Very new to solar. But I only want to take my AC unit off Grid. My Unit is a 3 Ton. 14 SEER. It said 75k BTUH Input and 60k BTUH Output. It’s a 220/240v but i get confused with no matter which calculators in using out there to find the power consumption in wattage per day for the AC they all give me different amounts. I don’t want to mess this up. Does anyone know how much usage that would be if it runs lets say 6-7hrs per day for example?
3 Ton AC unit how much energy?
- Thread starter Stevang05
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sunshine_eggo
Happy Breffast!
Look up your unit. There is a run current. Multiply that times 240. That's the number of Watts it burns. Then you multiply it by 6-7h, and that's your Wh/day it consumes.
Lastly, check the LRA value. That's the Locked Rotor Amps. That's the surge the unit will pull when the compressor starts up. It is often 5X more than the run current, and it will bring an inverter to its knees. Any inverter you plan to use must be able to handle the LRA surge. Most high frequency inverters can't hope to start an A/C compressor.
Lastly, check the LRA value. That's the Locked Rotor Amps. That's the surge the unit will pull when the compressor starts up. It is often 5X more than the run current, and it will bring an inverter to its knees. Any inverter you plan to use must be able to handle the LRA surge. Most high frequency inverters can't hope to start an A/C compressor.
I’m terrified, if I do the math it would be like 5kwh. ??
So I would pretty much add those things in Red for the compressor and blower(s)? How big of a system do you think I’d need guesstimating?
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sunshine_eggo
Happy Breffast!
Yep - about 5kW. In reality, those are current maximums, and your consumption is probably a little less. If you can get a clamp ammeter around one of the legs feeding the compressor, you can compare that value to the rating and scale things accordingly.
The really killer is the 79.0 LRA... 79 * 230 = 18.17kW - you'll need an inverter that can handle this surge.
^^^^^ What he said
Yes, the heat pump is the worst to start from an inverter.
You have quite a challenge!
My heat pump LRA is 132A.
No way my inverter can do that.
After starting, the heat pump & blower settles down to 2-3kw, which is fine.
I am going to add one of these to the heat pump compressor circuit.
It seems to be a type of VFD (Variable Frequency Drive)
The company tech support says it installing their device will reduce the start up LRA to about 38A, which will let my inverter start it easily.
eltwin-hyper.com
Yes, the heat pump is the worst to start from an inverter.
You have quite a challenge!
My heat pump LRA is 132A.
No way my inverter can do that.
After starting, the heat pump & blower settles down to 2-3kw, which is fine.
I am going to add one of these to the heat pump compressor circuit.
It seems to be a type of VFD (Variable Frequency Drive)
The company tech support says it installing their device will reduce the start up LRA to about 38A, which will let my inverter start it easily.
Eltwin Hyper | Eltwin
eltwin-hyper.com
How about telling us why you want to take only your AC off grid?
Do you have grid tie solar now? Just expand enough to cover the A/C.
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RCinFLA
Solar Wizard
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- Jun 21, 2020
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- 3,564
A 3 ton air conditioner is 36K btu. The 60 Kbtu number on label appears to be for gas heater.
Startup surge current can be, and usually is, greater than locked rotor current number on compressor as the number on compressor label is for lowest spec'd AC voltage so branch circuit breaker amperage can be set to ensure true failure continuous locked rotor trip at lowest AC voltage.. You likely have over 100 amp startup surge current.
My 4 ton (48k btu) Copeland compressor has labelled 109 amps LRA. Actual startup surge measured 198 amps for 400 msecs at 240vac with accurate closed loop hall effect sensor. Cheap clip-on ampmeters with surge feature often show lower surge numbers due to too much time averaging. Actual startup surge amps is dependent on grid voltage, wiring gauge and run length from breaker box to compressor.
