AC running on portable generator?

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SSDriver

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Electrician
I don't deal with generators much but I was curious if you think I might run into any issues running my AC and a few small things on my portable generator at my personal house. Looking at the numbers I feel it should be OK, I'm just not sure if I missed something other than starting currents that might effect its operation. I'm waiting on the generator to be delivered. It's one I ordered for work and was hoping i can use it at my house during summer as well.

Generator: WEN 875i inverter, 8700 surge watts, 7000 wats continuous.


Here's a pic of my house usage with the AC running. Note I probably wouldn't be running the dishwasher with AC on generator power. The two ACa are just the two CTs.

Screenshot_20220303-092645.jpg
 
The issue is their start up surge and whether the generator can handle it. Locked Rotor Amps can be pretty large on an AC unit. Are these AC units 120V or 240V? If the running amps is around 15, that is a medium size AC unit (like 2.5 to 3 tons each if 240V). Some generators say "will start a X ton AC unit". My 15KW generator says it will start a 4 ton AC unit.

May want to call WEN and see if they can tell you how large of an AC unit this will typically start.
 
suemarkp said:
The issue is their start up surge and whether the generator can handle it. Locked Rotor Amps can be pretty large on an AC unit. Are these AC units 120V or 240V? If the running amps is around 15, that is a medium size AC unit (like 2.5 to 3 tons each if 240V). Some generators say "will start a X ton AC unit". My 15KW generator says it will start a 4 ton AC unit.

May want to call WEN and see if they can tell you how large of an AC unit this will typically start.
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It's a single 240v AC unit. With a CT on each leg. AC is 29 years old, we hope to replace it next year.
 
suemarkp said:
The issue is their start up surge and whether the generator can handle it. Locked Rotor Amps can be pretty large on an AC unit. Are these AC units 120V or 240V? If the running amps is around 15, that is a medium size AC unit (like 2.5 to 3 tons each if 240V). Some generators say "will start a X ton AC unit". My 15KW generator says it will start a 4 ton AC unit.

May want to call WEN and see if they can tell you how large of an AC unit this will typically start.
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A rule of thumb I have always heard is that LRA (startup current in Amps) for an AC is about 6X the running current. You can ameliorate that somewhat with a softstart gizmo.
 
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I was looking and it seems a lot of people running off of smaller generators install hard start kits. I might try one as they are only $10-15 for my size AC. I'm curious to see what the inrush is before/after. I just went outside and the common terminal on my 29 year old capacitor looks like the solder joint is failing. Going to replace that as well.
 
SSDriver said:
I was looking and it seems a lot of people running off of smaller generators install hard start kits. I might try one as they are only $10-15 for my size AC. I'm curious to see what the inrush is before/after.
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Please do let us know, and whether adding it changes a won't-start-it into a will-start-it condition.

Is a hard-start (what it cures) kit another name for a soft-start (what it provides) kit, or are they two different things?
 
LarryFine said:
Please do let us know, and whether adding it changes a won't-start-it into a will-start-it condition.

Is a hard-start (what it cures) kit another name for a soft-start (what it provides) kit, or are they two different things?
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I will definitely post the results. I will check inrush before/after and starting voltage sag on generator before/after(if it will run before/after.)

A hard start kit is just a start capacitor with a lot higher uF raring and a potential relay that cuts it out of the circuit after starting. I actually ended up buying a better unit for $35 bucks.

A soft start is in the $300 plus range and has SCRs.

I'm hopefully replacing the AC in the next year or so and didn't want to spend too much on it but want to get through this summer. Also I would think a hard start kit might be better for high torque.
 
SSDriver said:
A hard start kit is just a start capacitor with a lot higher uF raring and a potential relay that cuts it out of the circuit after starting. I actually ended up buying a better unit for $35 bucks.

A soft start is in the $300 plus range and has SCRs.
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What is the functional difference?
 
LarryFine said:
What is the functional difference?
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I definitely don't have the experience with ACs and either of these units. My assumption would be the capacitor will still have the same LRC for starting but it would shorten the starting time/cycles dramatically to allow it to function and show a lower motor inrush on a regular meter that can only read every 100ms. And in turn doesn't bog the generator down.

The soft start I think(not sure) would work similar to a drive/inverter and ramp it up on start up. I belive it only ramps up the voltage, it doesn't change the speed/HZ like a VFD.
 
I should add I've heard a lot of guys with RVs use the hard start kits because of the cheap price and it does allow them to use smaller inverters to run their RVs with AC. For $35 I'm willing to give it a shot and I'm now curious to test and see readings, lol
 
Make sure the compressor has short-cycle protection so you're not trying to start it against high refrigerant pressure.

A hard-start kit is usually little more than a bigger capacitor in the start winding. I would think that the large capacitor means lower impedance in the start-winding circuit, which seems like it would increase current in the start winding. Am I missing something? Is there something about a greater phase shift due to the greater capacitance that reduces current in the start winding? Does it just look like lower inrush current on a slow-responding meter because the motor starts faster? Is it all a bunch of hooey, something we learned from our dads?
 
