Protecting your system and cables

South Africa
South Africa Solar Expert Posts: 295 ✭✭✭
in Solar Beginners Corner #1
Hi,

Before I buy again and sit with spare parts I cannot use, I have a few questions:

To disconnect the panels from the charge controller, will the Gewiss MTC60 B be sufficient for up to 1650w array? http://www.simcas.nl/wp-content/blogs.dir/198/files/2014/01/gw90328-series.pdf

To disconnect batteries, I read that it is better to have a switch to switch off the connection to the batteries AFTER the panels have been disconnected. I presume that means switches like these: http://www.solar-electric.com/blseabaswon3.html

Battery cables. Will 35mm 105A POWER CABLE, I think it is AWG 2 (33.6mm2) battery cables be sufficient to use between charge controller and batteries and between the batteries for a 24v system, using 102/105ah batteries?

I read a lot about the panels that has to be fused. What fuses would one need?
And for the batteries?

If panels are roof mounted on a metal roof, would one need to earth them, seeing the entire roof is metal?

I see one has to earth the inverter. I am told that I can use using the same earth as that which is commonly used in the house, inside the distribution board. Is this correct?
And can one also use the same earth for the Outback / Tristar controllers?
And for the roof mounted solar panels?
All connected to a 70A DIN MOUNT TERMINAL STRIP that is connected to the earth inside the distribution board?

What have I forgotten?
5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • BB.
    BB. Super Moderators, Administrators Posts: 33,590 admin
    #2
    Re: Protecting your system and cables
    South Africa wrote: »
    Hi,

    Before I buy again and sit with spare parts I cannot use, I have a few questions:

    To disconnect the panels from the charge controller, will the Gewiss MTC60 B be sufficient for up to 1650w array? http://www.simcas.nl/wp-content/blogs.dir/198/files/2014/01/gw90328-series.pdf

    It looks like the breakers may work... You have to look at the voltage rating of your array (Voc-cold)--As long as it is less than the DC ratring of the breakers you should be OK.
    To disconnect batteries, I read that it is better to have a switch to switch off the connection to the batteries AFTER the panels have been disconnected. I presume that means switches like these: http://www.solar-electric.com/blseabaswon3.html

    A battery switch is nice to disconnect the batteries (servicing, going away for a couple months, and you want to turn off all power, etc.).

    However, it is also a good idea to have a circuit breaker or fuse to protect your various DC branch circuits (AC inverter, charge controller, etc.)--Each should have its own protection device. Breakers are expensive, but they also make great on/off switches--And the fuses are not "cheap" if you have to have some spares on the shelf (high current DC fuses are not inexpensive).
    Battery cables. Will 35mm 105A POWER CABLE, I think it is AWG 2 (33.6mm2) battery cables be sufficient to use between charge controller and batteries and between the batteries for a 24v system, using 102/105ah batteries?

    Sort of working this backwards. Define the loads which define the battery bank. Then size the array to support the battery bank + loads.

    At this point, you will know the current requirements, can calculate wire size, and protective fuses/breakers per branch circuit.
    I read a lot about the panels that has to be fused. What fuses would one need?
    And for the batteries?

    Modern solar panels usually have a series protection fuse in the specifications (i.e., an 8 amp Imp panel usually has around a 15 amp fuse). The fuse/breakers should never blow in normal operation. You only "need" a fuse/breaker per solar panel string if you have 3 or more parallel solar panel strings in parallel. You do not need fuse/breaker for 1-2 parallel panel strings.

    Batteries--you need to define the maximum loads/charging current. In the US, for example, if you had a 1,200 Watt inverter running on a 24 volt battery bank, the branch circuit and fuse/breaker would be:

    1,200 Watts * 1/0.85 inverter eff * 1/21.0 volts minimum inverter voltage * 1.25 wiring+breaker derating = 84 Amp minimum branch/fuse wiring rating

    Normally you would round up to next standard size (90 or 100 amps).
    If panels are roof mounted on a metal roof, would one need to earth them, seeing the entire roof is metal?

    Metal roofs are not actually considered to be good electrical conductors--Not for electrical short circuits or for lightning strike fault currents.

    North American code requires that all electrical devices (solar panel frames, metal breaker boxes, etc.) all be connected with a "green wire" (or bare copper wire) and that wire end at a ground rod (and cold water pipe, etc.).
    I see one has to earth the inverter. I am told that I can use using the same earth as that which is commonly used in the house, inside the distribution board. Is this correct?

