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Old 07-07-2012, 04:59 AM   #16
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Kohler vs Generac standby


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With a home full of gas appliances (stove, dryer, hot water, furnace) and CFLs, how would you size the generator based on the AC. Kohler's site says the 14res can easily start a 5-ton AC. However, the generator rep out to my house stated I would need at least a 17 or 20 kW unit.
Not all 5 ton ac's are the same. Factors such as compressor type and age of the unit have a bearing on starting current. While the 14kw unit may start the ac with no other loads, if you are running things such as the microwave, refrigerator and lets say a hair dryer, there may or may not be enough excess capacity in the 14kw unit to start the ac.

Did the rep do a load calcuation at your house or did he just automatically reccomend the 17-20kw units?

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Old 07-07-2012, 06:34 AM   #17
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Kohler vs Generac standby


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Not all 5 ton ac's are the same. Factors such as compressor type and age of the unit have a bearing on starting current. While the 14kw unit may start the ac with no other loads, if you are running things such as the microwave, refrigerator and lets say a hair dryer, there may or may not be enough excess capacity in the 14kw unit to start the ac.

Did the rep do a load calcuation at your house or did he just automatically reccomend the 17-20kw units?

Im betting the farm I know how he decided this factor.
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Old 07-07-2012, 09:38 AM   #18
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Kohler vs Generac standby


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A "Hard Start Kit" will also reduce the amount of power that your ac needs to start. The kit has a Capacitor that helps to start the AC thus reducing the power needed to start it.
Yes.
The highest surge vs. rated watts ratio for a Grainger listed generator that I could find was 1.6 and many motors have a much higher ratio.

BTW, I don't guess PoCo ever has to worry about this ratio for their generators.
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Old 07-07-2012, 09:39 AM   #19
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Kohler vs Generac standby


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Not all 5 ton ac's are the same. Factors such as compressor type and age of the unit have a bearing on starting current. While the 14kw unit may start the ac with no other loads, if you are running things such as the microwave, refrigerator and lets say a hair dryer, there may or may not be enough excess capacity in the 14kw unit to start the ac.

Did the rep do a load calcuation at your house or did he just automatically reccomend the 17-20kw units?
He made his recommendation based on the LRA of the AC, 97 amps. He then looked at the electrical panel and said "you have no load on this house except the AC".
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Old 07-07-2012, 09:41 AM   #20
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Kohler vs Generac standby


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Yes.
The highest surge vs. rated watts ratio for a Grainger listed generator that I could find was 1.6 and many motors have a much higher ratio.

BTW, I don't guess PoCo ever has to worry about this ratio for their generators.
From what I have read, all the generacs are 150% at 30% voltage drop. The Kohler's with the PowerBoost feature are 185%.
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Old 07-07-2012, 09:42 AM   #21
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Kohler vs Generac standby


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Im betting the farm I know how he decided this factor.
He based the 17-20 on the LRA of the AC which was 97 amps. He also looked at the electrical panel and stated "you have no load on the house except the AC". He was the first rep out, more to come.

My simple understanding of electrical need is 97A x 240V = 23,280 watts to start the AC?

Last edited by 7474; 07-07-2012 at 09:49 AM.
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Old 07-07-2012, 09:46 AM   #22
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Kohler vs Generac standby


Another thing from Grainger is that the price per watt goes from $0.20 to $2.00 which is an order of magnitude. This seems to be an inordinately wide range.

And one contractor quoted me about $0.80/w for an installed, large, resi unit.

Is this variation due to supply and demand? Quality?
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Old 07-07-2012, 09:48 AM   #23
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Kohler vs Generac standby


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You might also consider Onan. Costco probalby has the best prices for the Onan generators. If must go with generac, I would go with the Quietsource series. They have automotive style engines and aluminium enclosures.

The best way to figure your AC starting current is to put a clamp meter on the unit and start it up. They can capture the starting current required.

A "Hard Start Kit" will also reduce the amount of power that your ac needs to start. The kit has a Capacitor that helps to start the AC thus reducing the power needed to start it.

Here is the kit I put on my AC:

http://five-two-one.com/



They cost about 45 bucks on ebay. It reduced the starting current of my four ton ac from about 90 to 42 amps. That allows me to run the ac on my 12kw generator without problem.
Further review on the HVAC site regarding hard start kits showed they may drop the amp draw with an amp meter but this is too slow of a measuring device. When measured with an oscilloscope the amp draw of the AC with a hard start kit is still the same as without.

However, you and many other have shown with their amp meters and real world experience the AC running on much smaller generators.

