16-SEER-12000-BTU-Ductless AC/Heater -- What do I need to hook this up?

[bcroe]

Its interesting, but a pure sine wave isn't the ideal input waveform for a DC rectifier, such as the mini has. A square wave might
work better. Besides higher SEER, I see the minis as a way to decentralize my heating/air cond. Right now my propane furnace
and heat pump all depend on one air blower motor; a failure would affect everything. With several mini splits spotted around one
failure wouldn't kill everything. As hard as I'm working my heat pump, I fear a failure could take out not only the unit, but my energy
reserve if not used on schedule.

I really need to get a mini going, then see just how that DC rectifier section is set up. Feeding it from both the line and an array
would not only be more efficient, it would allow some more energy collection not passing through the grid tie. Bruce Roe

[KMac]

Ok, First, my 1600 sf 35 yr old home with raised ceilings does have some extra insulation and I replaced a lot of windows, doors ect so it's much better but not super well insulated. There is another solar forum I hang on occasionally with several very knowledgeable people who either have mini splits or design solar systems so their customers can add a mini split. Several discussions about subjects such as how to regulate the mini split on low solar days (often using a relay hooked to the inverter or controller AUX) and ways to maximize current draw while keeping the home temperature acceptable and still getting the batteries into absorb early in the day.

While a lot of people on that discussion board ask about 120v and 48v mini splits these guys generally think 240v mini splits end up being the most efficient way to go because the modern inverters in the mini splits are very efficient so little advantage for a more expensive 48v setup and 120v mini splits are few and far between so not many high efficiency choices. With solar power and batteries efficiency is important.

Price vs efficiency and a name brand with a 7 yr warrenty is why I went with the LG 1.5 ton with 9,000 and a 12,000btu heads (about $2130 now, a bit less last year) By the size of the house I should have gotten a 2 or 2.5 ton unit but went with the smaller unit to make sure my solar battery bank could handle it at night. I'm more than satisfied with the smaller 1.5 ton unit with the 9,000btu head in the master bedroom and the 12,000 btu head at the other end of the house in the living room. Each head has it's own controls and timers so you can tinker with them to suit your temp and energy preferences.

̴I only run 1 inverter, a Conext XW6848. Judging by the 1300 watt max draw when on turbo cool a 1500 watt pure sine wave inverter should be able to handle my mini split.

Excellent, and your system seems sized just right for it. One 1500 watt inverter for two mini-splits is quite impressive! I guess that highlights the benefits of low startup draw and highly efficient machines.

It can remain very warm at night in summer here and so there is little choice but to run climate control if you want to sleep comfortably indoors, but on batteries without an automatic generator start one has to have a good plan not to drain them too far, while sleeping. I know you mentioned discussion about that follow solar days, but do you use a monitor estimating DOD or amps in/out for you, and/or a relay to alarm or shutoff if it gets too low?

[KMac]

Its interesting, but a pure sine wave isn't the ideal input waveform for a DC rectifier, such as the mini has. A square wave might
work better. Besides higher SEER, I see the minis as a way to decentralize my heating/air cond. Right now my propane furnace
and heat pump all depend on one air blower motor; a failure would affect everything. With several mini splits spotted around one
failure wouldn't kill everything. As hard as I'm working my heat pump, I fear a failure could take out not only the unit, but my energy
reserve if not used on schedule.

I really need to get a mini going, then see just how that DC rectifier section is set up. Feeding it from both the line and an array
would not only be more efficient, it would allow some more energy collection not passing through the grid tie. Bruce Roe

I am curious what you mean that pure sine wave is not as good for rectifier in these? I have been under the impression that psw is better. Can you elaborate on the reasoning a bit?
Thanks

[bcroe]

I am curious what you mean that pure sine wave is not as good for rectifier in these? I have been under the impression that psw is better. Can you elaborate on the reasoning a bit? Thanks

A sine wave is great for many things such as transformers and induction motors. But turning it into DC power is
a bit clumsy. Take a psw from a voltage source (in theory infinite current capability) and drive a diode connected
to a capacitor, charged to somewhat less than the psw peak. As the sine starts to rise from zero, no current flows,
because the cap is charged to a higher voltage. Eventually the psw exceeds the cap voltage, and the diode conducts.
There is a big surge of current as the psw does its best to yank the cap voltage up to its peak. The surge is big
enough that the resistance of all real world components eats into efficiency. It only happens on one polarity of
the psw, half wave rectification.

Shortly after the psw starts to decline, the current drops to zero till the next cycle. So the energy transfer to the DC
side happens in a short fraction of the time, increasing losses and giving a very poor power factor. With a full wave
(2 diode) version things are somewhat better, the cap doesn't discharge as many volts into a DC load. 3 phase is
even better. Things like chokes can be added to improve things; they work best when tuned to a fixed DC load.

If we had a square wave source driving 2 diodes (full wave), the diode would begin conduction at the beginning of
the wave and be nearly continuous through the half cycle. When the other half of the square wave comes, the
other diode continues to conduct in a nearly continuous manner overall. Ferro resonant transformers approximate
this and have been used in certain premium DC supplies.

Of late the power switching technology has attacked this problem. A switching front end can cause the supply
current to more nearly follow the voltage waveform; that is, a much better power factor. I'm aware of improvements,
but not nearly up to date with them. Bruce Roe

[John Galt 1]

Excellent, and your system seems sized just right for it. One 1500 watt inverter for two mini-splits is quite impressive! I guess that highlights the benefits of low startup draw and highly efficient machines.

It can remain very warm at night in summer here and so there is little choice but to run climate control if you want to sleep comfortably indoors, but on batteries without an automatic generator start one has to have a good plan not to drain them too far, while sleeping. I know you mentioned discussion about that follow solar days, but do you use a monitor estimating DOD or amps in/out for you, and/or a relay to alarm or shutoff if it gets too low?

At this point I haven't installed a relay to control the mini split during cloudy days and really haven't needed one. I've got an SOC monitor but often back it up with a SG reading in the morning. As far as power draw goes keep in mind that while the mini split may draw 1300 watts for and hour or two cooling/heating the home it then reduces it's draw to as low as 250 watts (6 amps) as it maintains the house temperature. Sometimes going up and sometimes going into standby using less than 30 watts so thus far I've not had excessive draw on my 790 amp/hr battery bank, On a hot humid GA night I may see an additional 6% (about 2.3 kwh) reduction in battery overnight with both heads working..

With the shorter winter days I rarely use it overnight with outside temps below 40 to minimize battery drain but it's perfect when I don't want to light the woodstove, especially during the daytime or first thing in the morning if the woodstove didn't burn all night.

[John Galt 1]

addendum to previous post

While the mini split uses about 1300 watts cooling on high it pulls about 1700 watts when heating. Something to keep in mind during shorter winter days.