Have a smallish backup generator? Want to run your house AC? May I point you to a potential solution?

OnlyOneDR

OnlyOneDR

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Long story short I bought a used 9.5kW Kohler natural gas standby generator off Craigslist a little over a year ago after yet another big afternoon thunderstorm knocked the power out and I had to run out and fumble with my 5000W/6250W surge portable gen to get it hooked up so we had the well pump, lights, and ceiling fans to run through the bathtime/nighttime routine with our little boy. I poured a pad behind the house a couple months later but only finally connected the natural gas and wired it in to the panel last week (added a breaker and installed an interlock, no ATS because it wasn't worth the hassle). As expected the three-year old 2.5 ton Lennox condenser unit would not start up, blinked the lights and dropped the voltage enough to reset quite a few things in the house, trip GFCI breakers, and reset the HVAC. So I went looking for anything that could do a soft-start on the compressor motor (it has a nameplate locked rotor of 78A, generator is rated for 39.6A, clearly not enough for a full-voltage start).

Lo and behold I find a company called Micro-Air that builds these Easy Start soft starters for home, RV, and Marine AC units. I ordered their 368 Series sized for my unit, it showed up in two days (FedEx actually came through for once) and I installed it on Tuesday. It runs five "learning" cycles to figure out how much it can throttle the start and you can use a rudimentary phone app (it has Bluetooth) to track the reduction. The first start clocked in at ~30A, the unit iterated down to where it leveled off at about 24A to start the condenser. The way it is connected the fan on top of the unit starts immediately (as normal) and the compressor comes in a very short time later after the fan is already rolling so you do not have both starting at the same time. The unit is permanently wired and operates all the time (not just when you are on generator) so like any soft start application you do get the added benefits of reduced contactor wear and reduced electrical strain on the motor. It also starts up a bit quieter than it used to.

After it finished the learning cycles on utility power I started the gen, transferred the house power, and let the AC start up whenever the thermostat called for it. I know the power roof fans (3) were running already and I am sure some other thing were running in the house. The condenser unit fired up without an issue, no light blinks or other issues in the house. My Powerware 5125 UPS for my networking and computer equipment detected a slight dip (there was a blip from the audio alarm) but everything worked fine. I checked the starting current at about 24A so it has slashed the startup surge to about 5800W which is well under the 9500W I have available. I still cannot run everything (we have electric water heaters, electric range, etc) but at least for power outages we can use the AC, well pump, refrigerator, freezer, lights, ceiling fans, TV, computers, etc and still have some margin left over with a machine that is half the size typically sold to run home AC units. Technically speaking I probably could have started up the AC on as small as a 6000W portable generator so I might attempt it with the portable unit at some point and report back.

The EasyStart Flex Home Soft Starter For Commerical or Residential By Micro-Air, LLC

www.micro-air.com www.micro-air.com

Best deal I found on them was here: Marine Air Conditioners - Soft Starters - WATER YACHT SOLUTIONS

There are also units from ICM and Hyper Engineering that I read some reviews on; they do the same thing and folks have reported good success. I liked the bluetooth and diagnostics available with the Micro-Air unit that you do not get with the other ones but they are less expensive.
 
They are hard on the compressor and will shorten life span. I wouldn't want them on when under utility power. But they are life savers for gens.
 
Ron said:
They are hard on the compressor and will shorten life span. I wouldn't want them on when under utility power. But they are life savers for gens.
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Maybe for an old piston compressor; this Lennox has an Emerson Copeland Scroll compressor that always starts unloaded. Emerson sells their own soft-start add-on for their scrolls, Lennox sells an add-on (which for their systems my dealer did not tell me about when I bought the system), and many others do as well. It does not affect the warranty on the condenser per Lennox (provided it in itself is not the cause of failure).

Having worked with soft starters for over two decades now in the industrial electrical world I have yet to see a three-phase unit be the cause of a motor or load failure when set up properly. I have zero experience with doing RVSS as single-phase but the concepts are nearly the same. Starting a motor requires enough torque on the rotor to get the load turning and locked rotor is generally a function of the impedance in the windings. It is force over time (work) to get the rotor to spin. It can either happen with more force and less time (cross line or hard starting) or less force with more time (soft start or VFD), same amount of work accomplished. Generally speaking locked rotor torque is rarely needed to actually get a load turning; I commissioned numerous RVATs running at 65% voltage taps (42% starting torque, 45% inrush) and only ever had one I needed to raise to 80% voltage to get a reliable start (large vertical turbine pump at a water plant with a "high efficiency" winding.)
 
Along these same lines are there any good load managers. Cutting power for non essentials in an order of importance?
 
OnlyOneDR said:
Maybe for an old piston compressor; this Lennox has an Emerson Copeland Scroll compressor that always starts unloaded. Emerson sells their own soft-start add-on for their scrolls, Lennox sells an add-on (which for their systems my dealer did not tell me about when I bought the system), and many others do as well. It does not affect the warranty on the condenser per Lennox (provided it in itself is not the cause of failure).

Having worked with soft starters for over two decades now in the industrial electrical world I have yet to see a three-phase unit be the cause of a motor or load failure when set up properly. I have zero experience with doing RVSS as single-phase but the concepts are nearly the same. Starting a motor requires enough torque on the rotor to get the load turning and locked rotor is generally a function of the impedance in the windings. It is force over time (work) to get the rotor to spin. It can either happen with more force and less time (cross line or hard starting) or less force with more time (soft start or VFD), same amount of work accomplished. Generally speaking locked rotor torque is rarely needed to actually get a load turning; I commissioned numerous RVATs running at 65% voltage taps (42% starting torque, 45% inrush) and only ever had one I needed to raise to 80% voltage to get a reliable start (large vertical turbine pump at a water plant with a "high efficiency" winding.)
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In my experience (certainly not all inclusive) resi HVAC units have much cheaper motors and less voltage tolerance .

