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Convert 3-phase 70V AC alternator to 12V DC

Discussion in 'Introductions' started by Dele, Aug 20, 2014.

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  1. Dele


    Aug 20, 2014
    How do I convert 3 phase 70 volts AC to single phase 12 volts DC
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Hello and welcome.

    Build a three-phase rectifier (similar to the ones described here). You will get Vdc=3*sqrt(3)*Vpeak/Pi (some theory here). You wil need to smooth ths using a fairly large capacitor (see "rectifier output smoothing in he Wikipedia article linked above). You can the use a step-down switching regulator to generate 12V. You can buy off-the-shelf modules for that purpose.

    Note: DC above 33V is rated as potentially life threatening (this voltage varies with country ;)). You need to take the usual precautions when working with this voltage (keep air gap and creepage distances, use good insulation, use fuses to protect from overcurent etc.). When in doubt, ask someone experienced near you to check your setup.
    Depending on the source of the AC voltage it may be advisable to use a three-phase transformer in front of the rectifier to add a level of insulation (and protection). While you're at it, you can also use the transformer to sep down the 70V AC to harmless e.g.15V AC, the you're save with respect to voltages on the secondary side of the transformer. Keep aware of high currents, though as a high current can be dangerous (it can heat things up and cause fre) even at low voltages (see arc welding).
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