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Old 01-19-2023, 02:13 PM   #1
live4fun
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Default Inverter Selection for TM2720- Solar Setup

I have 200ah capacity from 2 Lithium batteries (100ah) connected to (3) 100W rooftop Solar panels with a 30amp controller. I have very low loads, most everything is 12v/LED, and few AC loads for my system (air con. & microwave are all I can think of). USB plugs, chargers & computer/TV stuff is accounted for in the 12V loads.

Originally, I was going to purchase a small 12v autoplug 300w power inverter to have around in case I needed it for something (charging a drill, tire compressor, etc). i could also use it in my vehicle.

But I was thinking further that I possible could use our 700W microwave for 1-4 minutes occasionally every 2-3 days just for defrost or reheating foods. Would a 1000W to 2000W inverter handle this load sufficiently, and it be compatible with my solar 12v system as explained above?

What %SOC decrease or AH would you expect for a 1-4 minutes draw down on the batteries when used? Any ideas?

Question 2# If this larger inverter would work then; I assume this 1000W+ inverter would hardwired in my battery compartment instead of a 12v autoplug (next to my plug source). Then i guess I'd need an extension cord or a new 12AWG receptacle to my microwave location in the kitchen? Is that plausible? Are there other inverters or configurations that work better from this microwave use? I selected this lower wattage microwave thinking it might be solar/ inverter compatible.

Does anyone have a similar setup that could explain what you've done for this situation? All thoughts are much encouraged.

Let me Know, thanks Kurt
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Old 01-19-2023, 05:30 PM   #2
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For a 700 watt load, an inverter rated at 1000 watts (continuous) ought to be very happy.

Let's do some easy math, using round numbers.

While producing 700 watts for the AC load, the inverter would probably take 800 watts DC from your batteries, the extra happening because the inverter is not 100% efficient when converting DC to AC.

So the current out of the batteries is 800 watts at 12 volts, or about 67 amps. Call it 70 amps for ease of arithmetic.

You asked about amp-hours of capacity that would be used. If you draw 70 amps from your battery for 4 minutes, your consumption will be 70 x 4 = 280 amp-minutes, or about 4.7 amp-hours. Just a tickle for your 200 amp-hour battery set.

Now, how long will it take to recharge the batteries? You are pulling 70 amps from the batteries. Your 300 watt panels will generate 300 / 12 = 25 amps at full illumination. But to be conservative, you might want to assume that they generate 15 amps in partial illumination. This number is subject to a bit of tweaking, depending on time of day, cloud cover, what kind of charge controller you get, and so forth. But the bottom line result won't be a lot different.

So if you take 70 amps out for 1 minute, you have to put 15 amps back in for 70 / 15 = 5 minutes, more or less. If you take 70 amps out for 4 minutes, you have to put 15 amps back for 20 minutes.

Yes, you have a very conservative plan for the microwave. However, the air conditioner is a much bigger load, and I don't believe you will get there with the system you describe. I'll let the experts chime in about this, as well as information about installation of the inverter and related parts.

One other thing. A cigarette lighter 12-volt outlet is rated to carry about 10 amps max, so it is of no use to you in this situation.

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Old 01-20-2023, 05:08 PM   #3
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I have basically the same set-up that you have (230ah LiFeP04 - 400w solar)

I would recommend a 2000W pure sine wave inverter and forget about running your air conditioner. 2000W would allow you to run your microwave for about 5-minutes a day and coffee pot once or twice. I would not recommend getting anything less than 2000W. You will regret it in the long run. Just because the inverter is 2000W, that doesn't mean that it draws 2000W, it just means that it CAN draw 2000+W, depending on your load. It's better to have it and not need it than to need it and not have it.

I installed an ATS (automatic transfer switch) so that when the inverter is on, every 110V outlet in the camper is active (except the converter's charger). When I plug into shore power, the power from the inverter is shut-off and all of the outlets are live through the converter (including the converter's charger).

If you don't want an ATS, you'd be wise to just run an extension cord from the inverter to the devise that you want to power. Otherwise, you run into complications like burning up your inverter when you hook to shore power.

Check out the pic of my wiring. Take note of the wire sizes. Very important that you do not go any smaller on the wires with a 2000W inverter. BTW, I run a 110V dorm fridge (4.5 cu ft) 24/7.
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Old 01-25-2023, 10:05 PM   #4
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hey guys, I really appreciate the feedback and info. I was pretty confident my system would handle the short microwave loads since I’ve been observant to skinny down my use and loads whenever possible. its good to know how small the battery drain is.
That ATS switch is interesting along with the trying to understand the wiring for it. Without a detailed schematic diagram, fuse and wiring sizing, that setup would be beyond my capabilities to design and find the products. But it interesting to consider.
I have seen a few 1000w inverters that plug into a cigarette lighter plug and Ill look more into that or decide to run an extension cord. Either way, I’m very grateful for your opinions and it sheds a lot of light into how I handle my future loads and inverter. Thanks again, Kurt
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Old 01-26-2023, 09:05 AM   #5
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Quote:
Originally Posted by live4fun View Post
I have seen a few 1000w inverters that plug into a cigarette lighter plug and Ill look more into that or decide to run an extension cord. Either way, Iím very grateful for your opinions and it sheds a lot of light into how I handle my future loads and inverter. Thanks again, Kurt
I will try to help you understand the ability to run an inverter off of your 12V lighter socket.

