Mixing AC and DC power in a circuit


Posted on Feb 6, 2014

Control a furnace using a 3. 3V microcontroller. The furnace operates by connecting a common 21V AC `hot` line to one of two AC `neutral` output lines: Fan and Heat. When connected they have relatively low current flow, ~100mA. I`ve had some success using a TRIAC to do the switching - but I`m directly mixing the power sources by conne


Mixing AC and DC power in a circuit
Click here to download the full size of the above Circuit.

cting the DC battery negative to the common AC "hot" line. Battery negative/hot then becomes the reference at the TRIAC`s MT1, and I can switch the furnace on and off by sending +3V or 0V to the TRIAC base. Question is, is it kosher to mix power sources like this Do I risk an exploding battery, excessive battery drain, weird circuit behavior or anything like that If so, what would be the proper way to do this, to isolate the circuits I have no clue, but google shows some circuits setup in this manner. I`ll let someone else give an answer to that. My question to you though, why no go for isolation and use a opto-isolated ssr or triac, and not bother mixing them at all Passerby Apr 2 `13 at 4:19 Don`t know too much about the opto-isolated options out there - photo-triacs and SSRs look promising though, thanks for the tip. The few SSR`s I had come across before were all high-voltage types. QuadrupleA Apr 2 `13 at 4:29 Many household-grade thermostats use low holding current mechanical relays for this purpose. I`ve always been amazed that they can maintain several years of battery life with this approach, but they do. I`d expect a triac would be cheaper, so perhaps there are surge or mis-wiring risks inherent in such applications. HikeOnPast Apr 2 `13 at 5:20 Some triacs, when controlled from a unipolar DC to the gate with respect to MT1, won`t always conduct when the AC cycle goes negative i. e. they`ll trigger during the...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Digital Thermometer using
    Two channel frequency synthesizer
    Decibel-o-meter and white noise generator
    Serial Voltmeter using the PIC16C71
    LA3161 based Preamplifier circuit with explanation
    Shaft type part temperature measurement system become by 51 one piece organizations
    150 watt amplifier circuit
    linearizing circuit for thermocouples
    ham radio circuit audio filter
    temperature controller using ds1820 and lcd display
    ML7005 DTMF Transceiver ML7005DTMF Transceiver
    1W LED Driver
    Electromechanical relay logic
    Atari Punk Stepped Tone Generator
    Four Port Serial Adapter for the EB675001DIP



    Top