Disconnects

CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
Would appreciate some opinions on disconnects, both AC and DC. I am building a small off grid system. I have seen some videos on the net of other people's systems, and have seen what looked to be some pretty simple disconnects, but am having trouble finding that same type. Not looking for anything fancy. Some of the ones I saw looked kind of like manual locking hubs on a 4 wheel drive. Maybe I am just assuming these are disconnects?

Please give recommendations on brands/models you have been satisfied with.
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Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Disconnects

    are you referring to the blue seas switch which is in the 2nd column and 3rd row down?
    http://www.solar-electric.com/nsearch.html?catalog=wind-sun&x=0&y=0&query=switch

    that is a hefty dc switch that would work well for a dc disconnect. for ac most do use the circuit breaker for a disconnect, but a heavy switch may also be used there too just as long as it is rated for the ac voltage. circuit breakers are also used on dc circuits and are quite nice for this, but few have the dc rated breakers. midnite solar carries some nice ones. think of a disconnect as a fancy word for a switch, but it can come in many forms than a conventional switch.
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    Yeah that's the one. Thanks.
    Now what would you need a battery disconnect for?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Disconnects

    so that accidents don't happen when working in or around the batteries and as a means of shutting it off otherwise. same thought behind your house circuit breakers as you can shut them off to safely work with those circuits.
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    So I guess I would put it between the PV panels and the charge controller?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Disconnects

    you could, but you also need it between the cc and the batteries not to mention a fuse in case of shorts. this is why many opt for the circuit breaker as it does both protect and switch on/off.
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    Seems like a simpler method. How do you know what size breaker to use?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Disconnects

    you may need to explain what it is that you have.
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    Yeah. Ive got
    - 2 panels (12V 140 watt each)
    - 4 golf cart batteries

    Morning star Pro star 30 controller

    Inverter:Exceltech DC 12V (sys) 171 A @ 13.8V (nom) AC 117V 17.1 A 60 Hz

    I don't know how to draw a schematic on my computer, so ill try to describe it here.

    The 2 panels have to be about 80' from the cabin, so I built a "dog house" about 10' from the panels where I will have inverter, charge controller, battery charger, and possibly battery monitor in. Batteries will be in separate compartment.

    I will then run 10AWG (30 amp service) outdoor cable the 80' back to the cabin where that end of the system (AC) is already built.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Disconnects

    ok then try putting a disconnect inside the shed for between the pvs and cc as you won't really need the fusing for 2 pvs there. you may want a disconnect in between the batteries and inverter along with fusing there. the inverter manual usually specifies a fuse size.

    now being the ac inverter is remote to you, you may want to put a disconnect at your place so that you can shutdown all ac power without running out to the shed. this is not required, but a good idea to do.

    as most of the wiring is at a 120v potential i believe the #10 will do just fine for you. if you can try to get some heavier wire to interconnect the batteries and the wire to the inverter. again the inverter manual will say the best wire gauge to use.
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    Great! Thanks. Ill take a look at that manual, I seem to have misplaced it...

    So since I'm looking for something simple would something like this be a good choice for between the panels and the cc?
    http://www.solar-electric.com/blseabaswon3.html
    It's like the one you suggested except it is a simple on/off rather than a 3-position. I only ask again in case you had a cheaper option, or maybe you no longer suggest this type since you have a better idea of my system requirements. Or maybe you had a specific reason for the 3 position?

    Yeah I've got some heavier wire for the battery interconnects. Haven't got the wire from the batteries to inverter yet.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Disconnects

    yes, you can use that switch or if you can find another of that type. i'm sure it will be fine also because the blue seas is rated quite a bit higher than you'll need, but you won't go wrong with that one. the 3 position switch is not needed as it was just representative of what you may have spotted so no need to read into that further on the subject.

    now the battery interconnect wire should be just as heavy as the inverter wire you will be using and i usually say 3 gauges heavier as a recommendation to keep a better battery balance electrically for paralleled batteries or paralleled strings of batteries. if you have to use a lighter wire then no further than 3 gauges lighter than that of the inverter wires for each battery string. for example if you use #4 (not a recommendation) for the inverter then #7 could be used on each battery string. now #7 is an odd number so one would be inclined to go to #6 in that case.
  • H2SO4_guyH2SO4_guy Solar Expert Posts: 213 ✭✭✭
    Re: Disconnects

    The switch you showed will work just fine, however, why not use a circuit breaker between the batteries and the inverter so you can have a switch and circuit protection as well. While you run your 80' of cable to the cabin consider prewiring the correct type of wire for a battery moniter like the Trimetric. If you add one later, and most people want to know the state of charge of their batteries without having to go 80' to the doghouse. That way it can tell you at a glance what you are working with. I have Exeltech inverters and they have many great points, but low voltage disconnect is at 10.5 volts, which can harm your batteries, so it would be good to know before the voltage gets that low. You could also get a low voltage disconnect seperate from the system, but that adds considerable cost.

