SJ-Chris wrote:

swag....

Googling, I see that a 13000btu RV AC draws about 13amps at 120v. If your 12v battery is providing this through an inverter, it will be drawing roughly 130amps from the battery. There are also inefficiencies running through your inverter that will probably result in 5-10% more amps needed. So my swag/guesstimate is that your AC will be drawing ~140amps from your battery. Assuming your battery can handle this and that all wiring is adequately sized to reduce voltage drop/etc, it looks like your battery will power your AC for about 1hr 20 minutes. This assumes that your battery was fully charged and you aren't drawing significant power running anything else.

Summary: Not long at all. Use a generator to run your AC

Good luck!
Chris

theoldwizard1 wrote:

Or S.W.A.G. !

With a 12V LiFePO4 200Ah battery bank and a "typical" inverter and no solar, how many hours of use can I expect running only a 11,000BTU-13,000 BTU A/C before the inverter shuts down ?

Assume a 24' TT and outside temperature about 85° and inside set to 75°.

3 tons wrote:



*********************

So for a baseline, I’ll provide my own brand real world estimating method, though without concurrent harvest…My 11k btu Coleman typically uses 90-95a depending on ambient temperatures…

Since you’ve suggested an ambient of 85df this means only a 10 degree difference which is fairly easy to resolve, but which can be impacted by region and humidity…. Since you mentioned ‘inverter’ and the possibility of a 13kbtu air conditioner, I’d assume a 3kw inverter (most likely a PSW pass-thru inverter-charger type)…I’d also recommend a soft-start to limit start-up voltage sag, along with robust battery cables to reduce voltage drop feeding the inverter (I use 0004 AWG, for about 6-7’ R/T to inverter)…

Since you’ll be running an air conditioner, you’ll want to pick an inverter with a high surge rating ‘and’ duration - cheaper inverters are often rated at a high wattage, but of a lower surge duration…Recall that old adage, get what you pay for!!

Also consider duty cycle - for thumbnail calc’s, I generally use a compressor-run duty cycle of about 60%, though for the first hour’s initial cool-down I’d plan on 80%- this method with the fan on low speed continuous operation…

Since you’re using lithium, you’ll want to consider a battery’s continuous amperage and surge rating (often 1C and 2C respectively), and it’s allowable time duration spec while in a surge condition…

Now you’ll want to decide on your initial SOC and your acceptable DOD floor, this will tell you how much power your willing to commit to the air conditioner…

So hypothetically speaking, let’s say (assuming a full 200a/h charge…) you have 120a/h available for air conditioner usage before arriving at an acceptable lower battery limit of say 30% SOC meaning a reasonable 60amp/hrs being held back in reserve…

Now, back to duty cycle: Let’s assume a 13k btu air conditioner uses about 12amps AC (TBD… this, a combination of both compressor and fan running amps…due to various parasitics, and to be conservative I’ll skip the fine tuning of this math…). We can convert this to DC by using a multiple of 10, thus 12amps AC = 120 amps DC (as measured via metering…)

(Note, compressor amperage gradually increases a bit once at the early to mid 90 degree weather).

So, starting out at 200a/hrs x first hour at 80% duty cycle at 120a DC = 96a/hrs consumed, with 104a/hrs remaining, yet only about 44 remaining available amp hours to the target SOC of 30% (of original 200a/hrs)…

Beyond this initial cooldown period, lets assume a 60% duty cycle per air conditioner run hour, thus 72a/hrs per hour of operation…

So it’s relatively easy to see how you can extend air conditioner run times, and optimize next morning’s all important battery recovery times (e.g. non-air conditioning hours) with concurrent solar harvest…For this calculation, it’s important to consider the 4-5 ‘peak harvest hours’ and beyond, and what is a relatively rapid re-charge characteristic of LiFePo4 batteries…JMO

3 tons

SJ-Chris wrote:

swag....

Assuming your battery can handle this and that all wiring is adequately sized to reduce voltage drop/etc, it looks like your battery will power your AC for about 1hr 20 minutes.

ktmrfs wrote:

... And all this is assuming the inverter can even start the AC

3 tons wrote:

an acceptable lower battery limit of say 30% SOC meaning a reasonable 60amp/hrs being held back in reserve…

3 tons

ktmrfs wrote:



for us the issue would be the duty cycle. Ours is a large trailer and to get it cooled down even if the inside temp is say 85 will take several hours of run time to get it to the mid 70's. That's assuming an outside temp of around 85. Once outside temps are in the 90's that AC need to run 3-4 hours for much effect.

Now on my small trailer (14ft cargo) with a coleman 9K BTU AC an hour cools the trailer down even in the high 90's outside, so it would make practical sense. and it only draws about 9A, another big advantage.

I wish I could cool my trailer down enough in less than an hour to have a 80% duty cycle!! The disadvantage of larger trailers, 30Ft double slides. Even a 24ft seems like it would be unlikely to do enough cooling in less than an hour even at 100% duty cycle.