Author Topic: Disconnecting both Positve & Negative of array  (Read 189 times)

labusker

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Disconnecting both Positve & Negative of array
« on: October 01, 2019, 07:46:01 PM »
NEC 690.15 for 2017 states that the PV array must have a means of disconnecting both plus & minus conductors simultaneously . I am going to use the MNPV6 at the array to combine four 10amp circuits. After that I need to put this disconnect switch. It can be a breaker, switch, pull-out switch, etc. What do you have than can perform this without adding too many more dollars to the cost?
Drew

Vic

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Re: Disconnecting both Positve & Negative of array
« Reply #1 on: October 01, 2019, 09:40:38 PM »
Hello again labusker,

Not sure that anyone has yet welcomed you to this Fourm.

Welcome!

There are others who have more knowledge about this particular question.

However,   here,   most of are just folks interested  in Solar systems,   and are volunteers.   We are still trying to learn as much as possible about these systems.

Wonder about the outcome of the previous questions that you have asked,   as  have seen no responses about any questions (implied or direct)  that you might have.,   to previous comment from Members here.

For example:

  1.   http://midniteftp.com/forum/index.php?topic=4699.msg43766#msg43766

  2.   http://midniteftp.com/forum/index.php?topic=4708.0

Could you tell us more about the configuration of the PVs that you are planning to use,   the system voltage,   etc?   And,   how do you plan to wire the SPD into the Combiner?

 For many of us,   replies are how we learn,   perhaps you have not had an opportunity to try suggestions,   or have not had time to read any replies,   etc,   but   to me,   these hanging threads are in the back of the mind,   awaiting additional information.   Just as a Community member,  wondering   ...

TIA  for any replies to the previous questions.

FWIW,  Vic
« Last Edit: October 01, 2019, 09:42:44 PM by Vic »
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

FNG

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Re: Disconnecting both Positve & Negative of array
« Reply #2 on: October 02, 2019, 08:26:53 AM »
NEC 690.15 for 2017 states that the PV array must have a means of disconnecting both plus & minus conductors simultaneously. I am going to use the MNPV6 at the array to combine four 10amp circuits. After that I need to put this disconnect switch. It can be a breaker, switch, pull-out switch, etc. What do you have than can perform this without adding too many more dollars to the cost?

For 4 strings I would lean towards a couple of options:

MNPV12 used as 6 string with breakers for Pos and neg

Or the MNPV8HV-DISCO 3R keeping in mind the cost of this includes all fusing, strain reliefs and SPD

labusker

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Re: Disconnecting both Positve & Negative of array
« Reply #3 on: October 09, 2019, 07:20:19 PM »
I am still in the design stage and want to get all my facts together before I apply for a permit and order any equipment.
My plans are to mount 8 approx. 315w panels on a ground mount wooden structure that will need to be 9' from the side of the house and on 9' high posts to receive the winter sun.
I will put 2 panels in series for a total of approx. 80V @ 10A, with 4 of these sets in parallel. I will use the MNPV6 to combine the 4 circuits giving me 80V @ 40A. I will put the red wire of the SPD to the positive combined busbar with a screw. The other 2 wires will go to the negative & ground busbars.
A disconnect switch will have to be added that will disconnect both the positive & negative at the same time as per 690.15C, so it has to be one switch. Using the MNPV8HV will be quite expensive and the MNPV12 will require too many switches. The switch will have to handle approx. 40A x 1.25 @ 80V.
My 2 option thoughts would be to use the MNPV6, cut the positive busbar out for the last 2 breaker slots, add a double pole breaker here (MNEPV80), then wire in the positive and negative outs. The other option would be to add in a MNPV3, add a double pole breaker without the positive busbar, then be done with it. My 3rd option would be to use a cheap air conditioner pullout disconnect, but that may not pass code.
Drew

Vic

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Re: Disconnecting both Positve & Negative of array
« Reply #4 on: October 09, 2019, 08:40:03 PM »
I am still in the design stage and want to get all my facts together before I apply for a permit and order any equipment.
My plans are to mount 8 approx. 315w panels on a ground mount wooden structure that will need to be 9' from the side of the house and on 9' high posts to receive the winter sun.
I will put 2 panels in series for a total of approx. 80V @ 10A, with 4 of these sets in parallel. I will use the MNPV6 to combine the 4 circuits giving me 80V @ 40A. I will put the red wire of the SPD to the positive combined busbar with a screw. The other 2 wires will go to the negative & ground busbars.
A disconnect switch will have to be added that will disconnect both the positive & negative at the same time as per 690.15C, so it has to be one switch. Using the MNPV8HV will be quite expensive and the MNPV12 will require too many switches. The switch will have to handle approx. 40A x 1.25 @ 80V.
My 2 option thoughts would be to use the MNPV6, cut the positive busbar out for the last 2 breaker slots, add a double pole breaker here (MNEPV80), then wire in the positive and negative outs. The other option would be to add in a MNPV3, add a double pole breaker without the positive busbar, then be done with it. My 3rd option would be to use a cheap air conditioner pullout disconnect, but that may not pass code.

