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Started By
Message
Run Your Central Air with a Portable Generator
Posted on 7/9/21 at 2:38 pm
Posted on 7/9/21 at 2:38 pm
I’ve mentioned this in a few threads but figured it was worthy of its own.
The ticket to making this feasible is the MicroAir Easy Start 368 soft starter:
LINK
And for those who don’t understand soft starting, I’ll pull a quote from a previous post I made:
The size of your unit will obviously play a big factor but if you read the reviews on the MicroAir site, some people are able to run a 3.5 ton unit with a 5.5kW generator. A slightly larger portable generator may be needed if you have a 4 or 5 ton unit, but it is still considerably smaller than what would be needed without the soft starter.
I’m sure some of you may ask about hard start kits - they are similar to soft starters in that they reduce your starting current (although not as substantially). They add a capacitor to the starting circuit for less than a second to help the compressor get up to speed faster. They are considerably cheaper and if you measure a considerably lower starting current while using one, you may be able to get away with using a portable generator for your unit. It’s less likely but still can be done. This kit from Amrad is what I use and what I’d recommend. Pairing it with an Amrad run capacitor is ideal:
LINK /
Overall, soft starters and hard start kits can reduce your starting current and increase the life of your compressor. Compressors take the biggest beating when they initially start up and build heat internally. If you’ve seen the dimming lights in your house and heard the labored buzz from your unit while starting, either one of these could benefit you.
Good luck, DIY’ers.
The ticket to making this feasible is the MicroAir Easy Start 368 soft starter:
LINK
And for those who don’t understand soft starting, I’ll pull a quote from a previous post I made:
quote:
Most generators can power central air when they are running normally and up to speed. This would be considered “full load amps” (to keep it basic).
The problem most generators have is starting up central air units. They simply do not have enough juice to get them moving initially. Imagine trying to push a very heavy box across the floor - you need that initial jolt of energy and inertia to get it in motion. Once it’s in motion, it becomes less difficult to keep in motion. Starting up a motor works in a similar way in regards to electricity.
Ever seen the lights in your house dim when your AC kicks on? That’s typically from the initial jolt of “starting current” (also sometimes called locked-rotor amps, LRA). Considerably more electrical energy is needed to get motors in motion. This jolt doesn’t last long but can be 4-8 times the full load amps (depending on the motor). After a motor is started and in motion it will settle into its full load amps (FLA) and hover around it depending on the load. Most portable generators can handle the FLA rating of a compressor. Reducing starting current becomes the key.
What a soft starter does is power a motor slowly rather than hitting it with 100% of available power at startup - think of increasing radio volume slowly by turning a knob. The unit mentioned earlier can reduce starting current substantially in this manner.
The size of your unit will obviously play a big factor but if you read the reviews on the MicroAir site, some people are able to run a 3.5 ton unit with a 5.5kW generator. A slightly larger portable generator may be needed if you have a 4 or 5 ton unit, but it is still considerably smaller than what would be needed without the soft starter.
I’m sure some of you may ask about hard start kits - they are similar to soft starters in that they reduce your starting current (although not as substantially). They add a capacitor to the starting circuit for less than a second to help the compressor get up to speed faster. They are considerably cheaper and if you measure a considerably lower starting current while using one, you may be able to get away with using a portable generator for your unit. It’s less likely but still can be done. This kit from Amrad is what I use and what I’d recommend. Pairing it with an Amrad run capacitor is ideal:
LINK /
Overall, soft starters and hard start kits can reduce your starting current and increase the life of your compressor. Compressors take the biggest beating when they initially start up and build heat internally. If you’ve seen the dimming lights in your house and heard the labored buzz from your unit while starting, either one of these could benefit you.
Good luck, DIY’ers.
7
Posted on 7/9/21 at 2:47 pm to bapple
the main issue with generator power is a non steady voltage level output
fluctuating voltage kills compressor motors over time.
not saying it will fail right away but it does take years off of how long your compressor lasts
the key to generator power is to have a voltage regulator that maintains constant steady voltage and then your ok
fluctuating voltage kills compressor motors over time.
not saying it will fail right away but it does take years off of how long your compressor lasts
the key to generator power is to have a voltage regulator that maintains constant steady voltage and then your ok
Posted on 7/9/21 at 4:14 pm to keakar
Good info. Thanks for the addition. Definitely need clean power from the generator.
