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  1. duke37

    Replacing Christmas light bulbs.

    If the bulbs are in series, then the bulb current is more important than voltage. A low current bulb would go pop since the other bulbs in the string would control the current. How many bulbs in the string? To run off your mains you would need about 50 in series.
  2. duke37

    Pottery Wheel refurbishment - updating components

    It seems strange that it is a shunt motor, I would think that a universal motor would be more likely as in an electric drill. 240W is not small. Trams used shunt motors, a resistor was used to limit armature current and the shunt field was set to maximum. To speed up the tram, the resistor was...
  3. duke37

    Newbie needs help identifying correct capacitor replacement

    Measure the voltage on the capacitors and compare with the good channel, this will indicate whether the fault is in the power supply or later on. Just work through the DC voltages.
  4. duke37

    Need help testing this circuit

    I have some C106D SCRs, old but mature:). These will also do.
  5. duke37

    Transformer primaries in series, secondaries in parallel -- ok?

    The point is that the transformers were designed for the supply to which they were subjected. In the UK we have a supply of officially 230V to match the rest of europe. In practise it is more like the old standard of 240V (50Hz) I believe the US uses a centre tapped supply, I have seen voltages...
  6. duke37

    Pottery Wheel refurbishment - updating components

    You need to derive the circuit. A shunt DC motor will take a terrific armature current until the magnetic field has built up. What controls the motor speed?
  7. duke37

    Transformer primaries in series, secondaries in parallel -- ok?

    The voltage of the primaries are not important so long as they match the supply. The voltage of the AC line is unimportant. The secondaries are intended for 30V output but will give 15V in this application. They are independant so can be used as desired, not fixed for 30-0-30V
  8. duke37

    Transformer primaries in series, secondaries in parallel -- ok?

    There are two transformers, each with two output windings. In order to balance the two transformers, the primaries are connected in series as you show. This means the input currents are the same. Two secondaries are connected in parallel so the voltages are equal, including the primaries. You...
  9. duke37

    DC power supply with different V out

    9.6V to 9V seems too close. Would 8V do? Do not tap the battery or you will get some cells discharged too far and some overcharged. A single buck convertor could be switched for different output voltages.
  10. duke37

    Can you make my 12v LED light up?

    Offa had a lot to answer for. :D Trevor
  11. duke37

    Alternative for a relay or switch, switching a 12V 23A motor?

    The small automotive relays that I have are 15*23*25mm with spade connections out of the end 22mm long. These could be chopped down if the wires were soldered.
  12. duke37

    Need help testing this circuit

    I started off monkey see, monkey do by assembling Heathkit equipment. I learned what components looked like and how to solder but I learned more if the circuit did not work or failed and I had to find the fault. Some people change every component in this situation and never learn. I think I...
  13. duke37

    Alternative for a relay or switch, switching a 12V 23A motor?

    An FET needs to be switched fully on or fully off to dissipate little power. If the power supply is a little bit low, then the FET will disipate lots of power and burn out unless you have a heat sink much larger than a relay. To switch the positive side you will need a p-channel FET, these are...
  14. duke37

    Need help testing this circuit

    You have a +9V line - good. You have a 0V line - good You have the SCR below the ground line - bad You have the SCR connecting the ground to the ground, Why should it pass any current? See #2. There are two versions of SCR triggers. Look up the specification of the device you are using, it...
  15. duke37

    Audio tone generator

    Winding your own coil without proper design of the magnetic circuit will lead to very low efficiency. I would not be capable of deriving the equations. You should consider making the system resonant so that the transducer only has to provide the energy lost per cycle rather than the total energy...
  16. duke37

    Transformer primaries in series, secondaries in parallel -- ok?

    Connecting a pair of output windings in parallel will balance the system. Connecting a second pair in parallel will work only if all the windings are identical. If there is a slight difference then a lot of circulating current will be generated. Better to use one pair only for balance. If...
  17. duke37

    Cells with different voltage in parallel????

    Show us your circuit with resistances. How did you determine the internal cell resistances?
  18. duke37

    Audio tone generator

    A Variac is rated by the output current and is limited by the brush connection. Too much current can heat the winding and give a rough surface for the brush to slide over. Do you have a Variac or variac? An 8A Variac is a big,big lump.
  19. duke37

    Transformer primaries in series, secondaries in parallel -- ok?

    With the primaries in series, they will have the same current so the secondary currents will also be the same and power will be shared equally.
  20. duke37

    Transformer primaries in series, secondaries in parallel -- ok?

    If the secondaries are connected in parallel, then the primary voltages will be equal and given the correct connections, all should be well. The voltage on each of the primaries will be half the normal so the output voltage will be half the normal. The power rating of the transformer depends on...
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