Hi labusker,

Thank you for adding  some  more  detail  on your system  plans.

As  you probably know,   the  selection of PVs,   string  configuration,   battery type,   coldest temperatures,   system  voltage,    etc  are related.

If  you  are  planning a 48 V battery voltage,   especially if the batteries  are Flooded  Lead  Acid types,   then  PV string voltage can be a critical  decision for good  system performance.   Generally,  Classics  and other MPPT CCs,  prefer  Vin of  about  130%  of  the highest battery charging/EQ voltages ever needed.

Strings of two  PVs  with a 48V  system,  could be  a problem,   even  with 72 cell PVs.     And strings of two 96  Cell PVs,  probably have an excessive Voc  for a Classic 150,  and,  really an excessive Vin on a Classic 150 at STC ratings.   Strings of two 60 Cell PVs   would really not be  a good match on a 48 V system,  except,  possibly for Li batteries   ...

Exactly which PVs are you thinking of using?
What is the system  voltage,
AND,   what battery type  are  you considering?

Fine on the SPD,   sounds  like  that  is fine (am not a Code  expert).

Agree  that an A/C  pull out  Disconnect  would  probably not  work  well,    as,   at the very least,  it is likely not rated for  DC.

Using the  MNEPV80,  is  a  cute idea,   and might  pass inspection,    even minus the paralleling   terminals,  again,  am no expert.

If you are considering 60 Cell PVs and a 48 V battery,  perhaps planning on strings of three PVs  (3X3).

Just some opinions,   thanks again  for the update.   FWIW,     Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

Steve_S

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Re: Disconnecting both Positve & Negative of array
« Reply #5 on: October 10, 2019, 07:29:51 AM »
My own setup is 8 260W panels on a fixed ground mount, set as 2 strings of 4.  This means that only in March & September do my panels get the right angle & produce the most they can.   A tracker would increase efficiency considerable but as you likely found out, they aren't cheap, unless you DIY it and have the ability to do it.  As such, I am "technically" overpanelled but not beyond teh ability of my Classic 200 to handle, which helps compensate for reduced performance.  I'm now pondering adding another 4 panels @ 345W with separate classic and a different angle.   Bit of a bugger because i'm off-grid & in a coniferous forest, so I have to work around it.

I suggest you use the String Sizing tool here:  http://www.midnitesolar.com/sizingTool/
which will help you optimize things a tad.
Classic-200, Samlex EVO-4024 Inverter/Charger, 2080W of Canadian Solar CS-260P in 2 strings of 4,  8x Rolls Surette S-550 24V/856Ah battery bank.
System Detail: http://midniteftp.com/forum/index.php?topic=4643.0

qrper

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Re: Disconnecting both Positve & Negative of array
« Reply #6 on: October 10, 2019, 10:04:46 AM »
What about using double pole CBs?

That would mean you'd be adding a breaker in the negative side of the PV, but it would disconnect both poles.

Only a thought.

mike
System one: 7kWp with Trina 250 W panels wired for 90 Vdc. Via Classic 150 to 16-6 V U.S batteries. Trace 5048 sine wave inverter.
System two: 6kWp grid tie with solaredge inverter.

labusker

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Re: Disconnecting both Positve & Negative of array
« Reply #7 on: October 10, 2019, 10:22:30 AM »
Thanks Vic for the response again. I want a panel with a good wind load rating and be around 315 watts. It probably will be the Canadian CS3K, Mission Solar MSE315, or the Hanwha QPEAKDUO315. It all depends on the cost of the panel at the time of purchase. I have decided on going with a 24V system with eight 12V, 200AH AGM batteries. The MNPV8HV is to costly. I would like to put three panels in series but do not have room for nine panels. Steve, I do not want four panels in series due to shading problems in the morning and evening. I live in the city with only a 22' long area to play with trees behind and a roof to reach over. I do not want to put any panels on my roof.
Mike, yes a double pole would work but I need to find a place to put it. Question of the day: I will be using Din mount breakers. The positive side will go to the + of the breaker. What side should the negative go to, or do we care?
Drew

Vic

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Re: Disconnecting both Positve & Negative of array
« Reply #8 on: October 10, 2019, 01:34:37 PM »
Hi lab..,

For a 24 V battery,  strings of two PVs,  even 60 cell ones should be fine for the Vin of your Classic 150.

You seem  studious,  so,  look at   smartgauge.com for suggested wiring diagrams  for your batteries.

AGM batteries have a very low  impedance,   this can result in imbalance in charging and during discharge.  uneven  charging,  can kill some  batteries.   And,  with AGMs,  SGs cannot be directly measured.

Long Absorb times can be one way to try to get all battery strings fully-charged.   For cyclic daily use (like off-grid) systems,  long Absorbs are more difficult.

Regarding DIN breakers,  YES, the MNEPV breakers are Polarity Sensitive.   Does the first Post in the following Link,  answer  your question  (?):
http://midniteftp.com/forum/index.php?topic=113.0

Later,   thanks for the update on your system,   Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

ClassicCrazy

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Re: Disconnecting both Positve & Negative of array
« Reply #9 on: October 10, 2019, 01:53:16 PM »
It all depends on the cost of the panel at the time of purchase. I have decided on going with a 24V system with eight 12V, 200AH AGM batteries.

