Search results

Search Forums New Posts
  1. duke37

    Low voltage cut in/cut out

    Look at the LM3914 bar graph driver circuit, this has ten outputs and will add outputs as the voltage rises. You will need output driver circuits for each fan and an input circuit to give the required range.
  2. duke37

    Do I need a snubber/rc for high-frequency ignition coil driver?

    The flywheel diode restricts the high voltage on the 3055, there will need to be restrictions on a fet also but fets are often specified to take more abuse. There are many ways of restricting the collector voltage. 1. Place a resistor across the coil, if this is the same value as the coil...
  3. duke37

    I'm trying to rig a bike horn to an alarm clock

    That is what I suggested in #2. It may be possible to just use a power npn transistor if the clock can drive it, otherwise a Darlington may suffice.
  4. duke37

    I'm trying to rig a bike horn to an alarm clock

    This would never have worked. You will need a npn transistor (2N3904, 2N2222, BC548, 2N706, BC108 etc) as the input feeding the pnp driver. Keep the 1k input resistor, connect to base, connect emitter to ground, connect collector to 2N3906 base via a 10k resistor. You may need a capacitor gate...
  5. duke37

    Relay & switch wiring

    If you use a relay, then add a flyback diode across the relay coil to reduce switch sparking when switched off. Most motor equipment is crude and relies on fat cheap contacts.
  6. duke37

    Thermometer Circuit

    What is the IC? Does it have a ground connection?
  7. duke37

    Drill's battery not working.

    Charge the batteries for a day and see if they hold the charge. NiCads can develop an internal short which will discharge any energy put in.
  8. duke37

    Drill's battery not working.

    A battery will have a voltage depending on the chemistry. This voltage will not change if the chemistry does not change. Thus a battery may show the normal voltage with only a very limited charge, it doesn't say that there is any significant amount of energy stored in the battery. The charging...
  9. duke37

    APOLOGIES TO THE GROUP

    The production and use of HHO will obviously take energy but the hydrogen may alter the combusion of the main fuel, either increasing or reducing the engine efficiency. I have not seen data on this. NEW PARAGRAPH:) There have been sugestions of adding hydrogen to domestic methane gas supplies...
  10. duke37

    Help in deciding method for de-modulating? a signal to extract one frequency!

    Use a sheep dog for reception, distances of up to a kilometer should be possible, either using voice or whistle. Have you looked at the purity of a recorder tone. Even if there are many harmonics, three of four notes could be discerned within one octave. Early model control used tuned filters...
  11. duke37

    Help in deciding method for de-modulating? a signal to extract one frequency!

    Bagpipes will give a multiple drone which could be used as a security device. You may need a large output power to get the sensitivity.
  12. duke37

    Need to drain off curent.

    I assume the motor uses one polarity for forward and the opposite polarity for reverse. Adding a diode of the correct polarity feeding a resistance will dump current in reverse. Set the resistor to drain 20A or so. it will need to be fat to dissipate 200W.:) The zener diode trick will do the...
  13. duke37

    Need to drain off curent.

    It sounds as if the power supply can supply the current but cannot accept current if the motor is being driven by the load, this could damage the power supply. The solution could be to limit the voltage to just above what is normally supplied. A powerful resistor or a super dooper Zener diode...
  14. duke37

    Understanding impedance

    The output circuit should provide whatever current is needed so it should have a low impedance. Thus current draw will not change the voltage much. The input circuit should have a high impedance so that it draws little current and does not affect the voltage greatly. For maximum power transfer...
  15. duke37

    CONNECTION TYPE

    The RX connection has a two diodes connected back to back so will never pass any current.
  16. duke37

    39v 8a Laboratory Power supply circuit, Need Help

    I have a dual supply which has a pair of L200C control chips to set current and voltage. These with suitable extra pass transistors may do what you want. The box was bought many years ago and was well used then, there may be more modern devices. Edit: I do not know the maker.
  17. duke37

    39v 8a Laboratory Power supply circuit, Need Help

    I do not see any current control. R6 and R4 control current through D3 but this is not dependent on the current being supplied. The normal way is to measure the voltage across a low value series resistor and shut down the output voltage when the current limit is reached.
  18. duke37

    12 V motor loss of power

    I disagree. I made such a supply to drive a coil winder. It measures the speed by voltage 100 times a second and gives a boost if necessary. It will cater for motors with strong cogging. The larger the inertia the better for low speed use. It is awaiting being put into a box so may have to wait...
  19. duke37

    POWER TRIP

    Is it the current overload or earth leakage which trips. Either way, check the mains cable for damage.
  20. duke37

    Connect 12V relay to LED

    If you have a mechanical switch, you do not need a relay.
Top