Yea, I have been following those threads with great interest. Sure would like to not
have to buy different UPS models.
My proposed system can't power my AC
- Thread starter hodad66
- Start date
Yea, I have been following those threads with great interest. Sure would like to not
have to buy different UPS models.
Tesla tweaked the parameters on my system, so I will test it tomorrow and see if it works better. Fingers crossed.
New firmware and new parameters did the trick. Tesla's technician saw that my solar inverters turned off at 60.7 Hz, so he set the cut-off frequency at 61.0 Hz. Bingo. I turned off the grid power today and watched for a couple of hours as the solar inverters cycled off smoothly when the PW2s reach full charge, and turned back on when they dipped below full charge. I did not see any lock-up and the line frequency did not exceed 61 Hz. The A/C ran fine and the UPSs didn't beep. I am delighted.
If I have a Tesla Powerwall installed by a third party who was not Tesla/Solar City. Does Tesla still service my PowerWall and would they make this frequency change? Is there a phone number I'm supposed to call? There is a Service Request link for Powerwalls on the Tesla website, but I think my account information only pertains to my installer (it is one of the requisites to fill out the form) so I'm not sure if the request link would work.
david_42
Member
Have to agree 58 seems way too high. I had a two-ton heatpump on my last place and it was rated at 22 LRA. Running amps were around 12. Had a very difficult time convincing the electrician that is should be fused at 25-amps. He actually brought a 30-amp and a 40-amp breaker in addition to the 25-amp when he came to run the power. It was also a variable displacement compressor.
Well, I'm still having difficulty trying to have AC with my 2 powerwalls. The install
is scheduled for June 27 but I have found out that my compressor is not a scroll
but a reciprocating unit. (the original installer swore that it was a scroll). Tesla wants
a scroll at max of 56 LRA. I'm trying to see if we can install a new compressor unit
(scroll & 56 or lower) but the initial company said that all the newer ones were 60 LRA
or more.
I have a different company looking also for a Trane unit as well as giving me an estimate
on a mini-split system for just the bedroom (s). I need that like a hole in the head but I really
want SOME AC available after a hurricane.
is scheduled for June 27 but I have found out that my compressor is not a scroll
but a reciprocating unit. (the original installer swore that it was a scroll). Tesla wants
a scroll at max of 56 LRA. I'm trying to see if we can install a new compressor unit
(scroll & 56 or lower) but the initial company said that all the newer ones were 60 LRA
or more.
I have a different company looking also for a Trane unit as well as giving me an estimate
on a mini-split system for just the bedroom (s). I need that like a hole in the head but I really
want SOME AC available after a hurricane.
You can just buy a portable AC unit for about $300-400 for your bedroom.
https://www.walmart.com/ip/BLACK-DE...6y_U5uhOPN_jEbx1hveSWfBjhpfWBlksaArKeEALw_wcB
Although it is strange that they say that all new compressors are 60 LRA. It is probably because all new compressors COMPATIBLE with your air handler are 60 LRA. You may have to replace both your handler and compressor together to get to LRA < 30.
If your AC unit is more than 10 years old, I would consider replacing them. The new unit will be much more efficient, and the replacement will pay for itself within a few years.
P.S. I saw that your AC is from 2013. Probably not worth replacing it now. I would buy a portable AC for the bedroom or a mini-split system.
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Exactly right... I was trying to replace only the compressor side. If I go mini-split for the bedrooms
I may just go Mini-split when it comes time to replace the main unit! That will be the reasoning behind
whether I go heat pump or straight cool. My house is only 768 under air anyway.
Well the mini-splits are 5K for one room or 8K for two
rooms. I'm having a Lennox guy come out to give me
a price for replacing my whole system. Their "16" seems
to have an LRA of 52..........
rooms. I'm having a Lennox guy come out to give me
a price for replacing my whole system. Their "16" seems
to have an LRA of 52..........
Get a variable speed compressor, it has a much lower LRA.
The real issue is that my AC is only six years old and doesn't need to be replaced
so I'm taking a 20K (after rebate) home improvement & making it 29K for no reason other than
I support electric, self sustained, power and want backup.
Yeah, so that's why I would simply buy a $300 portable AC, keep it in storage, and take it out only when needed.
Frankman60
Member
I’m providing an update to what I posted previously about using an AC compressor with an LRA of 135 with 2 Powerwalls. After the Powerwall installation, the AC compressor wouldn’t even start spinning during a simulated grid outage. Other backup circuits experienced low voltage causing disruption to electronic devices, including some electronic device damage. The contractor installed a Sure Start device on the AC compressor. With that device installed, the compressor rotor will spin up but there is still a very low voltage condition on the other circuits causing electronic devices to reset, including the thermostat connected to the HVAC system. I did a little digging on the Sure Start to see if it should have worked in my situation and this is what I found. Electrical Engineers out there, please verify my calculations.