SSDriver said:
I was looking and it seems a lot of people running off of smaller generators install hard start kits. I might try one as they are only $10-15 for my size AC. I'm curious to see what the inrush is before/after. I just went outside and the common terminal on my 29 year old capacitor looks like the solder joint is failing. Going to replace that as well.
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Super capacitors just reduce the start time, not the inrush.
Still, the start times affect the generator as well..

hvacrschool.com

Start Capacitor & Inrush, Facts & Myths - Part #4 - HVAC School

Now is the part where we get specific about start capacitors and inrush. If you haven't read the first three parts, please do so before reading this one, or it may not make sense. (You can find Part #1, Part #2, and Part #3 at these links.) I'm going to come out and say it […]
hvacrschool.com hvacrschool.com
 
The AC is only a peice of the puzzle in determining load capacity needed and whether a specific generator will be large enough. Don't forget other automatic loads that might not have control of and may start simultaneously, refrigerator, freezer, and some have limited control by not using like the coffee maker hot plate that will cycle. I have a generator a little more than half that size and will shuffle loads as needed it will run both refrigerators and the freezer simultaneously without an issue, but when the hotplate kicks on you can hear its effect on the generator.

Now you also state you ordered the generator for work purposes, now those are mfg with a required GFCI and internal bonding. If intent is to use with a whole house transfer switch you will have issue with the dual N/G bonding and you will get GFCI tripping on the generator.
 
I had a 7500W (9000surge) generator I ran for years until I broke down to a whole house.
shuffling loads was the name of the game. Turn off well, heat water in water heater. Turn off water heater, turn on well pump to shower…etc..
I could run one three ton AC unit with it, but nothing else because of starting/stopping.
Didn't do that but once though. Normally here it’s just winter outages and we have a gas fireplace that heats well.

I did come in one evening and my wife told me, “That generator doesn’t like the dryer at all”😅
(my wife is a terrible load shifter)

That is a great generator. It’s a Lemarch(?) Still crank it to keep the oil stirred up.
 
SSDriver said:
I definitely don't have the experience with ACs and either of these units. My assumption would be the capacitor will still have the same LRC for starting but it would shorten the starting time/cycles dramatically to allow it to function and show a lower motor inrush on a regular meter that can only read every 100ms. And in turn doesn't bog the generator down.

The soft start I think(not sure) would work similar to a drive/inverter and ramp it up on start up. I belive it only ramps up the voltage, it doesn't change the speed/HZ like a VFD.
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The thing that complicates this is your generator typically can not deliver the current that the utility can, the utility voltage drop likely not as severe as the generator voltage drop the instant that load comes on line, on top of that utility frequency will remain constant, generator frequency will drop, possibly a fair amount in some cases. Any kind of soft starting method makes the startup last longer but will not take the voltage and frequency down nearly as much.
 
Quick update.

I ended up canceling my generator order for the WEN and went with a Duromax XP9000ih dual fuel for multiple reasons(quieter, dual fuel, 3 year warranty). The AC draws 107 amps on inrush and would not start on the generator. I ended up installing a soft start(Hyper Engeneering Sure Start) instead of a hard start as I got one for free from a friend. Both of my meters only show a 5 to 6 amp inrush as the unit is ramping up so im not really sure if that's accurate. The 5 ton AC does start everytime on the generator with the soft starter.

Second update:
Update on my Emporia. I noticed the amperage readings were quite low compared to my two meters(fluke and amprobe). I contacted tech support and they explained that the Emporua uses real power amperage readings instead of apparent power. If I viewed the wattage readings they lined up with my meter and within 2% of the reading on my POCO smart meter. They said they are working on adding apparent power amp readings and voltage readings to the app. So for the time being I will be in the watts reading configuration to see what's going on. My AC draws 19 amps when measured by my multimeter and the wattage lines up with the emporia but not amps if in amps view on the emporia. A-leg was at 26 amps and B-leg was just over 20 amps when the AC was running, AC blower motor, with a TV on and a few lights.

I will be converting the Generator to tri fuel soon so I can run it off of CNG and see how it runs.
 
SSDriver said:
Quick update.

I ended up canceling my generator order for the WEN and went with a Duromax XP9000ih dual fuel for multiple reasons(quieter, dual fuel, 3 year warranty). The AC draws 107 amps on inrush and would not start on the generator. I ended up installing a soft start(Hyper Engeneering Sure Start) instead of a hard start as I got one for free from a friend. Both of my meters only show a 5 to 6 amp inrush as the unit is ramping up so im not really sure if that's accurate. The 5 ton AC does start everytime on the generator with the soft starter.

Second update:
Update on my Emporia. I noticed the amperage readings were quite low compared to my two meters(fluke and amprobe). I contacted tech support and they explained that the Emporua uses real power amperage readings instead of apparent power. If I viewed the wattage readings they lined up with my meter and within 2% of the reading on my POCO smart meter. They said they are working on adding apparent power amp readings and voltage readings to the app. So for the time being I will be in the watts reading configuration to see what's going on. My AC draws 19 amps when measured by my multimeter and the wattage lines up with the emporia but not amps if in amps view on the emporia. A-leg was at 26 amps and B-leg was just over 20 amps when the AC was running, AC blower motor, with a TV on and a few lights.

I will be converting the Generator to tri fuel soon so I can run it off of CNG and see how it runs.
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Not certain exactly what you have there. I will say if it is measuring amps, then it should display amps.

If it is measuring watts, then it should display watts, which to do so on other than 1.0 power factor, you need to input both voltage and amps and the unit needs ability to determine what to display if the current is not in phase with the voltage - which is what you will have if not 1.0 power factor.
 
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