What Gauge Wire?

cswaite
cswaite Solar Expert Posts: 46
Currently the 45 watt panels I have are setting on our deck and I want to mount it up on the roof tonight or tomorrow. Currently I have a 19" 2AWG wire running from battery to 2000W inverter. In the inverter manual it noted to use 1AWG wire or smaller, I found 2AWG and figured it would be fine since I am not pulling a full 2000W or anything near that. Is this correct for me to assume?

Now my main question, I will need longer wire to run from battery to inverter since I plan on running from the ground (where the batteries will be) up through the window. I figure I would need about 10 feet of wire. I know you get voltage drop the longer the wires are.

My question, what Gauge wire should be used from battery to inverter to not only be safe, but to prevent voltage drop.

Thanks

Comments

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: What Gauge Wire?

    The gauge of the wire is strictly related to the current (in amps) that you expect to carry, and how much line loss you can live with. What is probably most important is fusing the wire for the smallest wire in the circuit.

    2000 watts @ 120 volts is ~17 amps. that same wattage at 12 volts is ~170 amps.

    If memory serves (and it often doesn't!) # 1 will carry ~120 amps,, #2 ~90, so you would want to fuse it with a maximum of ~90 amp fuse.

    If you are planning to send that many amps very far,, you should look at the voltage drop calculator in the sticky at the top of one of these threads.

    Perhaps the bigger questions is what are you going to power with this system,, and how well will 45 watts of Pv keep up that load?

    Tony
  • cswaite
    cswaite Solar Expert Posts: 46
    Re: What Gauge Wire?
    icarus wrote: »
    The gauge of the wire is strictly related to the current (in amps) that you expect to carry, and how much line loss you can live with. What is probably most important is fusing the wire for the smallest wire in the circuit.

    2000 watts @ 120 volts is ~17 amps. that same wattage at 12 volts is ~170 amps.

    If memory serves (and it often doesn't!) # 1 will carry ~120 amps,, #2 ~90, so you would want to fuse it with a maximum of ~90 amp fuse.

    If you are planning to send that many amps very far,, you should look at the voltage drop calculator in the sticky at the top of one of these threads.

    Perhaps the bigger questions is what are you going to power with this system,, and how well will 45 watts of Pv keep up that load?

    Tony

    Really since I only have 45 Watt of solar at the moment and (1) 125AH battery, I cant run a whole lot to begin with. I originally bought the larger inverter thinking I would be able to upgrade solar panels/batteries to run the window AC but that is out of the question.

    All that I run/will be running is (2) 32" LCD Tv's, a few small fans, and a couple CFL's.

    So are you telling me that the more power I am pulling through the inverter, the larger the wire I would need?

    What Gauge wire do you recommend with the above details about all that I am running would you recommend, if I dont plan on upgrading much in the future?

    Could I potentially get away with thinner wire, perhaps an 8 Gauge, or would I need the larger #1 or #2 Gauge even though im pulling such little power out of the inverter?

    Thanks much.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: What Gauge Wire?

    fuses or circuit breakers will make it safe and put that as close to the battery as you reasonably can. #2 is just a bit smaller in ampacity than #1 and i wouldn't worry too much unless you know you will be drawing the high wattages. for the record, you can't get rid of voltage drop, but you can try to minimize it. you can do this with thicker wiring as you already know, but the length of the wire also influences the voltage drop. this can be calculated using the voltage drop calculator in the sticky placed in the general solar topics area. if you have trouble using it then feel free to ask one of us to calculate it for you.
  • cswaite
    cswaite Solar Expert Posts: 46
    Re: What Gauge Wire?
    niel wrote: »
    fuses or circuit breakers will make it safe and put that as close to the battery as you reasonably can. #2 is just a bit smaller in ampacity than #1 and i wouldn't worry too much unless you know you will be drawing the high wattages. for the record, you can't get rid of voltage drop, but you can try to minimize it. you can do this with thicker wiring as you already know, but the length of the wire also influences the voltage drop. this can be calculated using the voltage drop calculator in the sticky placed in the general solar topics area. if you have trouble using it then feel free to ask one of us to calculate it for you.

    Yes, that calculator is very confusing to me, sorry.

    Would someone be kind enough to help calculate it for me.

    let me know if you need any information, and ill try to provide it.