    Slow down here--Ground bonding and neutral bonding is a complex subject... And it depends on the Inverter type (MSW vs TSW) and specific brand/models (some come pre-ground bonded neutral, others do not, MSW inverter generally cannot have a ground bonded neutral).
    And can one also use the same earth for the Outback / Tristar controllers?
    And for the roof mounted solar panels?

    More complex than that--And sometimes the grounding has to be modified for the equipment type, location, how far from array to battery bank, etc...
    All connected to a 70A DIN MOUNT TERMINAL STRIP that is connected to the earth inside the distribution board?

    Don't know--Need to start with your loads.

    My suggestion... Tell us what you need (amp*hours, Watt*hours, per day, peak wattage, etc.). Any specific starting requirements (off grid cabin, emergency backup power, leaving grid, have grid on property). And if you have some hardware (already have a battery bank, AC inverter, genset wattage/voltage, etc.). Where (major city) the system will be installed (amount of sunlight).

    It is a journey... Start with the paper design of the "generic" system that will meet your needs. Then start picking hardware to support those needs. Finally, design the interconnects based on those needs/hardware selected, battery bank configuration, etc.

    Your questions, at least in this thread, sort of just jump into the deep end of the pool.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #3
    Re: Protecting your system and cables

    Thank you BB.

    Yes, I have a working system in place for the last 2 years, therefor the jump into the deep end. :-)

    Ok, I hear you. I will get back to grounding the components. Lets start here:

    NOTE: As Cariboocoot and I summed up so nicely:
    PV direct GT system (only with an OG inverter) using as much power as possible during daylight hours in order to maximize the efficiency.

    Utilities grid is my backup, not primary source. Primary source is inverter (max 1300w) using all the incoming solar power on the spot. Storing spare power is a low low LOW 3rd consideration which is used for lights at night only.

    Thanks to Cariboocoot, I am now going to add as many batteries as the system can handle, have 4 x 102ah and 2 x 105ah batteries that are going to be my first sacrificial lambs, connected to make a 24v system.


    So based on the above, after having bought a lot of parts learning the hard way, realising the more you learn the less you know, I have concluded the following:
    1) Decide on the equipment based on my budget, that can be re-used.
    2) Match the load you want to power to the equipment values.
    3) Panels, buy them based on the best fit for the controller.


    System volts and inverter:
    inverter is a brand new 24v, 1600w Victron Phoenix inverter, therefor the system voltage is 24v.
    Max load the inverter will have to power is +-1300w, so that I never max it.

    Controllers:
    I hope to install what I need now, on the exiting system, and then when I move over to the FLEXMax 80A controller from Outback, the same parts can be used.
    To this effect I currently have a Tristar 45 controller with 3 x 310w Tenesol panels = 930w panels connected to it. Panels specs attached.

    Panels:
    The Tristar45 is maxed on the current panels 3 x Tenesol 310w panels.
    The FLEXMax:
    - will be maxed on 2500w for a 24v system.
    - incoming volts are a absolutely max of 150v.
    For the FLEXMax 80A, panels to be ideally configured for 48v, charging 24v batteries, to reduce the wire size required from panels.
    My plan is to get a maximum of +-1650w / max 6 panels, with the highest possible incoming voltage.

    Batteries:
    Thanks to Cariboocoot, and because I can get 102ah Royal batteries for a steal, will go for the max the system can charge comfortably.
    Cables, because the distances are short between the controller and batteries and between the batteries on shelves, I thought to go as big as is ok.
    Currently there is a 150a fuse on the batteries, which the + of the inverter connects to.
    On the negative side there is a shunt for the Victron battery monitor.

    So, my thinking is:
    If I can, using the FLEXMax 80A controllers max specs, put the breakers, battery cables etc. in place with the Tristar so that when I swap over, it is plug on play.


    So working from the FM80 equipment values, the values are:
    Max incoming voltage of panels can never ever exceed 150v.
    Max wattage of panels, due to inverters 24v, can never ever exceed 2500w. More like +-1650w.
    Peak wattage of inverter will be +-1300w @ 220v-230v @ 50hz.

    to sum up:
    - 1 x 2 pole Gewiss MT60 between panels and controller. It is rated at max of 220v DC @ 63amps
    - 1 x 2 pole Gewiss MT60 between controller and batteries.
    - There is a fuse between batteries and inverter. Currently I disconnect one cable to disable the batteries.
    - Power from the inverter to the equipment goes to a dedicated 220v DB board.
    - Max batteries would be, based on the array of 1650 Watts, would be 530 Amp hours of battery on four parallel strings of 102 Amp hours.
    - Panels:
    -- I intend getting the biggest wattage panels that the controller can handle comfortably to limit the amount of panels.
    -- Idea is to not have more than 6 panels on the roof. See attached graph from Outback.


