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Old 07-07-2020, 08:07 PM   #1
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Power Inverter without a fuse box?

I've done a lot of research on how to run electric to power the back of our skoolie but we were planning a trip before we are done with all of the conversions and I can't seem to find any info on my concern. We are installing a battery isolator, 2 deep cycle batteries, and a 3000 watt Xantrex power inverter this week. We are going to add a fuse box and finish the electrical work in the near future. In the meantime, can we use the power invertor as it is to power a small portable a/c unit? Specifically can we just plug the a/c unit into the power inverter which is connected to our auxiliary batteries with a battery isolator? We won't be running anything additional off of this power source until we've added a fuse box, and will only use the a/c while driving - when parked we'll use shore power. Any help is greatly appreciated.
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Old 07-07-2020, 10:16 PM   #2
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With a 3000 watt inverter to support, I hope your two batteries are rather large.

If your inverter has 120v receptacles versus hard wired 120v connection then you can plug into it without additional over current protection.
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Old 07-12-2020, 04:38 PM   #3
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Seems like your plan to use the portable A/C while driving or plugged into the grid (or a generator) should work. Iím guesstimating you will need about 75 amps at 12 VDC from the alternator to run the A/C. You may want to be careful about overheating the alternator while idling or in traffic jams. You may not get enough cooling air flow. Maybe turn the A/C off then. But if you have a large frame alternator it might not be a issue.
Your isolator should be at least 100 amp or larger. There are better options nowadays than a old fashioned battery isolator.
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Old 07-12-2020, 07:56 PM   #4
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Depending on your inverter peak start capacity and you AC start current this might or might not work. For "cheap " AC induction motors the inverter has to be oversized by a factor 5 to 10.
Only one way to try it out.
Good luck,
Johan
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Old 07-13-2020, 12:57 PM   #5
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Follow up

Thanks to everyone who answered, your replies are very helpful. I just have one other question if anyone would mind helping me out.

We bought a 3000 watt modified sine power converter and a 300 amp battery isolator. All we will be using on our upcoming trip is a portable air condition, so I know this is overkill, but eventually we want to install a fuse box for a refrigerator and a few other things, so we wanted to just invest in equipment with room to grow.

I know when we go to add additional items to the power inverter that we will need several batteries as well as an upgraded alternator. But for now, all we are running is one portable air condition (which I will unplug in traffic or any time the alternator seems to be straining). Even though the power inverter is capable of 3000 watts, if I'm running far less of a load on it, am I right that I can just hook up one deep cycle battery? I know this is not enough to power 3000 watts, but if we aren't using the inverter's full capacity, do we need to provide enough battery power for that?

My assumption was that we only need enough battery power for whatever load we were running from the inverter, but I wanted a second opinion.

THANK YOU VERY MUCH for all the help!!
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Old 07-13-2020, 11:49 PM   #6
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I believe you can do what you are assuming can be done but it is not recommended. If the battery, cables, fuses, etc are not sized correctly for the inverter then they may get hot, damaged, or catch fire. With only one battery you could also have a big voltage sag and the inverter low battery disconnect could become a nuisance. Or if the charge rate is too high the battery can be damaged and loose water. Is it a inverter/charger? Are you only charging with the alternator?
Your battery needs the reserve capacity and the inverter needs the surge capacity to start the A/C compressor. Soft start capacitors help with this. There are soft start kits people install in the rooftop A/C unit’s of RVs. I think the RV A/C are 12 amps@120VAC but not sure the starting surge. I’m guessing your portable is 8-10 amps running?
As previously mentioned you can try it and find out. See if it starts well. If it doesn’t work well add another battery. Is the battery new? What battery is it?
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Old 07-14-2020, 12:36 AM   #7
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You're not at overkill, you're at underkill. You don't have the battery bank to run a 3000 watt inverter, and it ain't even a sine wave unit. If you're thinking that the alternator will do the job, well that would be one trick set-up. What happens at a stoplight. And of anything that you need a fuse for, the inverter is at the top of the list.
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