what amp draw will I likely see?

Need a ballpark figure for the likely amp draw I'll see on a 4 ton residential air con and air handler unit for 1800 sq ft house. I don't know if air handler runs on 220v or not. I know the air conditioner unit does run on 220v.
I've got a 30 amp portable genset (that's 30 amps at 220v), and I just want to be sure it'll run my a/c and air handler units.
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wrote:

It would probably run it just fine, the trick is starting it.
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On Tue, 30 Aug 2005 13:33:10 -0400, snipped-for-privacy@aol.com wrote:

Oh yea.
A 30A gen is probably around 5500W ? So, that should have about an 8KW surge on it. You just might start it with absolutely no other load on the generator. The problem is, you can't then power up other stuff in the house because the A/C will cycle on and off and then you'll overload the generator.
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Look at the nameplate on the condensor unit. (I'm guessing it's about 10-15 amps). Now look at the nameplate on the air handler. (I'd guess it's about 1-2 amps).
Now when both induction motors start up they'll want gobs more current. (probably about 3X).
That means your generator will need to supply a surge current that could range between 35-50 amps. I think that'll end up being outside the motor starting envelope of your genset.
To be 100% sure, try contacting the A/C unit's manufacturer and get the motor starting code. Now do the same for the generator.
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Thanks for all the responses. I think a hard start gizmo is what I was being told about, but it somehow came out in my head as a "soft start" unit. .
Our house is 1800sq ft, and very thermally "lossy" (built in '65) . Doesn't have storm windows, or even thermopane glass. All I know is the 4 ton unit runs a lot keeping the house at 76 degrees.
The thing about using a couple of high efficiency window units is probably my best bet, short of going to a big, pad mounted genset. And, really, they would do us fine for keeping comfortable at night during extended power outages (the last one was 3 weeks during hurricane Ivan).
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unaffected area if you want to stay cool.
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I ran some numbers awhile back, don't have them in front of me. but my memory says 1 galon of gasoline delivers about 2,000 watts of electricity for an hour.
So, might want to figure on that, and have a couple extra gascans around. Or plan to siphon the car.
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Christopher A. Young
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Startup currents can be quite high. I tried this with a 6000W gen and a 4.5 ton unit and it just wouldn't work. It would trip the breaker on the gen after about 10 seconds. I think the start current needed was 90 A.
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I thought I'd just put a soft start kit on the thing to hadle the startup/inrush current draw problem. However, I'm now being told that soft start units aren't available for single phase motors, which mine are. Anyone heard that the soft start units are made for single phase?
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RB wrote:

Check with the manufacturer of the generator for an exact answer to your first question. They should have a web site.
A soft start (PTCR, which is a single phase motor assist) will *increase* the peak starting current.
hvacrmedic
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RP wrote:
A soft start (PTCR, which is a single phase motor assist) will *increase* the peak starting current.
hvacrmedic
RB
Try a true hard start kit. It has a large start capacitor and start relay in it to shift the phase while it increases torque. It will increase the start winding current, thus increasing starting torque. Because the start winding current is out of phase with the run winding, the common leg current will actually go down slightly. But even with a hard start kit, your generator will probably not handle the inrush (start) current. Try getting a window unit or 2 to use in emergencies. It will cool part of the house without the huge surge.
That is what I did when the last hurricane to hit my area wiped out the power for a couple of days. It did a pretty good job for my 2000 square foot house in place of my normal 2 ton heat pump.
By the way, do you live in a green house?? 4 ton sounds awful bigg for an 1800 square foot house unless you have a LOT of glass or very poor insulation.
Stretch
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My Coleman 2200 watt generator will run the 10K BTU window unit in my living room. Rotary compressor.
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Alt energy.homepower used to have some very good generator gurus at one time -- got no idea about now. Might give them a try. A 4 ton 12 Seer unit should theoretically draw 4000 watts, a10 Seer, 4800. (BTU rating divided by Seer rating). Then, watts divided by voltage gives you the amps. Unless you get a really big genset, the window unit idea is probably the way to go, as you are going to have other loads besides a/c-- lighting, ref/freezer, tv, etc. Larry
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RB wrote:

I don't know how much it will help, but if you start the compressor first, then the blower motor, you will have less peak start up current. The blower motor doesn't draw nearly as much as the compressor, but it's startup current curve lasts much longer. It can make a difference if it's borderline.
Tony
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You probably want a hard start device.
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long before I would ruin a new ac unit with a way to small generator, I would contact the proposed manufacture and see if they had anything in production. Maybe a two stage compressor unit.
Baldor seems to have some thing that will fit the bill. list is ~500 smackers, less contactor and enclosure.
Applications of softstarts and VFDs should be made by experienced folks that are familiar with all of the starting requirements of a given application. Let us not forget the voided ac warranty if something bad was to happen because of the generator/softstart combo.
http://www.baldor.com/products/detail.asp?1=1&page=1&catalogonly=1&catalog=S23CA&product +Controls&family=Soft+Start+%26+Dynamic+Brake%7Cvw%5FACControls%5FSoftStart&phase=1
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this is Turtle.
i will tell you what i did with a House electric system and a hvac system during a 5 day power outage and i don't recommend you do like me at all.
We had a 5 day power outage and i bought a 5,500 watt generator and a 7,000 watt surge ability. I hooked a 3.5 ton 9 SEER condenser , a 5 ton gas furnace , a refrigerator, 1 chest type freezer , and 2 plug in circuits in my house to regulate the lites needed by plugging in what I wanted. i figured the amp draw and it was good for just running but the start amps was way above the 7,000 watt surge rating if any two or more of the big items started together. We run like this for 3 days and had no trouble at all but still on paper we should have had hell.
Now it sounds like you got a 5,500 watt or a 6,000 watt generator by having the 30 amp breaker on it.
Now you need to search out a generator sight where you figure up the load needed and the generator out put and match your system to your load. If you can't find one. E-mail me and i will find the load match up papers for my generator otr direct you to my generator website.
TURTRLE
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