Whole house UPS

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Coppersmith

Coppersmith

Senior Member
Location
Tampa, FL, USA
Occupation
Electrical Contractor
We get frequent short outages of a few seconds to a minute. I have UPS's on my computer and the DVR which help, but I still have to reset a bunch of clocks like the range and microwave. Is there a small whole house UPS available I could wire in before the panel? If it had five minutes of battery power that would be plenty.
 
Calculate your total demand current first, and your run-time second.

I imagine an inertial type (motor/flywheel/generator) would work.
 
The clocks themselves take such little power that it seems overkill to consider a whole house UPS, even one with a very short runtime.
You'd only really need a UPS for the control circuits and clocks themselves, but that would involve digging into the appliances themselves (and issues with UL, etc. listing).
 
Coppersmith said:
We get frequent short outages of a few seconds to a minute. I have UPS's on my computer and the DVR which help, but I still have to reset a bunch of clocks like the range and microwave. Is there a small whole house UPS available I could wire in before the panel? If it had five minutes of battery power that would be plenty.
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problem is five minutes of run time for the clocks you are concerned about is only in the milliamp hour ranges, if your air conditioner is running when power goes out - you used up all the capacity needed for those clocks in seconds or even less if you tried to power the entire service during such outages. the small backup needed needs applied at each individual load.

Even something like the microwave clock needs applied within the microwave. If you tried to supply the entire unit with a backup source only sized to supply the clock, you use up backup power too rapidly should the utility fail while cooking something
 
Apparently there is some confusion with my request so let me restate. I want a whole house UPS that will power everything that is running in the house (200 amp service so assume 100 active amps max) for about five minutes. If it works correctly and outage is short enough, I won't even notice an outage occurred.
 
Ok first a typical relaxed startup time for a generator is 60 seconds. Critical load and industrial ones can do 30 seconds. So less than a minute realistically. You have the right idea.

Let’s do some math here. 100 A for 5 minutes is only 8.3 Amp-hours so hardly any battery drain at all. This is actually typical of what I see on server stacks, radio systems, control systems, and the like. So usually the UPS battery when it is just rude through is gross overkill.

BUT you pull it basically all at once so 240 x 100 = 24,000 VA or 24 kVA. Typical rack mount UPS for a server up to $1000 is around 2000 VA so way too small for your needs if that is your need. You will be looking at a big industrial one costing tens of thousands. Eaton sells the Powerwsre line for this.

Or separate the circuits in the panel. Put the receptacles on it only and you can probably easily fit on that 1500 VA unit like a Littlefuse or APC 19” rack mount unit meant for a server stack for a small to mid size IT department. It has a run time of a few hours which really means that you can use the battery well past the typical 3 year expected life. Let the rest of it come on with the generator. You will have to hunt around or get creative with splicing in those APC style units at that size though because they come with receptacles. I’ve seen lots of industrial control panels with the control system power connected to a cord that is plugged into a rack mount UPS. It’s probably a huge Code violation but nothing about it is unsafe.

Or buy clocks for around $20 each or less with battery backup built in. That’s far cheaper. The microwave at 2000 Watts has to go on a huge UPS anyways so the appliance circuits won’t be on the cheap UPS. The clock on it will still blink.

Or buy individual UPSs as cheaply as possible. But on a microwave there is no cheap. At over a hundred dollars per clock radio, not worth it.



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Coppersmith said:
We get frequent short outages of a few seconds to a minute. I have UPS's on my computer and the DVR which help, but I still have to reset a bunch of clocks like the range and microwave. Is there a small whole house UPS available I could wire in before the panel? If it had five minutes of battery power that would be plenty.
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um, no, i'm afraid.

i have never seen anything for single phase like that.
lot of stuff for three phase to hold until the backup genset kicks in.
it's be pretty expensive. it would have to hold the entire house without
a sag.... and if the A/C happened to be starting.... well....

i've switched to a cyberpower PR1500LCD for my office. everything runs on it,
monitor, laser printer, plotter, everything. laser runs thru surge supressor.
about $375. full sine wave UPS. had it for about 4 years now. well made.
 
Coppersmith said:
but I still have to reset a bunch of clocks like the range and microwave.
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My microwave clock will blank out after awhile if you don't reset it. That's just fine because I've never found a use for it anyway. As for the rest of your clocks, replace them with ones with battery backup.

This is going to cost you a lot of money just to not have to reset a clock or two.

