Inverter vs UPS for backup power

[Want2race]

Admittedly this may be a bit whacky...

I live on a street with overhead power lines and lots of trees. The 2 make a terrible combination. I would say we lose power 3x a year.

I have a portable generator and a transfer switch but it's a pain and my wife won't go outside and rip on the cord... So I had started looking at the Tesla power wall. After thinking about it I would basically have a UPS..


I have a friend that salvages batteries from electric cars and the thought of getting an inverter came to mind but then I realized I would need a charger as well. But the idea struck me.

Could I buy a used server UPS (10k watts) and run that into my transfer switch? It has 12v charging but I would probably add something else.

Anyone know if it would be ok to run around 3k watts out of am inverter for a few hours at a time? The idea seems too simple but if it can handle the draw I think it could be a winner. Its certainly cheaper than an inverter!

 

[ishiboo]

Admittedly this may be a bit whacky...

I live on a street with overhead power lines and lots of trees. The 2 make a terrible combination. I would say we lose power 3x a year.

I have a portable generator and a transfer switch but it's a pain and my wife won't go outside and rip on the cord... So I had started looking at the Tesla power wall. After thinking about it I would basically have a UPS..


I have a friend that salvages batteries from electric cars and the thought of getting an inverter came to mind but then I realized I would need a charger as well. But the idea struck me.

Could I buy a used server UPS (10k watts) and run that into my transfer switch? It has 12v charging but I would probably add something else.

Anyone know if it would be ok to run around 3k watts out of am inverter for a few hours at a time? The idea seems too simple but if it can handle the draw I think it could be a winner. Its certainly cheaper than an inverter!

A UPS that size probably has 24v, 36v, or more likely 48v charging... that'd be a LOT at 12v. You'd need at least four 12v batteries.

Yes, it's completely possible. And a UPS will be rated for X KW, it's okay to run that for as long as it's rated for.

UPSes are normally designed to act only until the generator starts... but all they are is an inverter, a charger, and a transfer switch built in together.

 

[American Locomotive]

Keep in mind that a server UPS is generally 240v single phase or 208/240 3-pahse. It's very likely that the single phase models are 240v only (as in the hot is at 240v with respect to neutral), which wouldn't be very useful in a home setting.

For all that money, you could just set yourself up with an automatic Diesel/LPG/NG fueled backup generator from Kohler or Generac, that will automatically start up if your power goes out.

 

[PhysicsDude]

Keep in mind that a server UPS is generally 240v single phase or 208/240 3-pahse. It's very likely that the single phase models are 240v only (as in the hot is at 240v with respect to neutral), which wouldn't be very useful in a home setting.

For all that money, you could just set yourself up with an automatic Diesel/LPG/NG fueled backup generator from Kohler or Generac, that will automatically start up if your power goes out.

^this

There are a lot of commercial grade UPSs that are 120V, but probably none that are 240v single phase suitable for home use.

Many commercial 120V UPSs are able to expand their battery capacity, they have a harness which you can connect to (usually) 24V lead acid batteries of your choice (well, preferably their branded battery tray) and you're good to go. Inside 90% of UPSs just sits a combination of generic 7AH or 12AH lead acid batteries anyway which you can buy for like $10 a piece if you know the right place.

I've seen many a business use deep cycle car batteries + an inverter for backup power. I did work at a Jail that used that system with an off-the-shelf automotive battery isolator to power their security equipment. As long as the inverter is rated for whatever power you're going to run on it, no reason not to do it.

 

[ishiboo]

Plenty of 240v single phase UPSes.

Don't use deep cycle car batteries. Use golf cart batteries.

 

[Want2race]

Keep in mind that a server UPS is generally 240v single phase or 208/240 3-pahse. It's very likely that the single phase models are 240v only (as in the hot is at 240v with respect to neutral), which wouldn't be very useful in a home setting.

For all that money, you could just set yourself up with an automatic Diesel/LPG/NG fueled backup generator from Kohler or Generac, that will automatically start up if your power goes out.

My city is a bit painful on generator install. Need a survey, multiple permits wtf. I looked into doing it but couldn't justify the $6k price tag if I did it myself.

