Author Topic: Looking for help Configuring a 48V System in Haiti  (Read 1001 times)

SunnyIAV

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Looking for help Configuring a 48V System in Haiti
« on: March 27, 2019, 04:18:26 PM »
Greetings,

Thank you all for contributing and making this forum a valuable resource in the renewable energy world.

I am upgrading an off-grid system (48V) in Haiti, and I would sincerely appreciate some help with a few technical questions I haven’t been able to find definite answers for.

Here is a quick system summary:

    •   Array: (6) 315 Watt PV = 1890 Watts – Two strings of 3 (3S2P)

          o VMP 37V – VOC 45.6V – ISC 8.93A – IMP 8.52A – Maximum Series Rated Fuse 15A

          o I have attached the Classic sizing tool result for my panel configuration.

   •  DC Disconnect /Load Enclosure: MIDNITE SOLAR MNDC250 MINI 250 AMP DC DISCONNECT

   •  Surge Protector : MNSPD-115 & MNSPD-300

   •  Charge Controller: Midnite Solar Classic 150

   •  Battery : (4) Trojan SPRE 12 225 – 48 V Charging Parameters @ 77°F/25°C – Absorption 58.0V – Float 54.0V – EQ 64.8V

   •  Inverter: COTEK SD2500-148 2500 Watt 48 Volt Pure Sine Wave Hardwire Inverter

   •  PV wire 8 awg = Distance from Array to DC enclosure 33 ft
 
Questions:

Combiner: Midnite Solar MNPV3

  •  My understanding is that 2 parallel strings may not need fusing, so where would the positive cables from the array get connected inside the Combiner box? Would it hurt to connect those strings to (2) MNEDC15 MNPV15 breakers?

DC Disconnect Enclosure

  •  I have the MNDC250 Mini-DC enclosure. Is the MNEDC250 inverter breaker suitable for the 2500 W 48V inverter, or should a lower amperage breaker be used such as MNEDC175 or MNEDC125?

  •  I have noticed the MNEDC125 breaker only comes as the RT model.

  •  Most importantly, how does one determine which inverter breaker to use?

Classic Controller Cabling and Fusing

  •  4 Awg THHN cables, rated for 90°C for will be used to wire the Classic 150. What size breakers should be used for PV input and PV output? I know this question keeps coming up in the forum, but yet I am still confused. I understand the primary goal of the
     breaker is to protect the wire (THHN rated for ) therefore can a 100A Midnite breaker be used for both?
 
  •  Can I use panel breakers instead of din rail breakers – removing the din rail may give a bit more room inside the enclosure, not to mention the panel breakers are cheaper.

  •  What are other differences between the two types (din rail and panel) besides the way they are mounted, and the way the cables get connected to them?

  •  Are there more parameters that need to be taken into consideration besides the wire ampacity when choosing fuses/breakers?

Thank you for your help.

Harry


« Last Edit: March 27, 2019, 06:09:54 PM by SunnyIAV »
48V Off-grid System

1890W panel array(6 x 315) in 3S2P configuration, MNPV3 Combiner, MNDC Enclosure, Whiz Bang JR, Classic 150 CC, 2.5K 48V Cotek Inverter, 4 x 12v 204 AH FLA Trojan (SPRE 12 225)...

tecnodave

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #1 on: March 27, 2019, 05:09:13 PM »
SunnyIAV,

Welcome to the forum,

Answers in order of asking:

Combiner....2 strings do not nessecarily need fusing because if one string shorts the other string will not have enough power to force power backwards through the failed string but when you have 3 or more the shorted string can be burned out and possibly set ablaze by the two good strings. If you have the MNPV-3 I would advise you to use it. It will be helpful for analysis of system failure by allowing you to test one string at a time.

The MNEDC breaker does not fit into the MNPV combiner, the correct breaker is the MNPV-15 wire the positive p.v. panel output to the + terminal of the PV breaker. These breakers are polarity sensitive.

