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Thread: UPS for modified sine wave system?

  1. #1

    Default UPS for modified sine wave system?

    Without getting in to the details of why I need this (shouldn't, but it's not my system and I can't do anything about it) I need a computer UPS that will accept modified sine wave from a Trace SW4048.

    I already know why most of them don't work, they think MSW is too "low" in voltage, pronounce a brownout, and switch to battery.

    I have some wireless network gear I need to keep up and running.

    Have any of you actually gotten an off-the-shelf UPS to work with MSW? My first couple tries with current UPS's didn't fly, I have an old APC that allows you to adjust the low-side cutout to 90V with DIP switches that I am going to try next time I visit the site.

    Thanks for any help you might be able to provide...

  2. #2

    Default Re: UPS for modified sine wave system?

    Unless I've gone completely senile in the past two weeks (possible) the Trace SW4048 is a sine wave inverter. It should have no trouble running a UPS.

    So perhaps that is not the problem you're experiencing. The SW series is no longer made and support/repair can be difficult to attain (as often lamented on this forum - they were good inverters).

    The logical question would be; if you've got a battery-powered, true sine wave invert, what do you need a UPS for? Could you give more detail as to the current set-up and what further you're trying to get it to do?
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  3. #3
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    Default Re: UPS for modified sine wave system?

    This question does not to me make a lot of sense.. If you using a msw inverter or any inverter for that matter running off batteries why you need to run a UPS from it as it in itself is really a UPS??? In fact its how I run my computer at all times off a inverter.. as then no possibility of power failure from grid mains.. The batteries are normally solar panel charged but if the battery voltage gets low an automatic voltage switch turns on the mains battery charger.

  4. #4

    Default Re: UPS for modified sine wave system?

    OK, I'll try to answer both of you at once here.

    The 4048 is indeed a MSW inverter.

    From the manual:

    "The inverter makes a stepped approximation to a sine wave. The number of steps typically varies from 34 to 52 per cycle."

    I can verify this as I have looked at the output with a scope.

    As far as to WHY I have to try to get a UPS to work:

    This isn't my system or house. I can't go around modifying it.

    If it were me, I would do just what you say and run the network gear off of the battery bank. That would be a lot of work as it's sitting +/- 200 feet away from the house in a freight container, but it's the right thing to do. Don't have time right now.

    The reason I need the UPS at all:

    We have a very large submersible well that has to be run off a generator once or twice a week to fill a 40K gallon tank. When we run the generator, the manager throws a transfer switch to put the house on genny power which also switches the 4048 to charger mode and gives the battery bank a little extra kick.

    It's that 1 sec. or so when the xfer occurs that I lose power to everything. The wireless access points I'm using come up in a random state - most often not working. Mgfr states that you should wait at least 30 sec. during a power cycle. I have investigated this as well and it's the truth.

    So, I need an uninterruptible supply of short duration to avoid needing to ask the
    manager to remember to wait for 30 sec. each time he throws that switch.

    I can do it with an AGM battery and BatteryMinder for the single piece of problematic gear, but I thought it might be nice to put the Starband Nova CPE on backup as well as it takes 15 - 20 min to find the sattelite again every time it loses power. Small UPS would handle everything nicely if it would just stop rejecting the MSW as non-compliant.

    Hope this all makes sense...

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    Default Re: UPS for modified sine wave system?

    so where is the inverter now sitting? you say..That would be a lot of work as it's sitting +/- 200 feet away from the house in a freight container, but it's the right thing to do. Don't have time right now. so how far is the ups? inverter?? a long way +/- 200ft or it really is just 200ft? how hard can it be to just run a 200ft length of building cable 200 ft?? if it is 200 ft at 120v from inverter? sorry if im not really understanding you..

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    Default Re: UPS for modified sine wave system?

    Quote Originally Posted by Vance G View Post
    The 4048 is indeed a MSW inverter.

    From the manual:
    "The inverter makes a stepped approximation to a sine wave. The number of steps typically varies from 34 to 52 per cycle."
    With 30 steps, I doubt there are many things that would complain about that.

    Most MSW inverters have 3 steps, which is really harsh on gear.
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  7. #7

    Default Re: UPS for modified sine wave system?

    Quote Originally Posted by john p View Post
    so where is the inverter now sitting? you say..That would be a lot of work as it's sitting +/- 200 feet away from the house in a freight container, but it's the right thing to do. Don't have time right now. so how far is the ups? inverter?? a long way +/- 200ft or it really is just 200ft? how hard can it be to just run a 200ft length of building cable 200 ft?? if it is 200 ft at 120v from inverter? sorry if im not really understanding you..

    The entire system is housed in a 20' freight container about 180' away from the house. 120V via 3 #8 in a conduit from the container to the house.

    Can't (shouldn't) run DC in a conduit with AC when the DC runs logic. Esp. when AC is MSW which will inductively couple all kinds of hash to just about anything else running in the conduit.

    So, need to dig 180' trench, lay pipe, pull wire. Becomes a big project when I am 400 miles away and only get up every so often.

    UPS solution is easy and fast.

  8. #8

    Default Re: UPS for modified sine wave system?

    Quote Originally Posted by mike90045 View Post
    With 30 steps, I doubt there are many things that would complain about that.

    Most MSW inverters have 3 steps, which is really harsh on gear.
    I only wish that were true. And I admit I have only tried one UPS so far. But the one I tried (APC ES250 I think it was) did not work. Kept switching from battery to AC and back about once every two sec.

    Realize that UPS's are DESIGNED to look for non-compliant AC (aka - perfect) and try to make it better with some kind of AVR or by switching to battery so... "Houston , we have a problem" when our AC is NEVER perfect (as in MSW).

    The UPS folks, to their credit, realize this and cover it in their FAQ's, stating that their devices won't work properly when powered by inverters or small generators.

    I was just hoping that one of you had forged ahead and tried a few and found one that worked. Re-wiring these folks house just to get this to work is NOT part of the project...

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    Default Re: UPS for modified sine wave system?

    WELL to me the only solution is to swap the MSW for a true sinewave inverter. it has to be the cheapest way to go.!!

  10. #10
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    Default Re: UPS for modified sine wave system?

    Or, as you have said, a AC small battery charger+inverter at the remote location.

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