Can my generator handle my AC unit?

[BraveSirRobbin]

Good post Rick. I had no idea the locked rotor amperage would dictate such a large generator starting wattage. From what I'm reading with the links you provided Dan would need a generator capable of 12.5KW starting (surge) capability mainly because of the LRA rating of 91 amps.

Does this sound right?

Again, thanks for those links!

 

[Rick_G]

Good post Rick. I had no idea the locked rotor amperage would dictate such a large generator starting wattage. From what I'm reading with the links you provided Dan would need a generator capable of 12.5KW starting (surge) capability mainly because of the LRA rating of 91 amps.

Does this sound right?

Again, thanks for those links!

BraveSir-

That seems right for the compressor, it looks like there is also a 1/4 hp motor that starts with it?, not familiar with AC I live in Alaska. Then you have to add in the load of the house when the A/C is being started.

There's a link on that page to a Generac sizing PDF. It appears that Generac is saying a 3ton/36000btu A/C unit has a typical LRA of 100 amps. Their QT series 3600 rpm 13kw has a 240v/95amp 30% under volt rating, the 16kw has a 240v/117amp 30% under volt rating.

In the real world you could probably get away with a GOOD 10kw generator, without causing any problems. With all the different variables they are rating based on worst case scenario. An 1800rpm diesel generator would be quiet, fuel efficient and long lasting.


Rick

 

[AnotherOne]

I have a generac natural gas generator and it's been great. Had it for 8 years now and have abour 400 hours on it (probably 100 of those hours are the run once a week for 15 minutes test). Had to replace the battery twice, but that's about it. I have it serviced (oil change, cleaned, checked for mice eating wiring, etc) every 16 monhts. We had a terrible storm last winter and lost power for 8 days. We just ran the generator from 9am to 11am and invited the neighbors over to watch football games, take showers and stay warm.

You only ran the generator 2 hours per day? I thought the point of natural gas "auto starting" generators was to provide power through the full duration of an outage?

Opps, make that 11PM not AM, we kicked it off at night to not annoy the neighbors and save some $$ since there's really not much of a load when we are sleeping. The ELK M1 battery backup did pretty good for the first 3 days, then on the first day, it sounded the low battery beep at 4AM. At that point, we turned the ELK off at 11PM as well. Guess I could have gotten the battery out of the car

 

[Digger]

I have a generac natural gas generator and it's been great. Had it for 8 years now and have abour 400 hours on it (probably 100 of those hours are the run once a week for 15 minutes test). Had to replace the battery twice, but that's about it. I have it serviced (oil change, cleaned, checked for mice eating wiring, etc) every 16 monhts. We had a terrible storm last winter and lost power for 8 days. We just ran the generator from 9am to 11am and invited the neighbors over to watch football games, take showers and stay warm.

You only ran the generator 2 hours per day? I thought the point of natural gas "auto starting" generators was to provide power through the full duration of an outage?

Opps, make that 11PM not AM, we kicked it off at night to not annoy the neighbors and save some $$ since there's really not much of a load when we are sleeping. The ELK M1 battery backup did pretty good for the first 3 days, then on the first day, it sounded the low battery beep at 4AM. At that point, we turned the ELK off at 11PM as well. Guess I could have gotten the battery out of the car

The ELk did not have enough time to fully refesh the charge on the batteries. Not saying that there is anything wrong with the ELK since it exceeds many other panels out there and exceeds UL and NFPA requirements (I know because I tested it). What I did in my house was put a UPS on the panel as well to buy me a little more time. So that I know when there is an ac failure I have a small relay powered by a wall wart on the same circuit as the M1 and put the contacts of the relay across a zone. I then have the ELK beep the keypads after 15 mins (if its during the day) and email my cell phone. Works pretty well but not exactly 100% to code .

Most 7 or 8 aH batteries have a maximum charge rate around 2 amps per the mfg specs. There are not many automotive car chargers out there that charge that low. I do have a few Vector brand (since bought by Black & Decker) 12 V battery maintainers that charge at 1 or 2 A (selectable) and when the battery is charged they automatically switch to a trickle charge. They would charge your bateries up faster (a few hours to 5 or 6 hours).

