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Is a blocking diode really needed ?

Discussion in 'Photovoltaics' started by daveem Dave M, Sep 7, 2004.

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  1. Hi all,
    I was just measuring the current flow between the solar panel and my
    batteries at night, to see what kind of loss I was dealing with, because
    I don't use a charge controller, and I was surprised to see it was only
    about 10 milliamps, When I considered placing a blocking diode in the
    system to pervent this small loss, it appeared that the .3 to .6 volt
    drop, depending on the diode used, would create more of a loss than any
    night time discharge current, and I wondered if I am missing something
    Thanks in advance.
  2. Windsun

    Windsun Guest

    Older panels used to have a lot more leakage back. We have found the same
    thing on newer panels, you lose more with the diode in daytime than you
    would lose back at night.
  3. Windsun

    Windsun Guest

    Uhm.. no.

    A blocking diode has nothing to do with that. That is an isolation or bypass
  4. john

    john Guest

    check the panel to see if there is already some sort of bd. alot already
    have them built in. the panel since it is silicon will not let much
    current flow in the reverse direction however, the diode is really to
    prevent the panel from shorting which will happen with the reverse polarity.
  5. boB

    boB Guest

    SO, I wonder what the PV manufacturers have to say, and/or what the
    real problems (if any) there are when a PV array is driven (with
    limited current possibly) at a bit higher than the arrays' Voc ???????
    (I think that's what you refered to it as leakage)

    I would think they would just dissipate that power with their large
    surface area. They do get warm in normal operation as well.

    Maybe it's an avalanche or zener rating... I've never seen any
    specifications or info on this.

  6. boB

    boB Guest

    Yes, of course... We don't normally think of that many diodes in
    series this way. That's the way to look at it. From my limited
    experience (but some) the drop is temerature related just like the
    Voc and should follow go up with the Voc at X mV/degress C.

  7. boB

    boB Guest

    OOps ! I meant should go down with increasing temperature.

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