Posted on 7/9/21 at 7:51 pm to bapple
believe it or not
i'm actually in the process of developing a soft starter for a portable air conditioner unit with use of an arduino, triac, start capacitor, and various other components
i've been poking around with this on a breadboard tied into a 8k(10k due to inefficiency) BTU stand-alone unit.
This is kinda a hobby project because I have a 2000W craftsman inverter generator that would take a good hit when the unit would kick on
These were the numbers i measured without the soft starter:
LRA - ~28A
FLA - ~5A
After I tied in my prototype soft starter:
LRA - ~10A
FLA - ~5A
so that's a good 60-70% reduction in start current
The circuit and programming isn't necessarily difficult, at least in my book since i don't have a learning system like the commercial ones do to fine tune the voltage ramp on the triac to get a minimum, it just took some manual tuning of the ramp to get it right
The process goes as such:
1. contactor closes, run capacitor + auxiliary winding immediately connected in
2. arduino boots up
3. start capacitor connected in parallel with run capacitor via relay triggered by arduino
4. voltage ramp starts on ONLY THE MAIN WINDING via triac
5. when the motor speeds up the voltage across the start winding rises, when it reaches 85% of the max start winding voltage (via back emf my start winding reaches 170V) the arduino drops the start capacitor out
6. triac immediately starts firing for full voltage after the start capacitor is dropped out
7. bypass relay bypasses the triac and the triac stops firing
8. compressor is now running
i'm actually in the process of developing a soft starter for a portable air conditioner unit with use of an arduino, triac, start capacitor, and various other components
i've been poking around with this on a breadboard tied into a 8k(10k due to inefficiency) BTU stand-alone unit.
This is kinda a hobby project because I have a 2000W craftsman inverter generator that would take a good hit when the unit would kick on
These were the numbers i measured without the soft starter:
LRA - ~28A
FLA - ~5A
After I tied in my prototype soft starter:
LRA - ~10A
FLA - ~5A
so that's a good 60-70% reduction in start current
The circuit and programming isn't necessarily difficult, at least in my book since i don't have a learning system like the commercial ones do to fine tune the voltage ramp on the triac to get a minimum, it just took some manual tuning of the ramp to get it right
The process goes as such:
1. contactor closes, run capacitor + auxiliary winding immediately connected in
2. arduino boots up
3. start capacitor connected in parallel with run capacitor via relay triggered by arduino
4. voltage ramp starts on ONLY THE MAIN WINDING via triac
5. when the motor speeds up the voltage across the start winding rises, when it reaches 85% of the max start winding voltage (via back emf my start winding reaches 170V) the arduino drops the start capacitor out
6. triac immediately starts firing for full voltage after the start capacitor is dropped out
7. bypass relay bypasses the triac and the triac stops firing
8. compressor is now running
This post was edited on 7/9/21 at 8:02 pm
Posted on 7/9/21 at 10:56 pm to DVinBR
That’s very impressive. Love a good electrical project!
Do you know if all soft starters use pulse width modulation? I assume it’s like a VFD but without the variable part.
I’m an electrical engineer in the industrial sphere so I specify those components pretty often. But I know there are various ways to soft start a motor without necessarily using PWM. How does yours deal with the stepping up of voltage?
Those are great numbers though. Sounds like you’re making a great setup.
Do you know if all soft starters use pulse width modulation? I assume it’s like a VFD but without the variable part.
I’m an electrical engineer in the industrial sphere so I specify those components pretty often. But I know there are various ways to soft start a motor without necessarily using PWM. How does yours deal with the stepping up of voltage?
Those are great numbers though. Sounds like you’re making a great setup.
