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Your opinion of PCB Express

Discussion in 'Electronic Design' started by Doug Goncz, Jun 7, 2004.

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  1. Doug Goncz

    Doug Goncz Guest

    and other free software PCB design companies? And of PCB Express _non_
    auto-routing software?

    It seems adequate for the two component board I am building.

    Oh, I forgot, I am supposed to add a balancing resistor. That's three


    Doug Goncz ( )

    Read about my physics project at NVCC: plus
    "bicycle", "fluorescent", "inverter", "flywheel", "ultracapacitor", etc.
    in the search box
  2. Tim Wescott

    Tim Wescott Guest

    They all produce captive files, that can only be used by the supplying
    company. There are price-competitive fast-turn houses that will take
    gerber plots, which you can theoretically ship around anywhere, and you
    can get freeware that'll produce gerber plots (see for Eagle).

    My former company had good success with little engineering boards built
    using PCB Express software and service -- they do deliver what they
    promise. Express PCB (which will receive some gerber plots from me as
    soon as I can verify them) _will_ take gerber plots and also has good
    service (they're also just down the road, so I can save a day of shipping!).

    But for three components you probably don't have to worry one way or
  3. Doug Goncz

    Doug Goncz Guest

    Thanks, Tim.

    I tweaked the board yesterday. The mini board holds two caps. Three boards hold
    six caps. Six caps hold 15 V. My inverter runs on up to 15 V. Perfect.

    Each mini board will be sheared into two micro boards. Each fits within the
    Maxwell PC 2500 ultracapacitor footprint of 62.5 mm square with 10 mm radius
    corners. Each pair of caps has Molex connectors on each end, and wire bridging
    the two micro boards.

    The application is dynamic braking for a bicycle, capturing energy to use to
    run an 8 watt LED headlight donated by Dialight, and a pair of tail lights from
    Bike Nasbar. Eventually, the tail lights will be wired as stop / turn / tail

    Each micro board hangs over and has a hole to mount a 20 A DPDT switch from
    Radio Shack, providing auxiliary controls wired in with crimp connectors as
    needed later. I just drill and ream a few holes larger than PCBEx supplied,
    then have the mini sheared in half, and they're ready to solder in the relays
    and mount to the caps.


    Doug Goncz ( )

    Read about my physics project at NVCC: plus
    "bicycle", "fluorescent", "inverter", "flywheel", "ultracapacitor", etc.
    in the search box
  4. Doug Goncz

    Doug Goncz Guest

    Christ, what a mess.

    The next time I create a four component circuit board I'm using an autorouter.
    When it comes to free software, you get what you pay for.

    Anyway, the boards go out for manufacturing in a few days. I went with a
    no-connector design. Solder it up and save 20 milliohms per contact. The caps
    are 1 milliohm each, the relays are rated 100 milliohms @ 1 A @ 12 VDC.

    That might be a contact potential of about 1 VDC plus a resistance of still
    around 90 milliohms, which is unavoidable. At only 2.5 VDC across the contacts,
    contact potential can become a problem. Hm.

    A serious problem.

    What is the self-contact potential of silver-nickel 90/10 alloy?


    My own post:

    Also, that contact potential is tricky. I know it's 0.64 volts,
    because I figured it out for the rated terminal resistance and
    armature resistance myself from the test current of 4 amps.
    That was for graphite brushes and a copper rotor. I have a lower figure for
    those brushes with their silver rotor. I have the silver rotor on my desk, and
    a motor with pinion failed to get even one bid on ebay. I really must relist
    that with a low-price listing. I put too many whistles on it the first time

    Is the self-contact potential _zero_?
    And I have two inverters, for a total voltage of 30 VDC, for maximum
    performance from the motor to its design stall of some five seconds at 12 amps,
    at which point it gets hot. But nobody will stall the motor. At least I dont'
    think anybody will. At stall, contact potential will isolate the cap bank,
    acting like back-to-back dioes. I think...

    Anything more than 30 VDC requires a controller. 12.5 amps will demagnetize the
    ferrite magnets by I'd guess a few percent, leading to poor generator

    The parallel bus and series bus on the board are separate, end to end. So when
    you stop pedaling, the inverter goes offline. And when you start, it comes
    online with a surge. I have some inrush current limiters to deal with this.

    With a normal cycle of operation established through on road testing, a jumper
    will join those two busses, providing a 6:1 series/parallel capattery directly
    linked to the motor. That's the design goal for now.

    Changing the voltage by 6:1 is like a 100 pound skater holding two grand pianos
    in close and whirling around, then letting them out to her full reach of some
    six feet. It's a real whack, but the generator has series resistance to keep
    from throwing you out of the seat. That resistance is just about unavoidable.

    I spoke with a product specialist and these relays will work well with the VAC
    from the pedal mounted generator. Just a matter of gearing to the rider. If the
    rider sprints, some MOVs can clamp the output to keep from overloading the
    relays. The coils are in series, and tend to fail open, safely.
    I have moved the tail lights to a newly mounted rack, greatly improving the
    manufacturability of the final product. The brackets had been modified and
    assembled along a threaded rod. Now, they're stock.


    Doug Goncz ( )

    Read about my physics project at NVCC: plus
    "bicycle", "fluorescent", "inverter", "flywheel", "ultracapacitor", etc.
    in the search box
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