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Dummies guide to building a 120watt 140 volt power supply to drive IN-9 Nixie tubes.

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by fireant007, Mar 18, 2016.

  1. fireant007

    fireant007 Member

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    Hi spec,
    Agreed,
    This project is basically a small toaster.

    Perhaps to cool this thing down I should try to duty cycle the anode voltage ?
    edit: or use some kind of multiplexing to light the tubes one at a time ?

    I have not had a chance to do much today as things have got in the way.
    But I did manage to test at 100 to 115 VAC

    At 100 VAC it just puts out 138 VDC (under small load)... so I might have to use the "spark me into life" circuit from Les as insurance.


    edit: I am concerned that is does say max 250v in the data sheet .. but as there is hardly any currrent due to the 2.2M resistor it should be ok.

    The case for this is going to be "difficult" ... you are right about the ventilation but I would prefer passive cooling if possible.

    Oh... the transistor I am using at the moment is a BF469 (overkill).
     
    Last edited: Apr 10, 2016
  2. fireant007

    fireant007 Member

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    Interesting that you have found a new transformer too spec.
    This thing is a lump.

    Thinking even more about this.
    And PLEASE correct me on this !

    If we can strike the tube using the Les voltage doubler idea.

    And

    As the data sheet sustain voltage is only 70Vdc
    Perhaps all we really need is as far as voltage output from the transformer is only the 55Vac.

    55Vac edit rms ? * 1.414 = 77.77Vdc from the rectifier.

    Using the diode doubler trick from Les double it again to 155.54Vdc

    Current draw would now be limited I am guessing .. but don't know by how much.
    Or how to calculate it.

    Then double again to 311.08 then to pop them into life.

    Then power consumption becomes.

    77Vdc * 0.012A = 0.94W per tube.

    Instead of the approximate
    155.54Vdc * 0.012A = 1.86W per tube.

    I might try experimenting with that idea.

    Make sense or just me going down the wrong rabbit hole ?
     
    Last edited: Apr 11, 2016
  3. spec

    spec Well-Known Member Most Helpful Member

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    Hy fire,

    It is bloody annoying when other things get in the way of electronics- my wife is particularly good at that.:grumpy:

    It is not too bad- only around 200W maximum, also there doesn't seem to be any serious size constraints . It is only the transistor junction temperature and collector resistor temperature that need to be kept within bounds.

    Multiplexing is a good idea in general, but not suitable for this application. The tube type and fine control that you require would not be comparable with multiplexing.

    Yes, I was worried about the low secondary voltage with 100V mains input. What rectifier diodes are you using? I know you are adverse to winding transformers but why not put another winding on the transformer core to increase the secondary voltage. As far as I can see, it would be dead easy- you may have to put the Old Rosie down though and use both hands. :D

    What exact transformer are you using?

    Agree, but Les has suggested a good way to reduce the striking power supply voltage.

    In parallel with the electronic design proving, it is best to consider the case design and thermal management for the 'production' model. In my experience, most home projects fail, not so much because of the technology, but because of a failure to complete the case and mechanical aspects- I had hundreds of technically proven projects that never got to fruition for this reason. If you see the case deign as a problem, just post your requirements and I or others will suggest a deign for you to consider. I think it would be a simple design, subject to your requirements that is.

    They are obsolete transistors but more than adequate for your job

    spec
     
    Last edited: Apr 11, 2016
  4. dave

    Dave New Member

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  5. fireant007

    fireant007 Member

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    Well... the case is going to be glass !....
    So no fire issues :)

    That is still in the secret spices and sauces stage at the moment.
     
  6. Les Jones

    Les Jones Well-Known Member

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    Hi fire,
    I think your basic idea in post #162 is a good one to reduce the amount of heat but you would be dropping the voltage too much with only a 55 volts transformer. You would be back with the possibility of tubes not striking and you would only get 70 volts DC on light load. You would also need to allow for a few volts across the control transistor. I think you would need a transformer with about a 70 volt secondary. As you have a variac you could test how low a secondary voltage you could go to using the existing transformer. Farnell do some 2 x 35 volt transformers which is about what you would want but the smallest power rating is 300 VA so they would be too heavy.

    Les.
     
    • Agree Agree x 1
  7. fireant007

    fireant007 Member

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    I have the same problem... can't keep their hands to themselves ..... "common baby it's bed time".....

    Yes .. that bottle of scrumpy is STILL in the fridge.
    I think it is making me go blind.
     
  8. fireant007

    fireant007 Member

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    My maths is errr... wonky ?
     
  9. fireant007

    fireant007 Member

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    You wanted naked dancing Russians .. you got it.
    Well one anyway.

     
  10. spec

    spec Well-Known Member Most Helpful Member

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    :cool: Hey, that works a treat.

    spec
     
  11. fireant007

    fireant007 Member

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  12. fireant007

    fireant007 Member

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    Got off my bum and risked life and limb walking to the shed in the dark.
    This is oz you know .. I might have been attacked by a wombat.

    Anyway.

    Diode is
    http://www.farnell.com/datasheets/1662165.pdf

    Using a 100uF/400V cap that is supposedly low ESR.
     
  13. spec

    spec Well-Known Member Most Helpful Member

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    The transformer is the one I have been working on so we are all singing from the same hymn sheet.