    For right now:
    a) Will the Gewiss MT60 B or C do the jobs I want to use them for?
    b) Are the 35mm 105A POWER CABLE acceptable for the above system, or must I rather go 50mm. See attached options I have for cable. it is not too expensive.
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Protecting your system and cables

    Array switching is the tricky part because a 1650 Watt array can be arranged different ways depending on what panels are used and how they are laid out. For exampl on a 24 Volt system the nominal array Voltage is usually no more than 48 Volts, which means a Vmp around 70 and a Voc around 86. The Voc is important here because ultimately that is the Voltage which must be interrupted. In that design one of those breakers you list would work.

    In fact it should in most any case because the DC rating is 220 Volts (except for one @ 110) and most charge controllers couldn't take that high of an input.

    The Blue Sea battery switches are great, and can be used for either controller output or inverter input. Usually controller output will be on a breaker as it needs over-current protection as well.

    Power cable: your proposed 80 Amp controller will not exceed 100 Amps nor will your present inverter so the 35mm/2 AWG should suffice.

    Array fusing depends on the configuration. More than two strings in parallel should have a fuse/breaker on each and every string. This is why combiner boxes were invented. It makes it so much easier! The rating is according to panel specs or Isc * 1.25 if no series fuse rating is given.

    If I ever write a book about this stuff I'm going to call one chapter "Grounding, Or How To Start An Argument". :D Yes, the panel frames should be grounded. No, the metal roof doesn't count as a conductor even if it too is grounded. The negative of the DC side and the neutral of the AC side are tied to one Earth grounding rod. Except if you are following the recent NEC DC ground fault regs where the DC negative is not grounded except through the DC GFCI circuit.

    Basically anything in a metal case is going to have a ground wire connection to that case. The DC negative is usually grounded from the battery post/bus bar. The AC output will have one (only) neutral-ground bond which is usually in the AC distribution box.

    Then we can argue (again) about connecting the panel mounts to the same ground rod as the AC and DC, especially if it means running ground inside the house from the frames (which can introduce lightning to the rest of the system).

    Confused yet? If not we'll try harder. :D
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #5
    Re: Protecting your system and cables

    Excellent.

    Note: I am aware one can save on breakers, cables etc but the day you alter anything on the system, as I tend to do, that is the day the initial saving goes out the door, with more spare parts to store ... been there, done that, got the parts, scars and T-shirts to prove it. :-)

    Ai, wish I could get all from Wind & Sun. Prices are good, they do not have 100's of items for sale which means they have it down to a fine art. Well done!

    Locally it is quite a mission when you know what you want because some people are really profiteering off solar parts here.

    Making things worse, to date I have not found a local electricians whom are DC comfortable nor DC people whom are AC qualified and the ones that are, normally engineers, tend to go a wee bit crazy with their prices / fees. Cannot wait for the day it is as easy and available as AC power is today, as it appears to me it is in the States and Europe. AWA, African Wins Again.


    Back to the matter on hand.
    It seems that to follow your controller max limits, is a very good guide on what to do. FM80 has a limit of 150v incoming, with max of 80a outgoing, irrespective of the array configuration which at all times has to fall within the limits as per the manufacturer.

    Right, to sum up, what have I missed:
    - The Victron Phoenix inverter will be connected distribution boards earth, inside the house.
    - Income array wires must all be on a Gewiss MT60C 2 pole circuit breaker. Doing this means no additional fuses are required.
    - Outgoing wires from the controller to the batteries must also be on a Gewiss MT60C 2 pole circuit breaker.
    - Plan on the other thread to use Anderson connectors for the battery bank solves that problem for easy swapping around of batteries.

    Grounding / earthing and all that, sounds simple enough BUT I am not anywhere near there.
    - The battery negative, array frame as well as the controller have to be negatively grounded. (I nearly bought positive grouding panels once!)
    - Seems to me it is safer to keep this outside the house, separate from the rest.
    I think I am going to see if I can find a local expert. Once they have advised how they intend doing it, post that solution here, before it is installed.

