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Thread: Portable Emergency Power - Inverter

  1. #1
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    Portable Emergency Power - Inverter

    I live in Florida, where in the summer, power can go out for days. I am investigating the use of sealed lead acid batteries and a 12VDC to 120VAC inverter for temporary, portable, emergency power to keep the refrigerator going and microwave, phone charger, lamp(s) as needed.

    The 2000 watt continuous (4000 watt surge) inverter I purchased has 3 prong receptacles on it. I opened the cover and found that the ground terminal of the receptacle is connected to the case of the inverter. There is no ground lug on the inverter and no mention of connecting the inverter to ground. The pictures on the inverter show it used in vehicles, tent camping and home use.

    The ground issue prompted me to investigate the NEC. There are code related to photo voltaic inverts wired into the house wiring, but I do not see anything related to a free standing inverter, not wired into the house wiring. My search on the web did not produce anything.

    Questions:
    1. Are there electric code(s) related to Temporary Emergency Power systems that are not wired into the house wiring?
    2. Should I ground the inverter to a copper water pipe with a ground clamp and a wire to the chassis of the inverter?
    3. Other means of grounding like using a plug with only the ground wire connected. Plug into local outlet and other end wired to inverter chasis?
    4. The wire provided for connection from battery to inverter is #4AWG, 600V, 105 degree C, VW-1. 2000W/10VDC(minimum inverter source voltage)=200Amps. This seems a little small for the ampacity.
    5. The wire is also not marked as being UL., nor is the inverter. Is this a problem?


    Thank you!

  2. #2
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    I am closing this thread, in accordance with the Forum rules. This Forum is intended to assist professional electricians, inspectors, engineers, and other members of the electrical industry in the performance of their job-related tasks. However, if you are not an electrician or an electrical contractor, then we are not permitted to help you perform your own electrical installation work.


    If I have misjudged the situation, if for example this project is related to your work, then send me a Private Message. If you can show me that I am wrong, and that you are a licensed electrician (or at least a licensed apprentice), then I will reopen your post, and offer an apology for the delay and inconvenience.

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  3. #3
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    I re-opened the thread after the OP contacted me and explained.
    If you aim at nothing, you will hit it every time!

  4. #4
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    is it a gfi unit? what make/model is it?

    i would not connect anything from that system to the house system.

    why is the egc of the outlet connected to the chassis a concern?

    and just as fyi, you should not be looking at 12vdc inverter, you should be looking at 48vdc inverters.
    i would highly recommend you do a lot more research into what you are trying to accomplish.

  5. #5
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    Welcome. It's likely your inverter will decrease output once the batteries drop from 12V, so that's more like 166A max. Two, it *could* have terminals rated for 105* as well, and free-air cables give you more ampacity over what the (conservative) 90* column would allow.

    It's more likely the inverter mfg never intended for but 1% of their product to see 2000W continuous for any real amount of time and will eat the 25% or so of that 1% that blow up.

    I would not connect it in any way to your house wiring. Some of those inverters have 60V on each side (60V on hot, 60V on 'neutral', vs 120V hot and 0V neutral) so a connection from ground to neutral will result in a short circuit.

    Portable/free standing power like gas generators and electric storage (what you are making) are largely beyond the NEC.

    Google reviews on your particular inverter. Im surprised it doesnt have a UL listing, even a forged one.

    PS: you will need a lot of deep cycle batteries at full charge to run anywhere near 2000W continuous, unless you are getting them for free you're probably better off with a small gas generator cost-wise.
    Electricians do it until it Hertz!

  6. #6
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    an inverter should operate full rated output until drop-out input rating

  7. #7
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    Quote Originally Posted by indcontrols View Post
    I live in Florida, where in the summer, power can go out for days. I am investigating the use of sealed lead acid batteries and a 12VDC to 120VAC inverter for temporary, portable, emergency power to keep the refrigerator going and microwave, phone charger, lamp(s) as needed.

    I think you will need a lot more battery than you think.

    The 2000 watt continuous (4000 watt surge) inverter I purchased has 3 prong receptacles on it. I opened the cover and found that the ground terminal of the receptacle is connected to the case of the inverter. There is no ground lug on the inverter and no mention of connecting the inverter to ground. The pictures on the inverter show it used in vehicles, tent camping and home use.

    I see no need to have a grounding electrode for such a device as long as it is used temporarily and not connected to the house electrical system.


    The ground issue prompted me to investigate the NEC. There are code related to photo voltaic inverts wired into the house wiring, but I do not see anything related to a free standing inverter, not wired into the house wiring. My search on the web did not produce anything.

    probably becasue if it is not connected to the house electrical system the electrical code does not much care.

    Questions:
    1. Are there electric code(s) related to Temporary Emergency Power systems that are not wired into the house wiring?

      Generally - no.
    2. Should I ground the inverter to a copper water pipe with a ground clamp and a wire to the chassis of the inverter?

      You could but it would gain you very little.
    3. Other means of grounding like using a plug with only the ground wire connected. Plug into local outlet and other end wired to inverter chasis?

      bad idea. don't connect to the house system at all.
    4. The wire provided for connection from battery to inverter is #4AWG, 600V, 105 degree C, VW-1. 2000W/10VDC(minimum inverter source voltage)=200Amps. This seems a little small for the ampacity.

      It is probably OK since it is out in the air and a higher temperature rated insulation.

    5. The wire is also not marked as being UL., nor is the inverter. Is this a problem?

      Only if it bothers you.


    Thank you!
    I think you will find that the battery stack you need to do any good will make some kind of gas or diesel generator a lot more attractive.
    Bob

  8. #8
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    Quote Originally Posted by petersonra View Post
    I think you will find that the battery stack you need to do any good will make some kind of gas or diesel generator a lot more attractive.
    2kw for days? yep, needs a hefty batt bank, and 4kw fueled gens is way less $$ on TCO than a batt bank (safer too).
    @OP - does it need to be automatic turn on if poco power is lost, or is it manual 'on'?

  9. #9
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    Quote Originally Posted by petersonra View Post
    I think you will find that the battery stack you need to do any good will make some kind of gas or diesel generator a lot more attractive.
    Amen. I still remember leaving the dome light on in my Miata for 90 minutes and having to get a jumpstart. Anyone want to do the math on a battery powered inverter supplying even 1000W for 72 hours? Im getting 72kW-hr, divided by 12V, is 6000A-H of battery power.. not counting losses. 75 80A-H batteries? 10-15k or so not counting wiring...

    120V loads that draw 'virtually nothing' at 120V draw a magnitude of order (10x) more current from 12V, before losses, which will be substantial anywhere near the inverter or battery's ratings.

    Meanwhile his neighbor is running a loud $500 5kw genny from HF or the like for a few dollars an hour.

    OP would be better off eating out and replacing the contents of his fridge 2x a year from here to eternity than try to put together a battery back up that can run what he wants.

    FZ, I gathered he planned on using extension cords to the unit - manual on for sure (I hope?)
    Electricians do it until it Hertz!

  10. #10
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    hence why you do not use 12v
    use 48v

    but it would be a large batt bank.

    solar panels for daytime running of equip, small batt setup for night time lights. ez, cheap.

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