cen-tech inverter

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  • Tony123
    Junior Member
    • Aug 2013
    • 11
    #1

    cen-tech inverter

    Hi I got a cen-tech (harbor freight) 5000 watt inverter. I bought 3 different ones and each time I tested them with a multimeter they all read around 94 volts. Am I missing something here or were all 3 inverters I tried defective? I also tried the 2000 watt model and it worked perfectly with voltage in the normal range.
    Tags: None
    • PNjunction
      Solar Fanatic
      • Jul 2012
      • 2179
      #2
      Is your multimeter a "TRUE-RMS" multimeter?

      While I don't know what the plus/minus specs of those inverters are, they are MSW or modified sine wave. A true-rms meter knows how to measure non-sinusoidal waveforms accurately. That may actually reverse your findings - the 5kw models might be truly close, whereas the 2K model is now a tad high!

        Comment

        • Tony123
          Junior Member
          • Aug 2013
          • 11
          #3
          I'm not sure if my multimeter is true RMS but the inverter failed to start my air conditioner. The 2000 watt model was able to start it for a short amount of time. That's what prompted me to test it.

            Comment

            • PNjunction
              Solar Fanatic
              • Jul 2012
              • 2179
              #4
              Ah yes - common problem.

              Just because an inverter has a wattage rating, it does NOT mean that your battery will actually support it! In addition, motorized appliance start-ups can generate huge inductive surge-loads which immediately overload the inverter too.

              I guess the question here is what is the capacity size of your battery (make / model / age help knowing too). I suspect that your battery is too small, and along with an inductive current spike, the battery voltage is just crashing too fast.

              Can your multimeter record min/max dc voltages? When placed across the battery terminals, and the air-con is started and dies, what is the lowest voltage it records?

                Comment

                • SunEagle
                  Super Moderator
                  • Oct 2012
                  • 15123
                  #5
                  Originally posted by PNjunction
                  Ah yes - common problem.

                  Just because an inverter has a wattage rating, it does NOT mean that your battery will actually support it! In addition, motorized appliance start-ups can generate huge inductive surge-loads which immediately overload the inverter too.

                  I guess the question here is what is the capacity size of your battery (make / model / age help knowing too). I suspect that your battery is too small, and along with an inductive current spike, the battery voltage is just crashing too fast.

                  Can your multimeter record min/max dc voltages? When placed across the battery terminals, and the air-con is started and dies, what is the lowest voltage it records?
                  It does sound like the 5000 watt inverter might be crashing the battery causing a low AC voltage output. Or with HF equipment there is always the chance of a bad batch of hardware.

                    Comment

                    • cmclane28
                      Junior Member
                      • Jul 2015
                      • 16
                      #6
                      Originally posted by PNjunction
                      Ah yes - common problem.

                      Just because an inverter has a wattage rating, it does NOT mean that your battery will actually support it! In addition, motorized appliance start-ups can generate huge inductive surge-loads which immediately overload the inverter too.

                      I guess the question here is what is the capacity size of your battery (make / model / age help knowing too). I suspect that your battery is too small, and along with an inductive current spike, the battery voltage is just crashing too fast.

                      Can your multimeter record min/max dc voltages? When placed across the battery terminals, and the air-con is started and dies, what is the lowest voltage it records?
                      I remember when I first got my solar starter kit I got one of those really small 12v 35ah batteries and a 1500 watt inverter and it actually powered up my small window shaker AC unit! I think back on that now and wonder how in the world it worked. haha. The AC unit only pulls like 550 watts, but I can't believe the surge and the tiny battery I was using still allowed it to work. Of course had I left it running I could have only gotten about 20 mins out of it, but it was cool to see it work at the time.

                        Comment

                        • posplayr
                          Solar Fanatic
                          • Jun 2015
                          • 207
                          #7
                          Originally posted by cmclane28
                          I remember when I first got my solar starter kit I got one of those really small 12v 35ah batteries and a 1500 watt inverter and it actually powered up my small window shaker AC unit! I think back on that now and wonder how in the world it worked. haha. The AC unit only pulls like 550 watts, but I can't believe the surge and the tiny battery I was using still allowed it to work. Of course had I left it running I could have only gotten about 20 mins out of it, but it was cool to see it work at the time.
                          Batteries have relatively very low impedance meaning even a smaller battery than you had can generate as much as 100 amps for short periods.

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