Inverter wiring for solar

[rickst29]

Originally Posted by rich2468

(Adding some clarity to what's already been shared by others)

Hi Mike- to accomplish what you've stated you'd like to accomplish (the ability to run the A/C from battery power) using off-the-shelf materials starting with an "average/factory" build TrailManor, you'd need around 100 Amp Hour of battery energy per each hour of A/C use.

Rich

That 100Ah per hour figure seems a bit short, even for the new and MUCH more efficient TrailManor AC units, due to the "100Ah" battery pack BMS stopping discharge before 100Ah has actually been used. If we forget about lead-acid battery types and focus only on LFP, the following math will apply. (Lead acid batteries can't handle all the rotor-start current, and they can't be discharged as deep.) In this, which is mostly an addendum to your excellent post about your results with a new AC unit, I focus on the much worse situation with older models:

The average running watts of those older 13,500 BTU air conditioners is 1600-1800 watts while the compressor is running (depends on weather, and the condition of the AC compressor motor, and which model it actually is). The total capacity of each "100Ah" LFP battery, discharging from 100% full down to ZERO, would be around 1280 watt-hours, if such a battery could be discharged that far.

Discharging to 0% destroys LFP batteries. Their on-board "Battery Management Systems" will shut down before reaching zero, typically at only 10% left. But going that far down, on a frequent basis, would still hurt battery lifespan pretty badly. I don't go past about 20% left. I further reserve the first 100Ah of my batteries to run TM 12v loads and appliances (including a fridge) through the night and into mid-morning of the following day, when significant solar power again becomes available for recharging the batteries.

So, we have 80% maximum usable from 1280Ah nominal capacity, right around 1024 watt-hours per 100Ah. Conversion from 12.8-VDC to 120-VAC (in the inverter) consumes about 15% of that power, resulting in maybe about 850 watt-hours of 120-VAC power from each 100Ah of Lithium (LFP) battery. To run the older 13,500 BTU AC for one hour, with the compressor mostly "on", you would need around 1600 watt-hours. That's roughly 200Ah of LFP batteries, not just one.
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In addition to the raw power consumed from the batteries, everything also needs to handle the extremely high extra "current load" which is required, for just a fraction of a second, to start the compressor motor. Each time the compressor turns "on" from an "off" State, the Coleman Mach 13,500 BTU compressor motor demands around 55 amps of current. (That's about 7000 watts). An Inverter smaller than "3500 continuous / 7000 peak" watts is unlikely to handle this "rotor start" loading, unless assisted by a high-quality "start-assist" device. With such a device handling "rotor start" peak loading, e.g. the 'SoftStartRV' (a load learning and really expensive one), you could get by with a somewhat smaller Inverter.

But not anything smaller than 3000/6000, because you'd be running at a high proportion of it's maximum continuous rated output. They're less efficient while being run that hard, and they burn out faster.

To feed a 3000/6000 Inverter, which will use more like 3500/7000 input watts at peak loading (because it is only around 85% efficient), you need "12VDC" wiring which provides a capability for more than 300 Amps. My own 2/0 wire pairs barely meet that requirement.

The costs add up, pretty fast. I know of only a 3 people who actually do this - JoeyCharismatic, Rich2468, and myself.