Can a 3U 3000VA UPS + Battery bank power a household?

[Anonymous user]

I recently got 1 APC 3000VA with 4x 48V battery packs (All 3U form factor) heavily discounted from liquidation sale.

My question is this.  _If_ I wanted to use the setup as a backup to power a 100A household panel via a manual transfer switch, Can I wire the 2x 20A & 6x 15A outlets on the APC inverter in parallel?  

I understand the system was not designed for this, just an idea / open question so please respond with that in mind. Thank you.

[voidstar_apc]

I doubt it'll work -- the voltage produced by the two UPSes will drift apart in phase. Inverters designed to be used like this have mechanisms to synchronize phase with their outputs and share the load.

[Anonymous user]

Thank you, I don't have two UPS's.  There's 1 UPS and 4 battery units connected to it.

My question is, can the outlets on the back on that one UPS be connected together to produce a combined amperage.

Sorry if the original question was not clear.

[voidstar_apc]

Oh sorry, my mistake, I should read more closely!

So, wattage depends on your exact UPS model, but lets say your 3000VA inverter supports 2700 W. At US voltages that is ~22A so it wouldn't be able to power a fully loaded 100A circuit. Since that's roughly the amperage of a single UPS outlet, I'm not sure what benefit you'd get from tying outlets together. Maybe you're powering something between 16A and 22A which is more than a single outlet, but still within the UPS' capability?

[Anonymous user]

Thank you!

My bad, I should have crunched numbers first.  My assumption that given it has 2 20A outlets and 6 15A outlets on the back it would have more capacity than your calculated ~22A

darn.  Well solves a problem of whether I should/can parallel the outlet together.  Thanks.

[Anonymous user]

If you wanted to use this UPS to power a whole bank of circuits not exceeding its capacity (bear in mind that loading the unit -- probably even in the case of an XL model such as yours -- to more than 75% of its capacity may not go over well for a long period of time) I'd suggest removing the outlets entirely and running much heavier wire out of the unit to your disconnect panel. It'll be more efficient and there will be far fewer chances for failure.

Or you could do what I have seen done in the past, though I'm not sure it was totally compliant with the electrical code: plug the UPS into an outlet on a dedicated circuit and then take the UPS's output onward to power whatever circuits need to stay on. That way you don't have to worry about any transfer switches, and the UPS can just kick in automatically to keep those critical loads going. When good utility power is available, your loads will run from that. This setup, as it was implemented, had a plug that was simply connected to the UPS's own outlets and went on to the rest of the circuit. (There were four such circuits, each one backed up by a different UPS.)

(Doing things this way also deals you out of having to worry about anything like the neutral/ground bonding arrangement if the UPS uses a "live neutral" configuration. I don't think the Smart-UPS models do this, but I haven't checked it to be sure.)

Even though the Smart-UPS models can run almost anything within their capacity limits as a result of having a true sine wave inverter (oftentimes cleaner than your utility power, at least until the batteries start going flat!), you would have to bear in mind the surge ratings of any devices with motors. These can pull several times their rated current when starting up, and the UPS might not take well to this, especially if it's already carrying a decent sized load or more than one motorized device tries to start up at once. In that case it might shut down suddenly or take out a fuse in a very impressive way.

Someone gave me an APC Smart-UPS 2200 XL (tower) and a BIG battery box to go with it. I've considered doing something similar, especially if I could get my hands on more battery boxes. I don't think it'd have enough oomph to do more than run some lights, small appliances and entertainment devices. It probably wouldn't like keeping a fridge going, or powering a microwave -- especially not at the same time!

[Brad_C]

I have a dedicated circuit reticulated for UPS. So the UPS sits out in the garage and plugs into the wall. That gets reticulated to all the places I need UPS. In the event of a prolonged outage I can plug other stuff into the UPS circuit should that be required.