I have an energy monitor and my house rarely exceeds 2200 watts so I was hoping to get a 5k UPS and call it good. Without batteries I've seen a few units sell for $200 outside of their warranty period

 

[American Locomotive]

You need to make sure the UPS has both 240v and 120v outputs, otherwise it won't be useful. A 240V only UPS (which most seem to be) will not be able to run your 120v devices.

You may also find that the price of batteries will balloon the budget considerably. Automotive batteries just won't have the capacity you need. Take something like an Interstate 2300S 6v Golf Cart battery - that's a $200 battery. If your UPS requires 24v, that's $800 in batteries you need to buy. If it's 48v, that's $1600 worth of batteries.

Then consider the run time, let's assume you have 48v system and 8 of those big 6v golf-cart batteries (They're rated for ~170 amp-hours). 2.2KW house load @ 48 volts yields 46 amps of current assuming the UPS is 100% efficient (which it's not).

That $1600 worth of batteries would get you just 3.5-4 hours of backup time.

 

[dogdog]

Not sure your budget and how much watt of a power you are running, seen these home use Li-Ion battery packs around from this company goalzero.... but they kind of made the battery non-replaceable..... more of for fancy *******.
http://www.goalzero.com/solarlife/2017/03/22/tech-video-yeti-400-yeti-1400-lithium/

Or if you have the $$$$ there are always use parts of the off grid solar inverters setup you can buy..... and setup. I think those are pure sine wave inverters.....

or if you have access to some old and free Server UPS... some are single phase 120/240 outputs but requires 48V battery...and the batteries are pretty expensive maintenance item. A lot of them don't work well with home generators.

 

[wyliesdiesels]

Admittedly this may be a bit whacky...

I live on a street with overhead power lines and lots of trees. The 2 make a terrible combination. I would say we lose power 3x a year.

I have a portable generator and a transfer switch but it's a pain and my wife won't go outside and rip on the cord... So I had started looking at the Tesla power wall. After thinking about it I would basically have a UPS..


I have a friend that salvages batteries from electric cars and the thought of getting an inverter came to mind but then I realized I would need a charger as well. But the idea struck me.

Could I buy a used server UPS (10k watts) and run that into my transfer switch? It has 12v charging but I would probably add something else.

Anyone know if it would be ok to run around 3k watts out of am inverter for a few hours at a time? The idea seems too simple but if it can handle the draw I think it could be a winner. Its certainly cheaper than an inverter!

U wont be able to start motor loads with that.

Keep in mind that a server UPS is generally 240v single phase or 208/240 3-pahse. It's very likely that the single phase models are 240v only (as in the hot is at 240v with respect to neutral), which wouldn't be very useful in a home setting.

For all that money, you could just set yourself up with an automatic Diesel/LPG/NG fueled backup generator from Kohler or Generac, that will automatically start up if your power goes out.

The potential between hot and neutral would always be 120v NOT 240v...

 

[reader2580]

A UPS is an inverter usually packaged with batteries. Nothing that magical about a UPS.

 

[theoldwizard1]

A UPS is an inverter usually packaged with batteries. Nothing that magical about a UPS.

Not exactly true. UPS are designed to only operate for a short time. Enough "ride through" to do a proper shutdown of "delicate" equipment. They will actually overheat and shutdown within 10-15 minutes of full power operation. Some have timers that shutdown the equipment. 24V and 48V are common because they use small batteries. Most do not have a way of easily adding batteries.


There are companies that specialize in solar inverter systems that have now added battery charging from "the line" and will automatically switch over to battery. GoPower has some nice larger (2kw, 3kw) models, but they are $$$ !!


Golf cart batteries (from Costco) are your best "bang for your buck".

 

[theoldwizard1]

Could I buy a used server UPS (10k watts) and run that into my transfer switch? It has 12v charging but I would probably add something else.

There are folks out there trying to do similar projects so it is not that crazy.

You can NOT use a typical UPS because the charger is designed for lead acid batteries and it will do "bad things" the Li-Ion, like possibly explode and catch fire.

 

[American Locomotive]

U wont be able to start motor loads with that.



The potential between hot and neutral would always be 120v NOT 240v...

