Q: How can you verify if an inverter is a pure sine wave inverter?

Discussion in 'General Electronics Chat' started by foolios, Jul 12, 2014.

  1. foolios

    Thread Starter Active Member

    Feb 4, 2009
    160
    1
    I just bought an inverter off of eBay and want to verify that it is a pure sine wave inverter. Is there a simple test or do I need to get some equipment that will test it?

    Thanks in advance.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,153
    3,059
    An oscilloscope would be the ultimate. You could use a cheap, software based one since the frequency is so low.

    Looking up the model number specifications would be a start. And maybe someone has already tested it.
     
    foolios likes this.
  3. foolios

    Thread Starter Active Member

    Feb 4, 2009
    160
    1
    A software based one? Something done on the pc? How does that work?
    Make sure the pc is on the inverter and then run the software to test?

    EDIT:
    I looked up the only number I could find on it and found this review:
    http://www.metco-electronics.com/AT300P/index.htm

    It seems it's not quite pure sine wave, since the reviewer states the wave form is ragged. Hmm... Not having anything attached to the ground plug-ins is a concern.

    Wondering if I should throw this thing away.
     
    Last edited: Jul 12, 2014
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,809
    1,105
    How far off is 'not quite'? Any switched-mode so-called pure sine-wave inverter can be expected to have some ripple on its output waveform. The better the quality the less the ripple.
    Can't you provide a ground?
     
    foolios likes this.
  5. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    The sine wave produced is not that bad, especially when you compare it to a modified sine wave model. I suggest you use it until you find something wrong. Also, your unit may have the right frequency oscillator in it.
     
    foolios likes this.
  6. wayneh

    Expert

    Sep 9, 2010
    12,153
    3,059
    You use the input for analog audio, if your computer still has one. The oscilloscope software looks at what would normally be a microphone or a line-in signal. They work OK for ~5-5000kHz or so, depending on your sound card. It'd be fine for looking at a 60Hz wave.

    You would apply the probes to the output of your inverter, and I'd do it while under load, perhaps just a light bulb.

    Note that you have to be very careful connecting anything to your audio-in port, or you risk damaging it. If this is all new to you, I wouldn't proceed until you're sure what you're doing.

    But in the meanwhile it sounds like your inverter is probably fine for most applications.
     
    foolios likes this.
  7. foolios

    Thread Starter Active Member

    Feb 4, 2009
    160
    1
    Would I just need to tap a ground onto one of the external chassis screws and then place the other end of that wire with an eyelet onto the ground plug of the power cord?
     
  8. foolios

    Thread Starter Active Member

    Feb 4, 2009
    160
    1
    Thanks for that info and getting me started in looking into this.
    I read that I would want to make sure I added some kind of voltage protection to protect the sound card from over-voltage/voltage spikes.

    I'm not ready to risk my laptop with my low skill level so I'm thinking of getting something like this:
    http://www.amazon.com/WMicro-DSO201-Digital-Storage-Oscilloscope/dp/B00D5P4B5C/ref=sr_1_56?ie=UTF8&qid=1405252078&sr=8-56&keywords=oscilloscope

    Some of the oscilloscopes I've seen that are cheaper require a PC, this one doesn't mention that so I'm hoping it will work as a stand-a-lone.

    Thanks
     
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,809
    1,105
    Someone with a knowledge of US wiring codes should be able to tell you.
     
  10. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Looks like a pretty good unit to me. Seems to work better what a fully charged battery.

    I wouldn't worry at all about the ground. By their nature, inverters are completely isolated systems, and as such, they don't have an earth ground. If you're really that worried, the only thing you can do is to connect a ground wire to a earthing rod driven into the ground, and connect that to the ground terminal on the plug. But I really don't think that's going to offer much in the way of protection. I'd just use it as it is.
     
    foolios likes this.
  11. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    The light just came on concerning the ground issue. A few years ago I installed an inverter into my RV. I connected up the ground and neutral of the output into the distribution/breaker box. When I turned the inverter on, there was a puff of black smoke, and that smell of burnt plastic that we all know and love/hate.

    The problem was that the output of the inverter was not floating relative to the 12 volt input. So, in an RV, the negative of the battery is connected to ground (chassis) as well as ground and neutral of the AC. Connecting AC neutral to ground was a dead short for the inverter.

    foolios
    I believe you have one of these kind of inverters. To test this, measure AC voltage from negative 12 volts to ether of the 115Vac pins. (Loading should not matter.) I think you will read 60 Vac from both AC output pins to -12V.
    What this means is that your load or your batteries must float. Do not connect that ground pin.

    Mark

    P.S. - The inverter I installed in my RV was a Xantrex Inverter1000.
     
    Last edited: Jul 13, 2014
    foolios likes this.
  12. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    To follow up I tested two other inverters that I have.

    PowerBright 400 watt
    Output ground pin connected to -12 volts in
    AC output completely floating.

    No name 125W
    Output ground pin connected to -12 volts in
    AC output - 66 Vac/66Vac to -12 volts in

    Mark
     
    foolios likes this.
  13. foolios

    Thread Starter Active Member

    Feb 4, 2009
    160
    1
    Thanks all for the info. I will test this out when I get back and post the results.
     
  14. foolios

    Thread Starter Active Member

    Feb 4, 2009
    160
    1
    With inverter on and no load plugged into the AC side, I am not getting any voltage from the 12v negative to either of the open AC slots in the open AC plugin port.
    With inverter on and a load plugged in, I get ~30v from Neg DC to either AC.

    Does this help figure this out? Let me know if there's anything else to test.

    Thanks in advance.
     
  15. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    I say there is nothing wrong with that inverter and it is time to end this thread.
     
  16. foolios

    Thread Starter Active Member

    Feb 4, 2009
    160
    1
    Ok, then that one doesn't need a ground, right? It's ok to use as is.
     
  17. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Threads end when nobody is posting anymore. Otherwise, they stay open so we can discuss to our heart's content.
     
  18. Chalma

    Member

    May 19, 2013
    54
    2
    I wouldn't recommend plugging your laptop into an inverter you believe MIGHT not be pure sign wave. If there is a piece of equipment you don't particularly care for that has sensitive electronics (especially TIMERS or AMP) I would plug that in and see if it operates normally.
     
  19. foolios

    Thread Starter Active Member

    Feb 4, 2009
    160
    1
    Is the general consensus that I should ground this inverter or no? Sorry if I am missing the answer.
     
  20. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    It is my opinion that your inverter is fine the way it is. I would not modify it. I would not hesitate to plug my laptop, dvd player, or monitor into it. These devices are in my RV and are currently running on an inverter that has worst specs than your inverter.

    Go forth and power up!

    Mark
     
    foolios likes this.
Loading...