Brick Wall

Discussion in 'General Electronics Chat' started by Wendy, May 11, 2008.

  1. Wendy

    Thread Starter Moderator

    Mar 24, 2008
    Someone was trying to duplicate this device, which got his thread rightfully closed.

    People deserve to make money from their ideas. I guess my question is, what are the odds this product performs as stated? I'm a little dubious, I am not a trusting person when it comes to the advertising crap.

    One of the things they advertise is that they don't divert a surge to ground. This strikes me as faulty logic, if both hot and neutral go to several KV then you NEED to dump that excess charge as fast as possible, which is the point after all.

    It also mentions that they use SCRs for their higher reliability. Sorry folks, MOV's and SCRs are in the same category when lightning is concerned. Faulty logic on my part?

    They also refer to slowing the rate of increase of the surge using inductors. To me this actually makes some sense, slowing the rate of increase to give the rest of the components time to respond might be worthwhile.

  2. Papabravo


    Feb 24, 2006
    I guess "works" is a very subjective standard.
    These devices are sold on the presumption that ordinary products are vulnerable to the events described. These events may or may not occur with some frequency. The device may or may not be vulnerable. We might want to examine the evidence for the existence of "surges" with respect to magnitude and duration. Then we should ask about the vulnerability of ordinary power supplies in the devices and equipment we possess.

    I'm sure that in the days of televisions with "hot chassis" power supplies, that things were different. Personally I don't find the arguments in favor of such devices persuasive. Maybe that's because I've never been the victim of a misfortune. Now I've been surrounded by electronics as a professional and a hobbyist for almost 50 years. Just because it hasn't happened to me doesn't mean it's not going to happen. Even if it does so what, the cost of electronics pales in comparison to almost everything else anyway.
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    My experience with SCR's suggests that their sensitivity to failure due to dV/dT should make it impossible for them to do any level of protection from damaging line transients. MOV's are much more likely to catch voltage spikes.

    At the extreme, I have never seen any home surge protector that a bolt of lightning couldn't defeat. My phone lines are buried. I lost 6 - 8 modems over the years. each one had surge protection, some pretty expensive.
  4. Papabravo


    Feb 24, 2006
    It occurs to me that there are several folks on this forum who could quickly whip up an LTSpice simulation of a transformer, bridge rectifier and capacitor filter whose input was 120VAC plus a periodic spike of a parameterized magnitude, and we could see for ourselves what the vulnerabilities of a standard linear power supply were and the efficacy of counter measures. I'd do it myself but I'm a bit weak on simulating the transformer component with coupled inductors.