Split negative bus bar in MNPV6-DISCO?

Started by ligwyd, June 19, 2018, 02:04:35 PM

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ligwyd

Hello there,

I am currently building two self contained off-grid solar systems in 20 foot shipping containers. I had originally purchased 4 mnpv6-disco's but have been told I can get buy with just one disco per unit by splitting the negative bus bar in the disco. I am just wondering what the most professional way to do that is? I am sure the answer is very simple once I have accurately provided the pertinent info, however I am currently unsure how to proceed. My supplier is no longer in business so I am left in the dark. Enjoying the challenge but need a little guidance. I have attached an image of the disco/ negative bus bar I am using.

I would think the solution would be to purchase two short bus bars, remove the existing longer existing negative bus bar and replace it with the two short ones?

Thank you for any assistance that may be avail.

John

ClassicCrazy

I guess I am not following you ?
How many strings of PV do you have ?

It is easy to cut the bus bar in half with a hacksaw though you would need to find something to support the loose ends.

But I am wondering why you need two separate negative bars if they are on the same system ?  One combiner for each separate system is what it sounds like you are doing right ?   So I don't get why you need to separate the negative terminals ? 
Need more info on exactly what you are doing there.

Larry
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

Westbranch

#2
Ditto, we need a lot more detail on your installed system and your proposed system to begin to understand  your problem...
We need to know what is  wrong with your current system?  ?
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CL150 29032 FW V.2126-NW2097-GP2133 175A E-Panel WBjr, 3Px4s 140W > 24V 900Ah AGM,
2 Cisco WRT54GL i/c DD-WRT Rtr, NetGr DS104Hub
Cotek ST1500 Inv  want a 24V  ROSIE Inverter
OmniCharge3024  Eu1/2/3000iGens
West Chilcotin 1680+W to come

FNG

If you are using Classics, or Outback controllers or Morning star controllers they all use common negatives so no need to split the negative, just install all the negatives on one buss. If using the Kid or Schneider controllers you need seperate negatives, The short buss bars would work but you would have to drill the holes in the chassis, The Short buss bars come with a template or dimensions for doing that so its not to bad.


ligwyd

Hi all and thank you for your responses. Please forgive my vagueness.  I am  learning as  I go as I am sure you can tell. Muchly appreciate your assistance, more than you know.

I am using 2 Schneider 150's charge controllers in each separate solar system. Each system has 18 - 260 watt Jinko solar panels totaling 4680 watts on each array.

I am pretty sure the Schneider 150's each require their own negative so that is why I am moving towards separating the negative bus in the Disco/Combiner.

I am getting pricing on the short black bus bars from Midnite and will order them soon and should have no issues securely installing them.

There is nothing wrong with my current system, its just that it is 90% complete and my tech support has had some life challenges and now is off line so I am left with this project to complete. With nearly 100 K already invested I want to make sure it is done right of course.

I did mange to have a few last short discussions with my supplier and he figures the positive bus in the disco also has to be split, which is pretty straight forward as per the info pamphlet that came with the mnpv6 Discos. The aim was to use only one disco per unit once that was realized as possible option.

I am unsure of the best way to wire up the panels so I do not yet know how many strings but if I am able to speak with my guy a wee bit more before he is completely unavailable I can get that answer and if not I will be thinking that one out also. I know it is straight forward, however until you know something, you don't know it, so just trudging ahead in the mist.

Thank you once again for you time and patience. I absolutely love working with this stuff. Just really want to get it done and get off grid asap.
Look forward to your response.




ClassicCrazy

Most controller manufacturers have a string calculator on their website where you enter your PV and it will suggest the string options.

Larry
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

ligwyd

#6
I'll be doing 6 strings of 3 panels each totaling 18 panels.

I believe the positive bus bar also has to be spit to accommodate my application. Can anyone confirm this?

The 18 panels will be wired up as two separate systems - 9 panels feeding each of the two charge controllers.

And then, from the split, positive bus bar in the MNPV6-DISCO, there will be two red 6 awg RW90 cables (one from each half of the split bus bar) running into the distribution panel to the DC breaker between PV and charge controller.

Can someone also confirm my below breaker calculations?

Each panel has an Isc (short circuit current) of 8.98 amps and each split half of the positive bus bar in the MNPV6-Disco will receive 3 strings of three panels each.

