AC/DC Switch ratings

Discussion in 'Boat Electronics' started by Steve, Sep 6, 2004.

  1. Steve

    Steve Guest

    I am building a new 12V DC switch panel for my boat and have a load of
    switches rated at 10A@125V or 8A@240V. Although they have 12V
    illumination there is not a DC rating in the datasheet. Does anyone have
    any idea what sort of rating can I assume for low DC voltage or are they
    totally unsuitable?

    The switches are Cherry RRA22H3BBRHN rocker switches.

    Thanks in advance,

    Steve
    Steve, Sep 6, 2004
    #1
  2. On Mon, 06 Sep 2004 20:04:20 +1200, Steve <> wrote:

    >I am building a new 12V DC switch panel for my boat and have a load of
    >switches rated at 10A@125V or 8A@240V. Although they have 12V
    >illumination there is not a DC rating in the datasheet. Does anyone have
    >any idea what sort of rating can I assume for low DC voltage or are they
    >totally unsuitable?
    >
    >The switches are Cherry RRA22H3BBRHN rocker switches.
    >
    >Thanks in advance,
    >
    >Steve


    I've always been told to use DC switches and breakers on DC.
    The arc is harder to break because there isn't a null period in DC
    like there is in AC.
    I wouldn't use them unless they are rated for Direct Current.
    Mark E. Williams
    Maynard G. Krebbs, Sep 7, 2004
    #2
  3. Steve

    Jim Donohue Guest

    Went around on this on some microswitches a while back. Basically it
    appeared that low voltage DC (less than 28 volts) had higher ratings than
    AC. I think that is the general rule. It is pretty well safe if it is a
    snap action switch. At higher DC voltage it is a nono. Too much arc. Take
    one load it up twice max current and run it a couple of hundred times. Then
    bust it open and look at the contacts. You will know if it is OK.

    Jim



    "Steve" <> wrote in message
    news:pSU_c.2313$...
    > I am building a new 12V DC switch panel for my boat and have a load of
    > switches rated at 10A@125V or 8A@240V. Although they have 12V
    > illumination there is not a DC rating in the datasheet. Does anyone have
    > any idea what sort of rating can I assume for low DC voltage or are they
    > totally unsuitable?
    >
    > The switches are Cherry RRA22H3BBRHN rocker switches.
    >
    > Thanks in advance,
    >
    > Steve
    Jim Donohue, Sep 11, 2004
    #3
  4. Steve

    Terry Spragg Guest

    Maynard G. Krebbs wrote:

    > On Mon, 06 Sep 2004 20:04:20 +1200, Steve <> wrote:
    >
    >
    >>I am building a new 12V DC switch panel for my boat and have a load of
    >>switches rated at 10A@125V or 8A@240V. Although they have 12V
    >>illumination there is not a DC rating in the datasheet. Does anyone have
    >>any idea what sort of rating can I assume for low DC voltage or are they
    >>totally unsuitable?
    >>
    >>The switches are Cherry RRA22H3BBRHN rocker switches.
    >>
    >>Thanks in advance,
    >>
    >>Steve

    >
    >
    > I've always been told to use DC switches and breakers on DC.
    > The arc is harder to break because there isn't a null period in DC
    > like there is in AC.
    > I wouldn't use them unless they are rated for Direct Current.
    > Mark E. Williams


    One way to help switches in DC circuits is to connect a capacitor
    across the switch. It sucks up the last bit of current as the
    switch opens, helping to prevent the formation of an arc. Fast
    acting 'snap' switches last better in DC. A few microfarads,
    properly polarised (positive towards the positive battery) can work
    wonders. I would try your switches, make them changeable and carry
    a spare for critical applications. They may survive the duty and
    conditions you throw at them, if not, go upscale. Try one. Work it
    to death. The rating is only intended to indicate safe working
    current, not indicative of arc tolerance, which usually means
    beefier contact and actuator design, heavier case, toggle, etc.

    A shorted arc suppression capacitor becomes a stuck 'on' switch in
    circuit.

