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Checking 12V solar system for obvious errors

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  • #16
    Originally posted by sensij View Post
    Just to be clear, for the sake of the OP. If it turns out that either of these conditions are true:

    1) Continuity between Solar DC- and Battery DC- terminals

    2) Continuity between the charge controller case and any of the DC - terminals

    would you advise grounding any part of the system?
    Sensi I know where you are going with this and there is not really a correct answer. Being a 12 volt system under 50 volts there is no requirement to ground the chassis of the system. Which means you could go either way or halfway. As for the panels with a single or even two strings there is no requirement to have any OCPD because there is no way the panels can generate enough current to heat up the wiring.

    The only thing in the system is the battery itself that is capable of generating enough current to burn wires. The only unprotected wiring is between the CC and battery term post. Assuming he has a listed CC, the charge controller internal fuse will protect the panel wiring from the battery. At 12 volts electrocution is not an issue, thus why no ground is required.

    My POV is if you do not have to ground the chassis or the system, DON'T! Grounding a system actually makes it dangerous and prone to unnecessary outages. That is why industry especially utilities, refineries, pharmaceutical, extrusion, or any process where unnecessary outages cannot be tolerated use Delta configuration. If there is a line fault, an alarm goes off to alert maintenance personal to schedule a controlled shutdown for repairs.
    MSEE, PE

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    • #17
      Originally posted by antobag View Post
      In any case, I would very much like to see that video. It'd be great to be able to use 40 or 120 amps - I'm quite limited with my current (no pun intended) 10 or 20 amps.
      This kind of like I do it with a couple of modifications.

      1. I use Flux on the wire Skinner and connector reciever. This just helps solder flow and helps clean the metal.
      2. I use a 40 watt pen iron to tin the wire skinner before soldering it onto the connector. This prevent a cold joint and speeds up the process.

      Tip keep a wet rag to cool things off like the wire insulation. Additionally do net let solder get on the outside of the connectors because they will not snap into the plastic connector. Once snapped in the pin and wire should rotate freely inside the connector. Keep it clean/tidy and only use enough solder to make the connection and fill the bullet without overflow or spilling. Other than that here you go.



      One last note. This is for small hobby stuff only. It does not comply with any UL or NEC practice, but a heck of a lot better than a cigarette lighter power port. 20 amps and less on a max #10 AWG using EC5 mm. GOT IT?
      MSEE, PE

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      • #18
        Originally posted by Sunking View Post
        Sensi I know where you are going with this and there is not really a correct answer. Being a 12 volt system under 50 volts there is no requirement to ground the chassis of the system. Which means you could go either way or halfway.
        I'm not disagreeing with anything you are saying. Really, I'm not. For the sake of information only, I just want to make sure the OP knows what code is.

        Leaving the system (the DC-) ungrounded under 50 V is clearly ok from 690.41. Leaving the chassis ungrounded is not as clear, since 690.43(A) makes a point of saying voltage doesn't matter. On some of the cheaper equipment out there, the system and the chassis are not isolated, further complicating it.

        Originally posted by NEC
        690.43 Equipment Grounding.
        Equipment grounding conductors and devices shall comply with 690.43(A) through (F).

        (A) Equipment Grounding Required. Exposed non–current-carrying metal parts of PV module frames, electrical equipment, and conductor enclosures shall be grounded in accordance with 250.134 or 250.136(A), regardless of voltage.
        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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        • #19
          Originally posted by sensij View Post
          I'm not disagreeing with anything you are saying.
          Never siad you were. My point is the OP said a Hut. I am treating it like a Boat, RV, mobile, or remote setup. Using cigarette lighter power ports is not a NEC or UL application.

          At 12 volts there is no danger of electrical shock. Only real danger is short circuit battery on unprotected conductors which I addressed. Right?
          MSEE, PE

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          • #20
            Originally posted by Sunking View Post
            At 12 volts there is no danger of electrical shock. Only real danger is short circuit battery on unprotected conductors which I addressed. Right?
            12 volts from a stiff enough supply could, under a very narrow set of unlikely circumstances, create some danger. However, within the context of this thread, yes, you are right. It wasn't clear that the OP had considered grounding at all from the drawing he shared. With this discussion, his decisions about grounding will be much better informed, and should he choose to expand the system eventually (either in voltage or in power), some thought as to when grounding may become appropriate would be wise.
            CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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            • #21
              Originally posted by sensij View Post
              12 volts from a stiff enough supply could, under a very narrow set of unlikely circumstances, create some danger.
              Well a battery is a fairly stiff supply of current. 12 volts is always 12 volts. Having said that I think you understand if you ground a system, you greatly increase the chances of receiving an electrical shock if you come into contact with the un-grounded aka hot circuit conductor. That is why they call it HOT

