UPS system on a Generator ? Will it run ? Advice?

Blitz Solar Expert Posts: 33
I hope this is the right section of this forum to post this simple question.
( if not , moderators , please feel free to relocate this question to the appropriate location )

I had to upgrade a computers power supply from 250 watt to 650w for various upgrades and video cards, etc... that require more power.

My current UPS system will only provide 350 watts, so I have to upgrade My UPS system as well.

Becasue I'm shopping these units, and looking at 1500 VA, or 900 watt units...

I now have a question about "potentially" running a UPS system from a generator.

Total power requirements will be somewhere around 800 watts, for X time ( I will be putting in a larger battery for the UPS, for NO power conditions )
I want to run the tower, monitor, LAN and internet... so maximum 800 watts ( Not that it matters so much for my question)

So I'm going to buy a new UPS unit...

In the future, I MAY need to run this unit off of a generator, that does not provide "Pure Sine Wave " output FROM the generator.

Are there some problems attempting to do this that I'm only vaguely aware of ?

Is there a better brand that will accept incoming Generator power with out hiccups ?

I'm looking a Trip Lite and Cyber Power: ( But I'm open to any suggestions in this power range and price range ( under 200 bucks ) )

Thanks for any advice or experience you can provide.

Because I'm buying a new unit ( UPS ) I might as well get one that I can run off a generator, should it ever become necessary.

( side note, I dont THINK that my computer system requires Pure sine wave power, so a UPS with Modified Sine Wave output would probably work for me as well ... It just needs to run off of a generator with out glitching out.

Best Regards,


  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    Re: UPS system on a Generator ? Will it run ? Advice?

    Make the generator an inverter type like the Honda EU series, or the equivalent inverter generator from Yamaha. That gives you pure sine wave power that is kind to anything you connect.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: UPS system on a Generator ? Will it run ? Advice?

    The problem with any size UPS on a traditional generator is its ability to sync with the frequency. Until you get into very large generators, non-inverter gensets have "dirty" output - and no it isn't the sine wave form which is pure sine wave by the very nature of how generators create electricity. Instead, the problem is they'll jump around from 59.9 Hz to 60 Hz to 60.1 Hz very quickly. Not a problem for electronic power supplies, small electric motors, or lights (although you'll see incandescent and some fluorescent lights flicker). The problem is UPSs don't like a high slew rate (change in frequency). They need to sync up all the time so if they do need to take over the load they already have the sine wave matched up to how the utility was when it dropped out. Some UPSs can be adjusted to achieve a higher slew rate although this also gives you more flicker in your lights.

    The smaller UPSs in the range you describe usually don't have a slew rate adjustment. So when you stick them on a traditional generator they'll drop off of the genset output constantly thinking that the utility output has dropped out. As mentioned above, an inverter-generator solves this problem. Or, go with a larger UPS that will allow you to adjust the slew rate.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Blitz
    Blitz Solar Expert Posts: 33
    Re: UPS system on a Generator ? Will it run ? Advice?

    Thank You Mountain Don and Techntrek.

    I have researched these all day, and Both of Your suggestions make a lot of sense.

    Mountain Don.... Perfect excuse to get a Honda EU : )
    I have wanted one of several models for a long time anyway....

    Yet, that's not in the cards this go around.
    Soo... I keep telling myself... very very soon !!!


    You hit it exactly.
    The UPS senses the variance ( slew ) in the output voltage of the generator, and kicks out to battery power.

    Exactly what i want to avoid, and You are 100 % correct.... the lower end units ( home office ) will not be adjustable or support generator function.

    most of the units I looked at have a
    50/60 Hz +/- 3 Hz (auto sensing) input voltage feature, which is "non user adjustable".

    once you start getting into rack mount and IT server room UPS systems, that option is available for user adjustment.

    Unfortunately.... we are talking thousands of dollars.