    DC and inductors like solenoids are a bitch on switches. A starter
    switch comes to mind as possibly the most critical. But, remote
    switching is only a luxury, non? There is always the modified hammer
    tool for jumping starter solenoids.

    A few wire nuts aboard, or even electrical tape can save an
    electrically challenging day.

    Terry K
    Terry Spragg, Oct 5, 2004
    #4
  5. Steve

    Steve Guest

    I had thought about the capacitor but wasn't sure if it would help much
    with the really big current loads which are all motors (bilge, toilet,
    fresh water, gray discharge etc.). Would a 100uF cap actually be enough
    to cope with such a large inductive load?

    The steady state load for all the inductive loads is around 7 amps with
    obviously a initially high startup load (around 10+ amps). From the
    postings I get the impression that it is breaking the circuit that is
    the issue with current rating and in these cases the norm current will
    be well below the 125V AC rated current.

    The mainly resistive loads (halogen lighting) has a high startup current
    also when cold. A cap could help here I guess.

    I guess I will try them and see how it goes. The only real reason I want
    to use these is that they are round and therefore easy to mount in a panel.

    Thanks for you help everyone.


    Steve
    Steve, Oct 7, 2004
    #5
  6. Steve

    rayjking Guest

    I may be a little late with this reply but you know you can conduct 10amps
    in the switch. The switching of DC is the issue. In the olden days when caps
    were added across ignition points to keep the points from arcing and eating
    the energy that is supposed to make sparks. They used a 0.22 uf cap to keep
    8 amps or so from causing a the slow moving points from arcing. To be safe
    I would suggest using a 100v minimum ceramic is best but an electrolytic
    will do. The value should be about 1 to 2 uf and to be super safe a series
    diode 2 amps average is ok in series with the cap. The anode of the diode
    should be at the + end of the switch and the cathode connected to the + end
    of the cap. Also a resistor must be added across the diode of 10 to 330 ohms
    at 1/2 watt for lead strength. This series string of cap and diode and
    resistor in parallel are across the switch terminals. This should protect
    the switch.

    Good luck Ray





    "Terry Spragg" <> wrote in message
    news:...
    > Maynard G. Krebbs wrote:
    >
    > > On Mon, 06 Sep 2004 20:04:20 +1200, Steve <> wrote:
    > >
    > >
    > >>I am building a new 12V DC switch panel for my boat and have a load of
    > >>switches rated at 10A@125V or 8A@240V. Although they have 12V
    > >>illumination there is not a DC rating in the datasheet. Does anyone have
    > >>any idea what sort of rating can I assume for low DC voltage or are they
    > >>totally unsuitable?
    > >>
    > >>The switches are Cherry RRA22H3BBRHN rocker switches.
    > >>
    > >>Thanks in advance,
    > >>
    > >>Steve

    > >
    > >
    > > I've always been told to use DC switches and breakers on DC.
    > > The arc is harder to break because there isn't a null period in DC
    > > like there is in AC.
    > > I wouldn't use them unless they are rated for Direct Current.
    > > Mark E. Williams

    >
    > One way to help switches in DC circuits is to connect a capacitor
    > across the switch. It sucks up the last bit of current as the
    > switch opens, helping to prevent the formation of an arc. Fast
    > acting 'snap' switches last better in DC. A few microfarads,
    > properly polarised (positive towards the positive battery) can work
    > wonders. I would try your switches, make them changeable and carry
    > a spare for critical applications. They may survive the duty and
    > conditions you throw at them, if not, go upscale. Try one. Work it
    > to death. The rating is only intended to indicate safe working
    > current, not indicative of arc tolerance, which usually means
    > beefier contact and actuator design, heavier case, toggle, etc.
    >
    > A shorted arc suppression capacitor becomes a stuck 'on' switch in
    > circuit.
    >
    > DC and inductors like solenoids are a bitch on switches. A starter
    > switch comes to mind as possibly the most critical. But, remote
    > switching is only a luxury, non? There is always the modified hammer
    > tool for jumping starter solenoids.
    >
    > A few wire nuts aboard, or even electrical tape can save an
    > electrically challenging day.
    >
    > Terry K
    >
    rayjking, Oct 25, 2004
    #6

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