Battery cut off

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greenthumb76
greenthumb76 Solar Expert Posts: 40
Can you please tell me how to disconnect my battery(ies) when working on my solar power system?

As shown in the illustration, one of the negative battery posts has a battery cut off switch. But all three negative cables are joined together before attaching to the cut off switch. Unfortunately, this still means that, after disconnecting at the cut off switch, one of the batteries is still powering the system.

Is there a better way to wire this, so that I can simply make ONE disconnection, at the cut off switch?

(If so, can you please tell me, in what order I should disconnect, then connect the cables?)

Thank you!!

Comments

  • stevend
    stevend Solar Expert Posts: 34
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    Re: Battery cut off

    You're right, it looks like battery 1 is always connected to the system.

    I've attached a picture with two diagrams. Normally the disconnect is connected to the positives. This is because the battery negative side should be connected to ground according to the US electrical code.

    Diagram 1 shows suggested wiring given what you have now but with the disconnect on the positive instead. The disconnect switch will disconnect both the solar controller and the inverter.

    Diagram 2 goes further. I've added a separate disconnect for the solar controller. This one can be a smaller DC breaker sized to handle the solar controller output. The inverter output is larger and so you have a larger disconnect switch there. One reasons for the separate disconnects is so that you can disconnect the equipment pieces individually depending on which one you want to do work on. This is the way it's normally done.

    Also in Diagram 2 I put a ground connection for the battery negative. As well, notice there's only one cable going from the disconnect switch to the positive battery terminal. That's for if you want to make the disconnection at the batteries, there's only one cable to remove.

    As for the wiring disconnect order for your current system, I'd suggest disconnecting the two positive connections at the positive battery terminal for the inverter and solar controller first. That's because the negative side is normally grounded. Then I'd suggest disconnecting the inverter and solar controller where they connect to your disconnect switch. Normally it'd be good enough to disconnect just from the positive but your wiring's a little strange so this is just to be extra safe.
    -Steve
  • greenthumb76
    greenthumb76 Solar Expert Posts: 40
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    Re: Battery cut off

    I don't understand the switch you are showing. What I am working with is this.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Battery cut off

    An automotive application battery disconnect. :D

    It is a kind of a switch. It should be wired as stevend suggests: all negatives tied and grounded; two battery positives connected; disconnect on one battery between both batteries and the inverter & charge controller.

    Now it could be a bit problematic getting the batteries tied together with that disconnect on one post; that's not how they're meant to be used. It might be simpler to buy a second disconnect for the other battery. Keep the cables to the batteries equal in length and size.
  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
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    Re: Battery cut off

    sounds like you don't have any disconnect in your system at all? You might want to check out some wiring schematics to see some ideas of how to set up a disconnect. Midnite solar has a lot of diagrams on their site; this is one on how to connect a PV array, Charge controller, Inverter/charger, and generator http://www.midnitesolar.com/pdfs/e-panelWIRE1revF.pdf utilizing one of their E-panels. While this might be more complex or expensive than what you need for your system, it's a good general idea and I have to say that I've found that adding one of their E-panels into my own system made for a much cleaner and tidier installation.

    It's good practice (and a code requirement I believe) to have a breaker or fuse in between your PV array--> charge controller, and another between your charge controller --> batteries. That way you can isolate your charge controller from the batteries and your PV array. Just make sure that any wires that connect to any potential power source (PV, Generator, batteries, utility etc) have some form of protection in either the form of a fuse or a breaker (appropriately sized, of course).
  • stevend
    stevend Solar Expert Posts: 34
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    Re: Battery cut off
    I don't understand the switch you are showing. What I am working with is this.

    That's the first time I've seen one of those - but since it's an automotive disconnect that would explain why. It still means you're right, that one battery is always connected.

    As for the wiring disconnect order, now that I've seen your disconnect means, I'd still suggest what I said before. Disconnecting all those positive connections at the battery postive terminal so that the solar controller positive, the inverter positive and the battery cable that were all on that terminal are all now separated from each other. That basically opens the circuits. Your automotive disconnect thing with the green knob is of no use on its own as a disconnect means since the components are all hardwired together there. Disconnecting the negatives are optional at this point - unless you have ground connections you haven't told us about.