DC disconnect......the 250 amp breaker is too big for that 2500 watt 48 volt inverter. The SD-2500-148 power draw is about 90 amps max so the MNDC-125 is the correct size there....don't worry about the remote trip, just don't use it......that is for birdhouse automatic shutdown.....usually not needed unless you get a picky inspector.  You will need an adapter to fit that breaker in that box....it's a smaller frame size than the MNDC 175 &250 breakers...see it on MidNite page.....
Breaker size for continuous duty breakers is 1.25 times the maximum draw of the device to be protected. The Cotek SD-2500-148 uses 6 times 15 amp fuses internally so max amps is under 90 amps...breaker size = 90 X 1.25 = 112.5 amps...sized up to next standard size = 125 amps

Classic breakers...the classic @ 48 volt battery can output a max of about 86 amps so a 100 amp MNDC -100 breaker for the battery side,  smaller for the p.v. Input

Please let me correct you on this....standard pricing the MNPV din rail breakers are less expensive than the MNDC breaker  about 11.85 for MNPV and 14.80 for MNDC from NAWS.....prices not exact but close.......also the MNDC breaker is larger than the MNPV breaker.......differences...MNDC breakers are 100% duty cycle...MNPV breakers are not and must be up sized by 1.25 when used as continuous duty....(National Electric Code Definition of continuous duty...The device will be operated continuously more than 2.0 hours).  This does apply to solar at least we hope for more than 2 hours of full sun.

I think that covers your questions.......stay tuned.....have fun with it and post any more questions here

David
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 4/6 Sanyo 200 watt multilayer 4/6 P
#4 Kid/WBjr 4/6 Sanyo 200 watt multilayer 2S 2/3 P

SunnyIAV

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #2 on: March 27, 2019, 08:15:28 PM »

Thank you Tecnodave  for the welcoming mat and your quick response. That was were very helpful. As usual, answers bring more questions  :)

Combiner....I meant to type the din rail breaker  MNPV15 for the combiner not the MNEDC15 panel breaker. I have edited the original post. The main reason I mentioned using breakers for just 2 parallel strings, even if they are redundant is because I don't see a way to combine the two positive PV cables  inside the MNPV3 unless I add an additional bus bar.

DC Disconnect...

I did notice the Cotek manual recommends an inline 90A fuse and 4 AWG  battery-inverter cable. I did reach out to them to find out if I could use a bigger cable such as 2/0. Here is a quote of their answer:

" Using those size cables will not affect the operation, the larger cables will have less of a voltage drop which is a plus."

If I am using 2/0 inverter cable, can I still use the 125 Amp inverter breaker on the MNDC enclosure? I wouldn't mine adding an inline fuse near the battery as well. I guess that fuse will have too be sized according to the inverter cable size. I am not sure why I think I need inverter cables that are bigger than 4 AWG.

I have yet to find an adapter that will allow the MNEDC125 breaker to fit in the inverter breaker cutout of the MNDC enclosure box - The opening is 1.5' wide, a perfect fit for the MNEDC175 and 250, but not for the MNEDC125 which is 1" wide. The only adapter I could find is the MNBREAKER which allows a a 3/4" breaker to fit in 1" opening. Midnite sell the MNDC enclosure with the MNEDC 125, 175 and 250; I wonder how they fit the 125 breaker in that enclosure

You are right regarding the breakers price difference. In general the panel breakers tend to be a bit more expensive than their din rail counterparts except for the 80 and 100 Amps breakers; the din rail units are 150% more that the panel breakers.

Classic breakers ... I am still hung on the idea that breakers are primarily there to protect the wire. Using 4 AWG  cable to wire the Classic was my reasoning to put a 100 Amp on the battery side of the Classic.
I did notice you agree with the same size breaker, but for a different reason, and I quote " The classic @ 48 volt battery can output a max of about 86 amps so a 100 amp MNDC -100 breaker for the battery side" You also mentioned I could use a smaller breaker for the PV output, what size would that be based on my system configuration? Do I still need to worry about wire ampacity?

Please bear with me, if I am asking a lot of questions, fusing a system properly has been my weaknesses for years, and I would be grateful if I could have a better understanding on the correct way to protect a system. I certainly don't want my system to keep tripping unnecessarily nor to be without proper protection because the fuses/breakers are too big.

So many of us think we can just Google it  ;), it's not that easy, thus the respect and admiration I have for all the folks who post their questions and those who try their best to help.

Warm regards,

Harry
48V Off-grid System

1890W panel array(6 x 315) in 3S2P configuration, MNPV3 Combiner, MNDC Enclosure, Whiz Bang JR, Classic 150 CC, 2.5K 48V Cotek Inverter, 4 x 12v 204 AH FLA Trojan (SPRE 12 225)...

