UPS as a "part time" inverter - Question

quid_non · June 2009

Okay, I know this has been discussed before. My search for threads was not productive, sorry for any repeat.

Got a CyberPower (CPS900AVR) 900VA (est ~500W) UPS. Batteries bit the dust for the 3rd time - decided not to replace the (2) 7ah sealed batts, but spring for a new UPS.

Here's the question--
I'd like to use this "shell" UPS and hook it up to my cabin system for "intermittent use" (charge notebook batt, run a blender now and then...:cool:

If I hook the unit up directly to my 12V system (properly fused) should it work (as long as I don't exceed the ~500W limit)? See any issues with short tem use of this? I do know that UPS devices generate a fair amount of heat = inefficient, but I don't have an inverter yet and thought this might be a great opportunity to re-purpose something rather than toss/recycle.

System is ~120W PV (assorted panels), 120AH Interstate Deep Cycle batt, SunSaver SS20 CC, Trimetric Batt monitor. Various CFL's. Est daily use is ~15Ah.

Thanks for any suggestions / advice/warnings!
Best
Wayne

BB. · June 2009

Re: UPS as a "part time" inverter - Question

As long as you understand the limitations--I guess it can work.

Some issues that I have seen... Many UPS's will not work if they do not have a solid AC ground--will yours start if there is no AC power connection?

When connecting the batteries--make sure that their +/- connections are well protected. They will probably have some version of 120 VAC on their terminals and should not be ground referenced or touched during UPS operation.

The UPS internal battery charger may not work correctly with your batteries (too large of batteries, incorrect charging voltage, no equalization). Also, if you try to use an AC genset to run the UPS / charge the batteries--the output of the genset may not be stable enough and cause the UPS to "turn on" and run from battery power.

-Bill

Cariboocoot · June 2009

Re: UPS as a "part time" inverter - Question

If you're talking about using a UPS unit with defunct batteries as a cheap inverter by powering it off your existing solar-charge batteries ...

There could be issues. As Bill suggests, DON'T put AC through the UPS under these circumstances as it would try to charge the battery bank and it won't be able to: probably burn something out. And it may not even 'start', depending on the unit.

First be sure the UPS battery voltage is the same as your bank (I've got one that uses 24 VDC). Then make certain there is a fuse between the UPS and your batteries, rated according to the unit's draw. Finally, be prepared for it to fail as this isn't the intended design and the units aren't built for continual "off-AC" power applications.

As long as you follow basic safety precautions and keep an eye on things, what have you got to lose? It's either that or the recycle bin, right?

nigtomdaw · June 2009

Re: UPS as a "part time" inverter - Question

Im following a guy all around Northern Spain who has fitted Tripplite UPS inverters mod/pure sinewave in off grid situations and replacing with Outback Units sorry to burst your bubble but buy what works for the location and not try to put patches on stuff that was not designed for where u want it .

quid_non · June 2009

Re: UPS as a "part time" inverter - Question

Thanks for all the feedback - appreciated. Plan is to try it next week - will report back. Will NOT run AC through the unit, I am sure it is 12V.
Great feedback - thanks!
Best
Wayne

n3qik · June 2009

Re: UPS as a "part time" inverter - Question

I betting it is a 24V system.

quid_non

Where the batteries wired is series ??

john p · June 2009

Re: UPS as a "part time" inverter - Question

I have never seen a 24v small UPS.. But that does not mean they dont exist.
But almost every small UPS I have seen is underdesigned .. They are only designed to be used for very short periods of time.Even then most get quite hot after a few minutes.

mike95490 · June 2009

Re: UPS as a "part time" inverter - Question

Check out your UPS, sometimes they are only made to run 5 minutes, till the internal battery dies, they have no heat sinking, assuming when the battery is dead, the heat will stop. If you go continuous, you will need a UPS with a cooling fan.

Also they vary between mod-sine and pure sine. be sure the one you have works your gear OK for long times, 5 minutes is not always enough to discover your laptop charger will fry.

quid_non · June 2009

Re: UPS as a "part time" inverter - Question

n3qik wrote: »

I betting it is a 24V system.

quid_non

Where the batteries wired is series ??

Thanks for the reply - I replaced the batts -definately in parallel - not series.
Thanks!

john p · June 2009

Re: UPS as a "part time" inverter - Question

n3qik wrote: »

I betting it is a 24V system.

quid_non

Where the batteries wired is series ??