    The large disconnect switch in my diagram was one like this:
    http://prismsolar.co.uk/shop/outback/ob-dc175-dc-breaker/prod_94.html?review=write
    It's an actual breaker which would trip when there's a short. It's just a very big breaker because if there's a short at your battery bank then there would be a lot of current. I just replaced a customer's inverter last year because of that. They did have a disconnect switch but they'd fixed it so it wouldn't disconnect since "that would be inconvenient". :( It's the same disconnect switch found in the E-Panel that @hillbilly mentions below.
    -Steve
  • greenthumb76
    greenthumb76 Solar Expert Posts: 40
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    Re: Battery cut off

    hillbilly, thanks for the help. I tried, but I'm just not comprehending the diagram. It has way too much info on it, for me to process.

    It would be easy to say that there's no need to understand it, just buy one and everything will be simplified--but I have less than $700 per month to live on.

    I want to be safe, but the price of an epanel is out of reach for me.


    The info I originally based my decision (to go solar) on, was obviously grossly oversimplified. I keep finding that things are way more complex than what I had previously understood. If I'd had the right info, I guess I never would have gone in this direction. However, I'm pretty much 'locked into' it now.

    Although I'd love to be able to buy a system that could fuel my previous lifestyle--what I'm trying to do now is simply put together a small, safe, functional, completely off-grid system that can fuel my basic needs for a fairly primitive lifestyle.
  • greenthumb76
    greenthumb76 Solar Expert Posts: 40
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    Re: Battery cut off

    'Coot,
    ya lost me here:
    two battery positives connected; disconnect on one battery between both batteries

    I'm not visualizing what you mean here:
    Now it could be a bit problematic getting the batteries tied together with that disconnect on one post . . . It might be simpler to buy a second disconnect for the other battery.
    Not sure in what way you mean that it could be problematic

    Again here:
    Keep the cables to the batteries equal in length and size.

    There are many cables attached to the batteries, which ones in particular are you referring to?

    Sorry to be a pain. I'm sure you know what you are talking about, and others who already understand this can 'fill in the blanks', but I don't understand this well enough to do that yet. So, drawings, or really 'spelling things out' would help me a lot. Thanks!!
  • greenthumb76
    greenthumb76 Solar Expert Posts: 40
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    Re: Battery cut off

    Stevend,
    so, if I understand correctly, the 100amp fuse I currently have on the cable between the batteries and the inverter would be replaced by the big breaker? Is this necessary for safety, or just for convenience? As I explained, I am severely limited as to what I can afford.

    Although I'd love to be able to buy a system that could fuel my previous lifestyle--what I'm trying to do now is simply put together a small, safe, functional, completely off-grid system that can fuel my basic needs for a fairly primitive lifestyle.

    I currently have a 110 watt array. The most I can conceive of being able to expand to is less than 500 watts, more likely about 300.

    I definitely want to be safe, and I'd like things to be convenient, but at this point, that's optional . . .

    unless you have ground connections you haven't told us about.
    the system is presently ungrounded

    I'd still suggest what I said before. Disconnecting all those positive connections at the battery postive terminal so that the solar controller positive, the inverter positive and the battery cable that were all on that terminal are all now separated from each other. That basically opens the circuits.

    so, to be clear: if I disconnect from battery 1, the positive cable that has everything attached to it (controller, inverter, battery #2) . . . and if I then disconnect the controller cable and inverter cable from the battery #2 cable, and from each other. . . then it will be safe for me to work on the system, without disconnecting anything else (as long as it is dark, or the pv array is prevented from receiving light)?
  • stevend
    stevend Solar Expert Posts: 34
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    Re: Battery cut off
    Stevend,
    so, if I understand correctly, the 100amp fuse I currently have on the cable between the batteries and the inverter would be replaced by the big breaker? Is this necessary for safety, or just for convenience? As I explained, I am severely limited as to what I can afford.

