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  1. crutschow

    Astable multivibrator circuit making me astable

    First rule of Spice. All Spice simulation circuits need a ground connection, so I added that. Also you had D2 in the wrong place. Note that you can use standard prefixes such as u, p, m, k, meg (not M), etc. for part values. And the circuit takes a few ms to start, so I extended the run time...
  2. crutschow

    Increasing the output voltage of a step-down transformer by reducing the number of coils

    Yes, if you can get at where the tap is made. An autotransformer has just one winding, and a tap is made on that winding to get the desired voltage. Thus for 120V from a 240V input the tap is about 1/2 from the bottom.
  3. crutschow

    Astable multivibrator circuit making me astable

    If it doesn't, post the .asc LTspice file and I'll take a look at it.
  4. crutschow

    Increasing the output voltage of a step-down transformer by reducing the number of coils

    Yes, since isolation is not needed for this purpose, it could likely be an autotransformer since they are smaller and cheaper to build. But you can still easily add windings to put in series with the output to increase the voltage. It doesn't appreciably affect the output voltage for a given...
  5. crutschow

    Increasing the output voltage of a step-down transformer by reducing the number of coils

    You are assuming that the transformer won't saturate from that, but that's iffy, since most commercial transformers run close to saturation in normal operation (to save on core cost). The label says 220V to 110V, so at 240V it will likely produce 120V out.
  6. crutschow

    Astable multivibrator circuit making me astable

    Falstad simulator may not properly model reverse operation of a bipolar transistor. Yes, LTspice does have a somewhat steep learning curve but there are many sample circuits and tutorials to help with that. You don't have to have a career in electronics, just a hobby interest, to find a good...
  7. crutschow

    A simple electric fence idea

    Yes. My point was, they use DC for that, not AC.
  8. crutschow

    A simple electric fence idea

    What exactly? Any amount of AC current the body above 10mA is dangerous. I would not count on a spontaneous recovery of the sinus rhythm from any value of AC current that has caused cardiac arrest. The defibrillator uses a large DC pulse.
  9. crutschow

    A simple electric fence idea

    Well if you go to the dangerous side of that, I trust you have good attorney to defend you against a wrongful death suit. :eek:
  10. crutschow

    A simple electric fence idea

    The impedance should be sufficient to limit the current to below 10mA. Also to be double safe, the applied voltage should be short duration of perhaps 100ms and interrupted periodically (once a second) to allow a person to let go of the wire and minimize the chance of electrocution. This can be...
  11. crutschow

    Astable multivibrator circuit making me astable

    Below is an LTspice simulation showing the characteristic curves of the same NPN transistor operating in both the normal and inverted mode: Note that Q2 still operates as a transistor when inverted, but the gain is very low with a Beta of about 3, versus over 130 for the normal connection. One...
  12. crutschow

    A simple electric fence idea

    The microwave transformer has about a 10:1 turns ratio whereas an ignition coil is usually 100:1, so the fencer output voltage would be reduced to about 800V, which may not be enough to get through the hair on an animal. My simulation also shows that the large inductance of such a transformer...
  13. crutschow

    A simple electric fence idea

    Certainly good to do if you have a Variac available. No slow electronikers allowed. :rolleyes: But it would need to go some above 100V before it starts stressing C2.
  14. crutschow

    A simple electric fence idea

    Since there is a possibility of overvoltage being generated on capacitor C2 if there is a component or wiring error, I recommend the following when you do your first "smoke test": Connect a battery powered multimeter set to the 100-200V DC range and connect it across C2 with clips so you don't...
  15. crutschow

    Lead acid battery minimum discharge level

    That shouldn't be a problem with most modern sealed (zero-maintenance) batteries.
  16. crutschow

    A simple electric fence idea

    Only for the person that is building and testing it, if they feel uncomfortable working on a main's circuit. As Minder noted, the waste-spark dual output coil will provide isolation from the mains to the output.
  17. crutschow

    A simple electric fence idea

    The Q1, D4 combination will actually limit the voltage to below 90V if the SCR fails open (I view the chance of the primary of the auto coil failing open rather remote.) But an added Zener to protect the circuit is probably a good idea.
  18. crutschow

    A simple electric fence idea

    That's a little too simple. A fencer powered directly from the un-isolated 220Vac is inherently dangerous and not allowed. Also the electrical power should be periodically interrupted (typically about once per second) to allow the person/animal to escape the fence. Below is the LTspice...
  19. crutschow

    Lead acid battery minimum discharge level

    See no reason for that. There has to be a current path between the two battery terminals to discharge it, and just setting it on concrete wouldn't do that. Sounds like an "old wives tale".
  20. crutschow

    Connecting a LED directly to a 230v isolation transformer

    An efficient way to limit the LED current is to use a series capacitor of the proper size, instead of a resistor. For example for 20mA of peak current at 50Hz, 230Vac, the value should be about 200nF. The capacitor must be non-polarized with a 400V minimum voltage rating. A inverse connected...
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