    Thank You
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What Gauge Wire?

    Keep the inverter and batter close together... Build a small shed to hold both.

    If you need to run any wire a long distance--send the 120 VAC instead of the 12 volts... The current at 120 VAC is 1/10th that of 12 volts...

    P=I*V
    1,200 Watts = 100 amps * 12 volts = 10 amps * 120 volts

    Also--the large 2kW inverter may not be appropriate for your current system/panel setup... Many draw 20+ amps with zero load on them... A smaller inverter (i.e., 3 watt will waste 1/3 of that power or less).

    And a warning, I am going to guess that this is a 2kW MSW (Modified Square/Sine Wave) inverter. Not all loads like MSW outputs... The "square" wave can cause noise in receivers, motors to run hot, and many little electronics (such as wall warts and cordless drill chargers) to fail quickly.

    Don't really expect too much from your system--A typical 32 inch TV may take 165 watts, CFLs 13 watts each, small fan 50 watts:

    P=2*165w + 2*13w + 2*50w=456 watts

    Assuming the inverter has 80% efficiency and you have a 125 amp hour batter that you will run to 50% state of charge:

    Batt Capacity = 125 amp * 12 volts * 50% = 750 Watt*Hours

    750 WH / 456 Watts = 1.6 hours recommended maximum run time

    And you can actually expect less time because you have such a heavy load on the battery.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: What Gauge Wire?

    ok i'll use the 90a (about 1000w) example from icarus and a total footage of wire to be 20ft, being the run is 10ft. we get a v drop of .28257v and that represents a 2.355%. not great, but doable for that power level. if you were to go to draw the full 2000w then this will cause the v drop to double using the same 10ft run of #2 wire making it .56514v and the percentage is too high with that imo. (yes higher amps = bigger voltage drops) if the run of wire was reduced to 5ft for a total of 10ft of wire and you draw that 2kw this has the same effect of doubling the capacity as it can now handle the 2kw and give that same v drop of .28257v. does this help?
  • cswaite
    cswaite Solar Expert Posts: 46
    Re: What Gauge Wire?

    This is a lot of information im trying to digest. LOL.

    Should I be connecting the inverter directly to the battery, or should it connect from controller to inverter?

    Should I stick with the #2 Gauge, even though im not pulling much power? I wanted to keep the inverter in the room so I could easily turn on/off, and to keep it out of the 100-110 heat this summer.

    Will the MSW Inverter Blow up my TV?
    It makes a light buzzing noise when plugged in, even if it is not powered on. Do I need to invest and get a Pure Sine?

    Thanks, sorry if these questions were somehow already answered.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What Gauge Wire?
    cswaite wrote: »
    Should I be connecting the inverter directly to the battery, or should it connect from controller to inverter?
    All charge controller, inverter, other loads should Home Run to the main battery connection points (bus bars, battery lugs, etc.).

    The battery will be the "center" of your "Star" wiring system. All + wires that leave the common connection point should have a fuse/breaker appropriate for the gauge/current of the wire leaving the battery common point.

    Should I stick with the #2 Gauge, even though im not pulling much power?
    I wanted to keep the inverter in the room so I could easily turn on/off, and to keep it out of the 100-110 heat this summer.
    Wire can be sized for the loads--Use a smaller Wire/Fuse if you are not using 100% of the inverter output. However, remember that you will still have voltage drop issues with smaller awg wire--and especially with 12 volt / high current applications--any voltage drop will hurt badly (a 2 volt drop will not affect a 120 VAC system. A 2 volt drop on a 12 volt system will kill it from working at all).

    Will the MSW Inverter Blow up my TV? It makes a light buzzing noise when plugged in, even if it is not powered on. Do I need to invest and get a Pure Sine?

    Impossible to predict... It is likely that your TV will do fine (although perhaps some electrical noise in the video/audio and some noise from the power supply). 80-90% of the stuff will work OK on MSW, 10-20% will not (and frequently die an early death). Hard to tell which falls into which category.

    Yes, a True Sine Wave (TSW) Inverter is a better choice for many reasons... But frankly, they are not cheap--so people accept the limitations with MSW inverters and sometimes pay a price.

    One suggestion--get a small (Morning Star 300 watt TSW 12 VDC inverter) to run your small/critical loads... And use your big 2kW MSW to power lights, electric drills, pumps, etc. when needed.