A commerical server 240v-only UPS will not do that. They output 240v between line and neutral.

 

[rlitman]

A UPS that size probably has 24v, 36v, or more likely 48v charging... that'd be a LOT at 12v. You'd need at least four 12v batteries...

The OP asked about using a 10kW UPS. Most of the ones I am familiar with in that size class use 120V on the DC side. I would not expect to find something in this size under 48V on the DC side. My 5kVA UPS at home uses 48V DC.

Keep in mind that a server UPS is generally 240v single phase or 208/240 3-pahse. It's very likely that the single phase models are 240v only (as in the hot is at 240v with respect to neutral), which wouldn't be very useful in a home setting...

^this

There are a lot of commercial grade UPSs that are 120V, but probably none that are 240v single phase suitable for home use...

BS. Single phase APC Symmetra series is the first to come to mind (though the Symmetra RM is 240V out only), but there are plenty of other options out there. It is 240V single phase in, 120/240V single phase out. The neutral on the input line only comes into play when you are on bypass. These basically have two 120V inverters that are kept 180 degrees out of phase. That's why the battery is 120V.

But be aware that balance can be critical on these. The true power output is actually half of the advertised number, on each 120V phase. So on an 8kVA unit, you can pull up to 4kVA on each 120V leg.

One catch with these larger UPS units is that many are "online" or "double conversion" UPS. These have lower power efficiencies than "standby" UPS. They provide better power, but that's not something you necessarily care about in home use.

Not exactly true. UPS are designed to only operate for a short time. Enough "ride through" to do a proper shutdown of "delicate" equipment. They will actually overheat and shutdown within 10-15 minutes of full power operation...

This is correct only for "under desk" sized small UPS units, where the internal battery capacity is designed to limit the duty cycle. Most commercial stuff can use external batteries, and these are necessarily sized for continuous use of the inverter at 100% duty cycle.

 

[grantw]

https://www.amazon.com/dp/B00HHNCQ00/?tag=atomicindus08-20

Look in to split phase inverters. Automatic charging and cut-over, remote displays and status monitors, and even generator startup signals.

http://invertersrus.com/product/aims-picoglf60w24v240vs/

If I had the spare cash, I'd build myself a sweet inverter system.

 

[theoldwizard1]

Most commercial stuff can use external batteries, and these are necessarily sized for continuous use of the inverter at 100% duty cycle.

In the "server room" I used to manage (about the size of 4 tennis courts) the UPS was the size of 4 or 5 double door refrigerators. It carried the room for over 30 minutes during the Great East Coat/Midwest Blackout ! And it was 3 phase !!

 

[rlitman]

https://www.amazon.com/dp/B00HHNCQ00/?tag=atomicindus08-20

Look in to split phase inverters. Automatic charging and cut-over, remote displays and status monitors, and even generator startup signals.

http://invertersrus.com/product/aims-picoglf60w24v240vs/

If I had the spare cash, I'd build myself a sweet inverter system.

Ummm, why? I don't get it. Yes, I suppose you could could match that with a charger and build your own UPS, but you'd still be lacking a static switch and bypass capability, and you'd spend twice as much for something no better than a UPS.

Something like that might only start to make sense if you had access to a large source of DC. On a diesel/electric vehicle perhaps?

In the "server room" I used to manage (about the size of 4 tennis courts) the UPS was the size of 4 or 5 double door refrigerators. It carried the room for over 30 minutes during the Great East Coat/Midwest Blackout ! And it was 3 phase !!

Yeah, the big stuff is of course going to be 3 phase. The 3 phase 480V UPS systems under me use 540V on the DC bus. The funny thing is that a lot of data centers are getting out of the battery UPS business. The inefficiencies of batteries, rising cost of lead, and improvement in alternatives have lead to many places switching to rotary UPS. That's also lead to a lot of power outages, but that's another story.

 

[grantw]

Ummm, why? I don't get it. Yes, I suppose you could could match that with a charger and build your own UPS, but you'd still be lacking a static switch and bypass capability, and you'd spend twice as much for something no better than a UPS.

Something like that might only start to make sense if you had access to a large source of DC. On a diesel/electric vehicle perhaps?...