 

[judge_l]

I've found (actually the neighbor complained) that when my AC starts, the lights in his house dim. The lights in mine don't. Although not as scientific as the other answers, I'm guessing that if it can dim power next door, the average generator isn't going to start it.

The electric company came out and did some tests and had a number of their people try to figure it out, but they never did.

 

[hockeypuck]

I install generators as part of my business, anywhere from 7kw up to 45 kw. You have to look at the specs of the generator you are installing. Most of them now tell you what size generator you need to start a certain sized AC condensor. They size you are referring to is way too small. Another consideration is what else will be on your generator (well pump, sump pumps, sewer pumps). I would be happy to send you a pm if you told me what your other loads are. Not looking to make the sale obviously, just to give you an idea on cost and size so you can go into this with some insight.

 

[hockeypuck]

I've found (actually the neighbor complained) that when my AC starts, the lights in his house dim. The lights in mine don't. Although not as scientific as the other answers, I'm guessing that if it can dim power next door, the average generator isn't going to start it.

The electric company came out and did some tests and had a number of their people try to figure it out, but they never did.

I would have the power company check the grounded conductors at your neighbors house and their pole. Its sounds like you have a very good ground at your house and the power company does not. Could also be the type of transformer they are using. Are you on the same transformer? Wierd things happen when the power company is loosing their neutral.

 

[huggy59]

I have a friend with a whole-house Generac natural gas-powered generator. Works very well, but is very loud. I've considered one as well, but my little portable gasoline 6500 does the basics for me at the moment, which includes an on-demand oil-fired water boiler (15A), but no AC and at present no water pump. I may look into diesel for my whole-house unit since they seem to be much more quiet. Does anyone have a really quiet natural gas unit?

 

[CollinR]

The noise level isn't inherent to the fuel they burn, if anything I would expect the diesels to be the loudest.

It's just like all other internal combustion engines, the routing of the intake and exhaust plumbing and their devices make all the difference. If the system is too loud just start swapping and/or modifing. Also you can draw heat directly from the exhaust, they produce much more heat energy (heat, light and sound account for something like 80%) then they do rotational energy (~20% of stored in fuel) to power the generator so you might want to look into ways to harness that energy too.

I guess it comes down to how portable do you want the generator to be... Most of my commercial clients who have them, they are almost silent if you aren't inside the sound walls. For a sound wall all you need is a wall with a hard surface that will bounce the noise upwards, I'm sure looking over the roof at them it would be much louder. I built one for my air conditioner in my last house for less then $100, serious improvement on my patio!

 

[hockeypuck]

I have a friend with a whole-house Generac natural gas-powered generator. Works very well, but is very loud. I've considered one as well, but my little portable gasoline 6500 does the basics for me at the moment, which includes an on-demand oil-fired water boiler (15A), but no AC and at present no water pump. I may look into diesel for my whole-house unit since they seem to be much more quiet. Does anyone have a really quiet natural gas unit?

Generac are some of the "most cost efective" generators out there. They are loud. You have to look for ones with sound attenuation built into the weather proof shroud and a good muffler. Honda always makes very quite units, but you will pay almost a buck per watt for it (a good one). Coleman makes a pretty quite unit so does briggs. Look at the db rating. They all have them listed on the spec sheet and then put them as far away from you home as possible on the opposite side of the house as the bedrooms.

 

[Rick_G]

The noise level isn't inherent to the fuel they burn, if anything I would expect the diesels to be the loudest.

Probably not in it's self, but what a diesel generator does in this size range is readily provide an 1800 rpm syc speed. The sound frequency will also be be quite different. Diesel has more BTU's per gallon then gasoline. Some parts of the country use diesel as fuel oil! If you do buy a diesel generator, don't forget stationary diesels are going to have to burn ultra low sulfur diesel too.

Huggy59- http://www.cumminsonan.com/residential/pro...re?gensetId=106 These are fairly popular up here.

Rick