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I need an Electrical Engineer!!!

Discussion in 'The Garage' started by rockink5, Jul 13, 2006.

  1. rockink5

    rockink5 1/2 ton status

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    I am tring to hook up my power inverter and I can't figure out the fuse size calculation :doah: . Page 3-8 http://www.xantrex.com/web/id/627/docserve.asp . It calls for figuring out the shortcircuit amperage of the battery, is this cranking amp? that would be 800. next does that meen an 800 amp fuse :eek1: :eek1: :eek1: . I DON'T UNDERSTAND!!!! I'm sure someone else uses or has a power inverter in there truck, what did you use? Or maybe someone can decipher this.
     
  2. guido666

    guido666 1/2 ton status

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    Are you mistaken? The short circuit amperage of a 12V truck battery is in the 1000's of amps! What Watt rating is your inverter? Watts = Amps x Voltage. So take the peak Wattage of your inverter, and divide by 12 (volts) and that will give you the peak amperage your inverter can draw. Put a fuse in that is close or slightly higher then that.
     
  3. guido666

    guido666 1/2 ton status

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    I looked at the manual, it says it is a 1000W unit (correct?). 1000W / 12V = 83.33A. 83A is a TON of current, probably more then your alternator even puts out. I would stick a 60A MaxiFuse in there or something and see if you blow it.

    As an aside, I would wire it straight to the battery [using a relay system if you want it to turn on/off with the ignition switch] and wire it with some heavy cable, maybe even thin battery cables if you can get a good deal.
     
  4. guido666

    guido666 1/2 ton status

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    Wow [sorry for triple posting], this thing sucks ridiculous juice. It's talking about using multiple batteries and circuit isolators, like winch manuals do. Maybe it would be worth the effort to install like a 100A fuse. If the battery short circuits, it is going to draw incredible power, 1000's of amps. A fuse above the peak draw of your inverter, but nowhere near the short circuit current of the battery will be fine so long as you don't have anything else on those circuits and you have thick cables and connections to handle whatever current the fuse blows at.
     
  5. 4xcrazy

    4xcrazy 3/4 ton status

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    well, usually, an invertor will have a built in circuit protection anyways, if anything loads upp too much for the invertor, it will kick off and into safe mode...

    i think an inline fuse, would really only be needed to protect from battery to invertor wiring that may short out.

    i'd just run like a 60amp fuse inline.
     
  6. guido666

    guido666 1/2 ton status

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    Like 4xCrazy said, I think I would start with a 60A fuse and see what happens. That would protect long before the inverter even reached the 1000W it's rated for. It would be very smart to get a fuse solution that have larger [100A] fuses in the same package format, so that if you find yourself blowing the 60A because you've just got to have that camping-microwave, you can just pop in a 100A without having to change out fuse holders. I think there are MaxiFuses that go up to 100A if I recall.
     
  7. rockink5

    rockink5 1/2 ton status

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    Yes it 1000 watt inverter, I couldn't make head nor tails of that whole thing, thats why I've taken a year and a half to do this.The cables are plenty big, 1/0 or 2/0 cable, I don't remember.The fuse thing for some reason is killing me. I had been told 1 amp for every 10 watts, that would make it 100 amps, but reading that thing I was thinking I was wrong. Being . The inverter has a on/off on it with a circuit protector, should I still put a second switch in at the battery too? I am going to fuse it there. But didn't think about a second switch.:dunno:
     
  8. Metrodps

    Metrodps Strange but nice guy Premium Member GMOTM Winner Author

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    OK me stupid why the frell would you need that large of one. I just have one that I plug into lighter adapter and clip to battery. I only use it for a drill or coffee maker. We did use it for a tv once.
     
  9. rockink5

    rockink5 1/2 ton status

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    Nothing like camping in the wilderness and busting out the electric homemade ice cream maker :waytogo: :waytogo: . We use it to fill air matresses, run a blender, things like that. I've always used my buddies but he sold his truck so it was time for my own. 1000 watts really isn't that big. And for what it costs why only by one that is like 250 watts. I think it only cost me 100 bucks at cosco, and its a good unit.
     