Why not get 2v cells so you can put them all in series and avoid the parallel imbalance problems ?
Look up Soneil batteries - hopefully they live up to their claims for longevity ( because I have some ! )
I am sure there are other brands of 2v gel cells too.

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

Vic

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Re: Disconnecting both Positve & Negative of array
« Reply #10 on: October 10, 2019, 05:13:13 PM »
 AND,

CC Larry brings up two very good points:

  1. Try to run a single string of batteries,  whenever possible.

  2. And,  try to have each of the batteries be a single cell,  when possible.

The above generally makes the  batteries appear to be a bit  more expensive,  per Ah of Capacity,   but,   generally the system is more reliable,    predictable,  serviceable,   monitor-able,   than would be multi strings of higher  voltage batteries.   A single battery string of single cell batteries,  could easily have many more years of service-life than the alternative,    IMO.

FWIW,   Vic

Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

labusker

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Re: Disconnecting both Positve & Negative of array
« Reply #11 on: October 13, 2019, 11:51:33 AM »
Vic, you are right, I am studious, too studious trying to look for answers, but it sure does hurt my brain when I get stuck!
The system I am going to build is for fun only and not interested in putting tons of money into LiFo or similar batteries right now, especially for my 1st system.
Are you saying a lower resistant battery can cause imbalances? Do you recommend flooded lead acid over AGM then?
I need about 4500 watthours per day and only want to discharge them from 25-30%. My calculations show that I need about 800Ah of batteries. How
can you make this with one string of batteries? For one string only I would need about eight 6v 370Ah batteries set to 48V. For a 48v system I would have to wire 4 of my 8 panels in series x 2. That would put my VOC from the array at 160V+ causing too high a voltage for all 150V breakers. I cannot do 3 in series for I do not have room for 9 panels. For a 24v system I would put four 6v in series x2. What do you think is the better choice? Shipping is high for batteries here. The local battery would be the 6v high Ah Duracell. The altE store can work with the Trojan battery with not too bad of shipping charges.  :-\
Drew

Vic

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Re: Disconnecting both Positve & Negative of array
« Reply #12 on: October 13, 2019, 04:39:27 PM »
Hi Drew,

Agree about using LA batteries for one's first system (especially for off-grid).

AGM batteries are lower impedance than Flooded LA batteries.   This can mean that one string of batteries,  in systems with multiple battery strings,  can hog most of the charging current,  until it become more fully-charged (this hogging can also occur during discharge).   This hogging can cause chronic undercharging of the other parallel strings,  and can lead to battery damage.   This is more of a problem for off grid systems  (daily cycling,   and shortish Solar days).   For backup systems,    and other systems (with parallel strings),  that spend most of their time on Float,   this is generally much less of a problem,   as current hog strings become  fully charged,   allowing laggards a chance to take more current,   and become fully charged.

Flooded LA (FLA) batteries  are generally considered better for daily cyclic use,   as  the Catalyst in AGM batteries,  which recombines the Hydrogen,  and Oxygen back into H2O  during Absorb,   gets consumed,  for every minute of Absorb,  over the life to the batteries.

In addition to a generally longer cycle-life,  another advantage of FLA batteries is,  that one can actually measure the electrolyte SG with a Hydrometer,  or Refractometer.   This cannot be done with Sealed batteries (AGM Gel, etc).   So  setting Absorb voltage and time can be more challenging with sealed batteries.

EDIT:  Using two strings of batteries is much better than four strings,  IMO.   Your 370 Ah reference puts you in the L-16 ballpark,   as you know.    FLA L-16 are quite common,  and not overly expensive.   If you plan to cycle your batteries daily,  would suggest FLA,  especially as your first foray into a power system.

Given your constraints,  it does appear that a 24 V system would be best,   probably  <

There are a number battery manufacturers which offer batteries in a wide range of Ah Capacities.

Surrette,   Trojan,  US Battery,   etc,  all offer a wide range of battery Capacities.

More later,   Thanks,   Vic
« Last Edit: October 13, 2019, 06:06:28 PM by Vic »
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

labusker

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Re: Disconnecting both Positve & Negative of array
« Reply #13 on: October 14, 2019, 04:17:49 PM »
Wonderful reply! Yes, batteries are L16's.
By the way, I had went to smartgauge.com and I like the section that talked about battery cost. He compared cost vs life cycles. A cheaper battery may have less cycles but its cost per cycle may be a better choice for budgeted minds and or temporary systems.
Choose Preference for kicks:
four 315w panels in series x 2 strings (2520 total), Voc = 160V, Isc = 20A, Classic = 200, voltage = 48V, eight 6V 370Ah batteries in series
two 315w panels in series x 4 strings (2520 total), Voc = 80V, Isc = 40A, Classic = 150, voltage = 24V, four 6V 370Ah batteries in series x 2 strings
Drew