ClassicCrazy

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #3 on: March 27, 2019, 09:02:23 PM »
Regarding the MNPV3 combiner box - each  positive PV string goes to the bottom of the breaker . The top of the breaker is a buss bar that connects all the breakers together and the main wire going back to the controller connects to that buss bar .  The negatives from PV and from the controller get connected together on the common buss bar on bottom left .
See photo
http://www.midnitesolar.com/productPhoto.php?product_ID=78&productCatName=&productCat_ID=9&sortOrder=4&act=p

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

ClassicCrazy

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #4 on: March 27, 2019, 09:11:39 PM »
Regarding sizing the wire and breakers
You first determine the available amps. Then you determine what size wire you need to use for the voltage and  amount of amps at the distance of wire you need. So you need to size for voltage drop and want to have it low enough .  There are voltage drop calculators online to help with that or charts.   If it isn't a far run what a lot of people might do is just size the PV input wire for the maximum the controller can handle and then fuse that size wire - which I think usually works to be 6 gauge for the Classic at 60 amps . That gives you option to add more PV in the future without having to redo the wiring too. 

So yes - you fuse the size wire you are using . You can use larger wire for less voltage drop if needed and use a smaller breaker if you already had it . But you can't go the other way and use a larger breaker for smaller wire past it's rated amp capacity .
Hope that helps .

Larry
« Last Edit: March 27, 2019, 09:20:45 PM by ClassicCrazy »
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

SunnyIAV

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #5 on: March 27, 2019, 09:21:30 PM »
Regarding the MNPV3 combiner box - each  positive PV string goes to the bottom of the breaker . The top of the breaker is a buss bar that connects all the breakers together and the main wire going back to the controller connects to that buss bar .  The negatives from PV and from the controller get connected together on the common buss bar on bottom left .
See photo
http://www.midnitesolar.com/productPhoto.php?product_ID=78&productCatName=&productCat_ID=9&sortOrder=4&act=p

Larry

Thank you Larry - My main confusion has to do with the fact my array configuration has 2 parallel strings of 3. I understand why breakers are not generally needed for such configuration, however if the MNPV3 is used, I guess breakers will be needed because I don't see where the positive PV stings will go without them.

Harry 
48V Off-grid System

1890W panel array(6 x 315) in 3S2P configuration, MNPV3 Combiner, MNDC Enclosure, Whiz Bang JR, Classic 150 CC, 2.5K 48V Cotek Inverter, 4 x 12v 204 AH FLA Trojan (SPRE 12 225)...

ClassicCrazy

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #6 on: March 27, 2019, 09:36:06 PM »
It is a lot easier to use a combiner box even if you don't need it.  Like Dave said - by using the combiner box it makes it easy to just flip the breakers off for the PV at the combiner location - helps with any service or trouble shooting you may need to do .

Otherwise if you didn't have a combiner box and Dave said you didn't need one for two strings - you would just get two separate buss bars to connect the two PV stings together with the wire going to the controller . I have done something like that using copper compression nuts and taped them up for insulation but not the best practice .  lf you have stuff around to do the job and a box to put the buss bars in then it is less expensive than getting a combiner box . 

Oh I think you mean that you have the pv3 combiner box and wondering how to connect the positive wires and still use the box.  You could just get a piece of buss bar and use that for positive and insulate it or make sure it doesn't touch the negative.  Or one of those giant wire nuts that could fit all those wires but that is frowned on for low voltage DC I think because of potential oxidation of wires and possible poor connections in future maybe.

Larry
« Last Edit: March 27, 2019, 09:41:17 PM by ClassicCrazy »
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

tecnodave

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #7 on: March 27, 2019, 10:02:37 PM »
Harry,

Mind fog has arrived!

I led you wrong!   The MNBREAKERADAPTER  is to use MNDC breaker in a competors box which originally used 1" wide breakers.....fog clearing a bit...its for the Outback panels (maybe)or maybe it for Mstar panels, I forget , but do remember going there, been a while

I'm using a different DC box than you are. I have the MNDC15 a box for 15 MNDC breakers and one 125-250 amp breaker. The box has a knockout at the position of the large breaker. The opening will fit the MNDC125. Breakout the knockout out  and fit the MNDC 175 or 250 into the larger opening.

I have not seen any of the other MN panels in an uninstalled condition but I assume that has the same knockout. 

