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O/T: Harbor Freight, or any modified sinewave inverters and electronics?

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  • O/T: Harbor Freight, or any modified sinewave inverters and electronics?

    I purchased a three of these along with some car battery jump boxes to power emergency LED lighting. I already made one setup and it lasted for 12+ hours on one charge.

    I would also like to power a TV and computer with it. The ad says its fine for that but one of the reviewers said it will ruin the TV and computer.

    I dont know anything about the modified signwave inverters. Looks to be a square wave. I dont see how it would affect the electronics. All they (PS) are doing is converting the "A/C" back to DC anyway so where could the harm come from?

    Any advice is well welcomed. Thanks. JR

    Inverter:
    https://www.harborfreight.com/750-wa...ter-66817.html

    Jump box:
    https://www.harborfreight.com/3-in-1...ter-62306.html

    Nice LED lamp:
    https://www.harborfreight.com/420-lu...ght-63278.html

    And YES, I do already have a small true sign wave inverter (Xantrex Prowatt SW2000). I just wanted something more protable.
    My old yahoo group. Bridgeport Mill Group

    https://groups.yahoo.com/neo/groups/...port_mill/info

  • #2
    For electronics you should use a pure sine wave inverter.

    Comment


    • #3
      I don't see a modified sine wave (clipped triangle wave?) damaging a computer or TV, particularly a laptop using an external brick p/s.

      I have a Generac 4.6KW so-called sine wave generator that produces a godawful wave, full of junk, but my TV and computers work fine on it. It does drive my stove crazy - the control panel beeps furiously and won't run. But no damage.



      I doubt that inverter looks anything near as ugly as that...

      -js
      There are no stupid questions. But there are lots of stupid answers. This is the internet.

      Comment


      • #4
        HIJACK ALERT!

        Well, sort of. If any of our electronics wizards has an idea how I could clean that wave up I'd be delighted to hear their theories.

        -js
        There are no stupid questions. But there are lots of stupid answers. This is the internet.

        Comment


        • #5
          I think your battery will last a lot longer if you get a 12 volt LED light instead of taking 12 volt and converting it to 120 volt.

          Brian
          OPEN EYES, OPEN EARS, OPEN MIND

          THINK HARDER

          BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

          MY NAME IS BRIAN AND I AM A TOOLOHOLIC

          Comment


          • #6
            Originally posted by bborr01 View Post
            I think your battery will last a lot longer if you get a 12 volt LED light instead of taking 12 volt and converting it to 120 volt.

            Brian
            I agree. Its just that these were the right price, inexpensive and I can use them (120ac) without the jumpbox gizmo I hacked together. And I only need 12hrs cause I can recharge batt. packs in the day with solar. JR
            My old yahoo group. Bridgeport Mill Group

            https://groups.yahoo.com/neo/groups/...port_mill/info

            Comment


            • #7
              Funny, I have a battery jump pack like that in use as an extended life UPS for the cordless phones in the house. It's on constant charge and feeds the phone "base station" in place of the wallwart. It can last days in a power outage.

              Dan
              At the end of the project, there is a profound difference between spare parts and extra parts.

              Comment


              • #8
                I don't have all your answers, but...

                Some wall warts use a nice little step down circuit based on matching the drain to the charge rate of capacitors. The square wave does not charge them at the same rate so the voltage is off.

                Dan
                At the end of the project, there is a profound difference between spare parts and extra parts.

                Comment


                • #9
                  Originally posted by bobbyg View Post
                  For electronics you should use a pure sine wave inverter.
                  Nearly all electronic power supplies will not care about square waves.

                  A transformer and rectifier will have a low output with the modified sine wave.

                  One of those supplies with a capacitor to do the dropping, will draw lots of current on the modified sine wave. Old Dewalt battery chargers used that system instead of a transformer. They blow their fuse if charged with a modified sine wave. DAMHIKT.......
                  1601

                  Keep eye on ball.
                  Hashim Khan

                  Comment


                  • #10
                    All my PCs and TVs (along with supporting hardware) run off UPS units that are modified sine wave. Or as APC calls it "Stepped approximation to a sine wave".

