70 Volt, 1.5 Amp power supply Help!

Discussion in 'The Projects Forum' started by nenadilic84, Aug 7, 2009.

  1. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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    Hi, I'm working on some motor speed control project and I need a 100w power supply that has 70 volts output. Any suggestions on how to build the power supply. I need it to be compact and at the same time cheap :)
    Maybe the best way is to build a transformer.
    Power source is 220V 50Hz

    Thanks,
    Nenad
     
  2. steinar96

    Active Member

    Apr 18, 2009
    239
    4
    If it's a AC motor you might get away with a step down transformer. Otherwise you are looking at a big linear supply or a design heavy switch mode power supply. At least if you insist on building it yourself.
     
  3. Tahmid

    Active Member

    Jul 2, 2008
    344
    25
    Hi,
    If your output is DC (assuming it is, as you mentioned power supply), a switch mode power supply won't be all that hard provided you have the experience and knowledge. If not then the linear transformer + diode + filter + regulation(if needed) method would be easier, although much more bulky.
    If it is AC you require, only linear transformer will do. If you plan the SMPS route, then your power supply must have a full-bridge section to convert the dc to the required frequency.
     
  4. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
    62
    0
    I have a signal generator, and I'm tyring to build an amplifier, but the amplifier requires a mentioned power supply, so I need 70 Volts DC and about 1.5 Amp from the AC grid (220V 50Hz).
    Please direct me to some circuit or tell me where to start... I'm stuck :)

    Thanks,
    Nenad
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    Can you use the LM 5000?
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    You can also get an eval board for this device
     
  7. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Its easy to build a PS from a transformer + rectifier + filter and mostly you wont need regulation as is for Amplifier.Its the cheapest soln. Do you need Dual supply??
     
  8. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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    I agree, but in my area I can't find a transformer suitable for my setup. I think I have to build a transformer. Dose anybody have an experience on that?? Help :)

    Thanks,
    Nenad
     
  9. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Building one requires a lot of working knowledge and experience if its a big one like yours. If it was for just coil gauge calculation and length, it would be easy, but you also need to calculate the core and flux. There are people in this forum who can guide you. Wait for them. You could also order them online or from a dealer to make one for your specifications. I get them made for any non-standard voltage.Also a 220 to 35-0-35 transformer will work if you omit the centre tap and use only the ends. But then you will need one with over 2 amps or maybe 3. But it is an option.
     
  10. t06afre

    AAC Fanatic!

    May 11, 2009
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    Remember that the max DC value you will get from the transformer mentioned by Joseph Alukka will give you up to 70*1.41 volt and that may fry your motor, unless you regulate the voltage.
     
  11. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    True, but when we get a transformer here, we ask for one which GIVES 70 after rectification. Sorry if it mislead you guys. Hope 25-0-25 would be fine for the case.
     
  12. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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    Can I use 12-0-12 with a voltage doubler??? Or would it be better for me to make a switch mode power supply???

    Thx,
    Nenad
     
  13. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Thats a big job. When you use a 25-0-25 itself, you need 1.5x2 = 3A transformer and voltage = 70.5
    When you use 12-0-12, you get 35v DC and if you intend to use a voltage doubler, your current will half, i.e, you need to use a transformer with atleast 7A to get what you need considering the efficiency of such a circuit which is very complex. You could build an SMPS compared to building a voltage doubler.
     
  14. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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    Any suggestions on building a SMPS??? Can you give me some directions on any book or html source or some basic circuit, I would be very grateful. I have an experience with 555 timers and software for circuit simulations.

    Thx,
    Nenad
     
  15. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    I am no expert on SMPS and its topologies. If you are determined to go for SMPS rather than simple transformer, I suggest contacting Tahmid, the guy on the third post of your thread. He knows a great deal on SMPS.
     
  16. nicsky

    New Member

    Aug 1, 2009
    8
    0
    a quick solution might be to connect a low voltage high current amplifer say 12V to a transformer of apropriate current rating
    you could use one that is normaly made for 120Vac
    This would save you having to get a 70v DC supply
     
  17. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
    62
    0
    Is there some one who can help me with building a switch mode power supply. I have experience with 555 integrated circuit and with software for simulation of circuit operation. Can you point me to some website or ebook on SMPS. I will appreciate your help...

    Thx,
    Nenad
     
  18. t06afre

    AAC Fanatic!

    May 11, 2009
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    Did you look at LM 5000 circuit?
     
  19. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
    62
    0
    Can I use a PC power supply and rewire it some how to get 70 Volts...

    Thx,
    Nenad
     
  20. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    You can't use a PC SMPS for a dynamic amplifer. However there are certain classes which are linear. You can only use it on them. Best of all is to avoid using it.
     
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