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Kerrowman

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  1. 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 as high as 1A. This was with a square wave input of 200Hz from the pulse circuit and 12V from the PSU as before but with my bifilar coils in place (Pic 3). Once again the voltage across the cell drops to 3-4V under load and reads about 220V when the cell is not connected. I know to expect a vo
  2. Thanks. I will see what current is flowing in the primary and report back.
  3. 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 unreliable in that context or the distilled water surrounding the cell is contributing in some way. With the resistance measurement that would suggest that the average current flow through the cell was 50/1.164 E6 = 42uA where 50 is a typical rounded voltage peak I'm getting on the scope. I'm unclear h
  4. 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 that I have yet to add in). Pic 4 is with the load attached, the load being a simple cylindrical electrolysis cell in distilled water. It seems that with the load attached, and only about 50mA being drawn from the Variable PSU, the voltage across the secondary windings and cell drops dra
  5. 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
  6. 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 secondary (no load) as in pics 2-4 which shows + and - voltage swings instead of just a + as in your simulation, which is what I need. Pic 2 has no diode, Pic 3 has cathode towards the IRF530 Source and Pic 4 has the diode cathode towards the IRF840 Drain (i.e. reversed). What do
  7. 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
  8. 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 guessing the primary has an inductance of around 5mH? That would be great if you can quickly simulate the circuit. 😀
  9. 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
  10. 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 control the maximum current flowing in it. Given the basic equation for power expended in a resistor of P=I^2R, I’m trying to work out the maximum power rating for the rheostat. If I set the input voltage to 50V and set a 100R rheostat to 50Ohms then my current should be 1.0A. In th
  11. Hi Harry, The good point you raise about voltage headroom is presumably why 18V is supplied by the transformer in the full power supply circuit shown on that first link. However, the note nearby says that it has not been built so is it a bit of a gamble that it will work as indicated? The FET approach to dropping volts will work for the time periods I’m using for certain tests but for long term running I will likely need something more efficient. For the FET approach, in Spice simulation the FDS6699S mosfet works we
  12. Hi Harry, As suggested above I have drawn my own version of the power supply on the first link you gave using 5 LM338s. I could try and simulate this in LTSpice but that will take me a while. Any thoughts on whether it would do the job - probably better than the Buck converter? Jules
  13. Hi Harry, I have used this buck converter before but its never supplied even 20A consistently. In the first link you gave it talks about using the LM338 in parallel, as in the attached. Can I not stack 3 of them in parallel to do the job? If so I will assemble a circuit and run it by you? Thanks
  14. Thanks but my particular need is to take 12V, 25A max and make adjustable from 6-12V and a max current of 25A so would the attached from the previous link be suitable? I find the text doesn't make easy reading and is hard to understand. J
  15. Hi Harry, Thanks for the suggestions. The voltage regulator seems a good idea but I don't need the whole power supply but just an add on set up to adjust down the 12V nominal output I already have. Would I need then item 4 in the list? If so how is the voltage energy dissipated and how efficient is it overall? The motor controller uses a PWM approach it seems (12kHz) and I already have a PWM in my setup. Jules
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