    I use the Trimetric that I got from the forum sponser. If you pay attention to it you can make judgements based on the amp hours and decide when to run stuff to not kill the batteries. If you never get a battery monitor, it isn't that much extra to run wires to hook one up. Just download the manual and see what type wire you need for that length of run. You may be glad you did.
    12K asst panels charging through Midnite Classic 150's, powering Exeltechs and Outback VFX-3648 inverter at 12 and 48 volts.  2080 AH @ 48 VDC of Panasonic Stationary batteries (2 strings of 1040 AH each) purchased for slightly over scrap, installed August 2013.  Outback PSX-240X for 220 volt duties.  No genny usage since 2014. 
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Disconnects
    H2SO4_guy wrote: »
    run your 80' of cable to the cabin consider prewiring the correct type of wire for a battery moniter like the Trimetric.

    That is very good advice. You should be able to monitor the doghouse from your cabin. However, you must run a separate conduit for monitoring and control wiring. Low voltage monitor and/or control wires do NOT coexist happily in a conduit with power cables.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    Thanks for the advice guys. Would a 20 amp DC breaker work for between the PV panels and charge controller, based on the size of my system?
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    In looking for my inverter manual, it occurred to me that I never saw one. I don't think I ever got it. Not to worry, I printed one out from Exceltech's website. I found an appendix with the following figures for my model.

    XP-2000 / 12VDC
    Rated current amps: 193.3 A
    Peak current amps: 450.0 A
    The manual says this is what I use to determine fuse size, and that it should be located very close to the battery's positive terminal, but I'm unclear on what these 2 numbers mean in regards to fuse selection...
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnects
    Caveman wrote: »
    In looking for my inverter manual, it occurred to me that I never saw one. I don't think I ever got it. Not to worry, I printed one out from Exceltech's website. I found an appendix with the following figures for my model.

    XP-2000 / 12VDC
    Rated current amps: 193.3 A
    Peak current amps: 450.0 A
    The manual says this is what I use to determine fuse size, and that it should be located very close to the battery's positive terminal, but I'm unclear on what these 2 numbers mean in regards to fuse selection...

    193.3 Amps is the current draw at minimum Voltage & maximum Watt output: 2000 Watts / 193.3 = 10.5 Volts (+/- a bit) below which the inverter will shut down.

    450 Amps is the current drawn at the surge rating Wattage (4kW?) and minimum Voltage.

    Now, how do you interpret that for fuse sizing? Well, how often are you going to use it at peak capacity? How long will it supply full surge potential? Do you really need to size the fuse to take 450+ Amps? No. For one thing, and fuse or breaker will take more than its rating for a brief period of time. But more importantly you won't be running the thing flat out at maximum power and minimum Voltage, will you?

    Try this: 2000 Watts / 12 Volts = 167 Amps. Under most circumstances, then, a 200 Amp fuse will be adequate. If you find it isn't you can go up to 250. But the most important thing to remember is that the wiring must be able to handle more current than the fuse; you want the fuse to give up first should the current go high.
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    Great! That's simple enough. Was planning on using 2/0 or 3/0 wire since I have a short run to the inverter (wire wont cost much being short, and I might upgrade in the future).
    Now, what about the DC breaker between the panel and the charge controller? How do I size that? Same as the fuse?

    Is this a good inline fuse for between the battery and inverter?
    http://www.solar-electric.com/fb-200t.html
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnects

    Yes, the T2 fuse style works well for inverters.

    The wiring & circuit protection for the charge controller is based on its maximum output. Now, even though you might be putting only 30 Amps through a 60 Amps controller, it's a good idea to wire it for its maximum. That way you won't have to rewire it should you expand.
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    Awesome! I guess that's the last piece of the puzzle (for now haha). I guess I'll get one of these:

    http://www.solar-electric.com/mnepv.html
    the 30 Amp one because I have a 30A controller.

    Sooooo... I've got his so far;

    Panels
    Inverter
    Charge controller
    Battery charger
    Batteries
    Battery interconnects

    What I am about to order:
    Trimetric battery monitor and enclosure
    Deltec 500 amp shunt
    (4) MC4 extender cable
    (2) Multibranch MC4 connectors, 1 M-F-F and 1 F-M-M
    (1) solar module grounding lug
    (1) 200A fuse holder, bolt terminals with fuse
    (2) inverter cables (1 red, 1 black)
    (Blue sea battery switch, 300A used for AC disconnect)
    (1) Midnite solar MNEPV 150VDC Solar array breaker - 30A

    Anything you think I might be missing?
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Disconnects
    Caveman wrote: »
    (4) MC4 extender cable
    (2) Multibranch MC4 connectors, 1 M-F-F and 1 F-M-M

    IMHO, you only need one MC4 extender. You cut it in halves, and connect one part to M-F-F and the other part to F-M-M. The bare ends would go to the charge controller (or PV disconnect). How are you going to use four of them?
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    Well that makes total sense, since I have to cut one end off anyway to wire into charge controller, I think I also have to cut off one end to wire into panel, because it looks like this;
    Attachment not found.

    the connector ends would be used to connect with the (Y) branch connector thingy's
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnects

    These days most people buy panels with 'pig tail' MC4 connectors and sealed junction boxes. Hence the plan of buying an MC4 extension and cutting it in half, allowing the panels to be connected to sire terminals in combiner boxes or charge controller.