    I actually did find one that will fit the bill for what I want. ( I HOPE )

    any possibility someone could give these specs a "once over" and see if I'm reading this correctly?

    The model is a APC SMART-UPS SC 1500VA SC1500 Rackmount/Tower

    According to the users manual, page 7
    the voltage input sensitivity is user definable
    for High , Medium and low sensitivity

    ***** Input Frequency 47 - 63 Hz *****

    Input voltage range for main operations 95 - 142V
    Input voltage adjustable range for mains operation 87 - 152V

    There are other user definable settings such as
    High and Low input voltage transfer points ( 127 volts ac and 106 volts ac )
    Synchronized turn ON delay ( delay before UPS turns back on after reconnecting line power )

    "Voltage Sensitivity
    The UPS detects
    and reacts to line
    voltage distortions
    by transferring to
    battery operation to
    protect connected
    High High sensitivity,
    Medium sensitivity,
    Low sensitivity
    Note: In situations of poor power quality,
    the UPS may frequently transfer to
    battery operation. If the connected
    equipment can operate normally under
    such conditions, reduce the sensitivity
    setting to conserve battery capacity
    and service life. "

    I think I may have found My huckleberry.

    Its no where near a 4200 watt unit like Techntrek is running, but it will sure work for what I'm doing... right?

    Thanks for the replies Gentlemen.

    If I'm spending some $, I might as well get something that will function in an off the grid situation.

    This problem never had occurred to me before I was ready to send Amazon some CASH... and started reading some of the reviews...
    And though I better ask You guys here.

    If anyone else knows anything, please chime in.. as i will be ordering this unit in the next 2 days, I'm sure
    After a little more research and comparison shopping.

    Best Regards,

  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: UPS system on a Generator ? Will it run ? Advice?

    You can find the SURT line on ebay for much less cash, used. The 4 kw unit I'm running cost about $250 (plus $250 for a used transformer SURT-003, necessary since the UPS output is only 208 or 240). You just gotta keep your eyes on the market for a while until the cheaper ones appear.

    You are in the right neighborhood, though. The SURT line has great features like full monitoring/control via Ethernet. I have mine on a wifi base so I can control it from my laptop or cell phone sitting on my couch. Access via terminal, ftp, http, with full logging (it amazes me how finicky and incomplete the monitoring/control features are with many of the grid-tie and off-grid inverters, based on what I've read here). The best feature is the SURTs do full online conversion AC-DC-AC so you get the best protection, even handling brownouts or sustained surges without going to battery power.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Blitz
    Blitz Solar Expert Posts: 33
    Re: UPS system on a Generator ? Will it run ? Advice?

    That sounds really good.
    Thanks for the model numbers to start looking for.
    I did see several yesterday that were 208/240 that I passed on for that exact reason.

    I'm pretty good at shopping and finding deals, as long as i have a direction to go.

    I read a few of your posts last night about the Prius and powering your system.
    4 kw would be really nice... and I will start researching that direction now.

    The NEW ones I saw yesterday were 1200 to 4 grand. ( direct from APC )

    Refurbished are about half that, and I'm sure private sellers will be even less.

    The AC/ DC / AC line voltage monitoring and conditioning make a lot of sense...
    They have a term for that... "Double Conversion" ONLINE.

    I appreciate the advice Techntrek.

    I will start searching them now.

    add to my wish list, a Honda EU 1000 ( or two ) or an EU 2000.
    I changed my thinking from a bigger Honda unit after reading here a while, for efficiency.
    ( I also changed my thinking about larger inverters, and the better way to go is smaller units )

    I believe in timing and the " fall in your lap " theory.... so I know what to be looking for now.

    Thank You again for the replies.

    I think I'm well on track now, and some questions I had yesterday have been answered.

    I'm really glad i researched these issues first.
    Not a lot of UPS manufactures "State" that their UPS systems are "generator capable"
    ( There are hundreds of UPS's available as well !!!! )

    I would have made a mistake.

    All the Best.