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O/T Power inverters from dc to ac.

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  • O/T Power inverters from dc to ac.

    I have a 300watt power inverter I bought around 18 years ago and still works like it should to this day. Looking for another now, maybe a couple, for the pontoon and camper. There are many different kinds now and amazing cheap! The one I see on ebay that looks exactly like mine is $20 now. I am wondering on the quality of those cheap units, anyone have any experience with those cheap ebay units?

    Does a bigger unit draw more power at idle than a smaller unit or is the draw totally load dependent?

    The one big thing I would like to be able to run in both the toon and camper is a small cheap vacuum.

    Thanks!
    Andy

  • #2
    The idle current depends on the design. Older tech had fairly large idle current. Modern IGBT based ones seem to work more efficiently.

    I can't speak to the "cheap ebay" designs simply because the circuits inside could be anything that might work.

    My "small, cheap vacuum" is a cordless Dissell that breaks down to become a Dustbuster style hand held. It charges from 12V DC.

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

    Comment


    • #3
      A vacuum cleaner is one of those motorized items that draws high continuous power, and actually begins to use less power when it's full or the filter is plugged. Typically they work better when more powerful. At the same time they usually draw quite a high start-up current- in all it's something that would strain an inverter and require it to have a high capacity.

      Better might be to find the best 12v vacuum cleaner that you can and just run it direct from the battery. Many of these are not much more than junk, but there must be some decent ones out there.

      On the other hand, if you already use a large inverter and capable battery pack, then just try to find a fairly efficient vacuum cleaner.

      There must also be a decent cordless vac, probably with a higher voltage battery than a 12v system would charge directly. I wonder if you could find a charger specifically made to work directly from 12v and boost that to whatever is required for the battery. A voltage doubler circuit would work for an 18v battery, provided the charge controller was included. Don't know if anyone makes such a thing, but it seems to me it would be good for portable applications where battery power is at a premium.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        Here's something to think about- I just saw an ad for an inverter, 2000 watt it says on the case. Further in the spec is says 'Mark 2000 watts, but real power output 900 watts'. I just bought a small inverter for $3, new in case, never been opened. It's marked 100 watts, 190 watts peak- but in the specs it says 80 watts.

        Has anyone taken their car to a dyno recently? I wonder if the claimed engine hp is fake too- your 115 hp might only be 75hp. What about wages- if you're making $25/hr, maybe it's only $17- let's see how well that would go over-

        I hate seeing trumped up specs-
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

        Comment


        • #5
          Yes always be wary of the Sears rating!

          Inverters have gotten lots better. They used to mostly put out square wave rather than sine wave AC. Now they mostly put out 'modifed sine wave' which is a fancy term for a stair stepped sine wave. We just put an 1800 watt continuous rated one in the company van so we can run a 7" hand grinder at jobsites. It works well, especially after we used 2/0 copper solar panel connection cable from the battery to the inverter to handle the 150 amps or so from the battery when you lean on the grinder.

          Comment


          • #6
            Modified sine wave still means square wave.

            "True sine wave" is the stair stepped wave, that's how PWM does a sine wave.

            Modified sine is square wave with same RMS voltage as the sine wave.
            1601

            Keep eye on ball.
            Hashim Khan

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            • #7
              That part always makes me wonder about the efficiency, or the efficacy of using an inverter- the 100 amp + current draw. Even a small vacuum might be rated at 1.5 hp, which converts to about 1500 watts, which converts to nearly 130 amps draw from a 12v source. That's before figuring in the losses and the consequences of dropping the voltage while drawing that many amps- in this case if the voltage available at the inverter dropped to 11v, the current draw to supply 1500 watts would be 136 amps (plus for losses).

              The car vacuums draw between 8 and 15 amps from what I've checked. The power level at 15 amps is 180 watts- it's no wonder that those things suck (not). I wonder how the cordless ones work by comparison- have not had one to try, though I did scrap one once and it had a very similar motor to what the 12v ones do.