I installed a capacitor boost / softstarter device, MicroAir Easy Start 368, which brought the startup surge down from 198 amps to 78 amps. I run my unit on 11 kW continuous low frequency inverter that has 124 amp surge capability for 3 seconds. Battery capacity must be capable of the large 48vdc surge current of 600-800 amps.
Startup surge current can be, and usually is, greater than locked rotor current number on compressor as the number on compressor label is for lowest spec'd AC voltage so branch circuit breaker amperage can be set to ensure true failure continuous locked rotor trip at lowest AC voltage.. You likely have over 100 amp startup surge current.
My 4 ton (48k btu) Copeland compressor has labelled 109 amps LRA. Actual startup surge measured 198 amps for 400 msecs at 240vac with accurate closed loop hall effect sensor. Cheap clip-on ampmeters with surge feature often show lower surge numbers due to too much time averaging. Actual startup surge amps is dependent on grid voltage, wiring gauge and run length from breaker box to compressor.
I installed a capacitor boost / softstarter device, MicroAir Easy Start 368, which brought the startup surge down from 198 amps to 78 amps. I run my unit on 11 kW continuous low frequency inverter that has 124 amp surge capability for 3 seconds. Battery capacity must be capable of the large 48vdc surge current of 600-800 amps.
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The AC unit has added much more usage that I was anticipating making my electric bill at an uncomfortable monthly amount.
I don’t have a system of any kind right now other than the grid connection right now.
If you are pulling nearly double the LRA on startup, you have bad capacitors, or a failing compressor… get a hard start kit installed… and get the system serviced…
RCinFLA
Solar Wizard
- Joined
- Jun 21, 2020
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Nothing wrong with capacitor. Read up on what LRA spec means. It is not starup surge current. It is much lower then typical startup because LRA spec is at lowest AC voltage and increased copper wire loss due to hot compressor. Also when rotor is not truely locked but rotating at a very low rpm allowing low frequency rotor induction current pickup the run and starter windings draw more current. How much power do you think it takes to take a rotor mass from zero rpm to 93% synchronous rpm speed in a very small amount of time and what does that have to do with a locked rotor situation.
For air conditioner compressors run capacitor is a compromise between startup and run power factor improvement. The start capacitor boost + softstarters temporarily increase starter capacitor value by about 5x during spin up to increase startup rotational torque for full 360 degree rotation angle. This must be mated with a voltage ramp soft starter otherwise the peak current will be higher for a shorter startup time.
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This right here. Let the utility company be the battery. This is by far the most cost effective way to do it.
MarkSolar
Solar Enthusiast
I'd start by buying a clamp on ammeter that accumulates power and make sure you know what the requirement actually is. You'll need to spend a lot of money to implement what you're trying to do, figure out how much it will save you on your power bill and how long it will take to break even.
You could install a grid tie inverter and let the utility company start your A/C, then if your array is producing power it can run or supplement the A/C draw, or maybe you can sell the power back if the A/C is not on. Not sure where you live, but A/C is likely a seasonal thing, you're going to spend a lot of money trying to support a device that may not run all the time. When I looked at our power requirements the cost of batteries made it impractical to go that direction so I went grid tie.
The other possibility is if your utility offers hourly pricing, you could use your house as a thermal battery. Run your A/C all night when the power is really cheap and get the temp really low in the house, then turn off the A/C all day. That can work well if you have a newer house that's insulated and your family won't move out and leave you.
You could install a grid tie inverter and let the utility company start your A/C, then if your array is producing power it can run or supplement the A/C draw, or maybe you can sell the power back if the A/C is not on. Not sure where you live, but A/C is likely a seasonal thing, you're going to spend a lot of money trying to support a device that may not run all the time. When I looked at our power requirements the cost of batteries made it impractical to go that direction so I went grid tie.
The other possibility is if your utility offers hourly pricing, you could use your house as a thermal battery. Run your A/C all night when the power is really cheap and get the temp really low in the house, then turn off the A/C all day. That can work well if you have a newer house that's insulated and your family won't move out and leave you.
