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* Small battery charger running off a Pure Sine inverter is overheating *

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  • * Small battery charger running off a Pure Sine inverter is overheating *

    Everything I have run from my 24V Pure Sine inverter has run fine so far,

    EXCEPT

    The other day I plugged in a small battery charger that charges AA size NiMH batteries. It overheated both the charger and the batteries near to the point of combustion.

    I know that Modified Sine inverters can wreck small battery chargers, but mine is pure sine (or at least that's what I bought it as).

    The inverter: http://waveinverter.co.nz/power-inve...inverter/2000w
    Specs sheet at http://waveinverter.co.nz/image/cach...-1000x1000.jpg

    The small batter charger: http://www.mahaenergy.co.uk/products...s-fast-charger

    My guess is that either it's a one-off with the circuitry of this particular battery charger that is somehow incompatible with a pure sine inverter, or the pure sine inverter isn't really pure sine.

    Any expertise to shed light on what the trouble might be, and how I can test would be much appreciated. One of the purposes of this system was to have a charging shelf for small battery-powered appliances, but now I am reluctant to plug any other ones in for fear they will be destroyed.


    Thanks in advance!

  • #2
    Inverters can only handle a PF of no less than .8. Your cheap battery charger has a high power factor of less than .8, more like .5 or less. In other words your charger is non-linerar and Inverters don't play well with non-linear loads.
    MSEE, PE

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    • #3
      Get a real pure sine inverter. I use a suresine 300w inverter with a small maha charger (Maha C401 aa/aaa Charger)
      and there is no overheat issue. A 2Kw inverter should have no trouble driving a sub 100w device. Nomad inverters are not a brand I have heard of before.
      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister

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      • #4
        It is also possible that the inverter output is only a good sine wave when it has an unspecified minimum load attached.
        My guess is that under the very light loading of the battery charger the inverter is putting out large enough sharp voltage transitions that the charger (which may be using a series capacitor to limit current and drop voltage) is not behaving well.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          Thanks very much for the responses. My meter shows the inverter output has a Power Factor of 0.97, does that mean the charger should work fine running off an inverter with this power factor?

          I do wonder if you might be right that the output signal isn't pure sine when the load is very small. Is there any way I can test the output to confirm this?

          Comment


          • #6
            FWIW - All my portable power tools have about the same problem with charging off pure sine wave inverters. I changed to DC-DC charging using automotive plugin style chargers and bypassed using inverters. Works great now.

            WWW

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            • #7
              Originally posted by Wy_White_Wolf View Post
              FWIW - All my portable power tools have about the same problem with charging off pure sine wave inverters. I changed to DC-DC charging using automotive plugin style chargers and bypassed using inverters. Works great now.

              WWW
              +1 great idea.
              MSEE, PE

              Comment


              • #8
                Originally posted by Wy_White_Wolf View Post
                FWIW - All my portable power tools have about the same problem with charging off pure sine wave inverters. I changed to DC-DC charging using automotive plugin style chargers and bypassed using inverters. Works great now. WWW
                Direct DC to DC is the way to go, if practical. Inverters must be worlds worst phantom
                loads, idling at partial to zero capacity. DC solves any surge issues.

                All AC powered battery chargers involve rectifiers, which are about as far from pure sine
                as you can get. Quality supplies will add choke input to help, but not cheap ones. I
                suspect the big hunk of power coming in at the rising peak is fouling things up. Bruce Roe

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                • #9
                  Thanks one and all

                  OK I am sorted now. I am buying a 24V-12V DC-DC converter and will use Car Chargers where possible.

                  That was a fantastic idea, thanks very much.

                  Comment


                  • #10
                    what is this 24 vlt-12 volt

                    What is this 24 volt-12 volt DC-DC converter? Is it the 12 volt cigarette plug on the end of the wire with the +/_clips for putting on my battery?
                    And how can I post an original question? I can't seem to find that function.

                    Thanks,
                    Tom

                    Comment


                    • #11
                      Careful - you triggered the AA nimh battery geek flag here.

                      The better answer is to run it from 12v DC. A major step up from the same:

                      http://www.mahaenergy.co.uk/products...rger--analyser

                      Of course it runs from AC as well. Go bananas with it, or just stick AA's in and walk away.

                      I don't normally recommend the 401FS. Designed many decades ago when nimh were high-resistance to begin with, it uses that negative-pulse jazz which is really unnecessary with cells made past the 1990s. Cells don't become too hot to drop, yet for most they are uncomfortably warm - even with low-impedance Sanyo Eneloops. Model used to come with a swing-open plastic cover, but now they don't - yet the hinge holes are still there. Nimh batteries are supposed to get warm during charging, (exothermic) but these days there is NO REASON to use the negative pulse algo along with the additional heating it creates.

                      The only reason it is still around is that it had a GREAT GREAT reputation amongst photographers and other users back in the 90's, when a 1200mah cell was about as big as they came. That rep exists today, even if AA battery technology has surpassed the negative-pulse algo long ago.

                      If you upgrade to the 9000, you'll be amazed at the temp difference. It was designed in coordination with Sanyo Eneloops for one thing.

                      Part of the issue with the 401FS is that the charge rates do not really coincide well with today's capacities. Thus the charge rates are in a gray zone no man's land between a slow float, and a decent enough charge to force the cell to create a decent EOC signal. Essentially, the 401FS overcharges today's cells, no matter what rate you choose. Oh the cells work, but you are not getting the *best* out of them.

                      The 401FS is also too agressive for "LSD" or low-self-discharge nimh, like the Eneloop. No need for the 1990's algo to charge anymore.

                      The 9000 will actually do capacity testing and the highly useful IR test and give you a number for baselining it. It will let you know how much damage your 401FS has done to your existing set.

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