48V DC rated switches

Discussion in 'The Projects Forum' started by emetzler87, Jul 9, 2014.

  1. emetzler87

    Thread Starter New Member

    Jul 9, 2014
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    I am using a DPDT keylock switch to turn on power for a 48VDC vehicle. The switch currently being used is rated at 20A 12VDC, 10A 24VDC, 4A 48VDC.

    These switches aren't lasting near as long as they should be. They are needing to be replaced after about 1000 cycles which is far less than spec. The inrush was measured between 5 and 6 amps and they voltage is often up near 60V when the batteries are fully charged. Is this why our switches are breaking prematurely?

    In searching for replacement that will last longer I have found that few switches are rated at 48V. Can I use a switch rated at 12V? And if so how do I derate the current spec for this 48V setup. Or how do I derate an AC switch to fit this application?

    Thanks
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    If its not rated for the specific voltage/current level you are seeing then it should NOT be used at all..
    They are breaking because you are using it above its rating..

    DC is much harder to switch than AC and thus requires better/stronger contact design,etc... an AC rated switch will NOT suffice. And there is no derating formula thats accepted by any safety agency.

    Finding DC switches rated that high can be challenging. Have you thought about a smaller switch triggering a relay.

    I've found that many circuit breaker manufacturers do offer a "switch" only version of their circuit breakers. They are typically rated to 60 or 80VDC and should easily fit the bill.
    (for example.. Airpax/Sensata "snapak" series)
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    How about mcgyvr's solution?

    Use what switch you have to enable a heavier relay.
     
  4. business_kid

    New Member

    Feb 5, 2013
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    It sounds like a Fork Lift. Often going to a Fork Lift supplier will get you the correct part. From personal experience, I have seen 400V parts in a Fork Lift blown by over voltage, so I'd treat that with respect, and err on the high side.
     
  5. emetzler87

    Thread Starter New Member

    Jul 9, 2014
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    You are partially correct that it is a forklift. The vehicle is a mecunum wheel omnidirectional system designed for a fork lift that is being used for a large set piece in a theater.

    Using the switch to enable a relay is an option we have talked about. We would prefer to not go that route because of a lack of space and that's one more possible fail point. But maybe that's the only option.
     
  6. mcgyvr

    AAC Fanatic!

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    again there are numerous form factors of "switch only" circuit breakers. (they basically take out the tripping coil/armature so its just a switch without overcurrent protection)
    I really like the airpax snapak's.. I've used them for 48V @15A reliably in a few professional products
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    As mentioned, when switching high energy DC the device should be have some kind of arc suppression.
    A relay such as the P&B PRD series are not that large and have magnetic arc blow-out feature.
    Max.
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
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    just think of the problems for designers when cars go to 70 volts soon. also, the current electrical safety standards will have to be changed.
     
  9. mcgyvr

    AAC Fanatic!

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    Thats what relays/contactors/mosfets, etc... are for.. ;)
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Diesel Electric Locomotives are presently high voltage with S.S. switching to AC brushless motors on each axle.
    The technology is already there!;)
    [​IMG]
    Max.
     
  11. alfacliff

    Well-Known Member

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    and then cars will be under nfpa70e as well as other safety standards for maintenance.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    ...Maybe they will have to conform to AAR standards! :D
    Max.
     
  13. emetzler87

    Thread Starter New Member

    Jul 9, 2014
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    After several hours of searching I found a switch that should work. The switch I found is made by NKK, Series S part #S823D
     
  14. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Does this switch turn on and off a motor directly or just the controller?
     
  15. emetzler87

    Thread Starter New Member

    Jul 9, 2014
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    The controller and some charging capacitors. Then a large contactor engages to give power to the drives and motors.
     
  16. mcgyvr

    AAC Fanatic!

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    You can get a MUCH cheaper switch than that.. granted I'm only looking at digikey pricing
    But that should be no more than a $10 or less switch in any volume IMO..

    of course if this is just a one-off deal then buy it and move on as you have already spent 10x that already I'm sure. But if this is for production then keep looking IMO.
    http://airpax.sensata.com/cb.html
     
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