Does AC soft start work on any AC

flexbex wrote:
So what's a reasonable WH for a 200aH lifepo4 battery?

12 volts X amp-hours = Watt-Hours. For 200 amp-hours that is about 2400 watt hours

But the bottom 20% should not be used, so divide the result by 4/5ths. That yields 1920 watt-hours.


Longer cycle life will result from not using the top 15%.

Use the measured battery voltage while it is under an equivalent load in your calculations of watt hours. LFP batteries will hold that voltage for quite a while but as SOC drops below about 40%, battery voltage will also drop, reducing wh even more.

So what's a reasonable WH for a 200aH lifepo4 battery?

Sorry to disappoint you, but you don't have enough ah/wh to do what you want to do. To begin with you can't use 14.4 volts to compute watt hours, that is an at rest voltage and will quickly drop once the A/C starts up. Plus you didn't factor in other loads like lighting or the inverter itself.

About the ac I am not fixed. Still figuring out what's possible. I just used one which was around. But it won't be the one installed. My calculation was under the assumption to have it cool in the night offgrid. So about 6-7h. But less is ok also. Let's say I have a 1kw AC. The room is about 2*4m. I have 400aH 14.4v-15v. I want the temperature from outside 32c down to 26-27c. So I was assuming that the compressor is on 50-70% of the running time. That would give me 500wh to 700wh. In 7 hours about 3500wh - 4900 wh. My batteries are capable to deliver 5800wh. At least that's my rough calculation. Hope it makes sense

We didn't NEED more battery storage - we just wanted it. Kinda like more horsepower. ;)

Cptnvideo wrote:
First mistake, Chum Lee, is making assumptions. We have ran an A/C unit several times off grid. And that was before adding the last 2 batteries.

You are correct. I am making assumptions here because I have to. (the OP has not provided enough information) Please note, . . . ahhhhh Captain, I didn't say it wouldn't work. I know it will AND you've proved it will. (for yourself) The questions are, "For how long?" and, "Is that sufficient to cool the vehicle in the OP's application?" You also seem to have recognized that you need more battery storage, which was the point of my post. Thank's for restating it.

Chum lee

First mistake, Chum Lee, is making assumptions. We have ran an A/C unit several times off grid. And that was before adding the last 2 batteries.

First mistake: Trying to run an AC off batteries/inverter.

Using a soft start may get your AC started, but, your issue is (will eventually be) the overall current draw of the running AC unit. Before you go any further, calculate the amp-hrs (ultimately the KWH) available in your fully charged battery bank and compare that with what your AC unit running demand is in KWH. You may be surprised about how little electricity is actually stored/available in your battery bank. I don't know what type of AC unit you have, but, my guess is that you will deplete your battery bank in under an hour. Remember, your battery bank voltage drops substantially as you drain the batteries and your inverter will only tolerate a given voltage drop (usually less than 2 volts) before it can no longer maintain the rated output current/voltage to run the AC.

Chum lee

dalej wrote:

I have never read of using an autoformer with an inverter. Can you expound a little

Hi dalei,


I'm replying in private as it is off topic.