Agreed fully on industrial motors and I’m usually arguing your side of the argument with FP soft start manufacturers not wanting to slow the ramp
 
Futbalfantic said:
Along these same lines are there any good load managers. Cutting power for non essentials in an order of importance?
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In a residential load center there really isn't anything for that yet. Eaton's EMCB fits in BR load centers and does have control capability but that would require having main metering with programmed IO that knows when you are on gen or not and measures the load. This is done routinely with automatic transfer switches, however, so if you have one of the more advanced residential ATSs this capability does exist. Eaton's Green ATS can load manage (drop loads and bring loads back online) but it generally requires addition equipment like contactors or relays on each circuit that needs control (because residential load center breakers do not have internal control other than that aforementioned EMCB). There are plenty of other ATSs that can do it as well.
 
Ron said:
In my experience (certainly not all inclusive) resi HVAC units have much cheaper motors and less voltage tolerance .

Agreed fully on industrial motors and I’m usually arguing your side of the argument with FP soft start manufacturers not wanting to slow the ramp
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Interesting; most of the time our folks never provided any guidance and left it for the field services folks (me and others) to come up with the start profile. Generally our product line did not want to start doling out suggestions.
 
paradisePWoffrd said:
i dont really know AC power, but would it be possible to put a large capacitor and timer on the compressor and fan, to help reduce the current spike on starting?
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Amazon product ASIN B008A3UJ82

Rectorseal makes exactly that, I use them on units with failing compressors you can get a few to several more years from a dying one using a kickstart.
I also use a soft start like linked above on my 15kbtu slide in ac and it lets me use a 2000w predator instead of the 3500.
That being said I agree with Ron, not knowing what condenser you have but you said it's 2 yrs old could very well be an ecm motor/controls and you could potentially be asking for trouble, or maybe not, hopefully it works out well. I would have assumed a 9500w gen would have run a 30kbtu ac though.
 
braxton357 said:
Amazon product ASIN B008A3UJ82

Rectorseal makes exactly that, I use them on units with failing compressors you can get a few to several more years from a dying one using a kickstart.
I also use a soft start like linked above on my 15kbtu slide in ac and it lets me use a 2000w predator instead of the 3500.
That being said I agree with Ron, not knowing what condenser you have but you said it's 2 yrs old could very well be an ecm motor/controls and you could potentially be asking for trouble, or maybe not, hopefully it works out well. I would have assumed a 9500w gen would have run a 30kbtu ac though.
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The Lennox condenser has an Emerson Copeland Scroll compressor with a standard capacitor start, no ECM. The only ECM is in the furnace, which I would really love to convert to a standard induction motor because the added complexity of the ECM doesn't do much when the unit runs at just one speed 95% of the time.

I was pretty certain the 9.5kW wasn't enough to start the compressor because the nameplate showed 78A locked rotor (18kW). Yes it is a surge but the regulator has to keep up with that and that is nearly twice the rating on the generator. When I tried it the voltage dipped substantially.
 
Those storms on Monday knocked out our power briefly during that "critical hour" trying to get the boy bathed and in bed. My wife joked that I was going to have to go outside and get things going; I laughed, walked over to the panel, turned the key switch I installed next to the panel to start the gen and flipped the breakers to transfer the house. The AC kicked on a few minutes later without issue and the only load I had to drop was the water heater which was in a cycle because we already ran the bath water. Man that was nice.

Related but unrelated I gutted the ECM blower a few weeks ago because it went on the fritz again the day we were leaving for a week's vacation; I had kept the old Goodman blower assembly, 24VAC CPT, and control relay so I retrofitted the motor into the Lennox blower housing, disabled the control board and retrofitted the old CPT and fan relay so the AC ran reliably while we were away. When we got back I bought an extra fan relay and wired it to Y2 and a higher fan speed winding (I had disabled stage 2 cooling for the temp fix) and now that works as well. I might just as well figure out how to do some relays to completely bypass the furnace control board and skip all that unreliable electronics crap altogether. Sad that I am really contemplating doing this permanently on a three-year old system but it is three years old and already crapped a thermostat (Honeywell VisionPro 8000) and either the ECM, the control board, or both (all I get is a comm failure to the ECM; I checked all the wiring and connections so it is either the $500 ECM board or the $500 control board). Either way it is kind of ridiculous but I need to figure something out before heating season since the furnace does nothing right now and we will definitely need that in a few short months.
 
Almost all of this convo is over my head......


So I'm wondering could all of it be solved by running something larger in the 10k range of output?
 
WARRIORWELDING said:
Almost all of this convo is over my head......


So I'm wondering could all of it be solved by running something larger in the 10k range of output?
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Per my original post my 9.5kW could not start the 2.5ton condenser unit. To do this most folks would get something in the 15W+ range which is more expensive and uses more fuel even on light loading. For me it was a function of what I found used at the time, had I found something larger I would have bought it. But this exercise taught me some things about running these AC systems on smaller gens.
 
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OnlyOneDR said:
Per my original post my 9.5kW could not start the 2.5ton condenor unit. To do this most folks would get something in the 15W+ range which is more expensive and uses more fuel even on light loading. For me it was a function of what I found used at the time, had I found something larger I would have bought it. But this exercise taught me some things about running these AC systems on smaller gens.
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Part of my question was to see if my current 10k mostly welder would do for my personal application......and I've always wanted more welder output. I have been studying on an upgrade. The question then is how much generator output is needed. Mainly because most DC output true welders make horrible generators. However modern inverter tech has hit portable welders so the game is changing some. With the added tech it can be a trade off in reliability and cost of repair. Ideally I want the best of both..... realistically you sacrifice one for the other.
 
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