Validate my wiring and lightning protection

dakaz
dakaz Registered Users Posts: 10 ✭
in Solar Beginners Corner #1
Hi all,

After 18 months of research, planning and learning (thanks everyone!) I am about to order my off-grid cabin solar equipment. I am hoping someone could validate my wiring diagram (am I missing something or wired wrong?) and also let me know, where do I hook up the lightning arrestors? Note I am likely going with the morningstar TS-MPPT-60 charge controller, 5x 300W panels, and likely an AIMS pure-sine wave inverter (I can't get past the cost!). Please let me know your thoughts.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Validate my wiring and lightning protection

    Well the batteries sure look wrong. Looks like you've 'laddered' five parallel strings of two, with the inverter connections at one end and the controller connections diagonal. If you're going with that many parallel strings (and you shouldn't; not on any system Voltage) you need to run equal length positive and negative wires from each battery string to a common connection point/bus bar. Then attach the inverter and controller wires there.

    It may just be the depiction, but there is a lack of fuses/breakers on the panels & charge controller output. Ideally each of those battery strings would have its own fuse as well.

    You don't want to use the same DC disconnect for both charge controller and inverter. The inverter's DC breaker is sufficient for this.

    Lightning arrestors have three wires: one goes to positive, one to negative, and the third to ground. You have to have the ground wire right but the other two are interchangeable (and will work on AC as well). The most important location for one is on the PV wires as they are most likely to pick up the energy of nearby strikes. Long or outside AC runs would be next most likely.

    The ground on the negative at the PV combiner is unnecessary. I think you are doing this instead of grounding the panel frames & mounts to a separate rod (which we often discuss here).

    Time for revision!
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  • dakaz
    dakaz Registered Users Posts: 10 ✭
    #3
    Re: Validate my wiring and lightning protection

    Hi Caribocoot,

    Thank you for the detailed reply and analysis. I have to admit I didn't follow it all but I did update the diagram from what I did understand. Specifically the concern over the parallel strings - what are my options here? I want to have 800aH of storage and need a 24V system. I added a busbar to the battery and fused the positive connection - do you think there are other areas I should fuse? Lastly, I still don't understand how I'd hook up the lightning arrestor. Should this just attach to the same connections that feed the charge controller from the PV combiner? Thanks again for any and all help!

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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
    Re: Validate my wiring and lightning protection
    dakaz wrote: »
    Specifically the concern over the parallel strings - what are my options here? I want to have 800aH of storage and need a 24V system. I added a busbar to the battery and fused the positive connection - do you think there are other areas I should fuse?
    Your battery connections are still very wrong.... guaranteed failure.

    Here's a short discussion about parallel batteries:
    http://www.wind-sun.com/ForumVB/showthread.php?14674

    This is from the smartgauge.com site that is linked in that thread:
    Attachment not found.

    Note: I recommend against putting 4 batteries in parallel, but if you are going to do it, that is the way.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
    Re: Validate my wiring and lightning protection
    dakaz wrote: »
    I want to have 800aH of storage and need a 24V system

    Better to re-boot and look at 400ah and 48v system Hope you haven't bought 24v gear yet. Once you depart from 12V land, may as well go deluxe and head for 48V, and half the amp hours that 24w would want.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Validate my wiring and lightning protection
    mike95490 wrote: »
    Better to re-boot and look at 400ah and 48v system Hope you haven't bought 24v gear yet. Once you depart from 12V land, may as well go deluxe and head for 48V, and half the amp hours that 24w would want.

    Yes.
    Right after you revisit why you want 800 Amp hours @ 24 Volts (up to 9.6 kW hours).
    Or go with larger capacity batteries so there are fewer connections.

    A bit about different system Voltages: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    Dakaz;

    what your diagram is showing now is your battery bank totally 'laddered'; all connections at one end. See the diagram vtMaps provided.

    You may find it easier to cope by breaking the system down into its separate (but interacting) circuits: PV to controller, controller to batteries, batteries to inverter, AC from inverter.

