1 2 3 4 Previous Next 83 Replies Latest reply: Aug 7, 2014 9:32 AM by help911 Go to original post RSS
  • 15. Re: Ask the Expert, David Norton
    denimageau Level 1

    Hello David,


    I'm looking for a DC-DC converter with this species :

    Vin = 12 Vdc

    Vout= 0 - 120 V dc

    I out =0- 1.5 A

    remote control via rs232


    i spent lot of time looking for that but it's not a standard converter. Could you give me some devices ?



  • 16. Re: Ask the Expert, David Norton
    mberman e14 Expert

    Hi Denis,

    Mr. Norton is not available to answer questions for the next 10 days or so.

    What you are looking for would require a custom solution.

    There are no off-the-shelf products that I am aware of that can meet your specs.

    The output you describe, with a RS232 remote control, can be provided by a lab AC-DC power supply.

    Here is a link to that type of power supply.


    The Model ZUP120-1.8/U will meet your output requirements.



  • 17. Re: Ask the Expert, David Norton
    elementjames Level 1

    i have a irfp204    mosfet  semi conductor it  says   



    r p748xb

    2v  7c                         were do i get some i need possably 6 and do the numbers translate to new ones

  • 18. Re: Ask the Expert, David Norton
    mberman e14 Expert

    Hi James,

    I located a website via Google where you can request a quote for the IRFP204 parts (see below).


    There are other websites like this one as well.

    I have no idea about the meanings of the other markings or possible alternate mosfets.

    You should be able to get your mosfets at one of these websites.


    Mel Berman

  • 19. Re: Ask the Expert, David Norton
    alytle Level 1
    I have a phase control thyristor (SCR-SF300U13) with a gate trigger current (Igt) maximum rating of 260 ma.  A vendor replaced it with an SCR-T700 with a rating of 150 ma.  The SCR failed.  Is it possible that the replacement SCR failed due to the lower IGT rating?  The only other difference between the 2 SCR's is that the original had a peak forward gate voltage rating of 16 volts and the replacement is something less than that, but relatively close.  Did I get the wrong replacement?  Thanks,
  • 20. Re: Ask the Expert, David Norton
    mberman e14 Expert

    Hi Allen,

    Our expertise lies in the application of commercial and industrial AC-DC power supplies and DC-DC converters.

    We are not prepared to answer questions about specific semiconductors or components used in these devices.

    May I suggest that you go back to the vendor who suggested the replacement SCR.



  • 21. Re: Ask the Expert, David Norton
    rcr22b Level 1

    I want to use two 7 event AC timers to control the same AC pump motor.


    How can I isolate each timer from the other?

  • 22. Re: Ask the Expert, David Norton
    mberman e14 Expert


    Don't understand why you need 7 different timers for the same motor.  Can't you combine some of the timing functions into one timer or a smaller number of timers?  Nonetheless, if you must use 7 different event timers to control the same motor, each timer must have "isolated contacts" that provide AC power to the motor when it requires the motor to operate. This can work if you wire it correctly.  For example, make sure you use the same AC power source for all 7 timers with the same Line and Neutral connections going to the motor.  In other words, make sure that in a worst case situation, that if 2 or more timers are "on" at the same time, they are providing exactly the same AC voltage to the motor from exactly the same AC source (same phase, etc.).  It's like have multiple power cords connected from the same wall outlet going to the same AC motor.  There would be no problem.



  • 23. Re: Ask the Expert, David Norton
    rcr22b Level 1

    Thanks Mel,


    I was not very clear in my previous post.


    There are only two timing devices with 7 events for each one.


    But my original thought was the same as yours.


    Wire neutral to neutral and hot to hot using two male plugs to plug into each timer.


    What happens is that when the first event is activated it zeros the data in both timers.


    I'm doing something wrong or maybe the digital timers are not wired to allow such a simple work-around.


    Anyway thanks for your reply.

  • 24. Re: Ask the Expert, David Norton
    jchere Level 1

    David: I need to connect 2ea 12V batteries to a charger. I want the 1st battery to charge until its voltage equals the 2nd battery, then to charge both, but to isolate the 2nd from the 1st whenever the 1st voltage is lower than the 2nd.

    In other words, I need an ideal diode. My idea is a compairitor and a power FET. Can you send me to such a circuit?

    Thank you.

  • 25. Re: Ask the Expert, David Norton
    TONYB58 Level 1


  • 26. Re: Ask the Expert, David Norton
    mberman e14 Expert

    Hi John,


    Our expertise is in the applications of AC-DC regulated power supplies and DC-DC converters.

    Battery chargers are very specialized devices, as are your design goals.

    Sorry, we do not provide circuit designs.

    However, I feel you are on the right track by considering MOSFETs as electronic switches (ideal diodes).

    Also, as you may know, Schottky diodes have a very low forward drop.

    Make sure you provide enough heat-sinking for the these devices, depending upon your worst case charging current.


    All the Best,


  • 27. Re: Ask the Expert, David Norton
    mberman e14 Expert

    Hi Robert,


    Unless you have many years of experience in the field of AC-DC Inverters, I would recommend that you do not take on a 10,000 watt unit as you describe. I deal in AC-DC power supplies and DC-DC converters only, not inverters.

    I don't think anyone would send you a schematic and parts list for this super high power Inverter.

    Nonetheless, if you want to know more about this subject I suggest you contact an applications engineer at International Rectifier.





  • 28. Re: Ask the Expert, David Norton
    Nortski e14 Expert

    Hi Robert


    Elgar / California Instruments has such products I believe.  (www.elgar.com)


    It costs several $100k to develop such products, so they will only sell you a complete unit.


    Best regards



  • 29. Re: Ask the Expert, David Norton
    jchere Level 1

    Hi Mel: Thank you for the reply, but it appears I didn't make my question clear enough.

    I am not asking for a battery charger. All I am asking for is a switch/diode circuit.

    Shotky diodes have about 0.45 volt foreward drop. A FET would have about 0.03 volt drop at 10 amps, or more than 10 times less.

    All I am looking for is a circuit that turnes the FET on and off depending on the voltage between the input and output.

    Thank you. John Christensen.

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