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Best way to use the transformer

Discussion in 'Home Brew' started by ElectronTubesRule, Oct 12, 2011.

  1. ElectronTubesRule

    ElectronTubesRule Active Member

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    So I have two transformer with a center tap voltage of 1100 Volts @ 1 amp and 150 Volts. My voltage and amp target is 2500V@.800ma as a minimum standard. I want this device to be durable and lst mr the rest of my life.

    I can :

    Wire to two to get 2200 volts@1 amp and and not need a doubler just need to rectify it and filter it.



    Wire them to get 1100V@2 amps and put that through doubler.

    My thinking is that it would be better to set up for current since it is so easy to multiply your voltage. So is that the correct way of thinking about this bias towards current since voltage is easier to multiply?

    Each transformer is between 13.5lbs.to 15Lbs. I used a bathroom scale to weight them so the resolution on the well is not that precise.

    For the record I can get two more just like these two. So I can add even more tansformers identical for the record.
     

  2. W5LZ

    W5LZ Crotchety Old Bastard

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    What do you plan on using the high voltage for?
    - 'Doc
     
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    If the transformers are rated for 1 amp and you only need 800mA then why bother wiring it for 2 amps and then having to mess with a doubler? Doublers are a cheap way to gain higher voltage from a transformer but are inferior to a straight rectifier unless you use very high value capacitors. The voltage regulation tends to be poor unless you use a fairly heavy bleeder current and that is just wasted heat and power. IMHO go with the secondaries in series and use a simple straight forward bridge rectifier.
     
  4. office888

    office888 Active Member

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    Two for 2200v.

    Less complex is always better.

    You'll pay a little more, but it'll be worth it.
     
  5. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    OK, I just reread this and see a problem or two. the first is that you said " I have two transformer with a center tap voltage of 1100 Volts @ 1 amp and 150 Volts." I take that to mean that you have two transformers and EACH has a centre tap with a voltage of 1100 volts when you apply 150 volts to the primary. First why apply 150 volts when the normal AC line is 120, second what is the secondary voltage with normal 120 volts applied to the primary, and lastly if the centre tap is 1100 volts that means the overall output voltage is 2200 volts for EACH transformer.

    The other problem is that if you have a secondary voltage of 2200 volts in whatever configuration you end up with then the filtered DC voltage will be about 3110 volts unloaded and will likely only drop a couple hundred volts at most under load depending on the filter capacitor value.
     
  6. ElectronTubesRule

    ElectronTubesRule Active Member

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    Well at 13.5 pounds they are not power houses that is for sure. I do plan on occasional prob. once every few years going on AM. I do prefer SSB so that is where I would more then likely spend 98% of my time.


    I do not need to hit my target of 2500V @ .800ma that would be if I wanted to get every last watt out of those tubes and I do not need to do that. I did not know which way would be considered more durable wiring them series or paralleled. I normally go for durability and cool running for electronics. So I was guessing that going for current and letting the doubler do it's thing for voltage would give me more head room and cooler operating. Since I have no practical experince in this area I figured I would ask.

    I am going to be powering 2 GI7BT tubes. They are rated at 350Watts each but most home brew guys are getting 500watts each clean on the scope for a total of 1000watts at 2500V @ .800 their is actually one guy getting 1200 at that power level. I think that was with 60 watts of drive. Most of the other ones I have seen they stopped at about 48 watts of drive.

    I have no desire or need to try to get all the power I can from them. My target is 600watts clean in all modes if I can get more then that fine but my goal for my first amp built from scratch is just 600watts. Like I said before I am not looking to get crazy and push the tubes to their limits if I need more power I can get bigger tubes!

    So if I am getting this right consensus is on wiring them 2200V at 1amp and not bothering with doubler at all just simple full wave rectifier. So a .200ma buffer from desired peak current of .800 is considered enough head room for long service life? My goal is to run those transformer's cool enough to not tax them too much.
     
  7. ElectronTubesRule

    ElectronTubesRule Active Member

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    No to be Clear.

    Input voltage is 120V off house mains.

    Out put: red and blue leads center tap 1100 V at 1 amp this is for one transformer.

    It has another set of leads that outputs 150V but I did not measure the amperage on those.

    The problem was that the leads are identical in color so one transformer has two red leads and two blue leads. I first tried them together and had heating happening too quickly. So I measured for continuity on the leads and took voltages separately and in various combination. This is how I discovered that I had identical colored leads but with different outputs voltages. The center tap HV blue and red leads are farthest from the center of the transformer with the lower voltage 150V red and blue leads being closer to the center of the transformer. They are marked identically to each other the color of the output leads that is.

    To make sure of this I went and got the second transformer wired it up and repeated everything to make sure this was in fact how it was supposed to be and not a bad transformer since it has been sitting for about 20 years in a storage facility. The second transformer behaved inthe same way and had the same voltages to within a few volts of the other transformer.

    So again the black leads are the input leads for the ac mains and I supplied 120volts main voltage to them from a 30 amp circuit.

    The output was 1100V @1 amp on one set of outputs.

    The out put on the other set of ouputs was 150V unknown amperage.


    So with two transformers I can either have a combined output of 2200V at 1 amp or 1100V at 2 amps before I rectify it or double it!


    I hope this is more clear.
     
  8. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Power consumed is power consumed and whether you use a straight forward rectifier or a voltage doubler the end result will be the same.If you double the voltage the current draw will be more from the transformer than it would be if a straight forward rectifier was used. You can't just create power from nothing.

    Voltage Multipliers
     
  9. Kamikaze

    Kamikaze Active Member

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    None of the description here resembles a center tap.
     
  10. Shockwave

    Shockwave Sr. Member

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    You might want to know the insulation breakdown voltage of these transformers. If the rated insulation voltage is too low, it could fail on a humid day due to the increased voltage between the secondaries, primaries and the iron cores. Many high voltage transformers are rated with ample headroom to accomplish series wiring. Some are not and can fail.

    Wiring the secondaries in series places more stress on the secondary insulation because you have double the AC voltage on them. The insulation now has to handle this high voltage AC and prevent it from arcing to the grounded core or the primary. In applications where the insulation rating is marginal or unknown, sometimes the doubler is the best choice.
     
  11. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Actually that is good advice. I wasn't thinking about that but I should have. A lot of old plate transformers meant to be used with a conventional full wave rectifier do not fair so well when used with a bridge rectifier to obtain higher voltage output. In any event when it comes down to a simple rectifier over a doubler, the simple rectifier/filter wins every time when it comes to ease and performance.
     

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