    Local electricians I have asked wants to dig a 2m hole, or as deep as need be, to get to a certain type of soil before they pound in a very long rod, as they would do with a new house. They are not DC experts, nor do they have ever worked or on installed arrays on a roof and the manuals make them cross eyed. At least, that is my experience so far. :-)
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Protecting your system and cables

    Well engineers tend to charge a lot 'cause they've got that university degree(s) to pay for. :roll:
    South Africa wrote: »
    Back to the matter on hand.
    It seems that to follow your controller max limits, is a very good guide on what to do. FM80 has a limit of 150v incoming, with max of 80a outgoing, irrespective of the array configuration which at all times has to fall within the limits as per the manufacturer.

    Note that the input maximum Voltage is based on Voc @ coldest temperatures and that the higher the array Vmp is in respect to the system Voltage the less efficient the controller will operate.
    Right, to sum up, what have I missed:
    - The Victron Phoenix inverter will be connected distribution boards earth, inside the house.
    - Income array wires must all be on a Gewiss MT60C 2 pole circuit breaker. Doing this means no additional fuses are required.

    Well, no. On the array side the important place to have the over-current protection is on individual strings when there are more than two. Otherwise PV is self-limiting in current so as long as the wiring is sized right it isn't possible for it to go too high.
    - Outgoing wires from the controller to the batteries must also be on a Gewiss MT60C 2 pole circuit breaker.

    Second not on breakers: DC does not require two-pole breakers, but if that's what you can get it will work. Normally negative is connected to ground and stays connected; only the positive is interrupted. The exception to this is with DC GFCI and that exception brings of some other safety issues and arguments with the NEC. You can use just one side of the double breaker and leave the negative connected.
    Grounding / earthing and all that, sounds simple enough BUT I am not anywhere near there.
    - The battery negative, array frame as well as the controller have to be negatively grounded. (I nearly bought positive grouding panels once!)
    - Seems to me it is safer to keep this outside the house, separate from the rest.

    Sort of. The panel frame/mount grounding is best run down the outside of the house to an Earthing pole. Negative is grounded at the battery post. Metal cases for equipment will have a grounding wire running to the common ground point (it can be sequential; you don't need a separate wire for every device).
    I think I am going to see if I can find a local expert. Once they have advised how they intend doing it, post that solution here, before it is installed.

    Good idea. Especially about checking on their proposed installation design. Remember I spend much of my time correcting "professional installations". There are too many "solar installers" who are merely adequate electricians. This usually isn't a problem as it can be as simple as following wiring conventions and code. Inspectors are the ones who often don't understand how the code applies to solar. Sometimes John Wiles doesn't. ;)
    Local electricians I have asked wants to dig a 2m hole, or as deep as need be, to get to a certain type of soil before they pound in a very long rod, as they would do with a new house. They are not DC experts, nor do they have ever worked or on installed arrays on a roof and the manuals make them cross eyed. At least, that is my experience so far. :-)

    Well grounding is grounding and doesn't care if it's AC or DC. I guess you must have lousy soil conditions if you need to dig a 2M hole first! We just pound a 10' rod into the ground. Very few locations where that doesn't work. Extremely sand, dry or rocky conditions require more effort to ensure low resistance between ground point and soil. Sounds like they're trying to find moist earth to contact.

    Electrical engineering does get specialized, including AC specialists and DC specialists and RF specialist. It's rare to find someone well-versed in any two of those.
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #7
    Re: Protecting your system and cables

    True about engineers, doctors, electricians, computer wizzes, mechanics ... need to find the one that has the right advice for the right price, not the wrong advice for the highest price. :-)

    Cape Town seldom gets below zero degrees Celsius. Average low per year is +-11. Highest is +-40, which is getting more and more the norm in summer, in my opinion. so the temp variance is not as big a problem.

    Panels are north facing on frames, so no hot air is trapped beneath them. And using the software from Outback, the max panels are adjusted based on temp.

    Array is either going to be 1 x 6 panels in parallel, or 3 strings of 2 panels per string, depending on panels I get. High watt panels = less panels to install and less connections.

    So the plan is to spend a little more thicker wires coming down per string instead of combining all on the roof with expensive connectors / fuses because plug and play connectors are quite pricey and the more connections there are, the more chance of issues over next 10-20 years, not forgetting the losses in the cables due to too many connectors.

    Make sense?

    I can get single pole breakers but after letting the smoke out of a few things (and I tried to put it back, believe me!), I came to the conclusion it is safer (for me) to completely disconnect devices with 2 pole connectors so that if I remember to disconnect the wires on the correct side of the breaker (to move / replace things), there is no chance of wires touching. :-)

    So I want to 'switch off' panels, per string, 'switch off' the controller from the batteries with little to no risk to the equipment and my fingers. :-)

    I do agree that if it was a install once, leave well alone installation, I would have paid someone to do it with properly designed, off the shelf parts. But it is me, trying out different things to 'feel' how it preforms / works, trying to make it as safe as I can be stupid. :-)

    So does it make sense for having 2 pole breakers, or are their problems coming?

