240V Mini-split....thoughts?

[PNW_Steve]

Originally Posted by Rawlings

These Tesla batteries are 5.7kwh what would that be in amp hours and how long would that give your 12k btu ?

Divide the 5.7 kwh by the battery voltage.

Example: I have a 10.3 kwh battery.

10,300wh / 24v= 430 amp hours

How long that will run your 12k BTU air conditioner depends on number of factors. Efficiency and duty cycle are key.

[Booyah45828]

Originally Posted by PNW_Steve

Divide the 5.7 kwh by the battery voltage.

Example: I have a 10.3 kwh battery.

10,300wh / 24v= 430 amp hours

How long that will run your 12k BTU air conditioner depends on number of factors. Efficiency and duty cycle are key.

This here. Most mini splits are super efficient. But that doesn't matter if it's running at max capacity all the time trying to keep a black tin can cool in the texas heat. Turn your bus into a yeti cooler and you'd be surprised at how little electric it will require to keep cool.

Unless you follow someone else's build closely, only you can determine your energy requirements.

[Doktari]

Turn your bus into a “giant Yeti cooler”...that would be great but hopefully not at Yeti cooler prices. DIY prices might be affordable for me. I managed to add 2” more foam to the ceiling so there is a total of 4” on the ceiling and I foamed in a few of the extra big windows I didn’t want. Then added a 9000 btu, 220 volt mini split A/C. I had a 3000 watt Outback Power Sytems autotransformer laying around to step up the voltage from the inverter. With 2400 watts of solar it ran good for a couple months then started just blowing warm air. What the heck?!
With the white plastic on the roof it stays cool all morning and sometimes into early afternoon depending on how hot the day is. By afternoon it starts to heat up through the walls and windows and can be uncomfortable even in the generally mild Puget Sound region. I can imagine it would be intolerable further south or inland. Just by adding the 2” of foam to the ceiling helped keep it cool inside from late morning a few hours longer into afternoon.
I have a xantrex 4000 watt autotransformer if anyone needs one. It’s a bit rusty looking but should work ok.

[TJones]

Originally Posted by miscrms

Here is the list of specs I've put together so far on various higher efficiency mini splits. I'm only looking at the higher efficiency units as I'm trying to do the impossible and be able to run off solar. Even with 3600w of panels, a high efficiency Schneider split phase 240v inverter and a ~20kWh 48v Lithium battery pack it's going to be a challenge.

Besides the difference in BTU sizing and SEER rating does the difference in price between brands indicate any higher or lower quality components being used. Would this make any difference for longevity using the mini split in a mobile application which it really wasn't designed for?

Ted

[kazetsukai]

Originally Posted by Rawlings

Has anyone done something like this? We are willing to have a generator as backup for days with low sun. But would the battery be enough to keep the AC on for the night?

I have three of the aforementioned Tesla batteries in my rig. There are a few factors that play into this:

First, Tesla batteries are an array of 444 18650's in 6s74p configuration. 6s puts these "24v" batteries in the lower 24V spectrum- they're 3 ish volts lower than an AGM/lead acid 24V bank, and 6ish volts lower than a 48V bank. This means two things:

1) You NEED to charge them to voltages appropriate to their 6S configuration (25.5V in 24V config,, or 51.5V in 48V config maximum)
2) You NEED to balance them. If you charge the pack to 25V and one cell in the series is at 4.5V, you are damaging that cell.
3) Because of their lower voltage, most inverters will not be able to use their full capacity, cutting off at around 30-40%. 24V AGM banks range from 22V- 28.8V while these range from 19.8V-25.5V.

I saw a youtube video of a guy who put one of these in their rigs with what looked like no balancer and completely inappropriate wiring/etc. The day they moved in the lights went out for good and it was game over for them. The guy made lots of mistakes...

What really matters is maximum draw/wattage. This 9k split is what I want:

https://www.ebay.com/itm/9000-BTU-37...cAAOSwxHlcWaYh

According to the spec sheet, 500W is the rated input (maximum). Which means in theory I can run the unit at full tilt for ~10H, multiply that by 65% because of the battery's usable capacity with my inverter, is 6H per battery. I have three, so 18H of runtime at _full_ capacity AND at the max draw rating of the unit.

In the real world, I'd see > 24H runtime: I have good insulation, the unit will not always be running at its maximum rating, and even though I have other appliances, etc, most of my electrical is DC and quite power efficient. The biggest influence for me on runtime is how much I do laundry.

I plan on 2000W in panels, which should make up for any losses at night and then some on decently sunny days.