                        Breaker location and knockouts
                               ___________________________
                               |__________________________|       < breakout tab for 175-250                           
                               |                                               | 
                        O     |                                               |   O   < opening for 125
                               |__________________________|       
                               |__________________________|         < breakout tab for 175-250

Hey no drawing editor.....just keyboard characters...that's creative!  Did not know I could that.
Anyway that is the idea.   Hope you followed that, not sure that I did...lol

David

Edit.    Posting inserted an extra line but get the idea.....maybe that is only on the MNDC15 panel, not sure

Edit II.      I am wrong on the MNDC15....... I have a aluminum adapter under the breaker protector to mount the MNDC125 breaker into the opening for the MNDC175/250.....I have seen that breakout tab situation somewhere.....I do too much electrical work to remember every panel and system I work on. Double checking MidNite drawings of the MNDC15 box, it does not show any such breakout tabs. I do machining and welding so if something does not fit, I make it fit. I'm not too concerned with the code on my own installations for my own use. Paying customers get full code compliance. I do utility electric for a living.....keep solar as a hobby.
« Last Edit: April 04, 2019, 10:31:23 PM by tecnodave »
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 4/6 Sanyo 200 watt multilayer 4/6 P
#4 Kid/WBjr 4/6 Sanyo 200 watt multilayer 2S 2/3 P

tecnodave

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #8 on: March 27, 2019, 10:26:30 PM »
Harry,

On the wire sizing..... Inverter feed cables.....the NEC rates 4 ga. Wire at 100 amps, that is the minimum size for that wire BUT that is not for continuous duty!  Normally for an inverter you do not want excessive voltage drop so we up size a bit.  I'm using 2 gauge on my Cotek SK-1500 and I will upgrade that a bit one day.    2/0 is a bit overkill. won't hurt a thing.  MagnaSine recommends 2X 2/0 for my MS4024AE Inverter.....4000 watt 24 volt with a 250 amp breaker at 5 feet maximum length wire......way more conservative than Cotek's recommendation. I'm using 2/0

David
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 4/6 Sanyo 200 watt multilayer 4/6 P
#4 Kid/WBjr 4/6 Sanyo 200 watt multilayer 2S 2/3 P

ClassicCrazy

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #9 on: March 28, 2019, 12:44:38 AM »
Harry,

On the wire sizing..... Inverter feed cables.....the NEC rates 4 ga. Wire at 100 amps, that is the minimum size for that wire BUT that is not for continuous duty!  Normally for an inverter you do not want excessive voltage drop so we up size a bit.  I'm using 2 gauge on my Cotek SK-1500 and I will upgrade that a bit one day.    2/0 is a bit overkill. won't hurt a thing.  MagnaSine recommends 2X 2/0 for my MS4024AE Inverter.....4000 watt 24 volt with a 250 amp breaker at 5 feet maximum length wire......way more conservative than Cotek's recommendation. I'm using 2/0

David
Interesting - Outback recommended 4/0 wire for my 24v 3500 watt inverter . Maybe it has a higher surge capacity they are rating it for.

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

tecnodave

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #10 on: March 28, 2019, 02:09:19 AM »
Larry,

MagnaSine and outback recommendations. are in close agreement


MagnaSine recommends 2 runs 2/0     266200 total circular mils. For 4000 watt.       .015 w/c.mil
Outback recommends.    1 run 4/0.      211600. "        "         "      For 3500 watt.     .016 w/c.mil

Cotek.                            1 run. 4         41,470.                           For 2000 watt.      .048w/c.mil

So by that calculation watts per circular mil  Cotek is running three times the watts of OB or MS per circular mil.

All the inverters are 24 volts

So by MS and OB standard that would be  133,100.  AWG  2/0.    for the Cotek

Yes, I think that the Cotek is on the light side recommending 4 ga at 90 amps

So @ Harry........2/0 is about right by American high quality inverter standards

david
« Last Edit: March 28, 2019, 02:38:33 AM by tecnodave »
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 4/6 Sanyo 200 watt multilayer 4/6 P
#4 Kid/WBjr 4/6 Sanyo 200 watt multilayer 2S 2/3 P

SunnyIAV

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #11 on: March 28, 2019, 12:59:51 PM »
It is a lot easier to use a combiner box even if you don't need it.  Like Dave said - by using the combiner box it makes it easy to just flip the breakers off for the PV at the combiner location - helps with any service or trouble shooting you may need to do .