Posted on 7/9/21 at 11:42 pm to bapple
3 phase can use a VFD but single phase can't because they are capacitor start/run, and the capacitor's impedance is frequency dependent
you have to use phase control of the voltage using a triac to soft start single phase motors (you can also do it for 3 phase it is an option)
the start capacitor provides the extra torque to the auxiliary winding
the triac slowly ramps up the average power to the main winding via phase control rather hitting it at full power at once
the triac is driven something like this by the arduino
i have a small transformer that steps 120V down to 12V, i have rectifier/capacitor to give me DC, then a 5V voltage regulator to power the arduino
i pluck off the 12V AC secondary of the transformer to run to an bidirectional optocoupler to sense the zero crossing of the AC waveform, the output of the optocoupler is connected to the arduino input
[/img]
Via an interrupt function within the arduino C language, every time the input senses a zero crossing, it triggers a function to fire the triac, within this function there is a delay with an integer number of microseconds before the function triggers the triac
you have to use phase control of the voltage using a triac to soft start single phase motors (you can also do it for 3 phase it is an option)
the start capacitor provides the extra torque to the auxiliary winding
the triac slowly ramps up the average power to the main winding via phase control rather hitting it at full power at once
the triac is driven something like this by the arduino
i have a small transformer that steps 120V down to 12V, i have rectifier/capacitor to give me DC, then a 5V voltage regulator to power the arduino
i pluck off the 12V AC secondary of the transformer to run to an bidirectional optocoupler to sense the zero crossing of the AC waveform, the output of the optocoupler is connected to the arduino input
[/img] Via an interrupt function within the arduino C language, every time the input senses a zero crossing, it triggers a function to fire the triac, within this function there is a delay with an integer number of microseconds before the function triggers the triac
This post was edited on 7/9/21 at 11:56 pm
Posted on 7/10/21 at 11:10 am to bapple
Get a window unit. More likely will lead to something breaking or trouble trying to run off a small generator
Posted on 7/10/21 at 1:50 pm to bapple
So for us non electrical types, if I get a soft start, what size generator can I run my central ac with?
The plate on my ac states:
Fan Motor: 1.3 FLA. 1/4HP
Compressor 17.9 RLA. LRA: 112
The plate on my ac states:
Fan Motor: 1.3 FLA. 1/4HP
Compressor 17.9 RLA. LRA: 112
Posted on 7/10/21 at 3:22 pm to Grassy1
So I’ll keep it simple and you can make the final call.
7000W/240V = 29.16A - so a 7kW generator can provide almost 30A @240V, but note this is fully loaded. So you would have basically no room for other loads on the generator. I wouldn’t advise getting to that upper limit and keeping it below 75% loaded at a maximum. This gives you a bit of a safety net. As for starting, generators also have a surge/peak rating. So your starting current would need to be at or below this threshold.
With that example, I don’t think you can make a full assessment until you’ve talked to MicroAir or purchased a soft starter. While their soft starters significantly reduce the staring current you won’t know for sure until you have it hooked up to your specific until. Given the numbers, you should be able to determine the best size generator with some simple math.
7000W/240V = 29.16A - so a 7kW generator can provide almost 30A @240V, but note this is fully loaded. So you would have basically no room for other loads on the generator. I wouldn’t advise getting to that upper limit and keeping it below 75% loaded at a maximum. This gives you a bit of a safety net. As for starting, generators also have a surge/peak rating. So your starting current would need to be at or below this threshold.
With that example, I don’t think you can make a full assessment until you’ve talked to MicroAir or purchased a soft starter. While their soft starters significantly reduce the staring current you won’t know for sure until you have it hooked up to your specific until. Given the numbers, you should be able to determine the best size generator with some simple math.
Posted on 7/10/21 at 3:30 pm to DVinBR
quote:
DVinBR
Some seriously in-depth work you’re doing there! Very nice.
Most of my work has been with 3 phase motors so I’ll admit my lack of knowledge when it comes to single phase motors. But what you said makes sense. I haven’t done a ton of work with semiconductor devices either but it’s amazing what they are capable of.
Posted on 7/10/21 at 3:52 pm to Grassy1
look at the peak surge rating of the generator, then decrease the LRA by the percent amount that a soft starter can decrease it by, if that reduction is within spec of the surge rating of the generator you are good to go
but you also need to consider other loads you have connected to the generator as well with this calculation
but you also need to consider other loads you have connected to the generator as well with this calculation
This post was edited on 7/10/21 at 3:55 pm
Posted on 7/10/21 at 4:46 pm to bapple
yeah this project is pretty sweet, im able to start that 10k BTU unit while my 2000W inverter generator is on eco mode
the next hard part is developing a compact printed circuit board along with an enclosure for it
the next hard part is developing a compact printed circuit board along with an enclosure for it
Posted on 7/10/21 at 7:11 pm to DVinBR
quote:
but you also need to consider other loads you have connected to the generator as well with this calculation
+1 to this
Once you figure out how much your HVAC is going to load the generator you need to be choosy with other loads. If you think you may forget, it's best to turn off all breakers in the panel and choose them one-by-one (now is a good time to label the circuits in the panel if they aren't).