How much was the bet? and can you sent it to each of us soon? thanks in advance

quid_non · June 2009

Re: UPS as a "part time" inverter - Question

mike90045 wrote: »

Check out your UPS, sometimes they are only made to run 5 minutes, till the internal battery dies, they have no heat sinking, assuming when the battery is dead, the heat will stop. If you go continuous, you will need a UPS with a cooling fan.

Also they vary between mod-sine and pure sine. be sure the one you have works your gear OK for long times, 5 minutes is not always enough to discover your laptop charger will fry.

Thanks Mike -
Got an extra 12V "muffin fan" I was thinking of putting in there in addition to drilling some vent holes in the plastic case. As you mentioned, even in the normal AC mode, it gets really warm!

Thanks

n3qik · June 2009

Re: UPS as a "part time" inverter - Question

john p wrote: »

How much was the bet? and can you sent it to each of us soon? thanks in advance

It was my first born. I am 40+ and no kids or plans for kids, so you guys/gals are out of luck.

:D:D

quid_non wrote: »

Thanks Mike -
Got an extra 12V "muffin fan" I was thinking of putting in there in addition to drilling some vent holes in the plastic case. As you mentioned, even in the normal AC mode, it gets really warm!

Thanks

Here is my first inverter/UPS:

quid_non · June 2009

Re: UPS as a "part time" inverter - Question

Bummer!
Hooked the UPS up to a 12V batt (~20aH) and no go. Got alot of "beeping" indicating that the unit was in the alternate mode, but it refused to make 120V AC (measured by VOM). In fact, it beeped ~3-5x then silenced. No AC voltage was measured.

Thanks for all the suggestions - guess this was one on those usnits that needed to se some AC first. The unit worked fine when taken off line (needed to replace batts).

I'll keep for a bit - maybe come across some inexpensive 12V AGMs and use it again...
Thanks for the advice and help!
Wayne

BB. · June 2009

Re: UPS as a "part time" inverter - Question

Some of the inverter need both an electrical ground and neutral connection (grounded in North American Code)...

Depends on the mfg. and model.

-Bill

niel · June 2009

Re: UPS as a "part time" inverter - Question

i have a few that need a load on at the time of the outage to activate the inverter. trip lites i think.

john p · June 2009

Re: UPS as a "part time" inverter - Question

Well thanks n3qik,, its ok as long as you were willing to pay up.

my ups is a 1000 w sine wave inverter connected to my solar panel/battery set up(need the high wattage as im still using a 19"CRT screen ,dont like the colours on LCD) It powers the computer full time.. the inverter turns on by remote switch at computer. Never lost a hard drive since doing this.. its simpler and far more reliable than just about any bought UPS.. and never voltage sag.

roks · July 2009

Re: UPS as a "part time" inverter - Question

I was thinking of doing something like this with a APC Smart-UPS 1500VA, the rack mount ones have built in fans.

My smart-UPS 700va has heatsinks in it, it starts up without AC and its run for 30+ quite a lot at 50% load, so I assume the 1500's should be able to handle it better.

As these are line interactive, are they not running through the battery anway or not? And as APC of high quality, 95% efficient, they should be able to run for several hours.

BB. · July 2009

Re: UPS as a "part time" inverter - Question

UPS's are nice if you have unreliable power or a critical application that cannot take a power hit...

My experience with UPS that are not continuous conversion types--is about 1 out of ten power failures will result in a computer reboot (standard desktop computer and good quality UPS)... Apparently, the 1 out of 10 times the UPS take a bit longer to switch over--or the power supply on the computer hiccups during the switch over.

Why, I do not know--and with basic lab tools (including a power failure simulator)--I could never reproduce those real-world types of failures (failures are probably not clean loss of power--but full of dirty spikes from arcs, local motors, and such that confuse the UPS circuitry).

If you need 100% fail over protection for a larger computer--get a continuous conversion type inverter (AC to DC to AC conversion, more expensive and probably a bit less efficient).

The other issue with UPS's is they still tend to be inefficient--especially if you have a large UPS on a small system (1.5 kW with a 10 watt load)... The inverter may almost double your power requirements in that case.

Personally, if you can justify a laptop (size, speed, options, etc.)--I would go with one of those instead. You have 2-6 hours of battery backup (depending on model and usage). And fully integrated power management native to the unit (no cables, add-in software, OS configuration issues). And, you will really save energy to boot.

I find the typical UPS seems to need new batteries approximately every two years. So--you have the added costs of the backup battery maintenance too.

