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Battery Box vent fan controller question?

Discussion in 'Photovoltaics' started by [email protected], Sep 26, 2003.

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  1. Guest

    Where can I find a controller to start and start my battery box vent
    fans? I have only found one so far at backwoodsolar. I thought I would
    check and see what you guys are doing for battery box venting. I have
    been using natural draft so far.
  2. Zathera

    Zathera Guest

    What do you want to do? fans on by temperature? fans on by time?
  3. The usual approach is fans on by battery voltage, i.e. you only run
    the fans when the batteries are gassing.

    Would be a damn simple circuit - a handful of components from Electron
    Hut would do it. Surely one of the DIY sites (, or Steve
    Spence's site) has published something? If not, they should.

  4. Guest

    Fans on at 13.8, Fans off at 13.8 that is what I would like to do.
    Voltage seems the best way to control them.
  5. Guest

    Oops on at 14 volts and off at 13.8 volts sorry.
  6. Would you want fans on while charging, or do they not make hydrogen
    until they are charged and going into equalization mode?
  7. Steve Urbach

    Steve Urbach Guest

    Since the batteries should only charge when there is sun on the
    panels, why not drive the fan from before the blocking diode on a 12 V
    panel (fused the leads).. The batteries will continue to out gas some
    after coming off charge, but the charge rate should diminish as the
    panel output falls. [email protected] 1N4004 (1A) feeding a computer case fan should
    do very nice. No fancy circuits.

    Steve U
  8. Unless, of course, you have a shunt-type controller...
    I'm still uncomfortable with voltage control (conceptually), wouldn't
    it be much better to run the fans whenever current is flowing into (*)
    the batteries and for some time afterwards?

    (*) Do batteries evolve hydrogen when discharging? Something makes me
    think they do... Maybe a small fan doing a continuous purge and a
    larger one for power venting when charging?
  9. Steve Urbach

    Steve Urbach Guest

    My main point is that batteries continue to Out Gas for some time
    AFTER the charge potential is removed. My idea allowed that the panels
    continue to output voltage (below that required to charge) for quite
    some time after dropping below charging threshold (my fans will
    continue to run on 10VDC) .
    If you use a generator, just use a second fan that is relay(or wire to
    the existing fan to transfer over) controlled ( this does have the
    instant stop venting problem on generator stop, though) from the
  10. While I like the idea of controlled venting (and I was drawn into this
    thread on that basis) simplicity is good. The type of fans typically
    used draw so little current that for all but the smallest systems you
    could just let them run 24/7. That's what the fan on our Sunmar NE
    toilet does.

    The toilet is about to be fired into the sun on the end of a rocket,
    but that's a different story.

  11. You might consider a lower voltage. The main problem is that a
    shorted cell will lead to overcharging of the other cells that are
    in series with the shorted cell.

    I sell telecommunication battery cabinets that use a hydrogen
    detector to operate first a vent fan, then activate the alarm
    system if the hydrogen is not cleared. Worth the cost on
    $18,000 battery system.

    Bill Kaszeta
    Photovoltaic Resources Int'l
    Tempe Arizona USA
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