    Earthing pole, yes, now I remember, they are after the wet soil. Water pipes are all the new plastic types so they cannot be used either. One electrician, whom I trust the most, does not want to connect the system to the earth rod of the house. He wants to install a new one so based on advices here, it sounds as if he is on par and must to do. The earth wire is just going to have to be a wee bit long to get to the earth to avoid having to go through tiles and a concrete slab. :-) But I recon if it is done, I just have to do it once.
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #8
    Re: Protecting your system and cables

    Have found the right DC fuses, and I seem to be on the right track, subject to final confirmation, that if you install the max voltages / amps the controller can handle, you are safe. If confirmed, this simplifies this process 100 times.

    Going for this range: http://em.co.za/product.htm?productID=914

    Grounding:
    After asking around here in SA, this is the latest summary I have been given by a engineer that installs panels, so that non-experts like me, can understand.

    2 thing stand out:
    Do not have a separate ground for the solar system unless it is tied to the house AC ground.
    And must be 8 feet deep, so the above point makes this also easier to handle, use the house AC ground point.

    Read it here: http://www.weatherimagery.com/blog/how-to-ground-solar-pv-panels-correctly

    Any thoughts?
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #9
    Re: Protecting your system and cables
    South Africa wrote: »
    Have found the right DC fuses, and I seem to be on the right track, subject to final confirmation, that if you install the max voltages / amps the controller can handle, you are safe. If confirmed, this simplifies this process 100 times.

    Going for this range: http://em.co.za/product.htm?productID=914

    Any thoughts?

    Really you need slightly higher than the exact match, we use the 125% rule on fuses. I just went through this on my grid tie system where the original installer used a combination of 10 amp and 8 amp fuses in the string combiner. The 8 amp ones were on the ragged edge for capacity, they last well over 4 years, but ultimately failed loosing a string. All replace with 10 amp ones, as the original installer should have done. So these are 125%+ by rounding up to the next available size.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Protecting your system and cables

    The breakers you linked are rated up to 1000 VDC. That's good. They are limited to 20 Amps. Is that enough? As you said go for the max the controller can handle and it's good because any short will be above that operating range in current.
    Do not have a separate ground for the solar system unless it is tied to the house AC ground.

    That's not phrased very well. Do not have a separate ground for the solar power system unless that ground is tied to the house ground (thus making it a single grounding point). If the solar power system is entirely separate from the house system it will need its own ground.

    And beware of the possibility of creating ground loops and double N-G bonds. (Oh yes; have we ever mentioned here how complex grounding is?)
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #11
    Re: Protecting your system and cables
    Cariboocoot wrote: »
    The breakers you linked are rated up to 1000 VDC. That's good. They are limited to 20 Amps. Is that enough? As you said go for the max the controller can handle and it's good because any short will be above that operating range in current.

    Sorry, was not clear.
    The fuses I am going for are 1000v @ 32amps per incoming string, the 2 pole fuse holder.
    Between controller and batteries, also 2 pole holder, are these @ 125a: http://em.co.za/product.htm?productID=190

    Cariboocoot wrote: »
    That's not phrased very well. Do not have a separate ground for the solar power system unless that ground is tied to the house ground (thus making it a single grounding point). If the solar power system is entirely separate from the house system it will need its own ground.

    Thanks, that got lost in the translation from Afrikaans to English. :-)
    Cariboocoot wrote: »
    And beware of the possibility of creating ground loops and double N-G bonds. (Oh yes; have we ever mentioned here how complex grounding is?)

    Way I have it:
    Inverter connects to DB earth point.
    Battery negative pole, controller earth and the solar panels are all connected to the grounding point outside the house.
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: Protecting your system and cables

    It's good to have the ground rod outside the house (not all are) and to have ground wiring from the array (and combiner box if used and outside) outside the house as well running to that rod. Then the grounding for all equipment inside the house can come outside to that point. This avoids using the array as a lightning antenna and its ground wire as a path to introduce that to the inside of the house!

    One of these days I am going to draw some grounding diagrams so we can have even more arguments, er, discussions about grounding around here.
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #13
    Re: Protecting your system and cables
    Cariboocoot wrote: »
    It's good to have the ground rod outside the house (not all are) and to have ground wiring from the array (and combiner box if used and outside) outside the house as well running to that rod.