I'm doing this with an old SU2200I that has been "upgraded" for some extended runtime. Having said that, I don't let it run at more than 50% for any period of time just to be kind. It does the job though. Being rated for about 1600W it will run a 900W inverter microwave on top of the 300W constant IT load. It also comfortably runs the telly & satellite box so I can watch the F1 at 2am without running the generator. It will start the fridge, so no biggie there either. Won't run the coffee machine or kettle.

I had our house re-wired last week and it did a sterling job keeping things going in between generator runs for the 3 days the power was out.

I did some work recently at a site that had a relatively new 80KVA 3 phase Emerson going begging, but even when I explained to the wife we could put it between the house and street and keep the entire house up, she wouldn't let me bring it home.

[Anonymous user]

Thanks William, I will take a look inside the unit to see how hard it would be to bypass the existing outlets.  

I'm going to go down the route of the transfer switch anyway just so I have the option to use a gas generator in a prolonged outage.

I am not in favour of the second option you suggest (permanent inline UPS) as the UPS draws a some current 24/7 running fans and it's brains.  I try to run a conservative power budget in our house.  The UPS would primarily support a pellet stove and some LEDs.  The stove has 2 small blower motors (1/4 watt) that I don't see having much inductive load at all.  I will have to test the refridgerator's compressor to see if it will trip a 15amp outlet on the inverter as-is.

Thanks for the suggestions, very helpful.

Thank you everyone for your feedback and help.  

[MarkC_apc]

I have an "off-grid" backup system for my rural cabin.  There are dedicated circuits of about 1500 watts (max) for several lights, ceiling fans, TV, refrigerator for some level of comfort/utility during an extended outage (mainly hurricane concerns).  The battery bank is my golf cart and a parallel set of spare batteries (8 -155 AH, 12 volt deep cycle batteries).  These power the DC/AC (only) section of my old ('07)  SUA3000RM2U (the battery cage is removed).  I've run this for test purposes a couple of times for the entire night cycle.  I recharge via solar during the day.  No signs of heat problems in the inverter section.

Warning!  You must be sure that the "UPS" circuits are dedicated and not have any possibility of feed back to the grid.  Of course, using the provided UPS outlets directly to actual users does this!

Happy to provide more details

Mark

[voidstar_apc]

On 11/17/2016 10:52 AM, radior said:

I am not in favour of the second option you suggest (permanent inline UPS) as the UPS draws a some current 24/7 running fans and it's brains.  I try to run a conservative power budget in our house.

It sounds like you do not want the UPS to be powered 24/7? Normally they are always plugged in which allows them to keep their battery topped up. If you disconnect the UPS, you'll need to maintain the battery some other way. At minimum, disconnect the battery from the UPS. When removed from the UPS, they'll self-discharge flat in ~6 months and then permanent damage occurs. Any discharge shortens the battery life.

[Anonymous user]

On 11/17/2016 9:52 AM, radior said:

I am not in favour of the second option you suggest (permanent inline UPS) as the UPS draws a some current 24/7 running fans and it's brains.

While that's certainly true, the considerable self-discharge rate of lead acid batteries may be an issue if you do not allow the UPS to maintain them or provide for some kind of external charger (which I really wouldn't recommend). The batteries could turn out to be depleted when you want to use them, and letting them go flat will damage them. Most of the power drawn by UPS when it is idle will be going to the charging circuitry (very efficient and easily comparable to the best "float" or "maintenance" charger you could buy). By comparison the fan and microcontroller are drawing nothing. Certainly having to replace damaged batteries will negate any cost saved on energy.

Used as it was designed, the UPS has provisions to disallow any backfeed into the electrical system, and as was mentioned, that is vitally important. If you opt for your own, external approach, you will have to very sure that at no time can electricity can ever backfeed outside of your building.

[Anonymous user]

(o;  yes, once a week I plug the bank in until the console reports a full charge.  Not only did I get the setup for pennies on the dollar, the batteries have a manufacturing stamp of Jan this year.  I definitely want to get the most of them.

