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  1. KrisBlueNZ

    diode for collapsing magnetic field

    Yes there's been a bit of confusion on the thread because there are two inductive loads. There's a heavy pump, rated at 30A at 12VDC, to which we are suggesting adding the 40A stud mount diode suggested by CDRIVE I think, connected in reverse, to suppress any back EMF that the pump might...
  2. KrisBlueNZ

    diode for collapsing magnetic field

    Agreed. Unfortunately, it's not going to be easy to work out how long the back EMF current pulse will be. I said less than 0.1 seconds but it's probably a lot less - less than 10 ms, maybe less than 5 ms. Mainly it depends on the inductance and mechanical characteristics of the big relay...
  3. KrisBlueNZ

    AC power problem

    Thanks for finding the schematic. Well, the power supply circuitry is very conventional. It should behave OK with DC or mains-frequency AC input. I notice that the video circuitry is next to the power supply on the schematic. That doesn't mean they're close by on the circuit board though. I...
  4. KrisBlueNZ

    diode for collapsing magnetic field

    It's just a quick way to check that the diodes aren't being forced to dissipate too much energy while the magnetic field is collapsing. But it's not a very useful test - not for the zener, anyway. The instantaneous power dissipation limit could easily be exceeded and the zener could fail...
  5. KrisBlueNZ

    AC power problem

    Can you find a schematic diagram of the NES? I tried googling it, but the closest I can find is http://nesdev.com/Ntd_8bit.jpg which doesn't include the power supply section, and may not even be for the NES - the title includes "NTD". I might have some suggestions if I could see a schematic...
  6. KrisBlueNZ

    2 pin flasher

    CocaCola, yes I think he wants to drive two bulbs in parallel and detect when one goes open circuit, and flash the other one twice as fast as a warning that a lamp has failed. I assume this is for the front and back indicator of a vehicle? I think that old-style electromechanical flashers have...
  7. KrisBlueNZ

    diode for collapsing magnetic field

    Blank Stare, and CocaCola, I agree with both of you. The polarity of the diode from hell across the pump should be pointing leftwards, as shown in CocaCola's version of your pic. For suppressing back EMF, the diode is connected so it doesn't conduct when the activating voltage is present. The...
  8. KrisBlueNZ

    diode for collapsing magnetic field

    That's a pretty good description. The characteristic of inductance is that current through the inductor cannot change quickly. While the inductance is energised by current flowing from the power supply (via some contacts), current flows from the power source, in the top end, out the bottom end...
  9. KrisBlueNZ

    diode for collapsing magnetic field

    You're confusing yourself again. 1. The diode ACROSS THE PUMP must be rated for 30A OR MORE. It is NOT A ZENER DIODE. The 1N1190 looks suitable. The 1N4001 is NOT suitable for this position; it's only rated at 1A. 2. The diode(s) across the COIL of the main relay can be a lot smaller. The...
  10. KrisBlueNZ

    Help with time delay relay circuit

    Hi Andy :-) OK, I'm assuming you're using the design from post #20 on this thread? So the wires to the relay coil both have 5V on them? There's something wrong there. One of them is connected directly to the positive power rail, which should be 12V. You'd better check that first. Also...
  11. KrisBlueNZ

    diode for collapsing magnetic field

    To the OP. You're getting confused. Here is a quick summary. Your circuit has two inductive components: (1) the load (the pump), and (2) the coil of the big relay. Inductance produces a voltage spike called back EMF when the inductance was being fed with a current, then something tries to...
  12. KrisBlueNZ

    diode for collapsing magnetic field

    Yes, a resistor would do a similar thing. The PDF I linked to (which is written by a relay manufacturer) recommends the diode and zener combination as the best option.
  13. KrisBlueNZ

    Help setting up project

    You need to connect your toggle switch as a "reversing switch" (this is a standard configuration; google it). It needs to be the "centre off" type. This will give you a DC voltage of one or other polarity to power your actuator. For the actuator, have you considered a small motor and a worm...
  14. KrisBlueNZ

    diode for collapsing magnetic field

    My comments relate to the connections to the coil of your big relay. In your circuit, the coil is energised by current flowing through one of two diodes. The diodes have their cathodes tied together and feeding one end of the relay coil; the other end of the relay coil is grounded. The relay...
  15. KrisBlueNZ

    Op-amp as voltage sensor

    In addition to Steve's excellent reply. I suspect that using a micro with a built-in ADC, as originally suggested by BobK and amplified by Steve, could be very worthwhile. You haven't described your circuit fully, but I take it that the microcontroller is interested in the battery voltage, and...
  16. KrisBlueNZ

    How does this circuit work?

    I wouldn't assume that the microcontroller is trying to start the motor and then discovers the sensor problem. I suspect it is refusing to start the motor because it has already detected that there is a problem with a sensor. This is consistent with the fact that the motor will start and run if...
  17. KrisBlueNZ

    diode for collapsing magnetic field

    Yes, but that doesn't give the full story. When the voltage on the anode of the diode disappears, the inductance of the relay coil will try to pull the diode voltage negative. Whether that is suppressed or not then depends on the circuitry connected to the diode's anode, which is just shown as a...
  18. KrisBlueNZ

    AC power problem

    Could you describe the wavy lines in more detail? Is there anything you've changed or added recently? Did the problem appear suddenly or has it been gradually getting worse? What is the screen? Is it part of the game, or an external monitor? Does it work OK displaying any other signal from any...
  19. KrisBlueNZ

    Feedback on creating circuit boards

    Nice work oyvdahl. You've created a resource that will be helpful for beginners, to show them that you CAN do a lot with free tools. I could write pages on PCB layout considerations, but I'll spare you most of the boredom. Sometimes beginners have trouble with selecting appropriate components...
  20. KrisBlueNZ

    diode for collapsing magnetic field

    Arcing in relay contacts can be worsened if the relay's contacts cannot move apart quickly; this can be caused by the relay's magnetic field being unable to collapse quickly due to current flow through the diode connected across the coil to suppress the back-EMF from the coil. I'm not sure...
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