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Old 08-04-2021, 01:03 PM   #1
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Power Inverter Question

I have 2 12-volt DC batteries in my 1997 Winnebago Brave 31RQ. I bought them recently, and upgraded to more powerful batteries. Based upon my reading, it appears that a 3000 W power inverter can run almost all appliances including a window unit air conditioner.

Iím planning on going up to New England and will not need to use air conditioning for much longer, and will probably not need one any greater than 5000 BTU. My question is, can 3000 W inverter only run the window AC and no other appliances, or is it enough to run that and others at the same time? Is there a maximum wattage without adding more batteries?

I have a gas generator that uses standard automotive gas and poles from the main tank. It is far too noisy to use very often, and not environmentally friendly and too expensive. Iím thinking of starting to add some solar panels little by little. I just want to know if anyone can recommend the best way to go about it so I donít buy something that ends up not being useful in the future. I might have to do some semi off the grid living, staying on friends properties and not having full hook ups.
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Old 08-04-2021, 01:04 PM   #2
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How many amp-hrs @12 VDC do you have.


That will determine how long you can run any load.
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Old 08-04-2021, 01:27 PM   #3
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Oh that’s a good question. How do I find that out?
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Old 08-04-2021, 01:40 PM   #4
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The specs for your battery will tell you. You need 2-6 volt batteries to get the amp-hrs specified usually about 200, so a 50% you have about 100 amp hrs. 2 100 amp hr 12 volt batteries will give about the same 100 amp-hrs useable.
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Old 08-04-2021, 04:02 PM   #5
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A hybrid inverter can boost the power of say a 2000-3000 watt generator or 15 amp shore outlet to start a and AC or microwave. After use of load is less will put chosen power load on inverter back into batteries. Victron and Magnum have 30amp... both started produce 50 amp RV pass through versions. Wiring 30amp for this take a bit more creativity.
The new 50 amp versions goes right in between shore power lines. These were in short supply though.
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Old 08-04-2021, 04:08 PM   #6
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Yup, the specs should either be on the batteries or on-line from their manufacturer.


Again, you want total amp-hrs at 12 VDC.



Easy math for 12 VDC batteries in parallel.


For 6 VDC batteries wired in series, each PAIR gives you the amp-hr rating of that pair (amp-hrs the same, voltage 6 + 6= 12 VDC).
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Old 08-04-2021, 04:54 PM   #7
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Forget the AC if you only have 2 batteries.

Book into a site that has power and be happy.

Sorry to burst your bubble. But someone has to.
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Old 08-04-2021, 05:12 PM   #8
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5 amps at 120 volts is 600 watts. That's about what your AC will draw.

600 watts at 12 volts is 50 amps. Your inverter will be say 95% efficent, so add another 5 amps. That's 55 amps per hour. Don't forget lights, TV, radio, etc. They all add up as well.

What are your batteries rated at for amp/hours? Total the 2 up and divide by 55 plus other uses. That will tell you how long your AC will run before the batteries are dead.

ps. running your batteries (guessing lead acid) down below 30-40% will shorten the life of them as well.

You will likely get away with the toaster or other short heavy draws. But not a long steady heavy draw.
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Old 08-05-2021, 07:29 AM   #9
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I'd suggest doing some searches on Inverter & Solar installations to educate yourself on what is possible with what components that are installed. Use the Search Box above and you'll get lots of hits.



I have four 6 volt batteries, 325 watt of solar, 2000 watt inverter. Can't run an AC but will run my residential refrigerator which has fairly low battery draw. On a really sunny day my solar will keep up with consumption but late in the afternoon I start depleting my batteries and will usually run my generator an hour or two to top the batteries off before going to bed. I may eventually install more solar but for now I will have to rely on my generator to top off my batteries along with conservative use of batteries.



I have read were people have installed a small AC unit in the bedroom and can run it off the inverters but you have to have battery capacity (6 or 8). PLUS you have to have a way to charge the batteries, either generator and or solar. My guess is ~1500 watt of solar but haven't looked at it close enough.


Again, do a search, educate yourself, and ask questions.
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Old 08-05-2021, 07:43 AM   #10
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There is no way 2-batteries of any kind will run anything but a small fan in your RV. And a 3000w inverter is capable of depleting those two batteries in a couple of minutes IF the wiring was adequately sized.

Your plan is just not possible let alone feasible. Full stop.
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Old 08-05-2021, 09:06 AM   #11
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Even with sufficient solar power to enable the A/C to run during daylight hours you would need adequate battery storage capacity or an alternate energy source, such as a generator, to power the A/C when the sun has set or the cloud cover reduces the solar panels ability to generate power. My coach has a battery tray that only holds 2 batteries so I could never utilize my batteries to run an A/C or other items that draws heavy amps.
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Old 08-05-2021, 09:26 AM   #12
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Agree with the others. Two 12v batteries will have a capacity of about 160-230 amp-hours, depending on size and condition. For maximum battery service life, you should only use about 50-60% of that before recharging, so figure you have about half that.



The 3000W inverter can produce plenty of 120v power if the batteries can supply it, but it takes about 11x as many battery 12v amps as the inverter output 120v-amps. Your batteries won't last long with any significant power draw on the inverter. The window a/c probably uses 4-5 amps @120v, thus the 45A-55A load on the battery. You might get an hour of runtime before the battery voltage drops too low for inverter use. If anything else is using power, the time gets much shorter.
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Old 08-05-2021, 09:31 AM   #13
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Quote:
Originally Posted by coachmanjay View Post
The specs for your battery will tell you. You need 2-6 volt batteries to get the amp-hrs specified usually about 200, so a 50% you have about 100 amp hrs. 2 100 amp hr 12 volt batteries will give about the same 100 amp-hrs useable.
Where did the other 100 AH go ?

No reason to stop at 50% , if you need to use more.

Here is a chart. The danger zone is 10%.
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Old 08-05-2021, 07:47 PM   #14
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Good advice. To make it simple, the inverter can run a lot including a 600 watt A/C, but the batteries are not even close.

Using the full capacity of the battery bank would be near 2000 watt hours. You will use that in a little more than three hours even if nothing else is running. Also, the inverter may trip "off" due to low battery voltage even before that.

For three hours, use the generator and charge the batteries at the same time.
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