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Automated Load Tester

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by tkc100, Feb 1, 2012.

  1. tkc100

    tkc100 Member

    Feb 5, 2010
    We come this far and I think finally we have got the theory down why not go for broke.
    A dual voltage range certainly makes the tester more versatile and will increase the chances of it being used more.

    11 - 4" resistors that's a lot of little heater to deal with but if it is at all possible I would like to avoid a fan. Depending on a fan means if the fan stops the whole tester goes up in smoke unless still yet another later of complexity is built in for some kind of thermal protection. Many of the power supplies I have worked with have a thermal limiter attached to the heat sink.
    Take another look at the picture I attached. I included the dimensions. Seems to me there would be adequate room in a box like that. I have looked and admittedly I have yet to find an empty box like that but there has to be something similar out there without the guts in it.
    If necessary I'm capable of doing some sheet metal work. The back could be completely ventilated and have an insulated partition separating it from the front.

    You know I was so disappointed when I found out that the 50 - 80% marks could not be used as a reliable capacity test that I just kind of gave up on the idea. You are probably right and given some field data there may well be a use for them but if it complicates the design I would say forget it. I haven't given it any thought. I have been convinced there are a number of variable some of which can be controlled and other than have to be compensated for. They all remain somewhat.......... unpredictable until the battery has completely discharged.

    Yes I do have a clamp on amp meter.
  2. ronv

    ronv Well-Known Member Most Helpful Member

    May 30, 2010
    Tucson, AZ. USA
    Lots of little details to work out.
    The size is somewhat dictated by the heat sink and power resistors.
    The heatsink for the Constant current transistor and reverse protection diode needs to be 4.75X5.5X2.65 high. Like the 427K if you look it up on Mouser.
    I had thought of putting the heatsink and resistors (9 of them at 4" long) outside the box on some plates separated by spacers. The box also needs to be ventikated as there are probably 25 watts there as well. Think of the whole thing like 1/2 toaster in a box that runs for several hours. ;)
    Maybe something like this would work. http://www.hammondmfg.com/dwg22.htm Then everthing could go inside the box. The difficulty would be making the front panel look nice. Maybe some black plastic?
    Almost done with the basic design - just need to make sure it all works together.
    Boxes are expensive! :mad:

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