-Bill

System2 · September 2009

Re: UPS as a "part time" inverter - Question

Wayne, did your experiment work? I found some cheap 800W pure sine wave UPS units and am considering going this route.

john p · September 2009

Re: UPS as a "part time" inverter - Question

all have a look at my post #16,, honestly it really solves many problems and an inverter (if a goodone) is designed to operate continuously.. and after working at a large computer wholesaler as warranty manager can tell you nearly all UPS tend to have short unhappy lives..and dont fully protect the computers they connected to.. as the power drop out is sometimes slow and "spiky" also so the UPS circuits dont respond quickly..

South Africa · May 2014

Re: UPS as a "part time" inverter - Question

Did similar test. Used a APC SmartUPS RT1000. Being a online UPS, we reasoned that the inverter works 24/7, same as a solar inverter, so why not.

We connected 4 x 102ah batteries as 48v and UPS powered about +-500w of lights for a good few hours. UPS and batteries survived.

Can never connect it to a AC outlet for the built-in charger will not handle the charging of the 102ah batteries. But, what if we charge the batteries from a controller and solar panels. That is the next experiment. :-)

And yes, online UPS is much less efficient than a solar inverter, or a in-line UPS, but I have 2 of them as spare so why not use them till they die.

nsaspook · May 2014

Re: UPS as a "part time" inverter - Question

I have a 1.4kW Toshiba online UPS for the home servers that I use as a opportunity diversion load, My diy BMS diverts AC power (DPDT relay grid power transfer switch) from the inverter to it when the batteries are fully changed and the calculated solar panel energy capture 'Q'uality (a running total of actual power vs max power of a few previous days) for the day thinks it can recharge any battery power lost before the day is over.

Todays BMS status: Recharging battery after diversion earlier today.

PV Voltage 13547mV, Charging Voltage 12991mV, Controller Voltage 12079mV, Charge Cycle Time Left 5:18, Absorp Current 000mA, End-Amps 5300mA
 PV Current sensor 24800mA, Inverter Battery Current sensor -20000mA, Inverter Load Current 4800mA, Current Power IN 335W, OUT 62W
 AC PWR Inverter 0, Utility 0, Glitch Count 2:  Strings 1&2 are GANGED, Power Diversion enabled: DIPSW7, Diversion Status 1: PWM 0%
 Todays Power Q level: 59, Yesterdays Power Q level: 40
 Total Charger Energy 14195Wh, Todays Charger energy 0Wh, Prev Charger Energy 0Wh, Diversion Energy: Total 6089Wh, Todays 989Wh
 Total      PV Energy 33714Wh, Todays      PV energy 1379Wh, Prev      PV Energy 926Wh, Total Usage 38439Wh, Todays Usage 1310Wh, Dayclock 1:
 Battery Status:
 Battery 1 Voltage 12943mV, Current -20000mA, Power -258W, Quality -5

techntrek · May 2014

Re: UPS as a "part time" inverter - Question

South Africa wrote: »

Did similar test. Used a APC SmartUPS RT1000. Being a online UPS, we reasoned that the inverter works 24/7, same as a solar inverter, so why not.

We connected 4 x 102ah batteries as 48v and UPS powered about +-500w of lights for a good few hours. UPS and batteries survived.

Can never connect it to a AC outlet for the built-in charger will not handle the charging of the 102ah batteries. But, what if we charge the batteries from a controller and solar panels. That is the next experiment. :-)

And yes, online UPS is much less efficient than a solar inverter, or a in-line UPS, but I have 2 of them as spare so why not use them till they die.

First sentence - true.

3rd sentence - not true. It will just charge at a slower rate than you need it to. Add an external charger in parallel and you'll be fine.

Final sentence - also usually not true. Modern inverter designs are all about the same. The big one I use (see my sig) is around 93% efficient.

South Africa · May 2014

Re: UPS as a "part time" inverter - Question

techntrek wrote: »

3rd sentence - not true. It will just charge at a slower rate than you need it to. Add an external charger in parallel and you'll be fine.

Yes, I am aware of adding a separate charger, therein the mention of connecting to an array. The APC comes with 4 x 7ah batteries. How would it work if you now add 102ah batteries? On the other hand, you can add more battery packs. But is it worth the risk to even try connecting to AC in case the built in charger is overworked? Local UPS people advise strongly against it. Then, again, one the other hand, they are not really into pushing UPS'es. :-)

techntrek wrote: »

Final sentence - also usually not true. Modern inverter designs are all about the same. The big one I use (see my sig) is around 93% efficient.

