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Inverter or Generator

  1. Jul 26, 2017 #1
    my name is Clay and I'm thinking of increasing my inverter in my RV ,from 160w to at least 1800w Invertor...($900) so I can run a oil heater at 750w drawing 2.3 amps or a Nutri bullet juicer rated at 900 watt, not sure what amps this draws,
    I have four solar panels on the roof and each one is 130 and is charging 2 x 12.6 agm batteries.
    My question is would I be wise to do this in fear of draining my batteries or would I be better to buy a generator ($2000 nz dollars) that can run these appliances,

    kind regards Clay.
  2. jcsd
  3. Jul 26, 2017 #2


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    Watts = volts x amps and watt hrs = volts x amps x hrs, so if you want to find out how long your batteries, if fully charged, will run those items take the amp hr rating of the combined batteries x their voltage rating and divide that by the watt rating of each of those items. That should help you decide which way you need to go.
  4. Jul 28, 2017 #3


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    Better to buy a heater designed for 12 or 24V but don't expect your batteries to run it for long. 750W is 62A at 12V so a 100AH battery would power it for about 90mins if you are lucky. A generator or gas heater would be much better.

    Using an inverter for the juicer should be fine as you won't be running it for very long.
  5. Jul 28, 2017 #4


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    You have two 100 AH batteries, for a total of 200 AH. At nominal 12 volts, that is 12*200=2400 watt hours. But for long life, never use more than 30% of that. So, figure 800 watt hours as the max you can draw from those batteries. Compare that with your load of 750 watts, you see that it gives you only a bit more than one hour.

    If you want to run that 750 watt heater 19 hours until the solar panels start generating again, you'll need about 35 of those batteries. Not very practical for an RV.

    But are you sure of your needs. You said "oil heater at 750w drawing 2.3 amps" that doesn't make sense. Are you heating your RV with oil? If so, why the big electric load? Once the heater is lit, it should draw almost no more electric power. 750w sounds like an electric space heater, not an oil burner. Or do you mean an electric space heater with a little oil reservoir to smooth out the heat? How did you calculate 2.3 amps?

    Running an electric space heater from the batteries of an RV or a boat is a very bad idea. You have to get used to consuming much less electric energy on the RV. I lived 12 years on a sailboat consuming only 600 watt-hours per day for two people, using 220 AH of batteries and 205w of solar panels. You need to get your consumption down to those levels.

    For heat or refrigeration, use propane, not electricity. There are small propane room heaters about the size and shape of an electric space heater. For entertainment, use a tablet and rechargeable Bluetooth speakers, not a TV. Electric should be for LED lights and to recharge your devices, nothing more. The AC is also not meant to be used when on battery power.

    Many RVers are unable to cut their electric consumption enough so they wind up depending on a RV park hookup all the time.
  6. Jul 28, 2017 #5


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    Unless you have a special need for pure sine wave, this inverter ($500.00 at the time I bought mine) has worked without fail for me (six years and counting). Battery capacity is the question you need to determine for your needs. I use 6 8d commercial batteries and have not had need for a greater storage.

  7. Jul 28, 2017 #6
    inverters run better at 48vdc input.

    general rule (derived from my own recent project/design/application), 200w continuous for ~8hrs needs 12v200Ah or 24v100Ah or 48v50Ah using deep cycle AGM to ~50% DoD.
    900w will run just under 2hrs (1800w less than 1hr) with any batt config mentioned before you need to put batts back on charger

    this general rule accounts for a ~89% efficient inverter. but as mentioned in other post, once you put inverter inline you are losing ~11% of your batt energy, best to use DC rated appliances/devices.

    from here OP should be able to figure out what's needed.
    Last edited: Jul 28, 2017
  8. Jul 30, 2017 #7


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    Perhaps he meant 3.2A?
  9. Jul 30, 2017 #8
    120vac * 6.25amp (all resistive heater) = 750w

    you need 10x that amps from a 12v source to feed that inverter + the ~11% losses of the inverter, so roughly 70amps of 12v.

    then you need batt capacity to run @70amps for any period of time.
  10. Jul 31, 2017 #9


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    Makes sense.
  11. Jul 31, 2017 #10
    I had oil heat at my home and it draws 900 watts as long as it is on, the igniter runs a 10,000 volt arc which keeps the oil lit. I changed to natural gas burner, a drop in replacement burner that also takes igniter power as long as it runs.
  12. Jul 31, 2017 #11


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    I think the OP means an oil filled electric radiator rather than an oil burning heater but I might be wrong.
  13. Aug 1, 2017 #12
    Oil burners I'm familiar with not only have an electric igniter but a motor that runs an oil pump and a blower to supply air for efficient combustion. I can believe the setup would take 750 watts. An oil-filled electric radiator would take more like 1500 watts. Yes, propane seems like a lot better way to go.
  14. Aug 1, 2017 #13
    I also have a van and would recommend not using battery power for anything big (ie heating or cooling).
    Use a gas heater or run the engine and use the RV heater.

    If you have a large invertor it will be very inefficient when being used at a low level.
    If you really want to do this maybe have 2 invertors one big and one small. Also good as a backup.
    And as mentioned you will need a LOT of batteries and solar panels to run it for any significant amount of time.

    Heating (and cooling) require a lot of energy compared to other electrical devices. Batteries have very low energy density so you need a lot of them. Gas and petrol have very high energy density.
    Last edited: Aug 1, 2017
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