Any devices that use electricity to generate heat will be your largest loads, including incandescent light bulbs. If you haven't done so, convert all your lights to LED and it will reduce your energy consumption where they become negligible to a generator.
quote:
then decrease the LRA by the percent amount that a soft starter can decrease it by
Some have reported different LRA ratings compared to others, depending on the unit. This is a good baseline but for the OP, I'd use their lowest reported reduction to be conservative - if they claim a 50-70% reduction in starting current, go with the 50% when figuring out sizing.
quote:
yeah this project is pretty sweet, im able to start that 10k BTU unit while my 2000W inverter generator is on eco mode
the next hard part is developing a compact printed circuit board along with an enclosure for it
That is pretty sweet. Can you source many circuit boards domestically? I know Covid shut down a big supply line for boards.
Posted on 7/10/21 at 8:38 pm to keakar
quote:
the main issue with generator power is a non steady voltage level output
fluctuating voltage kills compressor motors over time.
Yep…I ruined a refrigerator with a cheap generator during a hurricane one time. When power came back on I went to Lowe’s to get another fridge and there were three other guys buying new refrigerators for the same reason.
Posted on 7/10/21 at 10:20 pm to bapple
quote:
The size of your unit will obviously play a big factor
Ain't that the truth
Posted on 7/10/21 at 10:50 pm to Spankum
quote:
I ruined a refrigerator with a cheap generator during a hurricane one time
I can see how those voltage fluctuations and harmonics could affect a compressor.
Keep in mind that the soft starter does not drop out of the circuit after the compressor is running. If I remember correctly, there are a few built-in protection features like undervoltage and brownout protection. I imagine with how much the electronics clean up the signal that it could offset any dirty power the compressor could see.
I’ll have to do a bit more digging on the other technical aspects of the MicroAir but it was developed for RV compressors initially. I imagine they built them with generator power in mind.
quote:
Ain't that the truth
End of thread!
Posted on 7/11/21 at 10:33 am to bapple
Talk about a timely thread! Just did my 5hr break-in yesterday with my new Champion 100110, 11500W/9200W generator and testing of the new transfer switch process. It ran my AC unit fine yesterday but I shut off breakers to my other major appliances before starting the AC. These are the numbers on my unit.
Compressor RLA 17.9 LRA 104
Fan Motor FLA 1.6 HP 1/4
Compressor RLA 17.9 LRA 104
Fan Motor FLA 1.6 HP 1/4
Posted on 7/11/21 at 11:48 am to GCTigahs
quote:
Champion 100110, 11500W/9200W
That’s a pretty good sized generator. 9200W/240V = 38A fully loaded. That can easily handle your running amps and only loads it about 50%. Drop that starting current with a soft starter and you should be in business.
Posted on 7/11/21 at 12:06 pm to bapple
Appreciate the reply Bapple. Although I’ve used generators before, this is my first purchase of one. So needless to say, I don’t know much about what I’m doing besides talking with my electrician who put in my transfer switch and recommended this particular generator and watching a few YouTube videos.
The testing procedure went well yesterday. I ran the gen out of gas yesterday during the 5hr break in and will change the oil today. Will have her covered and stowed away in the garage. Hopefully won’t need it this summer but ready if I do.
The testing procedure went well yesterday. I ran the gen out of gas yesterday during the 5hr break in and will change the oil today. Will have her covered and stowed away in the garage. Hopefully won’t need it this summer but ready if I do.
This post was edited on 7/11/21 at 12:10 pm
Posted on 8/11/21 at 1:17 pm to GCTigahs
Im looking at getting the same generator 11500 Champion. I guess I will be ok. My AC numbers are below.
Compressor - RLA 19.9/19.9
Fan Motor - FLA1.2 HP 1/5
Compressor - RLA 19.9/19.9
Fan Motor - FLA1.2 HP 1/5
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