Found this whitepaper in the subject. (removed in case of copyright issues)

Cariboocoot, this is where I got the idea to protect the devices with the online UPS, as I got it for free. :-)

Cariboocoot · May 2014

Re: UPS as a "part time" inverter - Question

Be advised that paper is copyright 2004. It's ten years old already and therefor may no longer be accurate.

techntrek · May 2014

Re: UPS as a "part time" inverter - Question

South Africa, sorry, I thought I was clear in my last response. I've been doing exactly what you describe for years, don't worry as much, you'll be fine. 8)

You can't "overwork" the internal charger, with a larger battery bank it will just charge at its highest rate for longer, assuming you don't have a secondary charger attached to the system which would bring up the SOC faster. I just looked up the specs for your UPS and it is designed to handle up to 10 external battery packs (plus its internal pack), so don't worry about breaking anything by adding that external battery bank. All 11 battery packs almost add up to the one you want to add. Your local "experts" are wrong and likely just want to sell you more of the RBC31 battery packs that yours is designed for. My UPS is also designed for up to 10 external packs and for years it ran from 16 110 amp batteries in series (about 22 kw) with no external charger - although I did manually equalize with an external charger at times.

Your UPS is older, with only a 88% efficiency. As Cariboocoot said, the PDF you linked to is 10 years old. Much of the info is still accurate, but the figures they quote on page 11 are slightly out-of-date. This is a direct quote from the spec sheet for my UPS: "The UPS efficiency is at least ... 92% for the 5000VA and 6000VA models, without degradation of output regulation as specified."

South Africa · May 2014

Re: UPS as a "part time" inverter - Question

My apologies, was very late when I read it.

Excellent!!!

When I get the next 4 x 102ah in, I am going to see what the UPS do with them connected to AC. :-)

Now I can tell my pal to go-ahead, get a 48v system specced to charge the batteries in +-5.5 average daylight hours for SA, and use the UPS for lights, till it breaks. And if it lasts as long as we expect (few years), then using 2nd hand online UPs'es as inverter for lights is a very cheap way to get into solar. And if there is no sun, plug it into AC.

Ps. Out of interest. Most small UPS (+-500w upwards) that has 'failed', we take them in, replace the batteries (recycle the 7ah, put in a 9ah), and walla, they work again, cheaper than a new one. To date, out of the 25 I fixed, 24 of them was 24v. Trying a 1kva inline on the 102ah batteries, I did not look carefully, it was 12v!!! AAARGH ... one UPS down, next!? :-)

stephendv · May 2014

Re: UPS as a "part time" inverter - Question

Two disadvantages of using UPS's as off-grid inverters are the relatively high power consumption and that some can't handle the high voltages required for charging flooded batteries.
On the first point, I've heard of 3kW UPS with a 200W constant noload draw, ouch! Absorb charging of flooded batteries in the cold could reach 30V which may just be within the capabilities of some UPSs, but you'd likely have to disconnect the UPS when doing an EQ charge at +32V.

South Africa · May 2014

Re: UPS as a "part time" inverter - Question

I see the APC has a 100w battery charger.

MarkP · August 2014

Re: UPS as a "part time" inverter - Question

My APC SmartUPS3000 has been running continuously for the last year or more as my inverter. I tossed the old gel-cells and hooked it up to my 48 volt bank of golf cart batteries that are normally charged by 2,100 watts of solar PV. When I feel the need I will often fire up the Honda EU2000i and feed AC through it. While doing so the on-board charger dutifully charges the batteries. A string of LEDs on the UPS intended to indicate state of charge dutifully records the increase of charge and dutifully if not accurately records the decrease as well. I say inaccurately because the programming does not account for giant GC batteries and after about 15 minutes the on-board computer figures the batteries MUST be discharged. I did run a load test to shutdown with 1,000 watts of halogen lights and it ran at least 6 hours but less than 9 hours. I fell asleep and when I awoke the lights were off and 9 hours had passed. I forgot to feel how hot the lights were so I don't know how long they had been off. This did not reset the scale of the charge indicator.

Anyway the APC SmartUPS works OK as an inverter.

stephendv · August 2014

Re: UPS as a "part time" inverter - Question

Interesting MarkP, how does the UPS cope with the absorb charge at 57.6V? And what about EQ charge at 62V?

UPS as a "part time" inverter - Question

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UPS as a &quot;part time&quot; inverter - Question

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UPS as a "part time" inverter - Question