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Hall Effect Sensors — Parallax Forums

Hall Effect Sensors

PhilldapillPhilldapill Posts: 1,283
edited 2008-01-04 08:55 in Propeller 1
Ok, so I got 5 ACS754SCB-130-PFF Hall effect sensors from Allegro(samples). They are able to measure up to 130 Amps with fairly high accuracy. The output is 0-5V. My question is, where would I be able to get any kind of supply that will output at least 50 amps? I thought I could possibly use a car battery momentarily, with some high value resistors in parallel with each other and in series with the battery. What should I discharge all that power into? Another depleted battery perhaps? I also have a big welder that I might be able to use... Also, how should I go about getting an accurate measurement of the current, besides the hall effect sensors? i.e. caliberation.

Thanks guys.

Comments

  • deSilvadeSilva Posts: 2,967
    edited 2008-01-04 01:41
    For the first question: you could in fact start your car for some time with the Prop under the hood.
    This can draw 100A .

    Exact calibration is difficult. You can try to meassure the voltage at the battery. Knowing its internal resistance will give you an idea about the current. Internal restance can be estimated by drawing 10A which can be measured with standard equipment. This will need 1 Ohms@100W.. well..

    However as much chemistry is involved the internal resistance might not be such a constant value when drawing 100A smile.gif
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-01-04 01:55
    The unit pictured here might be able to provide the current you need! smile.gif

    -Phil
  • PhilldapillPhilldapill Posts: 1,283
    edited 2008-01-04 03:02
    I like that idea about starting the car, deSilva. I have many 10ohm, 10W resistors on hand which I can put in parallel.
  • PhilldapillPhilldapill Posts: 1,283
    edited 2008-01-04 03:09
    Wow Phil, I could have sworn that was the transoformer I built last weekend! Knotted strings and all!
  • Nick MuellerNick Mueller Posts: 815
    edited 2008-01-04 08:48
    Power sources:
    Stick welder: Not good, as the welder is self regulating (soft volatge / amperage curve) when you do have an arc.
    TIG welder: Like stick welder.
    MIG/MAG welder: bad at low currents, because you do have lots of short circuits in the arc and current varies a lot. Starting at about 200A (with a 0.8mm wire) you do have a spray arc that has a much smoother current consumption.
    Car battery. Not so good when starting your car, because it will (hopefully start) and then the current drawn will be much less. While starting, the current also varies a lot (piston at TDC or not).

    So take your battery and connect 20 50W bulbs and you have a constant self-regulated current and enough time to measure.

    Nick

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  • PhilldapillPhilldapill Posts: 1,283
    edited 2008-01-04 08:55
    I really like the car starting idea. The current variance in starting is no big deal. What I'll do is get the ouput voltage from the sensor and run it into a cap. and from there, through a resistor to another cap and so on. It ends up smoothing the voltage level considerably and more or less an accurate average over time. To prevent the car from starting, I'll just disconnect the ignition wires... I love jury rigging.
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