              Maybe what you need is a combo generator/vacuum, gas or propane powered. Never seen one myself, but offhand it seems like a reasonable idea. You'd probably set which mode you wanted before starting the engine, and it likely wouldn't function in both modes at the same time. For something as powerful as a shop vac it probably would have to be rated at 2000 watts or more.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

              Comment


              • #8
                I bought a solid state 200 watt (no fan or moving parts) 30 years ago said sine wave & was way ahead of the old Tripp brand. The only power draw was a red on light. It was made in Ireland or Scotland & it put out the full 200 plus & is still going strong. If you buy the same brand & size you can make 240v as I do with 2 2000 watt ones.
                "Let me recommend the best medicine in the
                world: a long journey, at a mild season, through a pleasant
                country, in easy stages."
                ~ James Madison

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                • #9
                  Originally posted by flylo View Post
                  If you buy the same brand & size you can make 240v as I do with 2 2000 watt ones.
                  Unless the inverters provide some method to synchronize their outputs that won't work. The inverters will drift in and out of phase with each
                  other causing the voltage to fluctuate between 0 and 240VAC.

                  Comment


                  • #10
                    These inverters make DC which is then chopped to make AC, which may be "modified sine wave" for cheap ones, or "true sine wave" which uses PWM and is more costly. The 120 VAC units have about 130-140 VDC while 220 VAC units have 240-260 VDC. If you are powering a tool with a universal motor, you may do better by using the DC directly. And if it is an appliance with a switching power supply, DC is also perfectly fine and perhaps better. You can also get inverters with 24V and 48V inputs for lower current draw.

                    I don't think you can make 240V by using two 120V inverters in series. They would need to be phased together, which is possible, but would require major surgery and tinkering. You can connect the internal DC supplies in series to get 260-280 VDC, and you can use that with a VFD to get three phase (or single phase). But the 12V battery on the "upper" inverter will be floating at the DC voltage output of the lower unit, so it will need to be carefully insulated.
                    http://pauleschoen.com/pix/PM08_P76_P54.png

                    Paul: www.peschoen.com
                    P S Technology, Inc. www.pstech-inc.com
                    and Muttley www.muttleydog.com

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                    • #11
                      My daughter in law has a cordless vac that she uses to do the whole house, the battery pack is at least 18v Li and she seems more than happy with it.

                      Comment


                      • #12
                        I am sure we could find a nice dc vacuum. But I figured having the available 110v available on board the toon and camper would be nice for other things as well.

                        I do know there is "peak" rating and "continuous" power rating for these things (like generators, amps, motors, and whatnot). I just assumed listed output was peak and continuous normally is around half that. I was looking at getting a 2000watt unit hoping the 1000 watts would be enough for a small vacuum.
                        Andy

                        Comment


                        • #13
                          Originally posted by J Tiers View Post
                          Modified sine wave still means square wave.

                          "True sine wave" is the stair stepped wave, that's how PWM does a sine wave.

                          Modified sine is square wave with same RMS voltage as the sine wave.
                          The term "modified sine wave" does not appear to have a have an official standard for the waveform. I've had some that produced a square wave and some that produced a stair stepped approximation of a sine wave, sort of like a pyramid. The stair step ones were generally sold as "modified" and the square wave were not.

                          The term "True Sine Wave" appears to be a trademark of Eaton. I could not find an image of their wave form. I'll take Jerry's word for it that Eaton uses the term to describe a modified sine.

                          In the inverter trade, pure sine wave generally means a reasonably clean sine wave with low THD. I've seen some that had a very clean waveform even when connected to lots and lots of noisy power supplies.
                          At the end of the project, there is a profound difference between spare parts and extra parts.

                          Comment


                          • #14
                            Originally posted by vpt View Post
                            I was looking at getting a 2000watt unit hoping the 1000 watts would be enough for a small vacuum.
                            That's a good thought.

                            I set up a 2000 watt inverter ($125 Xantrex from Costco) with a deep cycle battery for use during power outages. It failed miserably when the first power outage hit and I connected it to my coffee maker. Even with #4 cable to the battery, the inverter cut out with low voltage alarm before the first cup of coffee finished brewing.

                            And that's how I justified buying a generator.

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

                            Comment


                            • #15
                              I used a Harbor Freight inverter, maybe 1500 or 2000 watt, with a 12V deep cycle battery, for a friend's backup for a sump pump. I don't recall the rating of the motor, but probably 1/2-3/4 HP, and it seemed to work OK. It was a "modified sine wave" type, or rectangular wave.

                              I don't know how an inverter can produce a "stepped" waveform. This is what would be produced by a DAC, where the number of bits determine the step size. But to drive a motor or other heavy load would require a power amplifier. A traditional class A, B, or C type would be very inefficient, but perhaps it uses a class D amplifier, which is PWM.
                              http://pauleschoen.com/pix/PM08_P76_P54.png

                              Paul: www.peschoen.com
                              P S Technology, Inc. www.pstech-inc.com
                              and Muttley www.muttleydog.com

                              Comment

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