    Rod is outside, in my enclosed braai room outside the main house, where I just moved all the equipment. So I will do that.
    Cariboocoot wrote: »
    Then the grounding for all equipment inside the house can come outside to that point. This avoids using the array as a lightning antenna and its ground wire as a path to introduce that to the inside of the house!

    Here I am lost again. So you say that not only must the controller and battery negative be connected to the rod outside, but also the inverters earth?
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: Protecting your system and cables
    South Africa wrote: »
    Rod is outside, in my enclosed braai room outside the main house, where I just moved all the equipment. So I will do that.

    For those who don't know "braai" is South African BBQ (I know other people in SA :D ).
    Here I am lost again. So you say that not only must the controller and battery negative be connected to the rod outside, but also the inverters earth?

    One single ground point is the ideal.
    That includes the metal case of the inverter and the AC grounding (tied to Neutral on PSW inverters).
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #15
    Re: Protecting your system and cables
    Cariboocoot wrote: »
    For those who don't know "braai" is South African BBQ (I know other people in SA :D ).

    Indeed it is.

    BBQ is frying store bought burger patties on a gas BBQ. :-)

    A braai on the other hand is where you braai real meat on a grid over a open fire (flames high for steak) whilst having a beer arguing about politics, sports, politics, grounding, politics and whatever else you fancy at the time.
    When done,meat must be rare so that a good vet can still save the cow.
    For starters there would have been bacon wraps, and for salad there was chicken, all cooked on same braai.
    Pudding is 'braai broodjies' (tomato, cheese and onion sandwiches with a bit of Mrs Balls Chutney, toasted to perfection on the same fire), done before you add more wood to stoke the fire ... :-) :-)

    Local comedian, Barry Hilton, sums it up quite nicely here: http://www.youtube.com/watch?v=kYdQuj9UUIQ
    When he says: When a 'boerjie' says ... he generally refers to the Afrikaans speaking South Africans.
    The mumbling, jip, I recon it will sound like that to a English speaking person conversing with a 'boertjie'. We are quite a friendly bunch here. :-)

    Cariboocoot wrote: »
    One single ground point is the ideal. That includes the metal case of the inverter and the AC grounding (tied to Neutral on PSW inverters).

    Then that is how it is going to be. Nice big bush bar connected with 16mm2 wire to the rod to be able to connect all the negative earth wires from all devices comfortably, outside the house. Only link to the inside is the inverter's 220v AC.

    I think that then sums it all up. Once I have all installed, in a while, I will put the pictures up for the next person to see.
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #16
    Re: Protecting your system and cables

    To recap:
    Grid is my backup. Cannot legally go grid tie.
    Main function of the system: Power computers, a fridge and a few other things daytime with lights only at night.
    Secondary function: If there is a grid failure, only then use the system as backup for selected computers only.
    System charges batteries 1st before the loads are switched on, so all power the array can give, is used on the spot the rest of the day.
    As more power is added, I add more devices and in winter I remove some devices to keep it balanced as best I can.

    Idea is to install the biggest fuses the final controller can handle, which means all smaller ones will work.
    Wires are oversized so that fuse goes long before the wire.

    Currently I have:
    3 x 310w (24v) panels connected to a Tristar 45 controller. Not the MPPT one.
    2 x 200w (12v) panels connected to a Phocos 20a controller. Not a MPPT.
    24v battery bank (4 x 102ah batteries)
    Victron Phoenix 1600 inverter connected to a 150A fuse on the pos cable, shunt on the negative.
    Victron battery monitor.
    6mm wire for array, 16mm car battery cables for the rest, inverter came with its proper cables.
    Separate circuits installed for all the equipment powered from solar, with a clever box the switches power from inverter to grid and back based on battery SOC.

    Note: 200w panels and controller was in the 'shed'. Daytime they give that extra oempf to keep system on solar for longer. Ideally they will move to lights only system, one day.


    Next level:
    Outback Flexmax 80 with 48v+ array with max panels on 24v battery system. 2500w array and 145v incoming max is what I am catering for now.
    Batteries that the array and FM80 can handle.
    Victron Phoenix 1600 inverter for more loads I want to take off the grid daytime.
    Adding more loads for additional daytime savings.


    Having looked at the nice combiner boxes, DIN mounted parts are cheaper with same end result, take out fuses and panels / batteries are disconnected.

