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Min voltage drop in silicon rectifier?

Discussion in 'Electronic Basics' started by Ken, May 19, 2005.

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  1. Ken

    Ken Guest

    I want to isolate flooded lead acid batteries from each other using
    power rectifiers like these:
    http://www.ruttonsha.com/New_Folder/Ruttonsha/diodepdf/60hm.pdf

    I would charge them through the rectifiers.

    From the graps, it appears that there is a 0.5V drop across the
    rectifier even at low current.

    Inasmuch as the batteries could be ruined (boiled off) over time by a
    significant trickle charge, I need to know the voltage drop at, say,
    10mA -- so I know where to set the float voltage.

    How can this be ascertained, short of experimentation?


    Ken
    (to reply via email
    remove "zz" from address)
     
  2. The experiment is probably worth doing, because at 10 mA, the
    rectifier is operating way below the bottom of the graph. It shows
    that a room temperature diode drops about .65 volts with 10 amperes
    going through it. As the current falls, the voltage keeps falling at
    about 60 millivolts for each time you divide the current by 10 (for an
    ideal diode). So to get from 10 amps (the bottom of the forward
    voltage graph) to 10 mA, you have to divide by 10, 3 times, so the
    forward voltage will be somewhere around .65-.06-.06-.06=0.47 volts.
     
  3. John Smith

    John Smith Guest

    Which sounds garbage to me. The drop will remain fairly constant.

    That said: I think what the OP needs to do, is have some feedback directly
    from the batteries being charged, and use that feedback to control the
    charging voltage. The drop across the diode becomes irrelevant.
     
  4. Why? I thought this effect is expressed by Ebers-Moll, or so. At
    20C, 58.26mV/decade from (kT/q)*ln(10/1). But I'm a hobbist, so I'll
    listen to why it's garbage with rapt attention.

    Jon
     
  5. Bob Masta

    Bob Masta Guest

    Ahhh, I'd say that going from 0.65 to 0.47 over a 3 decade range
    of current is "fairly constant"!

    Best regards,


    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Home of DaqGen, the FREEWARE signal generator
     
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