Otherwise if you didn't have a combiner box and Dave said you didn't need one for two strings - you would just get two separate buss bars to connect the two PV stings together with the wire going to the controller . I have done something like that using copper compression nuts and taped them up for insulation but not the best practice .  lf you have stuff around to do the job and a box to put the buss bars in then it is less expensive than getting a combiner box . 

Oh I think you mean that you have the pv3 combiner box and wondering how to connect the positive wires and still use the box.  You could just get a piece of buss bar and use that for positive and insulate it or make sure it doesn't touch the negative.  Or one of those giant wire nuts that could fit all those wires but that is frowned on for low voltage DC I think because of potential oxidation of wires and possible poor connections in future maybe.

Larry

Thank you for all the info - I guess I will just use two MNEPV15, the rated breaker for my panels, and connect each string to a breaker. Even though the breakers will be redundant, but I won't have to think outside the box and will have a clean install + the ability to shut down 1 string easily for troubleshooting as you and Dave suggested . I will also add an MNSPD115 surge protector to the mix.

Harry
48V Off-grid System

1890W panel array(6 x 315) in 3S2P configuration, MNPV3 Combiner, MNDC Enclosure, Whiz Bang JR, Classic 150 CC, 2.5K 48V Cotek Inverter, 4 x 12v 204 AH FLA Trojan (SPRE 12 225)...

SunnyIAV

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #12 on: March 28, 2019, 01:34:38 PM »
Larry,

MagnaSine and outback recommendations. are in close agreement


MagnaSine recommends 2 runs 2/0     266200 total circular mils. For 4000 watt.       .015 w/c.mil
Outback recommends.    1 run 4/0.      211600. "        "         "      For 3500 watt.     .016 w/c.mil

Cotek.                            1 run. 4         41,470.                           For 2000 watt.      .048w/c.mil

So by that calculation watts per circular mil  Cotek is running three times the watts of OB or MS per circular mil.

All the inverters are 24 volts

So by MS and OB standard that would be  133,100.  AWG  2/0.    for the Cotek

Yes, I think that the Cotek is on the light side recommending 4 ga at 90 amps

So @ Harry........2/0 is about right by American high quality inverter standards

david

Thank you Dave ... So if 2/0 is Ok to use from battery to inverter breaker located inside the MNDC enclosure do I still need to switch the MNEDC250 to MNEDC125?

Moreover, if I use 2/0 and add an extra 250 Amp inline fuse  near the battery, which one would be recommended? I have been looking at class T fuses and MRBF that mounts neatly on the battery post, but it seems the MRBF fuses I have seen so far are not suited for 48V battery banks.

Harry
48V Off-grid System

1890W panel array(6 x 315) in 3S2P configuration, MNPV3 Combiner, MNDC Enclosure, Whiz Bang JR, Classic 150 CC, 2.5K 48V Cotek Inverter, 4 x 12v 204 AH FLA Trojan (SPRE 12 225)...

Doug

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #13 on: March 28, 2019, 01:50:47 PM »
Hi Sunny,

The breaker is sized to protect the wiring. A 250 amp breaker is too large for 2/0.
You should check an online ampacity chart for your wire and choose a breaker that does not exceed that rating.

Doug

SunnyIAV

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Re: Looking for help Configuring a 48V System in Haiti
« Reply #14 on: March 28, 2019, 04:04:33 PM »
Hi Sunny,

The breaker is sized to protect the wiring. A 250 amp breaker is too large for 2/0.
You should check an online ampacity chart for your wire and choose a breaker that does not exceed that rating.

Doug

Hi Doug - Thanks for the reply. I have looked at many charts, and it seems ampacity of   THW wire copper conductor 167 deg F is  175  and THW-2 is 195. Do those numbers needs to be multiplied by 125% for continuous duty? I am aware that Midnite breakers can be used at 100% rated current when mounted in a MidNite enclosure.

Cobra X-Flex wire recommended by Midnite has even higher ampacity for  2/0 Wire - 336 Amps - Wonder if I understood that wrong

Link http://www.cobrawire.com/x-flex/x-flex.php

Thank you all, I am learning 1 post at a time.

48V Off-grid System

1890W panel array(6 x 315) in 3S2P configuration, MNPV3 Combiner, MNDC Enclosure, Whiz Bang JR, Classic 150 CC, 2.5K 48V Cotek Inverter, 4 x 12v 204 AH FLA Trojan (SPRE 12 225)...