    In order to get to a point where I buy once, have lots of room to manoeuvre, using the max of a Outback Flexmax 80 controller on my current setup, am I right in getting these parts now?

    Array has 3 strings incoming, 3 x pos and 3 x neg, using 6mm2 wires.
    Each pair connects to these 2 pole 32A rated fuse holders (type 481233): http://www.em.co.za/product.htm?productID=914
    Fuses for the array are rated @ 20A 30kA per wire (part 491635): http://www.em.co.za/product.htm?productID=914

    From the fuses the cables are connected to 2 of these distribution blocks (type KJ02D): http://www.em.co.za/product.htm?productID=592
    Opposite side of block is connected to 16mm2 wire that goes to the controller.

    Controller connects to batteries using 32mm2 wires via a 2pole 125A fuse holder (type 485303): http://www.em.co.za/product.htm?productID=190
    Fuses rated @ 80A (part 422080): http://www.em.co.za/product.htm?productID=182

    Am I on the right track for what I have and for the future?
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #17
    Re: Protecting your system and cables

    Fuses for the array @ 20 Amps may be too large. Look at maximum series fuse rating for panels used. If that's not available look at Isc * 1.25, rounded up. If the Isc is something like 8 Amps and the fuse is 20 then two more strings could feed 16 Amps to one shorted one which could ignite if it's only capable of handling 15 Amps as a conductor (series fuse rating).

    And FM80 would have a 100 Amp fuse/breaker on its output, not 125.

    Otherwise so far, so good. Unless I missed something; it's very early here.
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #18
    Re: Protecting your system and cables
    Cariboocoot wrote: »
    Fuses for the array @ 20 Amps may be too large. Look at maximum series fuse rating for panels used. If that's not available look at Isc * 1.25, rounded up. If the Isc is something like 8 Amps and the fuse is 20 then two more strings could feed 16 Amps to one shorted one which could ignite if it's only capable of handling 15 Amps as a conductor (series fuse rating).

    Short circuit current per panel is 9amps, with current at max power 8.6, using 9amps as my base, 2 panels in series is still 9amps.
    My faulty logic was, do not ask, was 3 strings of 2 panels per string series is 3 x 9 = 18a, so therefor the 20a.

    So it is better to go for 10a fuse per incoming string of 2 panels?
    Cariboocoot wrote: »
    And FM80 would have a 100 Amp fuse/breaker on its output, not 125.
    I thought of a 80a seeing the FM80's max output is 80a, which it will never get to?
    The current controller is a maxed at 45a, so is my logic right that if I use a 100amp fuse, with the controllers not being the issue, but the problem being when I short the batteries again, the 100amp fuse will pop? :-)
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • BB.
    BB. Super Moderators, Administrators Posts: 33,590 admin
    #19
    Re: Protecting your system and cables

    9 amps Isc * 1.25 fuse/wire derating = 10.8 amps minimum

    I would round up to 15 amp fuse.

    You do not want fuses/breaker exposed to a constant current of any more than ~80% of their rating--That is usually the protective devices "trip point".

    With the typical solar panel, 2 panels feeding a shorted third panel is "on the edge" of needing a fuse/breaker per string... In your case, a 15 amp fuse being fed 19 amps is not a lot over the 15 amp rated fuse (it could take minutes to hours to trip a 15 amp fuse at 15 amps).

    But, according the the calculations (and US) code requirements--It is a requirement for most solar panels (there are some older thin film panels, probably no longer made, with high Vmp that have ~1.2 amp output and 15 amp fuse requirements--So they can connect multiple parallel panels without needing series fuses).

    Protecting the output of a MPPT charge controller is a bit more math... If you protect an 80 amp controller with 80 amp breaker/wiring, you really need to ensure that the output current does not exceed (80a*0.80 derate=) 64 amps. Since you can have a hot battery bank and a cold day, the solar array Vmp voltage can rise and the controller output more current than normal (you don't want to pop your 80 amp fuse on a cold/clear day).

    For example:
    • 80 amps * 0.80 derate * 21 volt (near dead battery) * 0.80 derate for cold weather = 1,075 Watt array maximum (derated)

    But, if you did the "correct" way of wiring with 1.25 (1/0.80) derating of wiring/fuses:
    • 80 amp * 1.25 derate = 100 Amp wiring+breaker

    Because MPPT charge controllers do (reliably/safely) limit their output current to rated value, we would say an 80 amp controller would support:
    • 80 amps * 29 volts charging * 1/0.77 panel+controller losses-derating = 3,013 Watt "cost effective" array

    Solar power has lost of deratings/design for safety/design for reliability requirements. When you optimally use the correct hardware with the correct wiring, you can have a safe/reliable and cost effective installation.