    You may find when you go to install you need to alter the plan a bit to accommodate the exact situation.
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Disconnects
    Caveman wrote: »
    Well that makes total sense, since I have to cut one end off anyway to wire into charge controller, I think I also have to cut off one end to wire into panel, because it looks like this;

    the connector ends would be used to connect with the (Y) branch connector thingy's

    You would need 3 MC4 extenders then.

    It's unusual that the panels don't have MC4 leads. But that gives you an opportunity to avoid MC4 stuff all together if you wish.
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    Gotcha, wasn't aware of the sealed box option....

    Thanks for all the help!!
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    I think I may have overlooked this.... what size wire do I need to connect charge controller to batteries? I have to go about 5 feet.

    Also, what size wire should I use to go from Iota batt charger to batteries? I have to go about 6 feet.
  • BB.BB. Super Moderators, Administrators Posts: 29,994 admin
    Re: Disconnects

    For a 12 volt battery bank, I would suggest to try and keep the maximum voltage drop on the wire around 0.05 to 0.10 volts maximum (2x for 24 volt bank, 4x for 48 volt bank).

    Using a generic voltage drop calculator (note, for 0.00 resolution, I multiply the feet by 10x).

    140 watt panels have:

    140 watts * 1/17.6 volts Vmp (guess) = 8.0 amps Imp

    And you have a 30 amp charge controller on a 12 volt battery bank. So, you have ~16 amps minimum and 6 foot run. Using this generic voltage drop calculator and plugging in 60 foot one way run (i.e., Vdrop will be 0.7 vs 0.1 round off) and the minimum AWG for 16 amps (16 amps * 1.25 NEC derating = 20 amp rated circuit) would use 12 awg wire minimum:

    -> 60' of 12 awg wire carrying 16 amps = 3.7 volts -> 0.37 volt drop on 12 awg wire @ 6 feet

    So, for 0.1 volt drop, we need about 4x more copper (or 1/4 the length)... there are 3 awg sizes for every 2x change in copper diameter:

    -> 60' of 6 awg wire @ 60' = 0.9 volt drop -> 0.90 volt drop @ 6 foot
    -> 60' of 4 awg wire @ 60' = 0.6 volt drop -> 0.06 volt drop @ 6 foot

    So--With 6 ft of cable (one way run), then you are looking at ~6 or 4 awg wiring to meet my recommendations... Of course, if you can get the controller run to 3', then you can go +3 awg smaller for same voltage drop.

    On the other hand, if you add another panel or so, you will need heavier copper wire.

    This is why we keep the wiring run from the controller to battery bank short and heavy... You don't want the charge controller to have 0.2 volt or greater voltage error when charging a 12 volt battery bank... This will slow down the battery charging quite a bit (14.7 volt is heavy charging current, 14.5 volts is less, 14.2-14.4 volts is pretty low charging voltage for a 12 volt flooded cell battery bank).

    Will it work with 6' of 12 AWG wire--Yes, you will just have a ~0.4 volt drop and significantly slow the charging of your battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnects
    Caveman wrote: »
    I think I may have overlooked this.... what size wire do I need to connect charge controller to batteries? I have to go about 5 feet.

    Also, what size wire should I use to go from Iota batt charger to batteries? I have to go about 6 feet.

    Biggest wire that will fit in the connectors usually solves the problem. :D
    Usually the manufacturers have recommended wire sizes for connections. Hard to beat them.
    Or check a wire gauge chart for current handling and then do a V-drop calc for the distance. Size up if needed. One such site: http://www.powerstream.com/Wire_Size.htm
    You always have to do a bit of interpreting. Remember a wire will handle higher current for less time, and mostly Ampacity is about being able to dissipate heat.
  • CavemanCaveman Solar Expert Posts: 83 ✭✭✭✭
    Re: Disconnects

    Thanks again for that explanation! Since it is such a short distance it wont be too expensive to overdo it, so I won't skimp.
  • Wis03BladeWis03Blade Registered Users Posts: 20
    Re: Disconnects

    I wanted to put a Blue Sea Battery Switch in to obtain the option to equalize either one of my battery banks ( that are now wired series then parallel) This way I can leave it on both banks ( 8- 6v Trojan in each string) when utilizing them, but have the option to switch to one or the other to equalize just one string. But the Blue Sea has a rating of 350Amps at 32 Volt max - I'm a 48 Volt system. the switches look like exactly what I need, with continuous connection, and with either both, one, or two , or off. did a search on battery selector switches for 48V came up empty. any ideas?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Disconnects

    odd i never noticed the lower voltage rating on it, but the straight on/off switch is rated for 48v. you would just need 2 of them to make it work.

    http://www.solar-electric.com/blseabaswon3.html
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