The three paralleled strings of 3 panels each is 8.98 A  multiplied by 3 = 26.94 amps multiplied by 1.25 (safety factor)= 33.68 amps.

So I presume that I should be using a 40 amp DC breaker in between the PV and the charge controller. Is this correct?

Also, for the PV breakers in the mnpv6-disco I am unsure of what size to buy? Each string has 3 panels each so again 8.98 Isc multiplied by 1.25 (safety factor) = 11.23 amps.
I have 12 amp breakers, - is this OK? Not sure if it matters but I think I will be using 12 awg PV wire.

Thank you to all who find the time and patience to help :)


Vic

#7
Hi ligwyd,

Yes,   you will want to split the Positive busbar in each Combiner,   as well as the negative bus  --  each CC will need a separate PV array,   and isolated negatives as well.

Understand that each 20' container has two CCs and 18 PVs.

RW90 cable has an Ampacity of:
EDIT to correct to  65 A at 75 degrees C.   So,  unless there are more than three current carrying  conductors in conduit this should be OK with #6 RW90 on the PV input side at the CC<

A 40 A DC breaker,  near the CC should be fine  with RW90 cable.

The Combiner PV breakers can be as large as the stated Maximum Fuse size on the label on the back of the PV (or in the spec sheet),   or for MidNite DC  breakers,  1.25 X string Isc,  rounded up to the next larger standard breaker size.   Most folks usually just install breakers equal to the stated Max Fuse size.
You do NOT want to use a 10 A PV breaker in the Combiners ...   a bit too small.

Just my take,   Good luck,   Vic
Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!

ligwyd

Thanks Vic.

I looked at the back of my panels and it states "Max Series Over Current Protective Device Rating 15A".

I checked and updated my last post. I do have 12 amp PV breakers from Midnite so that is what I will use.

Is there any reason at all that you can see why someone would choose an 80 amp breaker instead of a 40 amp breaker in between PV and Charge Controller?

My supplier must have made a mistake and thought the positive bus in the disco would receive all 6 strings - 8.98 Isc of PV strings X 6 = 53.88 X 1.25 = 67.35 amps. Probably just a simple mistake.

Have a good night and thanks again. Appreciate the help with my brain busters :)


Vic

Quote from: ligwyd on July 01, 2018, 09:54:23 PM

   ...   Is there any reason at all that you can see why someone would choose an 80 amp breaker instead of a 40 amp breaker in between PV and Charge Controller?

My supplier must have made a mistake and thought the positive bus in the disco would receive all 6 strings - 8.98 Isc of PV strings X 6 = 53.88 X 1.25 = 67.35 amps. Probably just a simple mistake   ...

Hi ligwyd,

Your guess is probably correct,  about the reason for  the size of the input breaker.

As you know,   besides being a very good disconnect,   the primary job for these breakers,   is to protect the cable connected to the breaker from excessive heating,   and that risk of starting a fire.

HOWEVER,   according  to Southwire,  the  75 C Ampacity of RW90,   is only 65 A.   Some of the previous post,   was based on my incorrect recollection that the 75C Amapcity was 75 A.

Need to attend to several things this AM.   I will need to review and probably correct some of the detail in the previous post.

Others can also  correct my errors.

More later,   Vic
Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!

ligwyd

Agreed with you Vic. Looks like I have to order 40 amp breakers....
My Charge controller can only accept 6 awg at the largest size, that is without adding a larger block to the PV+ input, however I should be fine with the 6 awg since I am only bring in Isc 33.68 amps MAX (already including 1.25 safety factor) into each Charge Controller from each half of the split positive bus bar in the Disco/ Combiner from 9 panels.
Appreciate the help as always. So far this has been the best forum I have been on.
Have a great day.  :)
John

Vic

#11
Quote from: ligwyd on July 01, 2018, 09:54:23 PM

   ...   Is there any reason at all that you can see why someone would choose an 80 amp breaker instead of a 40 amp breaker in between PV and Charge Controller?

My supplier must have made a mistake and thought the positive bus in the disco would receive all 6 strings - 8.98 Isc of PV strings X 6 = 53.88 X 1.25 = 67.35 amps. Probably just a simple mistake   ...

