Market research--electronic circuit breaker

Discussion in 'The Projects Forum' started by John P, Dec 14, 2012.

  1. John P

    Thread Starter AAC Fanatic!

    Oct 14, 2008
    I claim this isn't a commercial posting as the product doesn't exist yet!

    I had a mad idea. What about an electronic circuit breaker built on a small PC board? It would have a non-contact current sense unit (Allegro ACS714 or similar) and a power FET to break the current. There would be a little PIC processor monitoring the sensed current, and it could turn off the FET in case of an overload. The processor could also communicate via a serial link or SPI, to inform some central unit what the current was at any time, or if an overload had occurred. There would be a visible LED to indicate an overload and an optional pushbutton, which could be used to reset the unit. Alternatively, the unit could be programmed to turn power back on every second or so, to provide an automatic reset function.

    This wouldn't be intended for any use on the A.C. power line, but I'm thinking of uses at low voltage for benchtop devices or built into equipment where there might be (let's say) motors or heaters that draw low-voltage power and might be overloaded. Actually it might be usable on the A.C. line, but there I think control would have to be via a solid-state relay. To use a FET for control, the power and processor grounds would need to be linked, so it's definitely limited to low-voltage systems.

    Do you think you'd ever buy these at (wild guess) $15 each? Could it ever be any use at all?
  2. Papabravo


    Feb 24, 2006
    There used to be an old joke about the "expensive semiconductor" going up in smoke to protect the fuse. The reason we use fuses and circuit breakers is that AC line faults can start fires and kill people. Low voltage faults are less worrisome because their potential for damage is correspondingly reduced. In my product development experience a $15 item might be used with another item that cost more than ten times that amount or $150.00

    Now think about how much your budget would have to be to retail a product. About $1.50 for board, processor, FET, and sensor. I think it will be a challenge, but the bigger challenge is who will sell your device? Walmart perhaps, if you know somebody in purchasing in Bentonville, AR.
  3. wayneh


    Sep 9, 2010
    +1 But maybe a still bigger challenge is who will buy it. I don't have one now, so I must not "need" one, and frankly I can't think of what I would do with one in any sort of consumer application. Fuses are cheap and effective.

    If you have insight into an unmet need in some market niche, I would argue that is more valuable than any particular design in search of an application.
  4. John P

    Thread Starter AAC Fanatic!

    Oct 14, 2008
    Thanks both for the replies. Those are useful points and are definitely in the direction of "project design" so I think it was more or less OK posting the topic here. But naturally I'm disappointed at the thought that this is unlikely to make my fortune.

    All right, here's how I came up with the idea. It relates to a model railroad (copied from another place where I posted more information because there the topic is model railroads):

    At our club, we have a bank of circuit breakers protecting the various power supplies that run our electrical system. Recently one breaker has been popping a lot, and I think it's happening for the simple reason that we have too much stuff on one cable. As we extend the layout, we're just extending the power cable in a particular direction, and nobody ever gets around to measuring the current. I went and checked the panel, and we're using just about all the breakers we have installed, so the obvious plan is put in more of them, but when I looked at breakers of similar type on the Internet, I found that they're quite expensive.
    (I should probably add that are multiple cables, each with a breaker, coming away from each power supply, not just one breaker per supply.)

    So I was thinking we might make some electronic devices that could each monitor one branch of our power distribution system. As a bonus, we could use the measurement feature and microcontroller to check which circuits are drawing the most current, and that would help us to arrange equipment to use the breakers equally. Forget Wal-Mart; eBay would be more realistic!

    Papabravo, I entirely agree with you. If the current passes through silicon rather than metal, nobody will have much confidence that the device will survive when there's a fault. Your skeptical opinion made me wonder, why not control the current with a good old relay? They aren't expensive, and the isolation is total. It could even break power-line current then (oops, not allowed to talk about that).

    Note that I'm thinking about a current sensor like the Allegro ACS714, which has a solid metal current path through the IC. The sensing circuit is coupled only via a magnetic field, using a Hall sensor.
  5. wayneh


    Sep 9, 2010
    You might want to play with a Kill-a-Watt meter. It's something you could use immediately, it's not expensive, and will always be useful to have around whatever path you take afterwards.
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    John: if you add a control input to your breaker that turns the FET on and off you could sell it as an (un-isolated) Solid State Relay.

    In fact, many do, once they get the isolation in there.
  7. bundick

    Active Member

    Dec 19, 2007
    Long ago there was a Circuit like that.
    It was in a Uninterpretable Power supply.
    The Circuit felt Spikes and vectored them off to a MOS which protected the Devices plugged into the UPS.
    (Metal Oxide Semiconductor which was similar to a big pile of Oxide which absorbed the spike)