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  1. KrisBlueNZ

    What purpose does this capacitor/resistor serve?

    I think that's a pretty good solution. If you want to use resistors, you should get some 10 kΩ 10 watt wirewound resistors and connect them in parallel across the contactor coil. You'll probably need more than one, maybe as many as six. You can keep adding them until the contactor turns OFF...
  2. KrisBlueNZ

    Multiple Inputs/Outputs transmitter

    Can you provide manufacturer and part numbers for the transmitter and receiver? Link to data sheets? Do you want to do this without microcontrollers?
  3. KrisBlueNZ

    Watts equation

    That's right. I would say you multiply the voltage ACROSS the device by the current flowing THROUGH the device. That's true for DC. Things can get tricky with AC when capacitance and/or inductance are involved, but that's not relevant for incandescent light bulbs. Yes, and in Britain...
  4. KrisBlueNZ

    TRANSISTOR SELECTION

    Your circuit is not clear. Specifically it's not clear where and how the current flows in the switch. Normally, a switch is connected between a voltage source and a load of some kind. When the switch is open, no voltage is applied across the load. When the switch closes, the circuit is...
  5. KrisBlueNZ

    fuse

    What are the minimum, maximum, and typical voltages of the battery stack?
  6. KrisBlueNZ

    Designing a Time Delayed Relay

    SMT because normal cylindrical, axial THT diodes are difficult to heatsink. THT components have a closer thermal connection to the PCB. I've never seen zeners in heatsinkable packages, apart from one stud mount one that Digikey have, which is the wrong voltage and quite expensive. Any other...
  7. KrisBlueNZ

    Insufficient data received error in modbus

    Thanks for following up here. So that error meant that when a device stopped driving the RS-485 bus, it would be pulled into a break state? And that causes the Master to report "insufficient data" and a CRC error?
  8. KrisBlueNZ

    Designing a Time Delayed Relay

    OK, you're absolutely right, a switching supply is the answer to all of the problems caused by the "creeping load current" issue caused by first one, then two Allegro chips. I should have suggested it a long time ago, when it became clear that this wasn't going to be a design that could be kept...
  9. KrisBlueNZ

    Power Capacity of Resistors of Different Values

    There is one female who has just recently introduced herself. Otherwise it's the proverbial sausage-fest here :) That's right, as long as the resistors are all the same resistance. That's a fact AND a theory. Yes it is. Gryd3 has shown you how to calculate the dissipation in a resistor - it's...
  10. KrisBlueNZ

    fuse

    Hi and welcome to Electronics Point :-) Probably one or more big-a$$ MOSFETs to operate as a fuse. Try this search: http://www.google.com/search?q=electronic+fuse+mosfet&tbm=isch MOSFETs are available with current sensing in the source terminal, or you could just monitor the voltage across it...
  11. KrisBlueNZ

    Joule Thief Is Not Working

    Can you post a schematic?
  12. KrisBlueNZ

    Designing a Time Delayed Relay

    By RθSA do you mean thermal resistance from the un-heatsinked package to ambient? Do you think that's too high? The metal part of the package doesn't have much surface area... RθJC of 2.5 °C/W sounds right, and 0.75W is the worst case power dissipation. What does RθCS mean? Edit: Oh, do you...
  13. KrisBlueNZ

    LED switch wiring

    Yes that's possible. Also they could have used a high-efficiency LED. That would be a cheaper option. 1 mA at 220V = 220 mW. I agree AC can be assumed; not many people would be using 220V DC!
  14. KrisBlueNZ

    Hello world!

    Hi Sarah and welcome to Electronics Point :-)
  15. KrisBlueNZ

    Do I need a heatsink? How big?

    This is great stuff Steve! I'll post some minor comments when I get to the end.
  16. KrisBlueNZ

    Designing a Time Delayed Relay

    Yes, using PCB copper would waste a lot of space. You're probably right, a heatsink will be needed. Steve wrote a good introductory article on heatsinking: https://www.electronicspoint.com/resources/do-i-need-a-heatsink-how-big.29/
  17. KrisBlueNZ

    Help with making EMS

    Discussion of devices to be connected directly to the body is banned by Electronics Point policy. This thread is closed.
  18. KrisBlueNZ

    Boost converter 12V to 36V (25 mA load) using 555

    Not necessarily. Inductors have a specified maximum operating current and/or a saturation current. These should both be at least 500 mA in this application. The saturation current is determined by the number of turns, the overall permeability of the core, and the core material, but it's simplest...
  19. KrisBlueNZ

    Designing a Time Delayed Relay

    Using a TO-220 package won't help much unless you use a heatsink. θJC is a fairly small part of the total thermal resistance, θJA, and although it's important to keep the silicon cool, the most important temperature is that of the case and the PCB surface, which isn't affected by θJC; it depends...
  20. KrisBlueNZ

    Designing a Time Delayed Relay

    That figure, 92 °C/W, applies to the package itself, with no heatsinking. I suggested an SMT package so you can provide a copper area to spread and dissipate the heat. This reduces the thermal resistance to ambient. The data sheet for the Infineon 78M05 in TO-252 (DPAK) package says the thermal...
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