    For the lightning arrestor(s) look at a picture of one here: http://www.solar-electric.com/suprdemn.html Note that it has a red wire, a black wire, and a green wire. On the array (at the combiner box if possible) the red would go to positive, the black to negative, and the green to ground.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: Validate my wiring and lightning protection

    he still wants to know where to place any lightning protection and that can depend on how much you are willing to go with protecting it too. the first would be an spd at the ac output of the inverter. most damage occurs from the ac lines picking up spikes and sending them up into the inverter. next would be an spd at the input to either your charge controller, or in the case of those without a controller and batteries, the dc input of the inverter. this is because the dc wiring picks up the spike and feeds it into your equipment, but this spike is often smaller than the ac side of things due to the smaller area of wiring for pick up. these are the 2 most common vulnerable points. some also place spds at the pvs to ground out spikes there, but pvs are more resilient than the rest of your electronics and the spd before your cc will often suffice except when using long wire runs from the pvs. proper grounding is vital no matter what so the spike has a place to safely go to ground and i won't get into that as there are many threads on that you can look up.
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  • dakaz
    dakaz Registered Users Posts: 10 ✭
    #8
    Re: Validate my wiring and lightning protection
    mike95490 wrote: »
    Better to re-boot and look at 400ah and 48v system

    Okay - try 3, 48V this time :p. I increased the battery size (12V 225aH) and had to go to 6 panels instead of 5 to match the 48V. I found the Midnight Solar DISCO series of combiners which comes with both the DC Disconnect and Lightning protection so I think this is my best option. Its about a 40ft run from my roof to the load center so I figure I'll run two panels in series to the combiner and then have short connections between the combiner, charge controller, batteries and inverter. Please keep the great advise coming!

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Validate my wiring and lightning protection

    Okay let's check:

    Panels: two in series must have a Vmp of 35 each in order to work for a 48 Volt system. (I can't see the writing on the diagram myself). If not and they are Vmp 30 then use two strings of three in series.

    Batteries: much better. You've eliminated a lot of potential trouble going to 48 Volts. Keep in mind this means you need more expensive breakers that will handle the Voltage. Check to be sure the over-current protection/disconnects can handle the 60+ Volts that will be present.

    Ground: you should separate the actual ground wiring from the lightning arrestor wires on the diagram. As it is there's confusion of what is going where.
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  • dakaz
    dakaz Registered Users Posts: 10 ✭
    #10
    Re: Validate my wiring and lightning protection
    Cariboocoot wrote: »
    Panels: two in series must have a Vmp of 35 each in order to work for a 48 Volt system.

    Okay, the panels have a Vmpp of 36.68V, so I think that will be okay. Two more quick questions if you don't mind. Most installations put the combiner outside by the panels. I was planning on putting the MNPV6-Discon in my basement where the wires enter which is about 25' from the panels. I am concerned that the voltage loss over that run at 48V would be bad, but when I use a online calculator (http://www.calculator.net/voltage-drop-calculator.html) I see that I'd get 0.45V loss (0.94%) over that 25' run. Is that right, should I not worry about using #10 wire (most MC4 connector wire comes as #10). There will obviously be other losses in the system, but wondering what everyone thinks.

    Second question - should I have a fuse or DC disconnect between the battery bank and the positive bus bar - does this truly protect the batteries or would the fuses/breakers in the DC panel and inverter already provide enough protection?

    Thanks again all!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Validate my wiring and lightning protection
    dakaz wrote: »
    Okay, the panels have a Vmpp of 36.68V, so I think that will be okay. Two more quick questions if you don't mind. Most installations put the combiner outside by the panels. I was planning on putting the MNPV6-Discon in my basement where the wires enter which is about 25' from the panels. I am concerned that the voltage loss over that run at 48V would be bad, but when I use a online calculator (http://www.calculator.net/voltage-drop-calculator.html) I see that I'd get 0.45V loss (0.94%) over that 25' run. Is that right, should I not worry about using #10 wire (most MC4 connector wire comes as #10). There will obviously be other losses in the system, but wondering what everyone thinks.

    Usually the combiner is near the array so that there is only one set of wires coming from the array to the charge controller. If the combiner is near the controller then you have a separate "home run" for each PV string (one or more panels in series). As such you use more wire. You can weigh the cost of that against buying one run of larger wire for the single run.

    The losses on individual home runs may be less due to the lower current @ same Voltage per run. But the over-all amount of wire may be much more; in other words if you were to add up the cross-section area it would amount to a larger wire size than would be needed for all the strings together. Your choice.
    Second question - should I have a fuse or DC disconnect between the battery bank and the positive bus bar - does this truly protect the batteries or would the fuses/breakers in the DC panel and inverter already provide enough protection?

    Thanks again all!

    It isn't the batteries that need protection, it's what's connected to them. The batteries are the power source, and a short anywhere on any circuit connected to them can be subject to a huge amount of current. So you have a fuse/breaker between the controller and batteries to prevent that circuit in the event the controller shorts, and likewise with the inverter. Normally you try to put the circuit protection as close to the power source as possible, in this case the batteries. This is why I like the post terminal fuses (but they aren't suited to 48 Volt systems). That way you minimize the amount of unprotected wiring in the circuit.
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