John,   thinking a bit more about this,   would guess that you may be using Schneider Switchgear (conduit boxes).   If so,   believe that these boxes still use the larger E-Frame DC breakers,   which have been commonly available only in 60A and 80A sizes  (at least from the suppliers used here).    This could possibly be one reason for an 80 A breaker.

The latest manual (rev. G 5/15)  for the Conext MPPT 150 - 60 (or whatever they are calling this MPPT CC,  at this exact moment)  states,

"...   Battery Circuit
The NEC requires the battery circuit to be protected with a device rated for 125%
of the rating of the circuit. The DC-rated fuse or circuit breaker between the
battery and the solar charge controller must be rated for 1.25 × 60 A (the
maximum current rating of the solar charge controller)   ...".
[The above copyright 2013 - 15 Schneider Electric]

This would be a 75 A breaker,   and as stated,   not Maximum,   but  mandatory.   That is NOT what we have been doing around here,   but,  I am not a Code expert.    A 75A breaker  would usually dictate larger cable than the Maximum accommodated by the SCC.   Many/most DC circuit breakers,   that are in common use,  spec using 75C ratings for cables connecting to those breaker terminals.   Ampacity for the largest cable that connects to the SCC  --   #6 AWG  -- is 65A,   and to me would dictate a 60 A breaker maximum.

Would bet that FNG,  or other Code expert,    will have an astute judgment on these fine details.

FWIW.   Sounds like you are building a set of very nice systems. Each of the two Power Rooms here,   use  Cargo Containers.   One is a 20-footer,   and the other is a 20-foot container cut down to 10 feet,   and married onto the end of another 20-footer.   Solar is on that roof  --  that container string is 70 feet long.

Have fun,   Vic
Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!

ligwyd

#12
Noted!!

I'll try to order 40 amp breakers for PV to Charge Controller protection and if they don't exist I'll have to work with what I have.

Yes, I have an XW+ 6848 with PDP, in each system, and the DC breakers are rather big. Probably old design like the Charge Controllers?

Schneider Engineers said a 80amp breaker would be fine between Charge controller and batteries and in some cases (sunny day with cooling wind with an over sized array which I don't have -I only have 2340 watts into each CC) a 60 amp could nuisance trip, thus 75-80 amp would be the way to go. Decisions.. I like the idea of going easy on all the equip and not pushing it so as to get longevity and efficiency out of the system.

Just reading page 2-15 of the XW+ 6048 manual....like you said....1.25 x 60A (max current rating of CC) for PV circuit protection but...... due to my small array 2340 watts of PV going into each CC I might stick with the 60 amp breaker there and then the inspector will like the 6 awg wire I am using. Just gotta try to find some 40 amp breakers if they are out there, if not scratch the head some more......

Thank for the great info. Vic.
I like working better than typing but its all part of it.. eh! Canada :)
John


ligwyd

#13
Hi Vic

Just found that those back mounted DC breakers that go in the DC side of the Schneider PDP might be Magnet-Hydraulic breakers as per:

http://www.magnum-dimensions.com/sites/default/files/MagArchive/64-0041-Rev-B-DC-Load-Breakers-BM.pdf

The document states that these types of breakers although they operate affectively regardless of temp, which is a really cool thing when it comes to safety, they need to be de-rated by .8 (80%) for a continuous rating.

So, the 80 amp breaker I have would be 80 X .8 = 64 amps continuous which is pretty close to what my 60 amp Charge controller needs in between the batteries and charge controller.

And the 60 amp breaker I have would be 60 X .8 = 48 amps continuous which is pretty close to the 40 amp breaker I would need between my PV and charge controller.

I also noticed that the trip amps rating on the 80 amp breaker is 100 amps. Maybe the 80 amp breaker is actually a 100 amp breaker already labeled with the .8 de-rate made for Schneider? Who knows.

I am going to call Carling Tech (company who makes the breakers I have now) distributor and Schneider in the morning to confirm this and update this post.

Maybe my supplier did not make a mistake after all? Makes a guy wonder, if all breakers subject to temp fluctuation shoudn't be magnetic hydraulic eh?
Have a good night Vic.
John

ClassicCrazy

Won't the Midnite breakers fit ? They are Carling breakers .

Larry
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable