Powerwall 2 + UPS Connundrum - and solution

[HankLloydRight]

I was thinking the same thing recently, but for a "whole house" solution. What kind of super caps would you need to cover the faction of a second the PW2 is switching over from grid power? Just to smooth it out enough so the sensitive downstream electronic devices don't reset, so you can skip installing multiple small UPSs everywhere.

 

[aesculus]

It appears that the commercial supercap UPSs are not longer available in the small sizes needed. At least by my quick web search.

So while it is a better alternative than a battery based one technically, the cost and ease of obtaining one seems impractical.

 

[aesculus]

I was thinking the same thing recently, but for a "whole house" solution. What kind of super caps would you need to cover the faction of a second the PW2 is switching over from grid power? Just to smooth it out enough so the sensitive downstream electronic devices don't reset, so you can skip installing multiple small UPSs everywhere.

They would have to carry the entire potential house load you expect for a second or two. I suspect you will find these to be very expensive.

 

[jjrandorin]

I was thinking the same thing recently, but for a "whole house" solution. What kind of super caps would you need to cover the faction of a second the PW2 is switching over from grid power? Just to smooth it out enough so the sensitive downstream electronic devices don't reset, so you can skip installing multiple small UPSs everywhere.

Whatever that would cost, would likely be more than the "installing multiple small UPS everywhere" approach... especially since most people would only want UPSs on a few pieces of equipment:

1. Internet modem / router
2. Desktop computer(s) / Monitor
3. Any NAS (network attached storage)

All three of these are likely in the same room / could be plugged into the same device.

4. Any A/V equipment you might want to protect, like a TV / (Receiver / Separates) /Powered speakers

In my home I have (3) UPS devices, 2 of them cost $200 and one cost $80 or so. Thats $480, which I doubt pretty seriously any "whole home" solution, even if available, could be had for anywhere near that.

 

[HankLloydRight]

I realize all of the above, it was just a thought experiment. Right now my house is drawing 5.5kw with 2ACs running but those aren't backed up by the PW2. So the actual load is about 3kw. What would it take to buffer a 3kw draw (about 13 amps@240v) for 1/2 second?

 

[miimura]

I was thinking the same thing recently, but for a "whole house" solution. What kind of super caps would you need to cover the faction of a second the PW2 is switching over from grid power? Just to smooth it out enough so the sensitive downstream electronic devices don't reset, so you can skip installing multiple small UPSs everywhere.

Batteries and capacitors are DC devices. You're trying to maintain AC power, so you have to invert the DC power from the battery or supercap into a sine wave. Doing whole home backup from DC storage is inherently expensive. Doing it better than Powerwalls, which are grid interactive, requires double conversion. That means that you have inverters powering your whole house full time and the grid or solar is recharging the supercaps or batteries continuously. This is the way Datacenter UPS units work. You get clean continuous power, but suffer the AC-DC-AC conversion losses 24/7. You can also configure Hybrid Inverter systems like ones made by Outback Power to do this. However, since they use arrays of inverters, you can still get voltage sags if you have significant startup loads.

 

[gpez]

Batteries and capacitors are DC devices. You're trying to maintain AC power, so you have to invert the DC power from the battery or supercap into a sine wave. Doing whole home backup from DC storage is inherently expensive. Doing it better than Powerwalls, which are grid interactive, requires double conversion. That means that you have inverters powering your whole house full time and the grid or solar is recharging the supercaps or batteries continuously. This is the way Datacenter UPS units work. You get clean continuous power, but suffer the AC-DC-AC conversion losses 24/7. You can also configure Hybrid Inverter systems like ones made by Outback Power to do this. However, since they use arrays of inverters, you can still get voltage sags if you have significant startup loads.

This is a very fair point.

Ignoring AC/DC/AC losses and the nonlinear discharge curve of capacitors: 3kw for half a second is just ~0.42wh and a 2.7v 500F super capacitor fully discharged is ~0.51wh. You can pick those up for like $5.

Note: refer back to my statement about "knowing enough to be dangerous"...​

 

[GaitherBill]

We had a power blip this morning, just long enough for the gateway to disconnect from the grid for 5 minutes.

The Powerwalls were at 100%, and went right to 62.5Hz to turn off the PV.

I'm pleased to say that the new Eaton UPS I purchased did its thing, our Unifi USG-3 didn't hiccup.

Also, the two Tripp Lite UPS's continued to operate as normal. So I would say those work fine at the revised AC frequency.

Edit: The cheapy cyber power UPS I have the Fios ONT plugged into also worked just fine. Always for get that one.

 

[astrorob]

We had a power blip this morning, just long enough for the gateway to disconnect from the grid for 5 minutes.

The Powerwalls were at 100%, and went right to 62.5Hz to turn off the PV.

I'm pleased to say that the new Eaton UPS I purchased did its thing, our Unifi USG-3 didn't hiccup.

Also, the two Tripp Lite UPS's continued to operate as normal. So I would say those work fine at the revised AC frequency.

Edit: The cheapy cyber power UPS I have the Fios ONT plugged into also worked just fine. Always for get that one.

i have been wondering about this for a long time - i remember reading about it (probably in this thread last year) and i thought there was a way to have tesla lower the power-out frequency to a high enough value to turn off the PV but to not mess up a UPS.

is that no longer a thing? is the only solution now to replace your UPSs with ones that are tolerant of 62.5Hz?

 

[miimura]

i have been wondering about this for a long time - i remember reading about it (probably in this thread last year) and i thought there was a way to have tesla lower the power-out frequency to a high enough value to turn off the PV but to not mess up a UPS.

is that no longer a thing? is the only solution now to replace your UPSs with ones that are tolerant of 62.5Hz?

62.5 Hz is the lowered value. The default from Tesla is 65 Hz which does cause problems for most UPS units which tolerate +/- 3 Hz.

 

[astrorob]

62.5 Hz is the lowered value. The default from Tesla is 65 Hz which does cause problems for most UPS units which tolerate +/- 3 Hz.

ah, OK thanks. still sounded high given my adventure with the sunny boy 5000 refusing to produce if the AC voltage was +5.00001% out of spec. i'll bet it would shut down at 60.5Hz

will an installer be able to do this configuration or do i have to wade into tesla's telephone support? i have 3-4 el-cheapo cyber power UPSs which i'd rather not replace.

 

[miimura]

ah, OK thanks. still sounded high given my adventure with the sunny boy 5000 refusing to produce if the AC voltage was +5.00001% out of spec. i'll bet it would shut down at 60.5Hz

will an installer be able to do this configuration or do i have to wade into tesla's telephone support? i have 3-4 el-cheapo cyber power UPSs which i'd rather not replace.

Tesla Energy Support.

 

[GaitherBill]

Just give support a call, took no time at all for me, and they made the change in about a week.

 

[RobbL]

Tesla tech support would not lower the max cycles for my system unless I gave them a specific UPS even though I haven't purchased one yet. I told them the one that @cali8484 had suggested to me previously in this thread, CyberPower CP850PFCLCD PFC, and they then lowered the cycles to 62.75. Do people have a general product preference between CyberPower and APC? I just plan to use it for my Dell XPS desktop, cable modem and router. I recognize they only need to be provided with power from the UPS for a few seconds before the Powerwall can take over, and I assume either one will be happy with the now adjusted max cycles of 62.75.

 

[GaitherBill]

Tesla tech support would not lower the max cycles for my system unless I gave them a specific UPS even though I haven't purchased one yet. I told them the one that @cali8484 had suggested to me previously in this thread, CyberPower CP850PFCLCD PFC, and they then lowered the cycles to 62.75. Do people have a general product preference between CyberPower and APC? I just plan to use it for my Dell XPS desktop, cable modem and router. I recognize they only need to be provided with power from the UPS for a few seconds before the Powerwall can take over, and I assume either one will be happy with the now adjusted max cycles of 62.75.