My electrical understanding is minimal at best, but I think originally for yourself 90A x 240V = 21,600 to start your AC. Mine would be even higher with 97 amps. Based on this we would both need the 20kW at least, but you are getting by on much less.
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Old 07-07-2012, 09:51 AM   #24
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Kohler vs Generac standby


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He based the 17-20 on the LRA of the AC which was 97 amps. He also looked at the electrical panel and stated "you have no load on the house except the AC". He was the first rep out, more to come.

My simple understanding of electrical need is 97A x 240V = 23,280 watts to start the AC?
Odd, I've never done a load calculation by 'looking' at an existing panel. Lol...
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Old 07-07-2012, 10:11 AM   #25
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Kohler vs Generac standby


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Odd, I've never done a load calculation by 'looking' at an existing panel. Lol...

I appreciate your time with replying but you have yet to offer any insight only your pleasant sarcasm.

I provided you with my understand of the electrical requirements of the AC alone, 97A x 240V = 23,280, which on NG would be a 20kW at least. Is this correct?

The other electrical appliances in my home all running at once would be about 6 kW.
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Old 07-07-2012, 10:14 AM   #26
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You might also consider Onan. Costco probalby has the best prices for the Onan generators. If must go with generac, I would go with the Quietsource series. They have automotive style engines and aluminium enclosures.

The best way to figure your AC starting current is to put a clamp meter on the unit and start it up. They can capture the starting current required.

A "Hard Start Kit" will also reduce the amount of power that your ac needs to start. The kit has a Capacitor that helps to start the AC thus reducing the power needed to start it.

Here is the kit I put on my AC:

http://five-two-one.com/

They cost about 45 bucks on ebay. It reduced the starting current of my four ton ac from about 90 to 42 amps. That allows me to run the ac on my 12kw generator without problem.
I see there are (2) 4 ton options, the 3-5 ton and 4-5 ton. Which did you choose for your unit and why? Based on your price, I would believe it was the 4-5 one.
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Old 07-07-2012, 11:45 AM   #27
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Kohler vs Generac standby


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I see there are (2) 4 ton options, the 3-5 ton and 4-5 ton. Which did you choose for your unit and why? Based on your price, I would believe it was the 4-5 one.
I have the 4-5 ton one. I got that model because the capacitor is bigger and provides more "kick". You dont want to oversize the start capacitor too much however, because that can cause other problems.

Also consider that LRA or "locked rotor amps" is the current draw with the compressor not moving or stalled. While that has a loose correlation to the starting current required, it is NOT the same because obviously the compressor is moving when it is started.

Its probably true that the current required is the same with or without the hard start kit. However, if my fluke cant detect the current on peak hold mode, neither can the generator.
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Old 07-07-2012, 11:59 AM   #28
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From what I have read, all the generacs are 150% at 30% voltage drop. The Kohler's with the PowerBoost feature are 185%.

I would take all "surge" ratings from any manufacturer with a very, very large grain of salt. Most are very optimistic. A 30% voltage drop WILL cause a noticeable flicker in any lights that you have and also wont be very good for any sensitive electronic that you may have.
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Old 07-07-2012, 03:02 PM   #29
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When measured with an oscilloscope the amp draw of the AC with a hard start kit is still the same as without.
Then the kit must reduce the time it takes for the heavy current transient to die out, or somehow reduce the RMS current value, so that the total energy consumed by the transient is reduced.
It also depends on the transient response of the generator, and generic info on this is probably on the Web.
PoCo's transient response is probably less than 20 mS and they can deliver 24 to 48 kw or more to a house.

It seems like with 3 kw you get some inconvenience and with 20 kW you almost get life as usual, and you'll use your gen a few days every two or three years.

And a small fan takes 50w, a fridge 500w and a central AC 5000w.

This last time we used a table top single burner butane stove to do the cooking. Minimal initial investment and you only buy cartridges as you need them.

BTW, a 30% drop in voltage for incandescents will cause a 70% drop in brightness, in principle.

Last edited by Yoyizit; 07-07-2012 at 03:13 PM.
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Old 07-07-2012, 03:42 PM   #30
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Then the kit must reduce the time it takes for the heavy current transient to die out, or somehow reduce the RMS current value, so that the total energy consumed by the transient is reduced.
It also depends on the transient response of the generator, and generic info on this is probably on the Web.
PoCo's transient response is probably less than 20 mS and they can deliver 24 to 48 kw or more to a house.

It seems like with 3 kw you get some inconvenience and with 20 kW you almost get life as usual, and you'll use your gen a few days every two or three years.

.
Not sure how the kit works, as the HVAC experts say it decreases the time for start-up not the amp draw. But, I have seen numerous places, this thread included, where people are powering large ACs with relatively small gens because of the decreased amps noted with amp meter.

We could get by with very little and will probably rarely, if ever use it, especially with almost all underground utilities throughout our city. But, wife wants to make sure we have the AC available as family in Columbus, OH were without power for 4 days and especially since we have 3 under 3 y.o.

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