    Frankly, with the current size of your system--the Morning Star 300 watt TSW inverter would be a much better choice (for 12 volt systems).

    Read these two Inverter FAQ's to learn a bit more about them:

    All About Inverters
    Choosing an inverter for water pumping
    Thanks, sorry if these questions were somehow already answered.
    Not a problem--this would be a very quite board if we only answered questions the first time--and told everyone else to "search" for answers.

    We try to be nicer than that here. ;)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: What Gauge Wire?

    A couple of 32" lcd equal what,, say 125 watt each = 250
    A couple of fans say 15 watts each 30
    A few bulbs,, say 15 watts each 45
    Total load 325 watts

    325 @120 vac = 2.7 amps
    325 @12vdc = 27 amps

    I would go with the largest size wire you can.

    (325 watts of load won't run very long from a 45watt panel, something like 90 watt hours/day net/net. About 1/3 of an hour).

    Tony
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: What Gauge Wire?

    Solar -> Charge Controller -> Battery -> Inverter

    The only thing you need between inverter and battery is the wire and fuses to protect the wire.


    2000w @ 12v = 167 amps = 16.7a @120v.

    It's pretty easy to create a 16a load with 120v stuff, so yes, I would stick with the big wire.

    Here's a handy table:

    http://www.powerstream.com/Wire_Size.htm

    You are doing power transmission. If the battery and the inverter were bolted into the same box, then you could probably get away with calling it "chassis wiring".

    Chassis wiring would require #3 minimum for that load, but power transmission would require 00 also known as 2/0 (2 aught) - not "Number 2", which is a much smaller wire or a thing kids do in the bathroom.


    MSW for any electronics is a crap shoot - some things burn out, some things don't. If it's a halfway decent TV, then you can either roll the dice with MSW or get a PSW and not worry about it.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What Gauge Wire?

    Boy, we are a chatty lot this afternoon! :D

    Cory--we have all been where you are at today... And we have all smoked equipment, boiled batteries dry, etc...

    We are all trying to help save you some of the mistakes and money that we have already spent on our eduction. :roll:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cswaite
    cswaite Solar Expert Posts: 46
    Re: What Gauge Wire?

    Ok thanks again for all the generous help.

    Sorry if im beating this too much,

    would you think if I had a total 10 feet (or less) going each from the + and - of the battery to the + and - of the inverter (total of 20 feet or less). Would I be better choosing a #2 or #1AWG, I just want to be certain that I am doing things safely.

    Also, as far as fuses go, do I just wire a fuse harness on the positive wire between battery and inverter? How do I determine which size fuse to use. You can tell im fairly new to all this but love learning new things.

    Thanks for the patience.

    -Cory
  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: What Gauge Wire?

    Agreeing with the others, but have a couple points from personal experience...

    Definitely go with the biggest wire you can. I have found, for 12V applications, even the wire sizing charts are perhaps to optimistic. They are primarily concerned with wire heating, to be sure you don't melt something down. The voltage drop induced by that at 120V isn't such a killer - well within the tolerance of most equipment. But at 12V, where there is so little overhead to work with, it very quickly adds up.

    My system is 12V, since I have a large collection of ham radio gear that runs off 12V. I started out using the wire sizing charts, but even the "power transmission" charts gave me more voltage drop than I desired - or would have believed. I now have some funky large wires feeding things now! :)

    And I decided to spend the money and go pure-sine inverters. It is rare something is just plain going to die as soon as it's plugged into a MSW inverter, the effects will be cumulative, and by the time you realize it's not a good match it's too late. I very nearly destroyed a laptop power supply on a MSW inverter recently, all my older laptops had worked just fine with it but after about an hour of use with this one I started smelling the "magic smoke". Surprisingly still working for now, but how long? Considering the cost of the items I wanted to plug into the inverters, I decided the cost difference was well worth it to not be replacing the items being operated. (Refrigerator, computers, LCD panels, etc.) As a bonus, I don't have to listen to that very slight yet still annoying buzz you mentioned! ;) In my case, it was coming from the CFL light bulbs.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: What Gauge Wire?
    cswaite wrote: »
    Would I be better choosing a #2 or #1AWG,

    Thanks for the patience.

