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Thread: Combining two 8 AWG from battery to inverter

  1. #1
    Join Date
    Jul 2011
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    Riverside, California
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    16

    Default Combining two 8 AWG from battery to inverter

    Hi

    I bought 10 feet of electrical 8 AWG gauge wire. If I cut that in half can I combine them to have a total bigger gauge or will I need to buy a single bigger gauge wire? Each end will connect to one connector.


    My rig:
    Battery -> 2.5 feet -> 2500w 12v inverter


    Tech info from Sunforce Prosine 2500w inverter:
    8 AWG conductor diameter 0.1285 in. / 3.2639 mm
    2 AWG conductor diameter 0.2576 in. / 6.54304 mm
    - Solar Newbie

  2. #2

    Default Re: Combining two 8 AWG from battery to inverter

    Single bigger.. like ALOT bigger.. Im sure someone will pitch in here.. but your not even in the ballpark with #8 wire... you need 3/0 or 4/0 for that large of a 12v inverter... you really need to think about 24v/48v instead of 12v.

    Chris

    p.s. 2500watts/12v is over 200amps potential.


    Quote Originally Posted by gqroot View Post
    Hi

    I bought 10 feet of electrical 8 AWG gauge wire. If I cut that in half can I combine them to have a total bigger gauge or will I need to buy a single bigger gauge wire? Each end will connect to one connector.


    My rig:
    Battery -> 2.5 feet -> 2500w 12v inverter


    Tech info from Sunforce Prosine 2500w inverter:
    8 AWG conductor diameter 0.1285 in. / 3.2639 mm
    2 AWG conductor diameter 0.2576 in. / 6.54304 mm

  3. #3
    Join Date
    Jun 2003
    Location
    pittsburgh, pa
    Posts
    10,239

    Default Re: Combining two 8 AWG from battery to inverter

    although combining wires does give an equivalent gauge 3 points better, i would not advise you doing that with this inverter especially with that gauge of wire. a 2500w inverter at 12v can draw more than 200a through it and small gauge wires will introduce a severe voltage drop when high currents are present. i would not use less than #2 for this and #2/0 i think i'd at least prefer. if one goes by the nec at 90 degree c rating you'd need at least #3/0. you can see that in this wiki chart.
    http://en.wikipedia.org/wiki/American_wire_gauge
    edit to add: although the nec is clear that the minimum gauge would be #3/0, i assume that you won't be at the max 2500w very often and usually under 1000w most of the time or you soon won't have a battery bank left to speak of. #2 with a 2.5ft run at 208a will have a v drop % less than 2% and is why i mentioned #2.

    if you go with limiting the wattage of the inverter by putting in a circuit breaker or fuse the wire may be allowed to have a gauge appropriate for the current limit imposed. of course the wires should be as short as is possible too as long lengths will introduce more resistance and therefor a larger voltage drop. i went by a 2.5ft run to get less than a 2% v drop loss and getting that loss lower is very advisable.
    Last edited by niel; September 6th, 2011 at 11:40 PDT.
    NIEL

  4. #4

    Default Re: Combining two 8 AWG from battery to inverter

    Don't do this. It is a bad and unsafe practice to parallel inverter feed. If you parallel wires each must be fused according to its maximum current rating. Otherwise one may increase in resistance causing the load to shift onto the other - resulting in an overload of an individual wire before the whole circuit is overloaded to a point where the circuit protection trips.

    Furthermore:
    One 8 AWG wire can handle about 50 Amps. Two would handle 100 Amps.
    Wiring for an inverter should be based on its maximum output power divided by its minimum input Voltage. In this case 2500 / 10.5 = 238 Amps - more than double what two 8 AWG wires would handle.

    Do it right: get the bigger wire. You need at least 3/0 (000) and preferably 4/0 (0000). Five feet of that won't cost so much as to make it untenable. It would certainly be cheaper than starting a fire by overloaded a cobbed-up bunch of paralleled 8 AWG.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  5. #5
    Join Date
    Sep 2011
    Location
    Plant City, Florida
    Posts
    43

    Smile Re: Combining two 8 AWG from battery to inverter

    Quote Originally Posted by Cariboocoot View Post
    Don't do this. It is a bad and unsafe practice to parallel inverter feed. If you parallel wires each must be fused according to its maximum current rating. Otherwise one may increase in resistance causing the load to shift onto the other - resulting in an overload of an individual wire before the whole circuit is overloaded to a point where the circuit protection trips.