The unit I linked to passes through in real time. The purpose of this unit is to provide seamless backup power to a small array of protected circuits while the larger generator fires up in the background.

When power is cut, and the generator takes 30 seconds to start and stabilize before the automatic xfer switch cuts over, this inverter battery system will keep critical devices on, like home networks (with integrated telco maybe?) lighting circuits, NAS devices that don't like power cuts, or even the tv if you really wish.

If you are going to use acid batteries, please consider proper ventilation.

 

[rlitman]

The unit I linked to passes through in real time. The purpose of this unit is to provide seamless backup power to a small array of protected circuits while the larger generator fires up in the background.

When power is cut, and the generator takes 30 seconds to start and stabilize before the automatic xfer switch cuts over, this inverter battery system will keep critical devices on, like home networks (with integrated telco maybe?) lighting circuits, NAS devices that don't like power cuts, or even the tv if you really wish.

If you are going to use acid batteries, please consider proper ventilation.

Ok, I didn't see the integrated charger. So it's most of a UPS with generator start contacts, but without included batteries. You'd still need an ATS if you wanted to integrate a generator seamlessly, and every ATS I've used has its own generator start contacts, so I still don't get the point. It just seems overpriced for a UPS that you still need to provide a battery bank for. And that has no make-before-break safe bypass capability (i.e. no static switch), so it isn't useful on a critical load.

l could see this being used off-grid with a battery bank, but using it as a substitute for a UPS just doesn't make sense to me.

 

[grantw]

...just doesn't make sense to me.

It depends on your wants and needs. Yes, most ATS will have starter contacts, but you'll have 30-90 seconds of downtime in between losing grid and generator clicking over. Thats where inverters like this come in. Providing your own batteries, you can scale as you desire.

In the end, the tesla powerwall2 will probably put all whole-house battery systems to shame. Most users will be able to switch to a ToU program, and run off the powerwall entirely during peak times.

 

[American Locomotive]

BS. Single phase APC Symmetra series is the first to come to mind (though the Symmetra RM is 240V out only), but there are plenty of other options out there. It is 240V single phase in, 120/240V single phase out.

It's not BS, APC has many 240V only units, and many other 240v server UPS units are specified at 240v line-neutral. Yes there are 120/240v units available too. I was simply pointing out to the OP that many are 240V only, so be careful.

These basically have two 120V inverters that are kept 180 degrees out of phase. That's why the battery is 120V.

That's a nice theory, but 120 VAC is actually 170 volts peak-to-peak, the battery voltage is largely irrelevant to the output voltage since it all goes through a transformer eventually anyways. The battery is 120v because that's a particular voltage that keeps battery current and efficiency manageable given the power output.

In the end, the tesla powerwall2 will probably put all whole-house battery systems to shame. Most users will be able to switch to a ToU program, and run off the powerwall entirely during peak times.

It's funny that people think powerwalls will save them money by having it charge during off-peak hours. Guess what's going to happen when everyone's powerwall is charging during off peak time? It's going to become peak time and subject to the higher electricity cost.

 

[theoldwizard1]

The inefficiencies of batteries, rising cost of lead, and improvement in alternatives have lead to many places switching to rotary UPS.

WHAT !!!

I find that VERY HARD TO BELIEVE !! Rotary inverters were headed out the door 40-50 years ago. I can not believe they are coming back.

What is popular for small business is (what I call) fast start generators. The UPS only has to have < 1 minute of ride through before the generator is running and the load is transferred. With ultra-capacitors, a couple of minutes of ride through is very possible.

 

[rlitman]

WHAT !!!

I find that VERY HARD TO BELIEVE !! Rotary inverters were headed out the door 40-50 years ago. I can not believe they are coming back.

What is popular for small business is (what I call) fast start generators. The UPS only has to have < 1 minute of ride through before the generator is running and the load is transferred. With ultra-capacitors, a couple of minutes of ride through is very possible.

Believe it. And then there's low pressure helium filled flywheels. Both offer under a minute of energy storage, but both have deeper market entrenchment than ultra-capacitors, mostly because ultra-caps are so new on the scene.