    -Cory


    You should put the battery and inverter right next to each other. Put them both in the same box, slide the box under the mobile home to keep it in the shade, and run a normal 120v extension cord from the inverter to your TV.

    In that case you could use #2. If you knew for a fact that you would never hook up more than 13.5 amps of 120v load, then you could even use #4 which is smaller yet.


    EDIT: Forgot about the fuse. Here's what the fuse that you need looks like:

    http://store.solar-electric.com/infubr.html

    The fuse protects the wire. What size fuse you need depends on the rating of the wire you are protecting.

    For a "chassis wiring" situation, where you use #2 to connect from the battery to the inverter, then the wire is rated for up to 181 amps. Thus the fuse has to be 181 amps or less. The fuse has to burn before the wire does.

    So the perfect fuse would be 180a. But you might find that hard to get, so you might go with a 150a. Fine, but if you do, then you might as well go down to #3 wire since it is rated at 158a - which means a 150a fuse will burn before the wire.
  • cswaite
    cswaite Solar Expert Posts: 46
    Re: What Gauge Wire?

    Thank You everyone for your friendly responses.

    I think what I will end up doing is putting a box under the mobile home and have the battery right next to it (using about 19 inch #2). Than as mentioned run an extension cord up to the room, sounds like the voltage drop would be a lot less if I was to do it this way. Correct?

    Also, is it safe to have the battery and inverter in that close of proximity?

    I hope to expand and get more batteries and solar panels in the future. I do think I will get a pure sine as well, i dont want to risk blowing up our high dollar tv or anything else for that matter.

    Thanks a bunch.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What Gauge Wire?

    The battery box should be well ventilated (hyrogen)--as well as the inverter box (heat). Placing them in separate boxes is probably a good thing.

    Remember, you are placing this under your home--You don't want a fire "down below" to catch your home on fire. Remember, everything you do (running the wrong kind of extension cord, weather, sun, etc.) all can lead to risk of sparks/fires. People start wiring without paying attention to codes--but leave the system in place for years where sun/environment can really cause problems--exactly what the code was written to help protect against.

    Your 120 VAC current will be 1/10th (or less) of your 12 VDC current--so a standard 12 gauge wire from the inverter up into the home will be fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cswaite
    cswaite Solar Expert Posts: 46
    Re: What Gauge Wire?

    Just came to mind....


    What gauge wire do I need to run from the charge controller to the battery. I ordered a new charge controller. The one that came with the kit uses real thin gauge wire going from controller to battery, and attaches to battery with alligator clips, about as big round as pencil lead the wire is.

    I would think I would be fine using the same thin wire from controller to battery when I get my new controller, since my solar panels dont put out a lot of power??
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: What Gauge Wire?
    cswaite wrote: »
    Just came to mind....


    What gauge wire do I need to run from the charge controller to the battery. I ordered a new charge controller. The one that came with the kit uses real thin gauge wire going from controller to battery, and attaches to battery with alligator clips, about as big round as pencil lead the wire is.

    I would think I would be fine using the same thin wire from controller to battery when I get my new controller, since my solar panels dont put out a lot of power??

    What are the maximum amps that the charge controller can stuff into the batteries? Make the wire the right size to handle that amount of amps.
  • cswaite
    cswaite Solar Expert Posts: 46
    Re: What Gauge Wire?

    It's a 45AMP charge controller, but I should be fine with smaller wire until I add more solar panels, correct? Would I lose voltage from the panels to the batteries if I were to use larger wires now? The controller is rated for up to 750watts of panels, I only have 45 watts at the moment but may upgrade in the future to an additional 400+ watts of panels.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: What Gauge Wire?

    my answers in bold.
    cswaite wrote: »
    It's a 45AMP charge controller, but I should be fine with smaller wire until I add more solar panels, correct?

    correct, but you can also put in what your larger future needs would be in there now so you don't have to bother later.

    Would I lose voltage from the panels to the batteries if I were to use larger wires now?

    as i stated before, a voltage drop is always there and you just want to minimize it. a larger wire now does make it a smaller voltage drop.

    The controller is rated for up to 750watts of panels, I only have 45 watts at the moment but may upgrade in the future to an additional 400+ watts of panels.

    go for it and plan it out now so that you can more easily expand.