I’ve stopped buying APC. They’re notorious for overcharging the batteries causing them to wear out quicker than other brands.


I would recommend any of the Eaton units listed in this thread.

 

[gpez]

Tesla tech support would not lower the max cycles for my system unless I gave them a specific UPS even though I haven't purchased one yet. I told them the one that @cali8484 had suggested to me previously in this thread, CyberPower CP850PFCLCD PFC, and they then lowered the cycles to 62.75. Do people have a general product preference between CyberPower and APC? I just plan to use it for my Dell XPS desktop, cable modem and router. I recognize they only need to be provided with power from the UPS for a few seconds before the Powerwall can take over, and I assume either one will be happy with the now adjusted max cycles of 62.75.

I've always found CyberPower to be the right balance of cost and performance for what I need the UPSs to do. I have 5 of them and have never had an issue. They are perfectly happy with the ~62hz frequency from the Powerwall during off grid operation.

 

[jjrandorin]

Tesla tech support would not lower the max cycles for my system unless I gave them a specific UPS even though I haven't purchased one yet. I told them the one that @cali8484 had suggested to me previously in this thread, CyberPower CP850PFCLCD PFC, and they then lowered the cycles to 62.75. Do people have a general product preference between CyberPower and APC? I just plan to use it for my Dell XPS desktop, cable modem and router. I recognize they only need to be provided with power from the UPS for a few seconds before the Powerwall can take over, and I assume either one will be happy with the now adjusted max cycles of 62.75.

Now that you have the frequency lowered, another vote for the cyberpower here.

 

[RobbL]

I went ahead with the CyberPower, although opted for the CP1000 instead of the 850, as it was only $5 more through Amazon. With just my Dell XPS desktop, cable modem and router plugged in, it is way more than enough. I set it up on Thursday, and woke this morning to a local power outage which lasted over five hours. Everything worked flawlessly. The only thing I noticed was that the UPS reported voltage in and out at 116v when I first checked it. Over the next several hours, the voltage slowly increased to 120, and then 121. With power back on, it is at 119, which is where it was when I first set it up. Everything plugged into the UPS seemed to run fine at that lower voltage, so I assume that is nothing to be concerned about.

The power reserve on the UPS remained at 100%, so no issue with the frequency. It was likely running on the UPS for only 1 of 2 seconds before switching to Gateway mode, exactly as hoped and planned. Since it is summer and a sunny day to boot, the Powerwall started the day at 38%, just where I had the minimum set and then was recharged from solar until full after the house took its share which included doing a load of laundry.

 

[jboy210]

I went ahead with the CyberPower, although opted for the CP1000 instead of the 850, as it was only $5 more through Amazon. With just my Dell XPS desktop, cable modem and router plugged in, it is way more than enough. I set it up on Thursday, and woke this morning to a local power outage which lasted over five hours. Everything worked flawlessly. The only thing I noticed was that the UPS reported voltage in and out at 116v when I first checked it. Over the next several hours, the voltage slowly increased to 120, and then 121. With power back on, it is at 119, which is where it was when I first set it up. Everything plugged into the UPS seemed to run fine at that lower voltage, so I assume that is nothing to be concerned about.

The power reserve on the UPS remained at 100%, so no issue with the frequency. It was likely running on the UPS for only 1 of 2 seconds before switching to Gateway mode, exactly as hoped and planned. Since it is summer and a sunny day to boot, the Powerwall started the day at 38%, just where I had the minimum set and then was recharged from solar until full after the house took its share which included doing a load of laundry.

Nice! I assume the remainder of your appliances had no issue with the frequency increases to control the inverters?
I ask because they are changing my system to work with the CyberPower 850CFLLCD in a few days, so assume my PW frequency peaks will be the same as yours.

 

[RobbL]

I don’t know if the frequency actually increased to the new maximum. I just know that even if it did, the UPS still was able to switch back to standby mode quickly and was likely only supplying power for a second or two before switching back.