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  1. duke37

    High Low logic

    OK, I got it wrong, it has happened before.:) The difference is that 1.22V is across the 'bottom' resistor rather than the 'top' resistor. I wonder whether this is due to the fact that it is a low dropout regulator.
  2. duke37

    High Low logic

    The regulator keeps 1.22V between the output and the ADJ terminal. If this terminal is connected to ground. then the output will be 1.22V If the ADJ terminal is raised by a certain voltage, then the output will be the sum of the added voltage and 1.22V. The raised voltage is derived from the...
  3. duke37

    12 volt relay to start a 24 volt motor

    The reason is that 12V relays are common. I can take a walk over the fields and Rich will give me a couple free, he also lets me use his compressor to blow dust and spiders out of old radios. If I speak to him nicely, he would bring me the relays when he comes down to his mum's for lunch. 24V...
  4. duke37

    12 volt relay to start a 24 volt motor

    I do not think that much heat will be generated in a millisecond or so. Contacts wear due to the generation of an arc at switch off, the diodes will suppress this. The automotive relays seem to be rated at 40A so a couple should be able to pass 42A without trouble. 12V automotive relays are...
  5. duke37

    12 volt relay to start a 24 volt motor

    You could use a couple of 12V automotive relays with coils in series and output contacts in parallel. Remember to put a flywheel diode across the relay coil and also the motor to protect the contacts during switch off.
  6. duke37

    12 volt relay to start a 24 volt motor

    Why use a 12V relay? What is wrong with a 24V relay or mosfet (if DC).
  7. duke37

    Information on wiring a 5vdc fan and a 6vdc pump in a circuit

    I cannot say whether the 5V fan will burn out on 6V, it all depends on the fan. The speed of the fan will be roughly proportional to voltage but the torque and hence the current will be proportional to speed squared. At 6V the speed will go up by 20% At 6V the current will be up by 44% At 6V...
  8. duke37

    Information on wiring a 5vdc fan and a 6vdc pump in a circuit

    A diode does indeed pass current in one direction only but does not have minimal resistance. The voltage drop will be somewhat above 0.7V up to perhaps 1.2V at high currents. This action is different to a resistor which has a voltage drop proportional to current. A voltage drop of 1V at 6V is...
  9. duke37

    Fender stage 160 amp blowing fuses

    I doubt if the difference between 15 and 16V will be important. A powerful; zener can be made by using a smaller zener feeding the base of a large transistor (2N3055). The regulated voltage will be about a volt higher than the zener. It is not clear whether the zeners are to produce a...
  10. duke37

    need basic schematic for a 12v gradual power up for small water pump

    You could use a capacitor and resistor to charge it slowly, then feed this voltage into a FET to gradually turn it on. If you get it right, the FET would dissipate little power when fully on since low resistance ones are available
  11. duke37

    DG self starter motor and Dynamo

    "Battery positive end connected to self starter motor body," I think you have the circuit wrong. Normally, with recent equipment, the battery negative is connected to the chassis which the starter motor is bolted to. The battery positive goes to the solenoid which has two fat connectors. The...
  12. duke37

    Line tester

    Leather boots will be conductive, they may well be saturated with salty sweat. A neon tester will light up due to capacitance if testing an AC supply and might flash intermttently on a DC supply if there is some leakage.
  13. duke37

    help wiring 3 phase washing machine motor

    If it is a VFD (variable frequency drive) there will be a rectifier and big capacitor to give DC for the drive. Are the capacitors rated for AC or DC? Have you put the wrong type in?
  14. duke37

    Regulator question.

    The 7815 connections are In (+) Gnd Out (+15V) The 7915 connections are Gnd In (-) Out (-15V) I think the tag is connected to ground.
  15. duke37

    Regulator question.

    I follow the connections for the 78xx, with the ground at the centre. Did it work? The connections to the 7915 are different, have you got them correct? Where is the 7905 connected? Show a schematic.
  16. duke37

    Diode Da Lima

    Another way of looking at it is that energy is stored in the magnetic field of the inductor. J = I*I*L/2. This energy has to be dissipated somewhere other than in the switching device so the diode allows the current to continue until it is dissipated by the resistance of the coil If the turn...
  17. duke37

    Mimic a Type 80 rectifier tube

    According to my valve book the type 80 rectifier is full wave capable of 350-0-350V at 125mA. This does not agree with your specification. The output could be 350*1.414 = 500V, not 5V The heater takes 2A at 5V so a dissipation of 10W. As said this valve can be replaced with a couple of diodes...
  18. duke37

    Alternative Transistors for LM317 High Current Voltage Regulator Circuit

    I agree but the circuit shown in #10 has no current sense but there is no risk to the LM317 which has its own current limit.so shorting the output does not compromise the short circuit capability of the LM317. A circuit as described by Audioguru (#16) would be advised to protect the pass...
  19. duke37

    Alternative Transistors for LM317 High Current Voltage Regulator Circuit

    How does it do this? The current limit of the LM317 is set internally. The pass transistors are at risk though.
  20. duke37

    Antique Automotive Resistors

    It would help if you gave information that would help to solve the problem. TCI, The nearest I could get to motor cycling was Touring Club Italiano. If it is a custom motorcycle, i.e. one made specially for a customer, then you have little chance of finding the quirkes which have been...
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