                    Comment


                    • #11
                      The standard modified sine wave is a plain square wave with a pulse duration and amplitude that has an rms value equal to the intended sine wave.

                      No stepped sides to it
                      1601

                      Keep eye on ball.
                      Hashim Khan

                      Comment


                      • #12
                        Will it work? Where will the harm come from?

                        It will probably work. At least for a percentage of devices that you will power it with. Is there any way to predict this? Not anything that would be practical except to just try.

                        Where can the harm come from? Look at those waveforms posted above. They are not pure sine waves. They have those wiggles in them. Those wiggles are high frequency components and those high frequencies can get through the power supply of the device you are powering. Another name for these high frequency components is spikes. Now, for many devices they will not make any difference and all will be well. But some things can be sensitive to them and they can cause problems. Perhaps those problems will only prevent the device from operating properly but perhaps they could cause some real damage. Digital devices are particularly prone to problems caused by such high frequency components. When they get into the digital circuitry they can look like actual data pulses (ones or zeros) and can cause no end of confusion to that circuitry. The results can be very unpredictable.

                        So if you "just try" you do stand a small chance of damaging the device. How small? I don't know. And neither does anyone else.

                        How do you get rid of them? Filters. But 60 Hz filters for 115 VAC and serious currents will need fairly large inductors and capacitors and large equals expensive. That is why the manufacturers of these devices will skimp on these components. If you want to improve the devices, look up 60 Hz power filter design.

                        The other way to minimize those spikes is to use a higher switching frequency in the converters. I suspect that the devices sold by HF probably have a switching frequency in the 1 kHz range. Modern switching power supply chips that are sold today range up to the hundreds of kHz and even the MHz range. These higher frequencies are easier to filter so the coils and capacitors for it are smaller and less expensive. But changing the switching frequency for an existing design would be a major undertaking so it is not a practical idea.
                        Last edited by Paul Alciatore; 12-21-2017, 12:24 AM.
                        Paul A.

                        Make it fit.
                        You can't win and there is a penalty for trying!

                        Comment


                        • #13
                          Originally posted by J Tiers View Post
                          The standard modified sine wave is a plain square wave with a pulse duration and amplitude that has an rms value equal to the intended sine wave.

                          No stepped sides to it
                          And the one listed by the OP is no exception. The link to the OPs inverter also has the manual which shows a bipolar square wave with a 0 Volt
                          dead zone separating the pulses (page 5).

                          Comment


                          • #14
                            Originally posted by Jim Stewart View Post
                            HIJACK ALERT!

                            Well, sort of. If any of our electronics wizards has an idea how I could clean that wave up I'd be delighted to hear their theories.

                            -js
                            Hi Jim, the options to clean up the wave form are somewhat dependent on power and $$.

                            If you want to clean up KWs I suggest if you are really lucky you may find an old mainframe computer mains filter but I suspect that is very unlikely.

                            Do you have an old isolation transformer as were used as safety devices before earth leakage circuit breakers and such came into use? If you run your power through that it would be smoothed somewhat but I could not say by how much.

                            I expect you could (maybe not the neatest solution) construct a motor generator set from two induction electric motors.

                            If you only need a few watts then an active filter would do an amazing job of cleaning up your wave form and it may be enough power for the electronics of your stove. https://en.wikipedia.org/wiki/Active_filter

                            Heck, you might even dampen those spikes enough for your stove just by wrapping the cable through a stack of ferrite cores.

                            I know there are people here who know at lot more about this subject than I do and I trust they will feel the urge to demonstrate that by designing a passive low pass filter for your needs. How much power (i.e. watts) do you need to filter?
                            Last edited by The Artful Bodger; 12-21-2017, 01:04 AM.

                            Comment


                            • #15
                              Originally posted by Jim Stewart View Post
                              I don't see a modified sine wave (clipped triangle wave?) damaging ...

                              -js
                              Dont forget. A simple LC
                              filter will level out the ripple on most AC. JR
                              My old yahoo group. Bridgeport Mill Group

                              https://groups.yahoo.com/neo/groups/...port_mill/info

                              Comment

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