My plan is to use them as backup in the Winter and to try and use it as a charging source for an electric car in the summer.  I'm going to get enough solar panels to charge it during the day and plug a nissan leaf in overnight.  (deepcycling shouldn't be a problem given my commute but I'll keep an eye on that)

thanks everyone.

[MarkC_apc]

Interesting - I have a Leaf also and currently finishing a "solar" charge system - with an ultimate goal of using the Leaf's battery for emergency off-grid energy (V2H).  I'd be interested in your basic set up.

A couple of things to consider (realize you probably have, but if not) - the maximum charge rate is set by the Leaf's system and varies depending upon level 1 or 2 voltage.  After 2012, the chargers are max'd at 6.6 KW on level ii (208/240 VAC).  A 3000 VA (3u) high voltage unit will likely not support that power, unless you have a charge controller that can limit the amperes (such as OpenEVSE).  

On the other hand, using a "stock" level 1 charger will limit the charge rate to 12 amps or so which should be OK (~1500 watts).  The efficiency is not so great, so don't expect to get more than 3 KWH (maybe 10-12 miles) out of your system each cycle (keeping the SOC battery above 50%).  

https://avt.inl.gov/sites/default/files/pdf/fsev/SteadyStateLoadCharacterization2015Leaf.pdf

However it works out, it's a great learning experience!

Mark

[Anonymous user]

> On the other hand, using a "stock" level 1 charger will limit the charge rate to 12 amps or so which should be OK (~1500 watts).  The efficiency is not so great, so don't expect to get more than 3 KWH (maybe 10-12 miles) out of your system each cycle (keeping the SOC battery above 50%).  

That's the plan.  My commute is 16 miles each way and we have free charging at work.  My entire UPS setup has a total 7kW capacity.  Just leave it charge overnight, although I don't really need to do that given the 100 mile range, why not.. right?

As part of the bundle of equipment I picked up, there were two 1kW pure sine inverters.  I guess these were designed to be used to get AC out of batteries somewhere but I plan to use them as solar inverters.  I'll get details on them for you tonight if you want.

[MarkC_apc]

Sure - get what you can out of it.  The most important thing to watch (IMO) is the SOC (state of charge) of your 4 battery packs and cut the Leaf charging off when they reach about 50% depletion.  A network management card will give you the % of battery charge in the "logging" menu.  You can pick up a AP9617 (18) cheap on ebay.  The issue is figuring a way to automate it - and I'm not too sure of the accuracy of the % either.

Great experience anyway.

[Anonymous user]

It has that card in it.  That's what I'm using currently.  Automating it will be pretty easy, thanks!

[Brad_C · Accepted solution]

On 18/11/2016 8:52 PM, radior said:

yes, once a week I plug the bank in until the console reports a full charge.  Not only did I get the setup for pennies on the dollar, the batteries have a manufacturing stamp of Jan this year.  I definitely want to get the most of them.

The UPS reports a full charge well before the batteries are fully charged. a SmartUPS determines charge percentage based on a combination of battery voltage and a time fudge factor. Essentially once the batteries have reached float voltage the UPS says they are full. They're not (closer to 90%). Check any of the SLA battery data sheets and you'll see the batteries keep charging for somewhere between 10 & 20 *hours* after they reach float voltage. This charge period is essential to prevent sulfation.

None of this is an issue with normal UPS use, because the batteries are fully charged in the period immediately after the UPS reports a full charge, but in your periodic use scenario you will kill the batteries with increasing levels of sulfation. I would recommend only doing a monthly top up, but leaving it plugged in for at least 24 hours. Each charge cycle contributes toward cell plate corrosion, so you want fewer cycles if possible, but a complete charge each time.

Also, the self discharge period of about 6 months is only when stored at or below about 25C. The self discharge rate increases exponentially as the battery environment gets warmer.

If you really want to get the best life out of the batteries, grab the manufacturers data sheet for those exact units and do some reading.