Fast starting generators are old news. With computer controlled common rail diesel, and the block heaters that I have running even in the summer, it's between 9 and 12 seconds for two engines to start, stabilize in frequency AND parallel.

I've seen it done with a 16 engine setup, where two starters are engaged on each engine in parallel (from opposite sides of the flywheel), each with a pair of 8D batteries (actually two pairs, with an automatic selector switching setup that uses the backup pair if it fails to start on the first try). They can parallelize the whole bus and pickup the 20MW load in something like 6 seconds.

 

[TractorJeff]

I agree with what rlitman says!
At my day job We have built quite a few Motor-Gensets with a Diesel Engine clutched behind it! The motor drive runs the generator all the time. In an outage the Diesel starts up and electrically engages to keep the shaft spinning!
I test Diesels all the time that will start and accept load in 10 seconds. Not little ones either! Big 2 and 3 meg units are common.

 

[grantw]

yeah, okay, in the industrial sector, fast cut-over times are fast, but that 10 seconds needs to be filled by SOMETHING, and that is where a UPS comes in, either a large system sold as a solution, or a component system built with parts.

But, in the end, we're talking about residential solutions. Looking at Kohler's site, they have 10-second ready generators... Which is good for a residence. However, If you're going that far, I would try to bridge that 10 second gap as well, and this is where a nice 240V split phase inverter comes in to play.

 

[mopar4wd]

The biggest issue I would see for residential is battery maintenance. Other then that it should work fine. You could use AGM's but that will cost quite a bit.

 

[Falcon67]

Used data center size (like 16 kVa and such) go fairly cheap on the used market. They are not compact and you won't be up for long, not like with a genset. Also, older APCs and such can tell you a battery is weak, but many can't tell you which one it is. So now you have 36 or 48 batteries to test. Switch to manual bypass and have fun!

Haha on the Tesla - we looked at that for a small data center. $100,000+ No thanks.

 

[rlitman]

Used data center size (like 16 kVa and such) go fairly cheap on the used market. They are not compact and you won't be up for long, not like with a genset. Also, older APCs and such can tell you a battery is weak, but many can't tell you which one it is. So now you have 36 or 48 batteries to test. Switch to manual bypass and have fun!

Haha on the Tesla - we looked at that for a small data center. $100,000+ No thanks.

I wouldn't call 16kVA data center sized, but ok.

APC Symmetra is a modular system, and the LX offers a single phase 240V in 120/240V out and starts out at 4kVA, scaling up to 16kVA. These are all over the used market. The battery trays are modular too. No need to bypass to service batteries. The original Symmetra was quite a bit bigger, but also accepted single phase. These all run on a 120V battery bus.

APC had a line called Matrix that came in 3kVA and 5kVA sizes that would take single phase 240 in, and put out 120/240 single phase (they have a massive transformer inside to accomplish this). These units have odd idiosyncrasies, but since they're standby, they have better power efficiency than the online units above, and they have the advantage of using a 48V battery bus. You can find these on the used market too, but parts can be tough to get for these.

 

[nehog]

Big UPSs use lots of big batteries. I have one that has 10 (yes, ten) 12 volt batteries in it. Basically this allows for some very simple power generation without converting voltages significantly. It also significantly reduces battery current so that with (for example) a 2400 watt load, you're not trying to draw 200 amps from a 12 volt battery. Instead you're drawing 20 amps which is much more manageable.

BTW, my UPS is for sale...

 

[MikeF2316]

I can't help out directly, but I'll give you my experience. We use 2.2 kVA UPSes at work. We hook them (they have a DC plug in the back) to 2 large battery packs. The UPS itself has 4 12V batteries, each battery pack has 24!

Here are the problems with this setup: The charger is woefully underpowered. After a power failure, it takes days! to recharge the batteries. And as the batteries age, and start to fail, the charger eventually can't keep up, and the voltage slowly starts to drop. When the voltage gets down to a certain point, the unit just switches itself off. (There is some time beeping, but these are in a data room, unmonitored.)

Think of this: There are 52 batteries. There are 13 paths of 4 batteries each. The batteries are not paralleled except at the 0 and 48 volt points.