    In this set of examples, the first is designed for safety limits. The second uses the natural ability of the charge controller to limit outputput current--And we can use that capability to limit the variability of sun+solar panels+battery charging voltages.

    There will be (a relatively few hours per year) that the second system may not gather/use all of the available sun, but you can use an almost 3x larger array with the same charge controller--Safely. Your other option would be to buy three more charge controllers for 3x larger array--A huge cost hit.

    Of course, there is one last option. Some MPPT charge controllers have programmable output current limits (like the Outback). You could program its output to 64 amps maximum and then use a larger array (you now have an FM 64 model).

    Obviously, if you have the correct wire+fuse (FM 80, 80 amp wire, and 80 amp fuse)--The system would be "safe" with a larger array--But you will have nuisance trips on cold/clear days with low battery voltage--Not something that you would like for a "reliable" system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #20
    Re: Protecting your system and cables
    South Africa wrote: »
    Short circuit current per panel is 9amps, with current at max power 8.6, using 9amps as my base, 2 panels in series is still 9amps.
    My faulty logic was, do not ask, was 3 strings of 2 panels per string series is 3 x 9 = 18a, so therefor the 20a.

    So it is better to go for 10a fuse per incoming string of 2 panels?

    Probably 15 Amps. 9 Isc * 1.25 = 11.25, round up to 15. Two panels at Isc feeding a shorted one would be 18 Amps so the 15 Amp fuse should pop first. A 20 Amp one would not.

    I thought of a 80a seeing the FM80's max output is 80a, which it will never get to?
    The current controller is a maxed at 45a, so is my logic right that if I use a 100amp fuse, with the controllers not being the issue, but the problem being when I short the batteries again, the 100amp fuse will pop? :-)

    Er, yes?
    80 Amp controller can handle 80 Amps. If it shorts out current from batteries can go well over that. So the wiring and fuse/breaker is sized for normal maximum current handling. 80 * 1.25 = 100 Amps. Anything above that is in the danger zone. Again if the circuit protection is rated too high it may not go before something ignites.
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #21
    Re: Protecting your system and cables

    Then it will be so.
    - 15 amp fuses per array string.
    - 100 amp fuses between the batteries and the controller, when FM80 comes.
    - But, being a 45amp controller at present: 45 * 1.25 = 56.25 = 60amp fuses for now.
    - And array cables are neat with the combiners.


    Sum total of grounding I gathered in bits and pieces all over the site:
    - Ground all metal cases, array and the battery negative pole to existing ground rod of my house using 16mm2 cable.
    - Ensure earth bush bar can handle it.
    - This means I only have to have a fuse on the positive side of all cables due to the negative being grounded.
    - But if there is no grounding of batteries negative, then a 2 pole fuse (one for pos and one for neg) is a absolute must.
    - Using fuse holders that have 2 poles with 2 fuses in, ensures 1000% that if there is a mistake of whatever nature, that you are as safe as you can be.


    And:
    - Pulling both fuses - same as disconnecting with a breaker.
    - Using fuse holders that can handle bigger amps means more room to move with fuses versus breakers where you cannot just swap a fuse.
    - But, if your system is fixed for 10 years or more, then breakers are better if you tend to connect things the wrong way. :-)
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #22
    Re: Protecting your system and cables

    That's pretty much it.

    Leaving aside a few thousand exceptions encountered in unique situations. :p:D
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #23
    Re: Protecting your system and cables
    Cariboocoot wrote: »
    That's pretty much it.

    At LAST!!! Thank you / Baie dankie!
    Cariboocoot wrote: »
    Leaving aside a few thousand exceptions encountered in unique situations. :p:D

    Well, if you think back, in the beginning you and BB did ask me to first specify the load, which I ignored.
    See, the load will be as much as the system can handle.
    And the system can handle what my pocket can handle ... for now ... :D

    So I have learned that if you keep on expanding (I call it experimenting), you get yourself into a few corners so you best learn quick to look at things differently.

    Therein the specs to cater for min and max, a formula which will work IF you decided on a controller make (maybe two), to keep aside the few thousand exceptions encountered in unique situations.

    I THINK I have now have the formula solved IF I stick to the 2 controllers. :-)

    If it was not for this site, it would have never happened and I would be out of pocket even more. :-)

    If I was States side, I would most probably have bought all for the hosts of this site to boot.
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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