Starting Air Conditioner with Inverter

An airconditioner with inverter does not look larger than a conventional airconditioner, so, it s not true that air conditioners' inverters are "big." Inverter provides incomparably more precise integrated control of the temperature - compared to the conventional induction motor with split capacitor which either stays idle or is going at full load - thus, energy saving. Also, there appears inverters controlling relatively new types of motors - such as permanent magnet, and/or brushless direct current (difference between which is not clear to me yet). So, depending on the motor drive, the size of the latter is relative and may be a subject of long discussions.

What you are referring to is a more modern AC unit that uses a 3 phase motor and an inverter to create the 3 phase power from a single phase inverter. I was interpreting the OP's question as being about having to up-size an inverter if you want to run an existing AC unit that has a single phase motor on it.

Some of you guys make this so much more complicated than need be. Simply, your air conditioner and most other compressors require a starting current of about 6 to 8 times the running current. Most inverters can only supply 1.5 times their full load capacity,, however your "generator", which consists of an alternator and prime mover have a pretty good whack of rotating kinetic energy that allows the thing to supply 3 or 4 times their rated full load capacity for a second or two. Now the gen-set is going to slow down a bit, but your air conditioner doesn't mind a small drop in frequency and voltage while it starts and the gen-set picks up the load, simultaneously the air conditioner compressor load is dropping as it comes up to speed. Hopefully everything reaches a happy equilibrium before you gen-set breaker trips... Basically it comes down to inertia, the gen set has it, the solid state inverter doesn't.

Martin

"Some of you guys make this so much more complicated than need be."

Wait... didn't I say most of that, other than the rotating kinetic energy part?

That, and whole bunch more, some of which I disagree with, namely the lubrication thing and the thought that you can't run some compressor motors of a simple inverter. I was just trying to explain why your gen-set could do it and a similarly sized inverter wouldn't.

YMMV

Cheers

I have to agree with Baxterm here.I know most of you guys are engineers and what ever else, and you all talk in such technical terms that you lose most of us. But it has always been my belief that bigger is better. I am a simple person with no special training other than being blessed with good common sense. I evaluated my electrical needs when I decided to go off the grid. I did not need a 8,000 watt inverter, but I bought it anyway.I`m glad I did, and I also purchased a 10,000 watt step up transformer. I get 120 volts out of the inverter, going into the step up transformer giving me 240 volts to the fuse box. There is nothing on the planet this inverter setup with the stepup that I cannot start. I run several old tube transmitters, and receivers talking all over the world, and I have no problems. I have 6 batteries all 6 volt wired in series going to the inverter. These are rated at 310 amp hours each.I also have a second bank of batteries charging while on the first bank. 12 batteries total. With my battery switch I can bring both banks online if needed.I guess what I`m trying to say is: Think ahead, and plan for bigger than you think you will need.Living out here in these Ozark woods can be a challenge in itself, but I would not trade it for anything. I love the privacy and independence it gives me. I did have to make one concession. I stay off the grid 6 days a week, but I get on one day a week to keep my wife happy. That is the one day she does laundry. She refuses to do laundry, and then hang it out to dry, not when she has a new dryer sitting there.Small price to pay to save a bunch of money cause electric out here is about 700.00 a month. Not every month, but more than I want to pay. So, think BIG!!

The Air Conditioner compressor type is the issue here:

If the compressor is a positive displacement type that requires a high initial torque to start with, there is no way the Inverter can cope with it at 150% it's rated output.

If the compressor is a Screw type or any other type that can start with a low torque to pick up speed and then can run at different speeds to accomodate the required load, then the Inverter with a 150% rating can do the job. It all depends on the design/type of the compressor (mechanical side).

It has nothing to do with the lubrication. Compressors are normally bathing in it and the lubrication is done at what ever speed. The problem: Obtain the adequate compression with lower or varying speeds to still be able to pump the heat. that is why it must be designed properly at the start, otherwise the efficiency can be compromised at lower speeds than the original design speed.

The previous answers are correct. It takes many times the rated watts to start a typical a/c unit. Inverters are fussy, basically. You may be able to flip a smaller inverter off and on several times and get the a/c going, but the first time the compressor kicks back on, it will probably overload. Also, never disconnect an inverter from its power source while it is powering anything. The back emf can kill the inverter.

The length of the wires that lead to and from the inverter also affect how many watts it can actually run, due to line losses.

A generator doesnt cut out and quit/overload as easily, it keeps running and providing some current, so the a/c starts. Using too small a generator repeatedly though will probably mess up the gens output, or the compressor.

If you have the money, smaller thermoelectric peltier 12 volt a/c's are available, that run on straight dc, and have no moving parts, but they use a lot of battery juice compared to the cold they put out.

If your inverter will run a small refrigerator, use the fridge to chill water, then run your cold water through a fan and radiator setup to provide a few hours of cooling.

Otherwise, just get a bigger inverter and battery bank.

Well, its time to load some trash, food scraps and wood scraps into the bio-blaster, and heat this place up to 90f, lol. http://thechipheater.com

So, briefly what is the conclusion?

The inverter is not the right choice to run Air Conditioner ?

The conclusion is, if you want to run a small air conditioner; say, an 8000 btu, you are going to require a really big, costly, inverter. The inverter would cost more than a generator that would do the job. So, in conclusion, get a generator to run the AC and charge the batteries for the inverter. I use this system with my travel trailer. In the evening after it cools down, I turn the AC off and after the batteries are charged, I turn the generator off. But, if all the power for the situation is coming from solar and/or wind and stored in batteries, then a large inverter is required to run an AC. As previously mentioned, other types of cooling are available.

" in conclusion, get a generator to run the AC and charge the batteries for the inverter."

If you already have a generator ,what is the need for inverter,why the generator doesn't run the Air Conditioner directly without inverter ?

The inverter is to provide power without the generator running.

There are a lot of A/C's out there with variable DC drives. They use a rotary vane compressor, and can run from 20% to 100%. Either live with what you have or buy one.