off topic question, low-cost UPS units. msw or tsw?

bmetbmet Solar Expert Posts: 630 ✭✭
I have a Kil-A-Watt meter, and have seen how the VAC reading indicates low with my msw inverter. If my UPS indicates normal VAC(while unplugged from outlet), does this mean that it it providing tsw from battery? If so, that would be a good reason to search thrift stores, $25 for a tsw backup is a sweet deal ($10 for discarded UPS, $15 for new battery).
Thank you.


  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: off topic question, low-cost UPS units. msw or tsw?

    Not necessarily... You should be able to track down the model name/number on the Internet and get the specifications.

    Getting used UPS's... I would plan on replacing the battery pack (not always cheap). Typically they have been setting around for awhile and/or the battery is more than 1-2 years old--all good reasons to replace the batteries.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: off topic question, low-cost UPS units. msw or tsw?

    too bad you aren't near me as i'd give you an ups. the batteries tend to go after a few years and i bought my ups used with a new battery for about the same price as the battery would cost out of batteries plus. i've got the tripp-lite internet office 250. the battery is a 7ah agm that is now dead on all of mine excepting 2 of them now.

    the ups will pass household ac until that power is interrupted and then it'll activate the small msw inverter inside to power at up to the rating of the ups unless you are lucky enough to find an ups that is sine wave. batteries are small and good for usually 5-10 minutes at full ups power rating as they are meant to properly power down pcs during an outage.
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: off topic question, low-cost UPS units. msw or tsw?

    Heh. I just chucked four or five nice APCs because I couldn't find anyone to take them off my hands... :roll:

    All mine were "used" - other people throwing them away because they were "bad". I just got new batteries and they worked fine.

    Only problem with that is the batteries that will actually fit inside the UPS are EXPENSIVE because they know darn well what they're most often used for. (This is at a battery store, not from APC.) So I pigtailed some heavy-gauge wire outside the units and bought replacement batteries in a different form-factor. Usually got the same or a little higher AH rating, and the price was dramatically cheaper. Can't move the assembled UPS around very easily (especially the larger 24V ones) but can't beat the price.

    But now I have my entire network running on my Outback inverter, so no need for the UPSes.
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: off topic question, low-cost UPS units. msw or tsw?

    Most of the 1500VA or less will be MSW.
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: off topic question, low-cost UPS units. msw or tsw?

    I also checked the voltage with my cheap DVM (not RMS able), and it shows 120VAC out of the Belkin UPS. When measuring the output of my msw inverter, it was indicating 108VAC. I realize UPS are for shutdown, but I have a lot of small devices that need protection from the Co-Op.
  • 2manytoyz2manytoyz Solar Expert Posts: 373 ✭✭✭
    Re: off topic question, low-cost UPS units. msw or tsw?

    Like others, I get freebie UPS units. Batteries die, people end up throwing them out. Ditto the comment that many of them use odd sized batteries, making them prohibitively expensive to replace.

    Many times I get stuff in a couple of the all too common 7A 12V SLA batts. It may not have the duration of the original batteries, but has worked well during the many power bumps, or brief power outages.

    You can get larger external batteries, and operate them that way. But you need to consider these are only intended for brief periods. Consequently, only the large ones tend to have cooling fans. Even a 400W MSW inverter has a fan, but that's intended for extended operation. Not that an UPS can't be used for longer periods, but you might have to provide some cooling.

    As for not having an RMS meter, that's a common issue. The book that came with a 400W Vector 400W inverter discusses the low voltage reading issue:




    With a Fluke meter (true RMS), here's what I measured on a $29 inverter:


    The spec says 115VAC, and that's pretty close. I expect your MSW UPS to be the same. I have a stack of MSW inverters and UPS units. All have been tested, and all meet the manufacturer's specs for voltage and frequency.

    Ask around, you'll probably find a friend or coworker that has access to stacks of used UPS units. When I replace the battery, I also remove the piezo buzzer!

    Most of my home electronics are connected to an UPS, which is tied to a homemade transfer switch. The UPS takes the load when the grid goes down. It takes a couple of seconds for my inverter to come out of the Power Save (standby) mode, and take the load. When the grid comes back online, the relay engages, transferring the load back to the grid, causing the inverter to return to the Power Save mode. The UPS unit stops the load from being dropped during the transfer from/to the grid.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: off topic question, low-cost UPS units. msw or tsw?

    i should mention that if you go with a larger battery that the charger inside of the ups might not be able to provide the higher charge current needed by the larger battery to properly charge it. i never measured the charge current that my ups produces and recognize that it may be a higher current than our normal range of 5%-13% to quick charge the battery. anybody measure theirs? anyway, if the larger battery is at least able to get a 5% charge from the internal charger it may work fine, but otherwise another charging source is needed.
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: off topic question, low-cost UPS units. msw or tsw?

    I did this with a ACP 1000 VA. The OEM battery was a 24 volt 17 AH bank. Change it out to a 24 volt 55 AH AGM bank. Charge it w/o any problems.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: off topic question, low-cost UPS units. msw or tsw?

    Upsizing by 2 to 3 times the original size shouldn't be an issue, as long as you don't care about getting it back to a full charge quickly. Assuming they are designed to fully recharge within 12 hours after a complete discharge, which is reasonable to expect, you would be looking at 24 to 36 hours with a larger battery which is within safe limits.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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