

Y connectors are used to make parallel solar panel connections (typically 2 panels in parallel--Not "usable" for 3 or more parallel connections).

The 20 Amp Breakers are not usable (at least following code) for your combiner box... You need 15 amp rated breakers here.

If you choose not to follow code, you can use the 20 amp breakers in the Midnite combiner box (6x pairs of series connected solar panels)--But it is "not legal" and does not provide optimal protection against fire.

What are the chances you will have a failing solar panel or squirrels chewing through wiring on the panels/roof? I don't know.

We have relatively few electrical fires these days--And this is because insurance companies started UL (underwriters laboratories) to standardize testing/qualifications of electrical (and other) components. And the NEC standardized installation practices.

The problem is not following "code", you either end up with an unreliable installation (too much current through 20 amp breakers from 2x parallel connected panels) or an increase risk of fire (20 amps back feed through breaker + 9.41 amps from 2nd paralleled panel = 29.41 amps feeding a shorted panel/string that is only rated/tested to 15 amp series protection fuse.

And remember that Power = I^2 * R [fix typo--Not V^2, but I^2 -BB.]... (29.41 amps available / 15 am max rating)^2 = 3.8x more heat at point of short (your paralleled connections into a Y connector and 20 amp breaker vs my single 15 amp breaker connection for a series string)--That increases the chance of starting a fire.

Failures modes can be non-obvious... If you follow code/normal installation instructions, the chances of a failure/fault is much less... Plus your insurance company will not have a good reason to deny your claim if you ever do have a fire and followed code.

-Bill

hmong2017 · June 2019

I finished reading the link abour series and parallel. I'll Series 2x Panels into one breaker 15A and do that for the other 5 breakers. New question. If I series, would I have to change my system to a different Volt then? Because My system and battery bank is all 24V including my Power Inverter. I wouldn't want to replace them all, too. It's pretty expensive.

If I understand right, this mppt charge controller should be able to handle and charge the series added Volt of 76V into my 24V battery Bank with no problem. Right? The Amp would remain 8.82A, which the 15A breaker covered it. In total, That would be 456V and 52.92A coming from the Combiner box into my Charge Controller. Will my current 4 AWG 25FT PV wire handle these power from the combiner box to my charge controller now?

mcgivor · June 2019

@hmong2017

With panels in series the voltage is additive, current is constant, two in series voltage values will double, current remains what a single panel value is.

Panels in parrallel the voltage is constant, the current is additive, so voltage value will be what a single panel is current will double a single panel value.

The advantage of higher voltage is the amount of power that can be transported over a given sized conductor is increaced, think of how grid power works. The overhead local grid distribution is carried on reletivaly small conductors at high voltage, usually in the 12 500V to 25 000V range, a transformer reduces this to whatever local domestic voltages are used, 120/240V for example, if the grid was distributed at domestic values the overhead distribution conductors would have to me massive.

The same rules apply in solar, series connected panels allow a voltage increase which allows more power to be transported over smaller conductors. Because there are six parrallel strings of two, the voltage would be twice that of a single panel and the current would be six times that of a single panel.

This higher voltage will be down converted by the MPPT controller to the values needed to charge the battery, similar to what a grid transformer dose, only electronically rather than magnetically. Using the Vmp and Imp vaues of your panels, combined voltage would be 76V, current would be 52.92A. The MPPT controller will decrease the voltage to whatever is needed, which depends on state of charge of the battery, since voltage is inversely proportional to current, the current value supplied to the battery will be higher than what is being supplied to the controller at a higher voltage.

Using a voltage drop calculator https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.8152&voltage=76.6&phase=dc&noofconductor=1&distance=25&distanceunit=feet&amperes=59&x=32&y=15 the 4awg at 25 feet assuming copper, would be 0.96% which is an excellent value.

Note 1: The current values stated on the panels themselves is under perfect conditions, generally ~ 80% of this will be seen, very rarely will they meet or exceed that.

Note 2: The series parallel explanation above also applies to battery configuration

Hope this clears some questions, tried to keep it as simple as possible.

BB. · June 2019

If I understand right, this mppt charge controller should be able to handle and charge the series added Volt of 76V into my 24V battery Bank with no problem. Right? The Amp would remain 8.82A, which the 15A breaker covered it. In total, That would be 456V and 52.92A coming from the Combiner box into my Charge Controller. Will my current 4 AWG 25FT PV wire handle these power from the combiner box to my charge controller now? .

2 * Vmp=38 volt panels in series is 76 VDC Vmp-array ... You are adding 6 parallel strings, which adds current, not voltage.

Think of the MPPT solar controller like a variable transformer (variac). It takes 76 volts in and steps it down to 14.5 volt battery charging with ~95% efficiency.

Or, another analogy--The MPPT is like an automatic transmission between the engine and the wheels. It shifts, depending on engine RPM, horsepower, road speed, and loads (up hill, down hill, wind, etc.).

Your controller can take any input voltage between ~40 volts and 140/150 volts and down convert it to battery voltage (~20-30 VDC as needed) with 95% efficiency. So there is no need to change any of your DC hardware or programming changes to the MPPT controller (it automatically sets itself for a 12/24/48 volt battery bank charging requirements).

-Bill

hmong2017 · June 2019

So basically everything I have is correct. I just need to change my 20A breakers to 15A breakers, and series 2x panels into one breaker, and repeat this to the rest of the 10x panels and 5 breakers then I am all good and up to codes, right?

BB. · June 2019

From what I can see, yes.

What AWG cable from solar array to charge controller? How long will it be?

What AWG cable and length from charge controller to battery bus? What size breaker from battery bank to MPPT solar charge controller Vbatt connections?

-Bill

hmong2017 · June 2019

The copper PV wire is 4 AWG 25FT from Combiner Box to Controller. This should hold fine, right?

Which Breaker for combiner box should I go with?

Comments

Categories