Below is the guidance provided by the company that makes the Sure Start device. It says that the “generator surge capacity should exceed 50% of the Locked Rotor Amperage of the compressor in use.” The generator in this case is two Powerwalls. The surge capacity of two Powerwalls is 14 kWs (7 kWs each). The AC compressor has an LRA of 135 amps. Converting 135 amps to kWs at 240 volts is 32.4 kWs. Reducing 32.4 kWs by 50 percent still is 16.2 kWs to spin the rotor. That is more than the surge capacity of two PWs so the Sure Start will not work. Even if the Sure Start device could achieve a 60 percent reduction in required amps as mentioned in the literature, this would lower the kW draw to about 13 kWs.
If my math is correct (or if it gets corrected by other people much smarter than me
) others could use this to determine if there is any hope of backing up their home’s AC with Powerwalls.
Below is the guidance provided by the company that makes the Sure Start device. It says that the “generator surge capacity should exceed 50% of the Locked Rotor Amperage of the compressor in use.” The generator in this case is two Powerwalls. The surge capacity of two Powerwalls is 14 kWs (7 kWs each). The AC compressor has an LRA of 135 amps. Converting 135 amps to kWs at 240 volts is 32.4 kWs. Reducing 32.4 kWs by 50 percent still is 16.2 kWs to spin the rotor. That is more than the surge capacity of two PWs so the Sure Start will not work. Even if the Sure Start device could achieve a 60 percent reduction in required amps as mentioned in the literature, this would lower the kW draw to about 13 kWs.
If my math is correct (or if it gets corrected by other people much smarter than me
) others could use this to determine if there is any hope of backing up their home’s AC with Powerwalls.Attachments
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0641BD74-49EC-4432-9734-DA48B7CD7464.jpeg
power.saver
Supporting Member
Your calculations are correct. You would need at least 3 PWs to start that AC and even then, it is unclear if the PW can ramp up the output fast enough to provide the kW needed. Also have to consider the other loads that are on at the time. My 128 LRA AC will not start with the grid down using a Sure Start either. Best to not have the AC on the backup circuit because the brownouts they cause can damage other electronics, including your solar inverter.
I had the same issue when I was getting my HVAC system installed after I had 2 PW's hooked up. The Tesla design team said LRA needs to be <28a per PW to be fully backed up by the Powerwalls. They were afraid during a blackout, there wouldn't be enough current to start the HVAC system. I was getting a 3 ton Trane XR14 with an LRA of 72 so I couldn't have the breakers for the HVAC installed on the PW subpanel.
Frankman60
Member
You have two Powerwalls right? If you do, it is just below the maximum 56 amps that @clos000 reported for two PWs. Have you tried a simulated grid outage to see if you new Lennox AC compressor will start? Are you also using a Sure Start with your new AC compressor?
Frankman60
Member
The 28 amp maximum LRA seems too high for one PW. That is 6.7 kWs. I guess that assumes that the other backed up loads are less than 300 watts which doesn’t seem practical.
Double-check if it's 240 volts. My labeling says HVACs motors run at 208 volts on 240V circuits. So the 135A LRA @ 208V is 28.08 kW, and the PWs should only see it as a load of 117A. Split to two PWs, that's 58.5A each.I’m providing an update to what I posted previously about using an AC compressor with an LRA of 135 with 2 Powerwalls. After the Powerwall installation, the AC compressor wouldn’t even start spinning during a simulated grid outage. Other backup circuits experienced low voltage causing disruption to electronic devices, including some electronic device damage. The contractor installed a Sure Start device on the AC compressor. With that device installed, the compressor rotor will spin up but there is still a very low voltage condition on the other circuits causing electronic devices to reset, including the thermostat connected to the HVAC system. I did a little digging on the Sure Start to see if it should have worked in my situation and this is what I found. Electrical Engineers out there, please verify my calculations.
Below is the guidance provided by the company that makes the Sure Start device. It says that the “generator surge capacity should exceed 50% of the Locked Rotor Amperage of the compressor in use.” The generator in this case is two Powerwalls. The surge capacity of two Powerwalls is 14 kWs (7 kWs each). The AC compressor has an LRA of 135 amps. Converting 135 amps to kWs at 240 volts is 32.4 kWs. Reducing 32.4 kWs by 50 percent still is 16.2 kWs to spin the rotor. That is more than the surge capacity of two PWs so the Sure Start will not work. Even if the Sure Start device could achieve a 60 percent reduction in required amps as mentioned in the literature, this would lower the kW draw to about 13 kWs.
If my math is correct (or if it gets corrected by other people much smarter than me
58.5A is of course too close to 60A limit (for 2 PWs), but then the SureStart should have lowered the LRA enough without causing any other electrical damage. 58.5A / 2 (for 2 PW) / 2 (50%) = 14.625A per PW with the SureStart.
