Square wave inverter to LFP battery?

pianotuna wrote:
Almot,

You won't find a 1000 watt inverter that can reliably do a 1400 watt microwave, with the exception of the units that have their own built in inverter--so you can "dial them down"

Let's start with the size of the battery bank, and the chemistry.

Don, this is going to be a backup for short periods at a time. I am on grid power now, seasonal setup, but, being Mexico, there are blackouts nearly every week. Usually 1-2 hours or less though locals reported that there was 2.5 days blackout once. I am running 120 AH LiFePo battery now with 500W solar. In blackout I will scrap the luxuries like microwave but compressor fridge is important.

Solar (slightly tilted) easily harvests 1000-1200 WH a day, sun is not a problem most of the time. Fridge and a few minor loads would draw 1300-1500 WH/day. Only fridge requires an inverter, other gadgets can wait. In normal operating mode fridge won't need more than 200 W but starting power could exceed 1000 W. Battery-wise neither 20A constant nor 100A peak shouldn't damage LiFePo and a humble 120 AH bank with 100 AH usable charge should last ~ 2 days. I would have to buy another 120 AH LiFePO if the fridge comes to be - Murphy law, rain and clouds just when the blackout starts, who knows... Anyway, looks like 1500-3000W PSW inverter.

X2 Amazon PSW 500W $70

Considering how far prices have dropped for PSW inverters, I don’t get why one would choose square wave while saddled with it’s very limited uses??

3 tons

Almot wrote:
I would be interested in something over 1000W if I get around to adding a residential fridge and possibly a separate small freezer. I hear that compressor start-up wattage could exceed 600W - and if both machines start at the same time and I happen to run a small microwave at this exact moment (1400W input), I don't even know what could be the total wattage, 3000W?

First, refrigerators, freezers, A/C and microwaves do NOT do well on MSW inverters. They will run hot, and are less efficient.

Sizing an inverter and battery bank for "worst case" starting current is not logical. Unplug the 'fridge when you want to run the microwave and vice-versa.

Almot,

You won't find a 1000 watt inverter that can reliably do a 1400 watt microwave, with the exception of the units that have their own built in inverter--so you can "dial them down"

Let's start with the size of the battery bank, and the chemistry.

pianotuna wrote:

Most batteries hate heat. MSW inverters do cause batteries to get hotter when charging at least on my laptops.

What sort of wattage do you want to run? I got a very nice 700 watt psw inverter from Victron for $109.00 about 5 years ago. They may be cheaper than that now.

Here is a 375 watt:

https://www.amazon.com/Victron-Energy-Sinewave-Inverter-VE-Direct/dp/B01N0W4H34/ref=sr_1_3_sspa?crid=31YUZ7H28E0TD&keywords=500%2Bwatt%2Bpsw%2Binverter&qid=1682215042&sprefix=psw%2Binverter%2B500%2B%2Caps%2C514&sr=8-3-spons&ufe=app_do%3Aamzn1.fos.f5122f16-c3e8-4386-bf32-63e904010ad0&smid=ALRPFGEN62HZC&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzUjlSQ0ZYVlVURFZXJmVuY3J5cHRlZElkPUEwNjg5NjA5M1BPTUFPMVlQREtLSCZlbmNyeXB0ZWRBZElkPUEwMDIyNjUxMzQzVUxHWEY3QkhSNCZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU&th=1

Point about heat is taken, thank you Don. I would be interested in something over 1000W if I get around to adding a residential fridge and possibly a separate small freezer. I hear that compressor start-up wattage could exceed 600W - and if both machines start at the same time and I happen to run a small microwave at this exact moment (1400W input), I don't even know what could be the total wattage, 3000W?

If it works for the loads you have (which never run very long) stick with what you have !

If you are looking for something that will run a heavier load (more than 500W) then get a true sine wave.

The sad thing is, with modern electronics, for inverters under 1000W, there there is really only about $10-$20 more parts going from a MSW to a pure sine wave. Even for BIG ones, the additional part are under $50 (unless you are going with a low frequency inverter).

Almot wrote:
I've been charging small electronics with a small $20 SQ for years.

I had a $20 square wave too. Nothing ran the same. Bricks and small batteries got hotter, lines on the tv screen. But then nothing really failed either. Maybe it would have been a matter of time.

Long ago switched to sine wave and all runs same as utility power.

For a large 100+ Ah LFP it would mostly be the charger I worried about.

Drawing power from an LFP to drive a square wave inverter is not an issue.

Almot wrote:
I was mostly concerned about battery charging with MSW. LFP battery in laptop and phone, NiMH in cordless drill. I am not running any electronics on MSW. The only piece of electronics that I've been running on it was a corded electric shaver, it has an AC-DC converter hidden in massive 110V plug.

Most batteries hate heat. MSW inverters do cause batteries to get hotter when charging at least on my laptops.

What sort of wattage do you want to run? I got a very nice 700 watt psw inverter from Victron for $109.00 about 5 years ago. They may be cheaper than that now.

Here is a 375 watt:

https://www.amazon.com/Victron-Energy-Sinewave-Inverter-VE-Direct/dp/B01N0W4H34/ref=sr_1_3_sspa?crid=31YUZ7H28E0TD&keywords=500%2Bwatt%2Bpsw%2Binverter&qid=1682215042&sprefix=psw%2Binverter%2B500%2B%2Caps%2C514&sr=8-3-spons&ufe=app_do%3Aamzn1.fos.f5122f16-c3e8-4386-bf32-63e904010ad0&smid=ALRPFGEN62HZC&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzUjlSQ0ZYVlVURFZXJmVuY3J5cHRlZElkPUEwNjg5NjA5M1BPTUFPMVlQREtLSCZlbmNyeXB0ZWRBZElkPUEwMDIyNjUxMzQzVUxHWEY3QkhSNCZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU&th=1

I was mostly concerned about battery charging with MSW. LFP battery in laptop and phone, NiMH in cordless drill. I am not running any electronics on MSW. The only piece of electronics that I've been running on it was a corded electric shaver, it has an AC-DC converter hidden in massive 110V plug.