  10. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    Are you going to use the full 1000w? If so, you will be pulling 83+ amps (the inverters are not 100% efficient, only like 85%, so add another 15% to the 83).
    . Where are you going to mount it? If it came with cables, it probably came with 2ga cable (2/0 would be way huge for that). 2ga is good for 181 amps, more than you need. It will take way more for short periods of time (duty cycle or in case of inverter usage, surge). 2/0 (or 00) would be way huge.
    Your 1000w inverter probably surges to 1500w (to start motors and such),
    I'd put it on a 150amp fuse. 99% of the time, your not going to be using that much of it (laptop =80w, coffe pot 400-600w, tv 200w). If your using motors, they like the juice, especially at startup.
    I didn't put my 500w on a fuse. It's kinda of pointless to put a 120 150 amp fuse, if it shorts out at 80amps, it's going to spark anyway. The purpose of the fuse in this case would be to protect the inverter or battery incase of a short. If your mounting it close to a battery, I'd say definly no fuse required. It's your call though. Your starter cable isn't on a fuse, it draws about 80-100amps. If you did fuse it, go with a 150. If your not going to use the full 1000w, fuse it down at 80 or 100. Fusing it adds 4 high resistence terminations in the line (wire to terminal, terminal to fuse, fuse to terminal, terminal back to wire), causing a larger size wire to be required.
    The reason the manual goes into all that detail is because people use battery banks (like a large boat, or an off-the-grid home), so they include text for various setups.
    You are pushing the limits of your alternator and battery with a 1000w inverter, if you run it full titl for any period of time, you will drain the battery, even if the engine is running, unles you got a high-output alernator.

    Here's a rough wire size chart for you to automotive usage. Note that
    http://www.powerstream.com/Wire_Size.htm
    Go with the chassis wiring column.
     
  11. rockink5

    rockink5 1/2 ton status

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    Thank You!

    No, it will not probably never see the 1000 watts it's designed for. Its mainly there just for conveinence. I just wanted it to be fused correctly. It' s mounted in the the back,behind the rear panel that I made an access panel in.It's farther than the 5ft recommended distance, thats why the wire size,(1/0?).
     
  12. broke73

    broke73 1/2 ton status

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  13. guido666

    guido666 1/2 ton status

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    This will only suffice to protect circuits on the AC side. You will still need the large fuses mentioned above [60A-150A depending on what you want to go with] for the wiring on the DC side.

    The reason a company puts a 30-35A fuse on there is because it is greater then the peak current throughput of the device (inverter), but won't break it.
     
  14. goldwing2000

    goldwing2000 Guest

    Ummm... did you read table 3-1 in the manual? That pretty much spells out what you need.

    Recommended DC Input Wire Sizes & Lengths

    Cable length: Battery to inverter (one way): Less than 5 feet (1.5 m) Minimum
    Cable Size: No. 2 AWG
    Maximum Battery Fuse Size: 150 ADC

    All that crap about battery short-circuit voltage is just a bunch of useless info. Everything you need to know is in step 3 of that section:

    3. Pick the fuse/circuit breaker’s current rating based on the product used: 150 Adc

    You'll also notice that they recommend two or four deep cycle batteries to actually power this thing.
     
  15. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    If your running on just batteies, yes you need at least 2, four would be better. That setup is recommended for RV's or boats where people would sit for many hours running off the inverter at near full load.
    In a K5 though, one is probably fine, especially if your not running it at full load. It should be kept in mind though, that even with the engine running at idle, most alternators only put out about 1/3 of thier rated output, so in order to sustain full load on the single battery for any period of time you need some RPM's going on the engine.
    But, you can always make your own calculations on how long your battery will last. For instance, my Optima D31 has a 75amp hour rating. So, if I'm using my 500w inverter at full load with the engine off,
    (AC Watts divided by 12) x 1.1 = DC Amps
    so 500/12x1.1=45.8amps]
    Then take Amp Hour rating of battery/DC loaded amps
    75/45.8=1.6hours of runtime at full load.

    Keep in mind the optima D31 is the biggest single battery available. Amp hours are different than cold cranking amps. Some batteries (cheapones) don't list amp hours in their ratings.
     
  16. pvfjr

    pvfjr 1/2 ton status

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    I've got a 135 AH battery with a 1000W inverter wired with 2/0 and no fuse. The inverter has all the circuit protection which works quite well. I've tripped it a few times using the big angle grinder or the sawzall. Been working well for me, no problems at all.
     
  17. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    135ah?! What battery is that?
     
  18. goldwing2000

    goldwing2000 Guest

    So with all this hassle and extra wiring and mega fuses and whatnot, wouldn't it be easier to just get a small 1000W generator? Then you don't have to worry about crapping out your alternator, buying extra batteries, shorting out your electrical system... or whatever.

    I guess it would depend on what you plan to use it for.
     
  19. u2slow

    u2slow 1/2 ton status

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    Fuses also have an "interrupting rating" in addition to the normal rating. This is the amount of current flow (i.e. fault current) it can safely protect from. Its either noted in fine print on the fuse, or in the mfr's documentation.
     
  20. willyswanter

    willyswanter 1/2 ton status GMOTM Winner

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    Yeah as stated, they want a 150 amp fuse and a minimum of #2 wire. Thats what you use, period. The total short circuit capacity they are having you calculate just gives you the number that the fuse needs to be able to hold back in case all hell breaks loose. Most any 150 amp fuse will have the ability to hold this since most are rated in the 10's of thousands of amps.
     

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