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Calculating the fuse value

Discussion in 'Burnt Fingers DIY Effects' started by TwoBear, Apr 12, 2021.

  1. TwoBear

    TwoBear Tele-Holic

    Mar 31, 2020
    oc. CA.
    Calculating the fuse value. I’ve got two 7809 voltage regulators being fed from a small 12 V 7.6mAh sealed lead acid battery (About 7”x 4” x 2”) they’ll feed a pedalboard that grows and shrinks but mainly can be covered by one of the regulators, with a draw of 900 to 1200 mA. The other regulator may be called in to help power my cube Street that draws 700 mA. I had 9 V times 1500 mA which came out to something like 13 A just can’t be right. Am I overthinking it and should I just put a 2 or 3A fuse on each positive feed (B & C)? Or? Thanks and please excuse the crude plate drawing image.jpg
  2. dogmeat

    dogmeat Friend of Leo's

    Oct 12, 2017
    a 7809 is only good for about an amp and a half (with properly heat sink). if you need more you can use the 7809 to run a transistor.

    9 V times 1500 mA is 13.5 WATTS. you are concerned with the amp/milliamps

    the battery is prolly 7.6 Amp Hour

    3A fuse should be OK. even a 5
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