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Resitance calculation — Parallax Forums

Resitance calculation

haunteddansionhaunteddansion Posts: 68
edited 2006-12-28 03:44 in BASIC Stamp
I have a device that needs 30 volts @ 450 mA and I have a power supply that is 30 volts @ 1 amp what is the calculation I do to figure out the right resitor I should use to read my criteria, Is there a good website which can do this calc also, I have tried the LED resistance calculator websites but they do not have enough fields for me to fill in desiered amperage and established amperage. thanks much!

Comments

  • PARPAR Posts: 285
    edited 2006-12-28 02:08
    haunteddansion said...
    I have a device that needs 30 volts @ 450 mA and I have a power supply that is 30 volts @ 1 amp what is the calculation I do to figure out the right resitor I should use to read my criteria, Is there a good website which can do this calc also, I have tried the LED resistance calculator websites but they do not have enough fields for me to fill in desiered amperage and established amperage. thanks much!
    Your device only needs 450mA, and your supply can deliver that amount easily (it can deliver up to 1A). Seems like you are set to power your device as is?

    PAR
  • haunteddansionhaunteddansion Posts: 68
    edited 2006-12-28 03:10
    wont it supply 1 amp and over-current the device becuase it runs only on 450 mA
  • Martin HebelMartin Hebel Posts: 1,239
    edited 2006-12-28 03:40
    The rating on devices tell you how much current they will draw so you can size your power supply appropriately. In general, as long as your provide the device the right voltage with a supply rated for sufficient current, the device will draw what it needs. One exception to this is LEDs. They are simply diodes and have no little resistance. Connecting them directly with out a resistor to limit current flow will cause them to burn out. But most all other devices have resistance/impedance and will only draw what power they need.

    Think about things you plug in at home. The wall socket is 115V. You can power a 15A air conditioner or a 100mA air freshener without worrying about the current they need.

    -Martin

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    Martin Hebel
    StampPlot - Graphical Data Acquisition and Control
    AppBee -·2.4GHz Wireless Adapters & transceivers·for the BASIC Stamp & Other controllers·
  • haunteddansionhaunteddansion Posts: 68
    edited 2006-12-28 03:44
    Thanks soo much for clarifying. That makes perfect sense with circuit impedence. I am set to create now! cool.gif
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