Powering a 5000 BTU AC with a generator?

[AzAv8r]

I recently ran across a statement that a 1000W (or VA) generator could not power a 5000 BTU AC. This surprises me, since such ACs are typically rated for less than 5A, whereas the Honda and Yamaha 1000W generators are rated for about 7+ amps continuous and about 8+ amps surge. Is this true, and if so, why? (Is it because the startup current of the AC compressor exceeds what the generator is capable of? If so, by how much?)

If this is true: are there 1000W (or smaller) generators or inverters/power controllers which allow parallel operation with the house battery to take the surge (startup) current of the AC in parallel with the generator? This is a relatively simple electrical design (for an undergraduate EE student) for a synchronous inverter (it is essentially the same as a grid tie solar power controller), and both the Honda and Yamaha generators include a similar feature for paralleling the generators.

Assuming the AC surge is 10A, I need 2A extra for perhaps 1s, which assuming 80% efficiency works out to 25A @ 12V for 2s. A whopping (<- sarcasm) 14 mAHs per instance. If the cycling rate is every 5 minutes, this puts a discharge burden of less than 0.2 AH on the battery. Vs. the 24 AH available to recharge the battery from the generator if I assume 99.999% AC duty cycle and the same 80% inverter efficiency with those 5 minute intervals.

Best,
Jon

[asianflava]

My Kipor 2300 runs mine fine.

[Shadow Catcher]

One other alternative is a hard start capacitor http://www.supco.com/images/pdfs/AC%20H ... ooklet.pdf

"Most single phase air conditioners and heat pumps use non-bleed thermostatic expansion valves (TXV’s) to control refrigerant. A problem with TXV’s occurs when a reciprocating
compressor shuts off, refrigerant pressures don’t fully equalize. Pressures do equalize in scroll compressors; which, typically do not need hard start kits for this condition. In a reciprocating compressor, the discharge pressure will drop to about 150 psig and the suction pressure will rise only to about 100 psig. When the compressor tries to start, there’s too much load for the starting motor torque to overcome. This is especially true if the supply voltage is low. To increase starting torque, a start assist device can be used. When a TXV is used, a potential relay hard start kit is employed. This will increase starting torque by a minimum of 300 % over using just a run capacitor."

The only way you will find out what will run your AC is to try it, the hard start capacitor is certainly much less expensive than a new generator and it may be, ya just gotta see if it works.

[TENNJIM]

+1 on the hard-start capacitor. You will not know until you try it, but it is inexpensive. I have operated a 13,500 BTU A/C with a Yamaha 2400 in altitudes up to 8000 ft with a Supco capacitor.

Jim B / Utah

[bdosborn]

I recently ran across a statement that a 1000W (or VA) generator could not power a 5000 BTU AC. This surprises me, since such ACs are typically rated for less than 5A, whereas the Honda and Yamaha 1000W generators are rated for about 7+ amps continuous and about 8+ amps surge. Is this true, and if so, why? (Is it because the startup current of the AC compressor exceeds what the generator is capable of? If so, by how much?)

Starting current is typically 5-7 times run current. While my 1000W yamaha will start the 5,000 btuh AC initially, it won't start it after it cycles due to the reasons that SC posted.

If this is true: are there 1000W (or smaller) generators or inverters/power controllers which allow parallel operation with the house battery to take the surge (startup) current of the AC in parallel with the generator? This is a relatively simple electrical design (for an undergraduate EE student) for a synchronous inverter (it is essentially the same as a grid tie solar power controller), and both the Honda and Yamaha generators include a similar feature for paralleling the generators.

Really? How about posting some circuit designs, I'd be interested in seeing them. They're probably all over the 'net if they're that simple...

Assuming the AC surge is 10A, I need 2A extra for perhaps 1s, which assuming 80% efficiency works out to 25A @ 12V for 2s. A whopping (<- sarcasm) 14 mAHs per instance. If the cycling rate is every 5 minutes, this puts a discharge burden of less than 0.2 AH on the battery. Vs. the 24 AH available to recharge the battery from the generator if I assume 99.999% AC duty cycle and the same 80% inverter efficiency with those 5 minute intervals.

Best,
Jon

Magnum makes an inverter/charger that will do exactly what you want, draw from the battery to augment the generator starting capability but they're not cheap: Magnum Linky. It would be cheaper to buy a bigger generator.

Bruce

[Socal Tom]

I have a honda EU1000,
It starts and runs my cheapo 500BTU Home Depot special 5K BTU air conditioner just fine, but I'll admit I was surprised for all the reasons listed above. The more effecient A/C units may have hard start capacitors built in?
Tom

[Bogo]

Another issue is square wave, and modified square wave outputs, like used in the inverter generators, are less efficient at powering a typical AC motor. It can require as much a 30% more power to run the motor than if a proper sine wave AC power source was used.

[AzAv8r]

Thanks for all the great info. Sounds like (a) the operation is doable, but there are complications, (b) restart is the problem, (c) the complications are reduced with the cap as a cheap and simple solution, and (d) there is therefore no demand for such a product in the RV market.

Our central AC units have timer protection to prevent restart for about 5 minutes or so. I gather that window ACs include no such complications?

"They're probably all over the 'net if they're that simple..."
Hey, what a great idea! They are! (Google "synchronous inverter design" or "...schematic", or "grid-tie..." YMMV, but some are reference designs by power and control semiconductor companies.)

Jon

[bdosborn]

Another issue is square wave, and modified square wave outputs, like used in the inverter generators, are less efficient at powering a typical AC motor. It can require as much a 30% more power to run the motor than if a proper sine wave AC power source was used.

That's more of a inverter issue as opposed to an inverter generator issue. All the outputs waveforms I've seen from inverter generators ( Honda, Yamaha, champion) are true sine wave. Some are posted on YouTube, FWIW.

Bruce

[bdosborn]

+1 on the hard-start capacitor. You will not know until you try it, but it is inexpensive. I have operated a 13,500 BTU A/C with a Yamaha 2400 in altitudes up to 8000 ft with a Supco capacitor.

Jim B / Utah

I looked at doing that to a 5k unit but I just couldn't find room inside the A/C to put it. I'd be interested in seeing a clean install if a cap on one of the little A/C units that I could copy.
Bruce

[Shadow Catcher]

Bruce, pulling the thermostat out of the AC unit to make it remote left a good bit of room, and who says it has to be internal to the case, just really well protected. We have a 2300W Kipor industrial generator (8hr run time) so not a big concern.

[bdosborn]

Even then it would be a tight fit. The one I bought awhile back was really meant to go inside a 13.5 kbtuh unit and it's just too big for the little A/C. It still floating around the garage somewhere, maybe I'll dig it up and look at it again.

Bruce