    I didn't realize you had a 100 amp fuse there. You still have no switch for disconnect but the fuse will protect your inverter.

    Keep in mind, your system won't be in compliance with the electrical code, but I take it you can't afford to anyway.
    Although I'd love to be able to buy a system that could fuel my previous lifestyle--what I'm trying to do now is simply put together a small, safe, functional, completely off-grid system that can fuel my basic needs for a fairly primitive lifestyle.

    I currently have a 110 watt array. The most I can conceive of being able to expand to is less than 500 watts, more likely about 300.

    I definitely want to be safe, and I'd like things to be convenient, but at this point, that's optional . . .

    Out of curiosity, what info did you base your decision on to go solar that made you think it would be affordable?
    so, to be clear: if I disconnect from battery 1, the positive cable that has everything attached to it (controller, inverter, battery #2) . . .

    ... and separate the cables (controller, inverter, battery #2), then at this point your system is safe. Though before you do anything, make sure your loads are not connected as Neil suggested and that your PV is not generating anything.
    and if I then disconnect the controller cable and inverter cable from the battery #2 cable, and from each other. . .

    The above is optional. Also, be careful not to short out your batteries. No positive should touch any negative.
    then it will be safe for me to work on the system, without disconnecting anything else (as long as it is dark, or the pv array is prevented from receiving light)?

    Well, working with batteries, even without anything wired to them requires precautions: googles, gloves, don't short out positives and negatives, no sparks. Maybe someone here can point out a good document on safe working with batteries. Given the information you've given us here then it should be safe.
    -Steve
  • greenthumb76
    greenthumb76 Solar Expert Posts: 40
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    Re: Battery cut off

    Here's what I read: http://www.grandpappy.info/wsolar

    Knowing what I know now, I guess he wasn't too wrong. But, when I read it (knowing nothing about solar), I went away thinking all I needed was a marine battery, cheap solar controller, a couple of panels and a 1500 watt inverter and I'd be able to use my microwave or 12 amp vacuum!

    It sure adds a lot of expense, when you figure in the proper cabling, connectors, fuses, breakers, etc. Not to mention that you have to have a pretty good sized battery bank to pull 12 amps, even for just 15 or 20 minutes!

    And I can't tell you how many hours I spent searching the internet for answers to the simplest questions, until I found this forum.

    I have spent about $700 and countless hours just to have a 110 watt mini system, that still isn't up to code. But, hopefully I'll soon have the right cabling in place that all I would need to do to upgrade, this summer, is to get another battery or two (at least until next winter, when more panels would be necessary).
  • greenthumb76
    greenthumb76 Solar Expert Posts: 40
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    Re: Battery cut off

    Out of curiosity--
    while it was dark tonight, I pulled out the fuse that connects the panels to the controller, in the hopes that, after disconnecting the batteries tomorrow, it would be ok to work on the wiring. Is it ok to disconnect the solar panels in this way?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
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    Re: Battery cut off

    Solar panels can be disconnected just fine... (or even shorted together). They will not be damaged.

    What will ruin a solar panel is to hook it up backwards to a battery--Solar panels are just "diodes" and will carry all of the current from the battery (dead short) and instantly become worthless (always check solar panel polarity before connecting them.

    What can be damaging is disconnecting solar panels under power with MC type connectors--it is possible that the arc (spark) from breaking/making contact will damage the connectors (these are small connectors).

    I have not read anything that this will cause damage--but I would error on caution and not unplug MC connectors when the solar panels are under load.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • greenthumb76
    greenthumb76 Solar Expert Posts: 40
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    Re: Battery cut off
    What will ruin a solar panel is to hook it up backwards to a battery--Solar panels are just "diodes" and will carry all of the current from the battery (dead short) and instantly become worthless

    I always check and double check, but still . . . that's a very scary thought.

    I guess, in spite of their cost, it is nice to have the MC connectors, for that reason. (There is a warning on the MC4 connector not to disconnect it when under load).

    I would have just disconnected them at the MC4 connectors, instead of pulling the fuse, but it's calling for rain. :D