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Old 07-08-2020, 04:15 PM   #1
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How to determine Inverter Size

I'm sorry if this has already been answered, but I need some clarification. I am calculating my power bank size, and I'm going to be using close to 800W of solar, with 3-4 100ah lithium batteries. My only question is how to calculate inverter size. Do I add up all of my watts using AC power that will be running all the time/frequently? The biggest wattage any of my appliances will consume is 1800W. I am planning on having a fully electric build (minus the actual bus part). This means I will have a water heater using 1300W, an induction stove using 1800W, a ninja foodi using 1460W, a convection oven using 1500W, and then the rest of everything using about 550W (give or take). Using the knowledge I have, I'm thinking i'll need about a 5000W inverter if I wanted to run a majority of these things daily. Just would like some clarification on the semantics of how the inverter works, thank you!
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Old 07-08-2020, 04:45 PM   #2
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hello

Sorry I can't answer your question, but I can tell you how you can figure this out...https://diysolarforum.com/. Maybe you have been there already?



There's a tab on that site called DIY Solar Blueprints. Study those, maybe buy Wills book. In a short time you'll have answers to all your questions.


There are other sites that are very helpful - but those guys on the DIY forum are super nice.


Good Luck
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Old 07-08-2020, 04:47 PM   #3
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Thank you so much!
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Old 07-08-2020, 06:54 PM   #4
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Originally Posted by emilymci99 View Post
Thank you so much!

Hey Em,


You are on the right track estimating and adding up all your AC power consumers. You want to think about the maximum concurrent AC power draw. You don't have to add all the appliances together just the ones that might be running at the same time. And you definitely want some overhead, as some appliances (especially things with motors, compressors, etc) draw a lot more power than they are rated for for short periods of time.


I second the recommendation to spend some time over at Diysolarforum. Lots of info over there and a really easy to use search feature compared to most forums.


A couple things to be aware of:
1. In my opinion there is no reason to even consider modified sine wave these days, spend the money on pure sine wave.
2. Especially with cheaper and off brand 12v inverters, ratings are often pretty inflated. In my opinion these inverters are best avoided but if you do buy one make sure to de-rate it in your head.
3. There are 'low frequency' and 'high frequency' inverters, both have strengths and weaknesses. Low frequency is much better at handling high surge loads, much more robust, and often a bit more expensive. Manufacturers rarely state low frequency, but if its big, heavy, bulky, with a high (~3x surge rating) and a built in charger it is probably a low frequency inverter. For your situation, LF probably makes the most sense.
4. 4-6000W sounds like you are in the right ballpark if you want to be able to run 1 maybe 2 appliances + the water heater (which I assume you won't be able to easily control) concurrently. What will your system (battery) voltage be? In my opinion 12V is not advisable at that power level.
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Old 07-08-2020, 06:55 PM   #5
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This paper from samlex (an inverter manufacturer) has a lot of good info in it
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Old 07-08-2020, 10:08 PM   #6
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Thank you, this helped me out a ton. I was reading through the other forum, and started to realize running a 12v system just wont work for me with that amount of wattage needed. I'm considering the transition to making my battery banks hook up to make 24V, then getting a 24v to 110v inverter. I'm wondering if I could also hook up a 24v to 12v inverter just to run my lights, fan, and then charging my devices using 12v dc. Or maybe split up the batteries, making 3 of them 24v, and the other one 12v. Other than that we're coming to realize the cheaper option would just be to use a 3000W 12v to 120v inverter, and only plug the water heater in twice a week or so to shower. Then just use each of our cooking appliances one at a time, unplugging before using something else.
I'm really not interested in using any gas or propane, as I don't feel comfortable having that in the bus.
Any thoughts would be appreciated!
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Old 07-09-2020, 07:58 AM   #7
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Thank you, this helped me out a ton. I was reading through the other forum, and started to realize running a 12v system just wont work for me with that amount of wattage needed. I'm considering the transition to making my battery banks hook up to make 24V, then getting a 24v to 110v inverter. I'm wondering if I could also hook up a 24v to 12v inverter just to run my lights, fan, and then charging my devices using 12v dc.

Yes you definitely can do this, this device is called a "dc dc converter" a "step down converter" or a "buck converter." a high quality one will be pretty efficient.


Here is a nice (and high current) name brand one


And a cheap no-name version


Also, a lot of 12v devices are actually 12/24 or there are 24v versions available so you should be able to find a good amount of equipment in 24v. check the input voltage to find out.
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Old 07-09-2020, 02:00 PM   #8
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Welcome Emily! Judging by your user name, appears that you may be a fellow MCI owner - congrats! We are the best!!

Good info from DZL. I've tried a couple of the cheap step down converters (from Uxcell on Amazon) and had terrible service life from them. Might just have been me - I purchased better quality (more expensive) and have had no problems.

Definitely a good move on 24vdc battery bank.
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