High Current Controller

Discussion in 'General Electronics Chat' started by DC_Kid, Oct 15, 2015.

  1. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
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    looking for a crude way to do current control from about 10-40A of low vDC (12-24v marine battery) or 120/240vAC(60Hz).
    i need to lab up a test using some #14 NM-B wire, basically measuring wire temp vs amps.

    basically looking to short a piece of #14 to the power supply, but control the amps, etc.

    ideas?
     
    Last edited: Oct 15, 2015
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    #1- why? wire gauges are already defined and standards exist for proper sizing based on current through the wire.

    #2- Just build/rent/buy a load bank using resistors/lightbulbs/heating elements or whatever

    and 14 AWG is NOT suitable for 40 Amps.. 20A max
    See NEC table 310.16 (or 310.17 for free air applications)
     
  3. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
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    ah, my lab testing does have to do with NEC ampacity #'s (which are partially derived from Neher–McGrath). its too complicated to explain here in detail.

    this post is a Q around a current controller, variable would be nice, fixed also works as long as i can swap a component to get different currents, etc.

    so make a load bank using a bunch 500w halogen sticks? that would work as i could use incrementals to get the between currents. i can then use my amp clamp to get accurate amps reading. sounds simple and crude.

    was also wondering about something crude using triac, etc.
     
  4. #12

    Expert

    Nov 30, 2010
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    Work with the obvious. I think I saw 65 watt headlights. That's about 5 amps per bulb on a 12 volt source.
    Not cheap? Try a junque yard.
     
  5. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
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    i can use the T3 halogen sticks, 240vAC 1kW each. i can just stack them, etc. this can get be the load i need for testing. $32 for ten of them.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I'd love to know just a bit of detail.. curiosity
    NM-B wire wouldn't be used inside someones product and no building code inspector (AHJ) is going to disregard standards based on your lab testing so I can't possibly imagine why you would need to test it for anything..
     
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
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    When you say short. How short?
    Important only because what isn't dissipated in the wire is dissipated in the device.
     
  8. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Light bulbs work well if you don't need better than 5% or 10% accuracy. For better than that you need a true control loop.

    If you search for current regulator circuit you will find many schematics that cook down to 2 or 3 basic approaches. All of them rely on a current sense shunt resistor. A bank of transistors to handle 40 A is relatively easy, as is a large heatsink with a fan (you don't say how long each test runs). The expensive part is a 40 A shunt that is accurate over temperature; its error usually swamps all other error sources in the circuit.

    Another approach is to use a closed loop Hall effect sensor.

    ak
     
  9. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
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    well, i switched the setup over to a 120vac 20A variac feeding a large microwave xfrmer (mot) where secondary has been removed and wound with a few turns of large wire.
     
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