Battery Cables

SystemSystem Posts: 2,511 admin
I have 4 L16 (6v) batterys I want to wire in series and parallel. They are 420 AH each. I will be using a C40 charge controller and a 1500 watt inverter. What is the recommended wire sizes for these? I have a single 125 watt panel but plan to expand 2-3x. Thanks.

Comments

  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: Battery Cables

    So, please see the sketches here: http://www.smartgauge.co.uk/batt_con.html
    about a good way to connect your batteries.

    Now for the electronic part - you have (or will construct) a 12V 840AH "battery"
    You have a single 125W panel. For derateing purposes, consider it a 100W panel (specs by the same standards that put the "mileage" estimates on car windows.) and that you get 5 hours of "good" charging light a day. That's 500 Watt hours per day, MAX, that you can take, without draining the battery. (for the purists - yes there are other factors that add in here, but this is a rough est). The single panel is not very big, but it could run a 20W cf lamp all night, or a laptop (100W) for 5 hours. Or your microwave oven for 10 minutes.

    Knowing what your loads are, you have to decide on a pure sinewave or a mod sine inverter.
    There are several threads on how to decide, and how expensive the items are that you plan on running off the inverter.
    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 ,

  • System2System2 Posts: 6,290 admin
    Re: Battery Cables

    Thanks for the information and the web site to visit. I am still trying to decide on the inverter. Cost is a factor with me right now. I am leaning towards a 1500 watt MSW. A friend has a xantrex 1750 plus in like new condition he will sell for $100. Any thoughts
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Battery Cables

    The wire size for the inverter battery cables will be dictated by the size of inverter you fit, the inverter instructions should help, also remember to fit the correct size breaker or fuse within the battery inverter connection. The breaker or fuse is sized to protect the wiring.

    Its basically a similar story with the solar side. Decide what size solar charge controller you will eventually need to cover your final PV setup and if possible but just get one to cover the final PV count. Once selected its the the controller capacity ie 20-30-40-60 amps that will dictate the wiring and breaker-fuse sizing.

    Nigel
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Battery Cables

    Cable size can be calculated based on conditions of use, the NEC, and the cable specs. The inverter’s user manual usually contains guidelines for sizing the cable and the DC fuse or circuit breaker. Here’s a link to the user manual for the Xantrex 1750 Plus:

    http://www.xantrex.com/web/id/198/docserve.aspx

    You’ll need 2/0 AWG battery cables (minimum) for interconnections between the batteries.

    See: http://store.solar-electric.com/bainca.html

    MSW inverters are inexpensive, but they can cause some loads (i.e., motorized) to run hot and/or fail. Some manufacturers recommend against using MSW inverters for powering their products.

    HTH,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: Battery Cables

    What are your expected loads? When we know that, we will be able to offer recommendations on inverter, then go from there. Otherwise it's not unlike asking what size engine you should put in your truck, without knowing the size of your truck, or what you intend to haul with it. This post is not intended as a put down, or to be flippant, rather just trying to get at info required before proper help can be offered. There are definite disadvantages to using an inverter too large, or MSW vs Pure Sine. Some loads are OK on MSW, others will smoke within minutes, or even seconds. An unnecessarily large inverter will put excess drain on your system just to run the inverter, and with only a single 120 watt panel, that becomes very important.
    Cheers and peace
    Wayne
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Cables

    what size the cables will depend on the current passing through them be it the solar charging current or the loads and the distance that current has to flow. the current with a determined wire resistance will show what voltage will be dropped. that voltage drop should be kept low to reduce those losses and the percentage should be 2-3% or less of the battery voltage.

    noting the current rating of your battery bank to be 840ah you should be aware that this battery bank will require a large charging current. the charging range for most batteries will be between 5-13%. i seem to recall someone stating the recommended for trojan l16s to be 10% and that would be 84 amps. the minimum of 5% would take at least twice as long to charge the batteries with 42 amps of current. not meeting this current need in properly charging the batteries could result in diminished capacity or premature death to the batteries. splitting the batteries to make 2 seperate 12v banks is one possible way to cut the input current needs by 2 as you could be using one bank while the other charges, but keep loads down to the point that allows the other bank to charge before depleting the loaded bank to 50% capacity. the further you drain the batteries the shorter lifespan you'll expect to have from them.