              True story. When I was in my twenties in a telephone office we had a power contractor installing a battery plant. Plant was constructed and after testing connection resistances I found a couple inter-cell bus bars that failed 10 micro-ohm contact resistance test. I informed the foreman and he proceeded to take inter-cell connector off to clean, reassemble, and torque it down. Once he had it cleaned and reassembled he was tightening it down. He was left handed so using his left hand on the wrench. The wrench slipped and his hand went into the steel supporting frame, and his wedding ring made contact with the frame and BOOM!

              It vaporized about 1/3 of the ring with a matching chunk/hole to the bone. He was a tough ole bird. We spent the next hour with him looking for the diamond and found it. He stuck it in his pocket along with what was left of his ring, finished the job, and came back the next day right on time with a band aid like nothing ever happened. I seen him about 6 month later on another job of mine and he was fine. We went to the bar and had a good laugh about it.

              What was really funny at the time when he blew his ring of his finger, all he said was; "damn my wife is going to be pissed if I don't find that diamond'. I will never forget that.
              MSEE, PE

              Comment


              • #22
                Originally posted by Sunking View Post
                Well a battery is a fairly stiff supply of current. 12 volts is always 12 volts. Having said that I think you understand if you ground a system, you greatly increase the chances of receiving an electrical shock if you come into contact with the un-grounded aka hot circuit conductor. That is why they call it HOT

                True story. When I was in my twenties in a telephone office we had a power contractor installing a battery plant. Plant was constructed and after testing connection resistances I found a couple inter-cell bus bars that failed 10 micro-ohm contact resistance test. I informed the foreman and he proceeded to take inter-cell connector off to clean, reassemble, and torque it down. Once he had it cleaned and reassembled he was tightening it down. He was left handed so using his left hand on the wrench. The wrench slipped and his hand went into the steel supporting frame, and his wedding ring made contact with the frame and BOOM!

                It vaporized about 1/3 of the ring with a matching chunk/hole to the bone. He was a tough ole bird. We spent the next hour with him looking for the diamond and found it. He stuck it in his pocket along with what was left of his ring, finished the job, and came back the next day right on time with a band aid like nothing ever happened. I seen him about 6 month later on another job of mine and he was fine. We went to the bar and had a good laugh about it.

                What was really funny at the time when he blew his ring of his finger, all he said was; "damn my wife is going to be pissed if I don't find that diamond'. I will never forget that.
                Hahaha that is a fantastic story! You've put me off wearing rings for life.

                Again, thanks for all the help everyone. It's very much appreciated.

                I set up the panels today with no load, just to keep my battery charged and check if everything's working. A friend came round to help out. While I was setting up the panels outside, my friend wired up the MPPT charge controller to the battery and solar cables. Unfortunately, he wired the solar cables to the controller with reverse polarities. The charge controller was showing a 0.00W charge rate and I noticed his mistake, but only after about a minute of it all being connected. Could this have caused any permanent damage to the panels/controller/battery?

                Now that I've rectified the problem, everything seems to be working but I'm not sure if the output is normal for my conditions. It's a cloudy winter's day in London, and the temporary location in which I have the panels means they are partially shaded (this will obviously be different when I set it up permanently). With my 200W panels I'm getting anything from 5 to 15W with clouds, and about 15 to 25W when the sun comes out (these readings were taken at about 2pm here). This seems pretty low, but I was just wondering if that's pretty standard for my bad conditions.

                My fear is that the reverse polarity wiring could have caused some damage - if this was the case, could it potentially have reduced the output of my panels, or would it stop the output altogether?

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                • #23
                  If you have a decent controller they have Reverse Polarity protection built in and it sounds like you controller does otherwise you would have let out the magic smoke and it would not be working. If your battery is charged up and no load on them no power will be generated from the panels. No place for it to go.
                  MSEE, PE

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                  • #24
                    And it is very difficult to see how the panels could be damaged, except if the CC failed in a way which let the reverse polarity show up on the CC input terminals.
                    That would very quickly smoke at least one bypass diode in each string, after which there would be some tendency to smoke the panel whose diode was blown. And that in turn could end up taking out the panels, one by one.
                    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                    • #25
                      Thank you both, you've put my mind at ease. My friend will certainly feel less guilty now! I guess the low output is just due to the poor light conditions then.

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