Most lighter sockets are controlled by a 15A fuse. Some have a 20A fuse and a few may have a customized 30A fuse but I would never trust it.

If you have a 700W microwave (for example), the 1000W inverter will be maxed out because a cheap inverter is about 80% efficient, which means that it will really only run an 800W device but it will draw 1000W from your battery. 1000W = 83.3A @ 12V. While the microwave is running, the battery voltage will quickly drop to 11.5V which means that it will draw nearly 90A. Your 15-20A fuse will blow long before that.

Even if you buy a top quality, "Pure Sine Wave" inverter, the 700W draw would require about 60+A.

A cigarette socket type inverter will only be able to run a device that draws about a 200W device and then only if it has a 20A fuse. 200W won't drive much, absolutely no microwave, coffee pot or any other heating devise.
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Old 01-26-2023, 09:51 AM   #6
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Quote:
Originally Posted by live4fun View Post
I have seen a few 1000w inverters that plug into a cigarette lighter plug
I'm thinking that what you saw was a rating of 100w, not 1000w. As Wavery points out, the difference is not even close. At 12 volts, 1000w = 80 amps, which requires a wire more or else the size of your little finger, and contacts and connectors to match.

Sounds like a typo somewhere to me. If you can find a cigarette lighter inverter that boasts 1000w capacity, please let us know. It would be a big seller.

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Old 01-26-2023, 12:51 PM   #7
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I find that cigarette lighter outlets can barely even deliver 100 watts. It's such a poor quality connection, and that leads to significant resistance, and even at a 2-3 amps (24-36 watts) for extended periods (an hour or more), it can get pretty warm. And typically, cigarette lighter circuits are fuse protected at 120 or 180 watts, so drawing any more than that, if the outlet doesn't melt by then, the fuse would blow.

This all makes sense because these outlets were never designed with the intent of delivering power. They were designed to generate lots of heat to light cigarettes, and they are very good at that!

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Old 01-26-2023, 06:13 PM   #8
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Originally Posted by ShrimpBurrito View Post
This all makes sense because these outlets ... were designed to generate lots of heat ...
... FOR A VERY SHORT TIME !!

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Old 02-24-2023, 10:01 PM   #9
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Default LiFePo to Inverter Wire Size & More

Sorry to getting back so late. I was away for the month in Big Bend with poor service coverage. But home now. My solar system is working great and I average 7amp/h use per evening, so have plenty of battery capacity. I have a few lasting questions about the inverter.
1. If I located my new 2000w inverter <2 feet from my batteries, what AWG would you recommend for this 65-80amp load from my microwave? #2 or #4 wire at 12v?
2. Do I need to fuse protect the inverter along this circuit?
3. Iím planning to run 12g wire (to a new receptacle )or extension cord to the microwave 12 ft away for the 700w load. Do I really need to plug the microwave into a regular 120v receptacle (and unplug the inverter receptacle) when on shore power even if I only run it less than 5 minutes per day? It seems like I should be able to keep running off the inverter receptacle if my 5 min use per day doesnít change.

Do you see any conflicts? Thanks Kurt
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Old 02-25-2023, 10:31 AM   #10
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Quote:
Originally Posted by live4fun View Post
Sorry to getting back so late. I was away for the month in Big Bend with poor service coverage. But home now. My solar system is working great and I average 7amp/h use per evening, so have plenty of battery capacity. I have a few lasting questions about the inverter.
1. If I located my new 2000w inverter <2 feet from my batteries, what AWG would you recommend for this 65-80amp load from my microwave? #2 or #4 wire at 12v?
2. Do I need to fuse protect the inverter along this circuit?
3. Iím planning to run 12g wire (to a new receptacle )or extension cord to the microwave 12 ft away for the 700w load. Do I really need to plug the microwave into a regular 120v receptacle (and unplug the inverter receptacle) when on shore power even if I only run it less than 5 minutes per day? It seems like I should be able to keep running off the inverter receptacle if my 5 min use per day doesnít change.

Do you see any conflicts? Thanks Kurt
Welcome back.......

A 2000W true sine wave inverter is a good choice.

1. Your microwave will require about 100A while running and about 200A on start-up. If you total run from the battery terminals to the inverter terminals is 2', your total run (round trip) is 4'. This will require a minimum of 2G wire but that would be pushing it (never wise with electrical). I run 1/0 wire and all is well.

2. Proper fusing for lithium batteries is important. Proper protection for a lithium battery is a "T-Class, fast acting" fuse that is attached directly to the positive terminal of the battery and the positive cable attaches to a HD busbar, then a 1/0 battery cable to your inverter. I used a 350A T-Class fuse.

3. An extension cord or a separate outlet will work. However, you may want to wire your inverter to activate ALL of the 120V circuits in the camper. That would require an automatic transfer switch (ATS). If you're interested in doing that, let me know and I'll walk you through it, if you'd like.
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