    The diodes may be causing an unnecessary voltage drop.

    You do know that you could solve all your problems with an extra winding comprising a few turns. :D

    (1) put 4 test windings on transformer.
    (2) measure the RMS voltage from the windings.
    (3) calculate RMS Voltage/4 to give turns per volt (TPV).
    (4) Then number of turns = Required Voltage/ TPV.

    spec
     
    Last edited: Apr 11, 2016
  14. spec

    spec Well-Known Member Most Helpful Member

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    Afraid diodes not optimum for this application- more for low power switch mode PSUs. You need high conductance types. 10A or more schotkky types would be ideal- sorry

    http://www.farnell.com/datasheets/1662165.pdf Using a 100uF/400V cap that is supposedly low ESR.[/QUOTE]

    Cap Sounds good. Do you have a capacitance function on the Fluke- if so check the actual value of the capacitor.

    spec
     
  15. fireant007

    fireant007 Member

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    Agreed .. will look at another one.

    Really ? :grumpy:

    I am going to build some voltage doubling circuits ah la Les and have a play around see what I get out of it.

    What is the limitation (current wise) of building voltage doublers by stacking the two diodes and the cap.

    Three neurons uses the same trick.

    https://threeneurons.wordpress.com/nixie-power-supply/hv-supply-kit/
     
  16. fireant007

    fireant007 Member

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    Will check cap tomorrow. Bought it from a local electronic shop. No sheet.

    Agreed. Better diodes are needed.

    This is all as rough as buggery at the moment as you can tell in the video.

    Still liking the idea of putting in a "trippler" circuit and taking the lowest voltage for running and the highest voltage for striking though.

    Think it would be the final solution but Les does not seem to think my calculations are correct (I think).
    So... build it I guess... only a few components needed to see what is what.

    End of the shift here.

    Night all and thanks for all the interest.
     
  17. spec

    spec Well-Known Member Most Helpful Member

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    Having a 1.2A 90V, worst case minimum power line to supply the tubes when struck and having a modified Les boost circuit to provide 170V worst case striking voltage would be optimum according to the internet and my calculations.

    The worst case situation is:
    (1) Mains supply = minus 5% = 0.95
    (2) 100V mains supply feeding 115V primary = 0.87
    (3) Mains transformer fully loaded (55V winding = 55V).
    (4) Ripple voltage 5V Peak to peak

    The best case situation is:
    Mains supply = plus 5% = 1.05
    (2) Transformer not loaded (55V winding = ???).

    Les and I do not disagree with your approach or calculations, it is just that worst case tolerating is the problem which means that sometimes the circuit would work OK and other times not.

    A transformer with a secondary voltage of 67V RMS would be ideal.

    I don't like to keep on about winding more turns on the transformer, but all you need is another 12V RMS and if you put that in boost with one of the 55V windings you would have the 67V RMs required and could have an optimum PSU. It would only amount to 12 to 24 turns and would only take 5 minutes to do. :woot:

    spec
     
    Last edited: Apr 11, 2016
  18. Les Jones

    Les Jones Well-Known Member

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    Here are two more suggestions to get the right voltage. 1 Connect a 12 volt transformer (Such as this one.) in series with the 55 volts (With windings in parallel.) so that you would have 67 volts AC.
    2 Sit the high voltage supply on top of the raw low voltage supply to add that voltage to the high voltage supply.

    Les.
     
  19. spec

    spec Well-Known Member Most Helpful Member

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    Good idea Les, but not sure if fire would like two transformers. :(

    I am in the middle of doing the worst and best case calculations and it looks like a crude regulator at 90V (70V tube operating voltage + 20V across the transistor and emitter resistor) will be required. This would mean that the hot collector resistors could be eliminated. The requirement to power the transformer with 100V on the 115V winding is the killer. It means the secondary voltages would be only 0.87 of their nominal voltages.

    spec
     
  20. Les Jones

    Les Jones Well-Known Member

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    Hi spec,
    Fire would probably need just a 5 volt low voltage supply so a 9 volts transformer would be about right. So if he used a 9 - 0 - 9 transformer with a bridge fed from the ends and the negative output of the bridge to ground he could feed the 5 volt regulator from the centre tap (About 12 volts peak) The positive of the bridge would give about 24 volts so if this was added ( HV supply - to this + 24 v) to the 77 volts (55 x 1.414) he would have an HT supply of about 100 volts. This would mean that if the 115 volt mains input was down to 100 volts he would still have 87 volts. I don't think you need to allow as much as 20 volts across the transistor and its emitter resistor. He would not be driving the base with any more than 5 volts so there would only be about 4.4 volts across the emitter resistor so the transistor should still work with about 8 volts on its collector. I think he should try it with the existing power supply and see how low he can turn down the voltage from his variac before it stops working.

    Les.
     
  21. spec

    spec Well-Known Member Most Helpful Member

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    Hy Les,

    Good points, but I think you need the 20V max across the transistor to allow for a whole slew of tolerances.

    I am now evaluating a completely new approach which, at first stab, seems to solve all the problems, although it is a bit bulky, but not expensive.

    Probably be able to publish later tonight or tomorrow am.

    spec
     
    Last edited: Apr 11, 2016

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