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  1. Kerrowman

    Looking for an Optical RPM module

    Thanks. A useful idea but wouldn’t need to house in a case. More a question of how to place all the parts on and around my circuit.
  2. Kerrowman

    Looking for an Optical RPM module

    I have built a device that has a spinning rotor that I would like to display its rpm. I have been using a handheld laser device that bounces off a reflective strip on the rotor (see pic). I’m looking for a permanent module attached to the base plate with a small display unit I can mount and...
  3. Kerrowman

    Detecting Resonance in an Electrolysis System

    I know nothing about your post or why it was removed.
  4. Kerrowman

    Rheostat power rating

    Hi Harry, That makes sense but in the case of the ignition coil HV systems, like in the link you gave, they can operate at a similar frequency of say 200-500Hz and still give very powerful sparks so is the construction of an ignition coil, and also a flyback transformer, different to such a...
  5. Kerrowman

    Rheostat power rating

    Thanks Harry, I will certainly look into using ignition coils or perhaps a Tesla coil. If it's a question of impedance matching then surely I only have the option to up the secondary coil's impedance. Given that at the moment its resistance is about 1 Ohm, then does it make sense to add a 1...
  6. Kerrowman

    Rheostat power rating

    It's interesting that you, in effect, got + and - 3.7kV across the output of the coil. That is certainly the sort of level I would expect, in which case I would expect more than the 3V I get when I attach my secondary to my load (water cell). Which brings me full circle to my earlier question...
  7. Kerrowman

    Rheostat power rating

    Harry , I need to unpick what you have found. The highest output across the secondary of your coil was 159.8V, when I presume one would expect several kV? (I don't know what the turns ratio is in such a coil but ignition systems are designed to produce 5-15kV) Am I correct in saying that to get...
  8. Kerrowman

    Rheostat power rating

    Harry, that's very industrious of you to build a physical version of the circuit. Have you have substituted my upper 530 for a light bulb because it is just acting as a variable resistor? Also could you clarify if you got a high voltage on the secondary of the ignition coil? If you did, even...
  9. Kerrowman

    Rheostat power rating

    Hi Harry, I'm not clear where your two variable resistors are and in the attached Pic 1 I have put where I think one is. My supply is set at 50V and the gate pulses at 200Hz, 50% so 'hoping' to be able to get 750-1kV out at the secondary when connected to the electrolysis cell. As I come from...
  10. Kerrowman

    Rheostat power rating

    Hi Harry, In your first reply at the start of this thread you suggested using a second MOSFET to control the current instead of a variable resistor, which is why I modified the circuit to include the IRF530. While it works to allow fine control of the current are you now suggesting I put a 50...
  11. Kerrowman

    Rheostat power rating

    Hi Harry, I inserted a 1.5 Ohm resistor into the Source line of the IRF840 as suggested (Pic 1) and calculated typical readings of the primary current of 30mA when the secondary was unloaded and about 160mA when the cell was connected (Pic 2), The value under load could have gone higher but not...
  12. Kerrowman

    Rheostat power rating

    Thanks. I will see what current is flowing in the primary and report back.
  13. Kerrowman

    Rheostat power rating

    Hi Harry, The cell measure 1.164 M Ohms and a capacitance measurement using the same meter showed 1.058mF. That last reading is surprising since I did a calculation last year based on plate area, separation and the dielectric of water which came to 5.18nF so either the meter reading is...
  14. Kerrowman

    Rheostat power rating

    Hi Harry, I tried using a 0.22uF, 2kV capacitor across the secondary windings and Pic 1 shows the result without it and Pic 2 with the capacitor. Pic 3 is with no capacitor but instead with a diode across the secondary windings, as shown in the circuit in Pic 5 (but without the bifilar coil...
  15. Kerrowman

    Rheostat power rating

    Harry, I will set it up with the load in the next day or so and also add a 1uF, 2kV capacitor across the secondary coil and report back. I'd be interested to see what the simulations shows. Thanks Julian
  16. Kerrowman

    Rheostat power rating

    Hi Harry, I have now built the circuit using an additional FET to regulate the current as shown in pic 1 and it does give me fine control.   I’ve used a diode in two different orientations, and also without it to, see the effect on the output but in all cases I get a waveform on the transformer...
  17. Kerrowman

    Rheostat power rating

    Thanks for doing that. The sharp pulses are fine for what I want which is to feed an electrolyser. You used an IRF530 and, as I have quite a few, I hope the IRF840 will work just as well. Thank you J
  18. Kerrowman

    Rheostat power rating

    I'm putting in gated square wave pulse where the HF part is 100-500Hz and the gating frequency 10-20Hz. I've tried to measure the primary and secondary inductances and got a reading of 720mH for the secondary but just a resistance reading of 155 Ohms for the primary. Based on the turns ratio I'm...
  19. Kerrowman

    Rheostat power rating

    Thanks Harry, That Rheostat is far too big to incorporate and your idea of a MOSFET (or BJT?) to control the current is far more elegant and practical. I have revised my circuit in the attached so would that work ok? Jules
  20. Kerrowman

    Rheostat power rating

    I have a circuit (see pic) that includes the primary winding of a 1:20 self wound transformer. Without some form of additional resistance this circuit will draw too much current from the power supply and damage the FET I’m using so I plan to put a rheostat inline with the primary winding to...
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