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  1. duke37

    gu-81m heater soft start?

    It seems as if your transformer either has a shorted turn or you do not have enough turns on the primary so the transformer is going into saturation. Try running it with the primary in series with the largest light bulb you can find and see if the primary approaches the mains voltage. The...
  2. duke37

    Traffic Lights

    I have an old 11A Absaar charger here and will look to see if the components will fit inside. It is a simple transformer/rectifier which is just what is wanted. It is quite battered but there are new ones advertised which may be the same circuit. You do not want one of the controlled type, some...
  3. duke37

    inductor

    There are several ways of making a step up dc voltage converter. the simplest is a push-pull transformer, driven just fast enough to prevent saturation. A mains transformer with metal laminations can be used or a ferrite core at higher frequencies. If you wish to go to the single ended type...
  4. duke37

    Help hacking a quartz clock...I'm so lost!

    There are many ways of doing what you want, most of which I have an idea of what can be done but would need to do considerable study to derive the optimum. A counter set to 60 (10 times 6 or 12 times 5) will store the increasing number. It could then either output 1 pulse or 60. If you drive...
  5. duke37

    Traffic Lights

    This should be possible without too much trouble. I think it could be done with 2 chips, three power fets and a handful of diodes. The main problem will be the power supply, it will need to be 12V at 10A. It may be possible to find a simple battery charger to do this job. If this can be...
  6. duke37

    Sequence 10 leds on power up

    That is what the LM3914 does as long as there is power.
  7. duke37

    Help hacking a quartz clock...I'm so lost!

    Clocks usually use a solenoid to step the second hand at once per second and a gear train drives the other hands. I would think that the easiest way do do what you want is to remove the second hand, store 60 pulses and then output them as quick as the solenoid can respond.
  8. duke37

    Sequence 10 leds on power up

    The LM3914 chip will drive 10 leds in a 'thermometer' style depending on a voltage input. You will need a resistor to charge a capacitor for the input to the chip, to get the rate correct. You can also get 10 leds in a little block as a matching display.
  9. duke37

    timer motor circuit

    Ouch. Put a 1k ohms in series (leave your original resistor where it is) to limit the current to about 10mA. With a transistor gain of more than 20 it will be possible to turn the transistor on sufficiently to provide all the current the motor requires.
  10. duke37

    timer motor circuit

    I have not checked the 555 circuit but you do not want a variable resistor in the motor supply. If you take out the 1k variable and replace the 1k base resistor with a 10k variable, most of the lost energy will go into the transistor which can be fixed to a heat sink.
  11. duke37

    Please Help!

    In the UK the authorities need a log of the problems and any other proof that you have before they investigate. If the problem occurs at 3am each day, there is little point them sending out someone after they have had their coffee. My computer fan makes enough noise as it is and I do not use...
  12. duke37

    Please Help!

    I suggest getting some recordings as proof.
  13. duke37

    Need some RF circuit suggestions

    If the objects are non-conducting, then a tuned circuit will absorb energy at its resonant frequency. Placing such a tuned circiut near a micro transmitter will affect the output which can be detected. Look up grid dip meter.
  14. duke37

    Sound alarm on cut wire

    Sounds like a burglar alarm? All you need is a 12V relay which drops out when the loop is cut. Connect the siren and lights through the back contacts.
  15. duke37

    DIY UPS unit?

    A perfect 240 to 9 V transformer will have a ratio of 26.7 but things are not perfect. There will be some voltage drop due to the resistance of the windings. The 9V transformer is therefore likely to be wound to give out 10V when unloaded, a ratio of 24. If this transformer is used in reverse...
  16. duke37

    A 'space heater'

    It would help if you could say just what you are tying to do. Your power supply will provide about the same amount of heat as a light bulb so will have little effect in a room. AC and DC current has the same effect in a resistor, the AC measurement is chosen to be the same as the DC even...
  17. duke37

    A 'space heater'

    What is wrong with Nichrome that you need something better? You can search for details of Nichrome, Kanthal and Constantan on the web. You will need about 2.5 ohm of wire so choose a diameter and length to suit. Nichrome can easily go up to 1000C so 400F would be a doddle. The temperature...
  18. duke37

    UPS with 24V External Batteries

    I would disconnect the two additional batteries, connect them in parallel and charge them to 14V for a day or two. Then reconnect to your UPS and put your charger in a drawer. The UPS charges the internal 24V battery and should do the job for an external one. Charging one battery unbalances the...
  19. duke37

    DIY UPS unit?

    You have to be very clever to negotiate the RS on-line catalogue, everything else is easy! I have old paper catalogues for RS and Maplin, these give:- RS Transformers 805-057 or 231-8252 FET IRF540N 244-9536 or HUF75333P3 294-9626 Maplin Transformer DH26D FET HUF75337P3...
  20. duke37

    DIY UPS unit?

    There are many ways of generating a sine wave, the problem is making a power amplifier which is efficient. Since the voltage and current are changing over time there is always power lost in the system, hence the big heat sinks on audio amplifiers. If you use a square wave, the output devices...
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