Inverter connected to UPS - blowing

Discussion in 'General Electronics Chat' started by alkit, Feb 8, 2015.

  1. alkit

    Thread Starter New Member

    Feb 8, 2015

    My office is set up that 2 computers and router are connected to a UPS (650VA, offline). The UPS is then connected to the AC wall socket.
    I measured the total wattage of everything connected. It ranges between 200-250W.

    As we had a power outage the other day, I did the following, and these were my results:
    1) Connected a 500W cheapo inverter to 105Ah deep cycle battery. Then plugged the UPS into the inverter. There were sparks coming from the battery positive terminal, and then the inverter voltmeter went from 13V down to 0V.
    2) Then connected a 720W Quantum inverter (larger, in plastic box with cooling fan). As soon as I connected the main plug, inverter made a slight pop, and fan went dead. Inverter will not power on at all now.
    3) Then connected a 500W inverter (car style, without built-in charger) to the UPS. It powered on my setup without an issue for 5 minutes. I then turned off the inverter and turned it on again. There were sparks at the battery, and inverter made a long beeeeep.

    I can no longer use any of these inverters, as they all do not work now.

    I just want to know where I went wrong?

    The only thing I can think of is the fact that I connected all of these to a UPS.
    Could it be that either the UPS:
    1) Needs power from pure sincewave inverter only?
    2) Possibly has a large amount of surge wattage which could have blown the inverters? (Also find this hard to believe as it is a 650VA ups (360W), so shouldn't be able to surge that high, even when in charging mode).

    Alternatively, is there something else I could have done wrong? I just want to make sure I do it correctly next time so that I don't blow anything again (costing $$...)

    Thanks in advance for the help!
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    Why would you need to power a UPS via an Inverter in the first place.
    Doesn't the UPS have a battery ???

    Second is if the inverter cannot handle inductive loads it will go pooooop!
    UPS cannot handle inductive loads but most inverters can.

    I really do not understand what went wrong but an Inverter should be able to power a UPS. Inverter should be a H-Bridge type.

    It could be that none pure sine wave from the inverter is creating havoc. Or you might be creating an earth loop.

    You should show your every connection detail. Exactly how you connected every single wire

    Lastly if you just wrap the cable around the battery terminal you will get sparks no matter what. You should use battery connector with Lugs and screw them tight.
    GopherT likes this.
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
    It could be that the ups was trying to recharge its battery and overloaded the inverter.
  4. alkit

    Thread Starter New Member

    Feb 8, 2015
    The inverters that I have are either too noisy to keep plugged in, or don't have an Auto Switch function.
    I therefore need to UPS to keep the computer on, while I go to the plug and move it from the wall to the inverter unit.

    I will post pictures. What image hosting site would you recommend?

  5. Reloadron

    Well-Known Member

    Jan 15, 2015
    The forum allows images to be directly uploaded to the forums, there is no need for a hosting site.

    Connecting a UPS to an inverter isn't a good idea. Inverters come in several flavors with lower cost units outputting a modified sine wave and better units outputting a true sine wave. The same is true for UPS units by the way. Better UPS units also allow for the connecting of an external battery which is a good way to go. If you want or need extended runtime from a UPS, exceeding the internal battery capabilities then the best way to go is to provide the UPS with an external larger battery rather than power an inverter (12 VDC or 24 VDC) to get line voltage and then power a UPS. If that were the case it would be better to just power the office computers or whatever directly from the battery powered inverter. Why add a UPS in there?

    When the lights go out (mains power loss or failure) the lights go out. All you should need is a UPS with a high enough VA rating to support your hardware and a battery large enough to extend the time to what you may need.