-Hal
 
What everybody else already said + more.

Have been involved in big UPS for everything from minuteman missile sites to 400 A 3 phase 480V systems on military base essential systems.


Not cheap. If it absolutely has to work to 99.999% or the time, cost is more than your house.

Battery clocks: the battery cost is less than the $5 a year to run 60 Hz clocks.
As someone else already said, if you have any electronics capability a diode and 8 AAA cells added to a microwave will run the clock thru a 2 year long outage. (If you don't already know how to do that, don't ask, not DIY even for many electricians)
 
zbang said:
Will the powerwall continue to supply power to a dead service? My understanding is the the PW is basically a line-interactive inverter with some batteries, so when the line voltage goes away and so does the PW.
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I don't think that's correct. There was a huge thread some little while ago where a fellow in PR was setting up something to use mostly solar, with occasional assist from the grid. I think it really depends on the inverter used.
 
Coppersmith said:
Powerwall does seem to be a possible solution. Can it be charged from utility power instead of solar?
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Yes. The only restriction is that in the US, because there is currently a tax credit for solar installations, and because that tax credit applies to Powerwalls if they are charged only from solar, then if you have solar at the time of Powerwall installation, Tesla insists on configuring the Powerwall to charge from solar only.

Cheers, Wayne
 
As others have said, the issue is that you are asking for a UPS with _huge_ power capacity but very small energy capacity.

Your 200A service probably never sees more than 100A at any given time, but that is still 24KVA.

According to the datasheet, a powerwall module is capable of 7.2kVA for 10 seconds. 5.8 kVA on a continuous basis. https://www.tesla.com/sites/default.../Powerwall 2_AC_Datasheet_en_northamerica.pdf

So you would need 3 or 4 of these modules to have the power handling capacity to run your house...and you would be paying for significantly more energy capacity that you say you need.

-Jon
 
winnie said:
So you would need 3 or 4 of these modules to have the power handling capacity to run your house...and you would be paying for significantly more energy capacity that you say you need.
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When I look at Tesla's site and run the calculation for handling my house size, it recommends two powerwall modules. They don't say how long two modules can run the house, but I assume it's a lot longer than five minutes, therefore I can probably use just one or a half of one if I can find a similar product in a smaller size.
 
Coppersmith said:
When I look at Tesla's site and run the calculation for handling my house size, it recommends two powerwall modules. They don't say how long two modules can run the house, but I assume it's a lot longer than five minutes, therefore I can probably use just one or a half of one if I can find a similar product in a smaller size.
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I think you miss the point. The powerwall consists of several components: the actual energy storage (battery), the power electronics to convert the battery DC to AC, and the electronics to charge the battery, etc.

The _electronics_ is limited to a certain maximum power output. To be able to power your house for 10 seconds or 10 hours you will still need transistors of a particular size.

The battery itself will have both an energy storage capacity and a power handling capacity. Think of the battery as having a built in resistor; draw more current and its output voltage drops. You can only get so much power out of the battery before you are dissipating more heat in the battery than delivering energy to the load.

You are looking for something with a completely different ratio of energy storage to power handling capacity. Something like a flywheel based system or a capacitor based system...but once you are paying so much for the electronics you might as well have the battery and be able to be off grid for a while.

Another way of thinking about this: you want a 25kVA generator with a 1/2 pint gas tank, but most people sell them with much larger gas tanks.

-Jon
 
Powerwall can do it if you have their gateway that disconnects the powerwalls output from the grid when the grid is down. Is the range gas or electric? If gas, perhaps get a UPS like a Eaton 9SX3000HW which is a 3kva hardwired pure sinewave UPS and feed your 120v range clock and microwave, maybe the fridge too from it.
 
gadfly56 said:
I don't think that's correct. There was a huge thread some little while ago where a fellow in PR was setting up something to use mostly solar, with occasional assist from the grid. I think it really depends on the inverter used.
Click to expand...

That was me in that thread and yes, it was a bit of an ordeal, but it turned out the problem was Tesla rebooting the system after upgrading something and because we were off-grid, as usual, all power went off for a bit until the Tesla reset itself, sometimes with a 'jump start' by feeding grid into the gateway momentarily. It has been working like a big dog for well over a year now with no prolblems.
 
For the cost of two power walls you could probably have a standby generator to power the entire house; Something to think about. And it would carry you through a prolonged outage if necessary.


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