    Furthermore:
    One 8 AWG wire can handle about 50 Amps. Two would handle 100 Amps.
    Wiring for an inverter should be based on its maximum output power divided by its minimum input Voltage. In this case 2500 / 10.5 = 238 Amps - more than double what two 8 AWG wires would handle.

    Do it right: get the bigger wire. You need at least 3/0 (000) and preferably 4/0 (0000). Five feet of that won't cost so much as to make it untenable. It would certainly be cheaper than starting a fire by overloaded a cobbed-up bunch of paralleled 8 AWG.
    Above a certain size NEC permits paralleling of conductors and they may share a combined fuse size ( 1 fuse for total ampacity) However they must each be of equal length. My 2000W 12 volt Vector inverter actually recommends and has connections for parallel 2 awg. #8 is absurd of course.
    12 x 85W, OB FM80, 585 AH, MaxPower 75A 12V charger, 400W & 2KW inverters.
    I would quote NEC articles but @ $90 buy your own.

  6. #6
    Join Date
    Jul 2011
    Location
    Riverside, California
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    Default Re: Combining two 8 AWG from battery to inverter

    Thanks you all for your advise. I chose the 12v inverter so I can take it to places and use anyone's car to supply AC power aside from the home.


    I'll just re-purpose the cable to the Morningstar MPPT to battery then. I think that should work since the PV cable I bought is 10AWG going to the MS MPPT.


    Config:

    Siliken 2x 205watt/24 volt (in series) -> 75ft PV cable 10AWG -> Morningstar MPPT. -> x ft (allowable using 8AWG) -> Trojan T1275 battery -> (will get a bigger gauge) -> Sunforce 12v 2500watt inverter.
    - Solar Newbie

  7. #7
    Join Date
    Apr 2010
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    Near Phoenix
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    Default Re: Combining two 8 AWG from battery to inverter

    Hook that to a car battery and load it you will need some jumper cables in short order to get the car going again.
    My TED 5000 system
    Sticking it to the power company one watt at a time!
    60 Ningbo Electric 175 watt panels and 12 Canadian Solar 180 watt panels with 2 PVP 5200 Inverters

  8. #8

    Default Re: Combining two 8 AWG from battery to inverter

    Not necessarily, I could see using it to power a much smaller load than its rating, or a larger load while running the engine.
    12 kw Generac, Honda EU3000is, 4.2 kw APC UPS powered either by battery or a Prius. Really.

  9. #9
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    Default Re: Combining two 8 AWG from battery to inverter

    Quote Originally Posted by techntrek View Post
    Not necessarily, I could see using it to power a much smaller load than its rating, or a larger load while running the engine.
    Or a heavier load for a very short time.
    One note however re using with a car. If you use jumper cables to the battery, there is a big difference in resistance between the connection of jumper cable clamps and a good solid bolted connection, so if going the clamp route, expect the inverter to shut down due to low voltage if you apply more than a small load. Been there, done that and thought the inverter was defective, until I opened my eyes.
    1900 watts PV, (1000 watts PV feeding MidNite Classic 150; 900 watts PV + 160 watts micro hydro both feeding into a single shared Morningstar TS-MPPT-60) ; Xantrex Pure Sine 1800/12 for heavy loads; Xantrex Pure Sine 1000/12 on 24/7 for everything else; six Rolls Surrette 2 volt L16 @ 12 volts.
    Domestic hot water totally provided by the sun 8 months out of every year via thermal panel.

  10. #10
    Join Date
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    Default Re: Combining two 8 AWG from battery to inverter

    A 2500 watts inverter is beyond what power should be drawn for a 12 v inverter.

    Rule of thumb is 1000 watt to 1200 watts per 12v increment. The reason is keeping the battery cable current to a reasonable value.

    Assuming you have a massive enough battery so it doesn't collapse in voltage under such high current, for 2500 watts @ 12 v with 85% inverter efficiency will draw 245 amps at maximum power.

    For two 2.5 lengths of wire, total 5 foot of wire for pos and neg lines:

    two #8's in parallel, each line, will have 0.4 vdc drop, 3.4 % v drop, and 98 watts of wire heating.

    #2 each way will have 0.20 vdc drop, 1.6 % v drop, and 49 watts of wire heating.

    #00 each way will have 0.10 vdc drop, 0.8 % v drop, and 24.5 watts of wire heating.

    #00 is minimum wire size for 2500 watt, 12v inverter, 2.5 ft from battery.

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