What is this Ultra-Cap doing?

Discussion in 'General Electronics Chat' started by RichardO, Aug 18, 2016.

  1. RichardO

    Thread Starter Well-Known Member

    May 4, 2013
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    This picture is of a box under one of the back seats of a city bus. The box is very roughly a foot on a side.

    Does anyone know what the Ultra-Cap is used for in the bus?

    Ultra-Cap.JPG
     
  2. MrSoftware

    Active Member

    Oct 29, 2013
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    Is it a hybrid bus? We have hybrid buses in my area, but they say hybrid on them and the roof area is extra thick, as if they're keeping the energy storage devices in the roof.
     
  3. RichardO

    Thread Starter Well-Known Member

    May 4, 2013
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    No, a Diesel bus.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    I'm guessing the bus, like many ocean going cruise liners and locomotives, has a diesel engine which runs a generator which provides power for an electric motor. The ultra capacitor stores energy while the vehicle is idling, and provides current to accelerate or climb hills.
     
  5. RichardO

    Thread Starter Well-Known Member

    May 4, 2013
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    I don't think the bus is Diesel-electric. I would think they would say so on the outside in big print. :D

    Also, it does not make any funny sounds. The smaller, hybrid or electric (I'm not sure which) mall buses sometimes sound like they are stripping gears.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    In a Prius, the motor/generator on the engine goes into generator mode when dynamic-braking, and the current produced is jammed into the battery pile pretty much as fast as it can handle it without bursting into flames. Everything about a bus is bigger, including the current produced when braking. There is too much current for batteries to absorb safely, so it goes into a supercap array that can handle a much greater di/dt. Also, the charge/discharge profile is very different for a bus. With thousands of cycles per day, normal batteries wouldn't last a week. The energy storage density of any rechargeable battery chemistry decreases with each cycle, while a well-built capacitor is capable of near-infinite cycles with much less degradation.

    ak
     
  7. WBahn

    Moderator

    Mar 31, 2012
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    Why does the rate at which the current is changing such a big deal? I would think it would be the magnitude of the current itself (dq/dt) that would matter much more.
     
  8. MrSoftware

    Active Member

    Oct 29, 2013
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    Also there are many Prius in use as taxis with hundreds of thousands of miles on the original batteries. They don't last forever, but they last a reasonable amount of time. Part of the trick is they only use a fraction of the capacity of the batteries.
     
  9. ISB123

    Well-Known Member

    May 21, 2014
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    Its used to start the bus since it reduces the battery count from 4 to 2.
     
  10. AnalogKid

    Distinguished Member

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    Ohhh I like that. Lower weight, higher reliability.
     
  11. RichardO

    Thread Starter Well-Known Member

    May 4, 2013
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    So, how does it do this? By lowering the output resistance of an existing battery? By doubling the battery voltage?

    I think older buses used compressed air to start the engine. I assume this is the modern equivalent?
     
  12. ISB123

    Well-Known Member

    May 21, 2014
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    They use
    I think that you can find the answer here:
    http://www.koldban.com/Kapower_Information_Center_s/28.htm
     
  13. RichardO

    Thread Starter Well-Known Member

    May 4, 2013
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  14. WBahn

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    Mar 31, 2012
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  15. WBahn

    Moderator

    Mar 31, 2012
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    Oh, I see that the article I found is on the Kold Ban site that ISB123 recommended, so it may be redundant.
     
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