    this was a general statement based on what was given by you. you may find the voltage drop calculator usable as the source of the electricity is irrelevant. you can find that link to the calculator in general solar topics in a sticky and you would need to use excel or its equivalent with it.
  • System2System2 Posts: 6,290 admin
    Re: Battery Cables
    What are your expected loads? When we know that, we will be able to offer recommendations on inverter, then go from there. Otherwise it's not unlike asking what size engine you should put in your truck, without knowing the size of your truck, or what you intend to haul with it. This post is not intended as a put down, or to be flippant, rather just trying to get at info required before proper help can be offered. There are definite disadvantages to using an inverter too large, or MSW vs Pure Sine. Some loads are OK on MSW, others will smoke within minutes, or even seconds. An unnecessarily large inverter will put excess drain on your system just to run the inverter, and with only a single 120 watt panel, that becomes very important.
    Cheers and peace
    Wayne

    No put down taken....this is meant for weekend getaways. I calculated about 750 watt hrs/day. This is probably high. Most of this is lights, a little tv/satellite maybe a dvd movie, fan, 5 minutes for toast, small radio. I can use the generator for bigger stuff if I need. I cannot see being off grid for more than 3 days max. The other days will be full charging days sun permitting.
  • System2System2 Posts: 6,290 admin
    Re: Battery Cables

    I calculated about 750 watt hrs/day. This is probably high. Most of this is lights, a little tv/satellite maybe a dvd movie, fan, 5 minutes for toast, small radio. I can use the generator for bigger stuff if I need. I cannot see being off grid for more than 3 days max. The other days will be full charging days sun permitting
  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: Battery Cables
    5ohSteve wrote: »
    I calculated about 750 watt hrs/day. This is probably high. Most of this is lights, a little tv/satellite maybe a dvd movie, fan, 5 minutes for toast, small radio. I can use the generator for bigger stuff if I need. I cannot see being off grid for more than 3 days max. The other days will be full charging days sun permitting

    Loads that can fry on a mod-sine inverter:
    tv/satellite
    dvd
    fan
    radio

    lights & toaster are OK with mod sine. (usually, I haven't heard of mod-sine frying CFL's)

    Your electronics and motor will really appreciate it, if you use a pure sine inverter. Perhaps the new MorningStar SureSine inverter (300W cont, 600W 5 min surge fanless) can run your electronics, and you can fire up the big squarewave inverter for the toaster when needed.
    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 ,

  • System2System2 Posts: 6,290 admin
    Re: Battery Cables
    mike90045 wrote: »
    Perhaps the new MorningStar SureSine inverter (300W cont, 600W 5 min surge fanless) can run your electronics, and you can fire up the big squarewave inverter for the toaster when needed.

    My thoughts exactly. I have 2 SureSine's and very impressed with them. Have big MSW for heavy loads not affected by MSW. Works fine for me.
    But I don't think things will work out for you with only one panel. Not enough to replace what you will be using AND properly charge the battery.
    Peace
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Battery Cables

    Couple of points, coming in in the middle of the thread, I confess I haven't read from the beginning.

    Cfl's do fine on Modified sine wave inverter
    I have run satellite modem, as well as router (inter) as well as charger for Mac lap tops. ( wouldn't trust my experiance with the electronics howwever!)

    I now use the Morning star sure-sine 300 and am very happy with it. My only complaint is a induction of noise on the AM radio, but since the cfl's do the same thing, and there is nothing on AM anyway I don't really care.

    As for using the toaster,,, " a few minutes with the toaster" would use much my daily average use combined. I suggest using a stove top toaster instead. I am still searching for a really good one. The best idea I have ever seen was a Coleman Canada catalytic heater that ran on a small disposable tank. Square in shape, w little shelf to hold the toast. Hasn't been made in years. I have looked on E-bay for years for one. A toaster of 800-100 watts for 6 minutes is somewhere in the neighborhood of 8 amp hours (12vdc) We use about 30 amp hours a day, for computers, small tool charging, internet, phone, water pumping and lighting. If we were to make toast for two we would use ~25% of our daily total. We live very comfortably with this, with good lighting, the radio and the internet on much of the day etc. Our big plus is no T.V. We also do run our big loads (water pump) during the day if possible.

    It's just like the shop tools. I didn't build my system for the big loads of shop tools that run a (relative) short time, but rather a system to run our house 24/7 without much need for the generator. The cost of a much bigger system to run the rare large loads make little sense.

    Good luck.

    Icarus
  • System2System2 Posts: 6,290 admin
    Re: Battery Cables

    I've also found the SureSine to produce noise on AM radio, but not nearly as bad as some of the MSW units I've used. One of those was so bad that it even made a bad buzz on the landline, corded telephone. That was bad.
    Re the cfl's, I used them for years with no failures on MSW, no problems, except for a slight buzz from the CF's that isn't there on the Sure Sine.
    Wayne
  • System2System2 Posts: 6,290 admin
    Re: Battery Cables

    your point about the toaster is well taken and it is something we could surely do without. My goal here is to offer a few comforts while enjoying the quiet of the mountains! Based on what I have been reading it seems like an investment in a pure sine inverter may be worth the money.
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