MOSFET based DC motor controller design help

Discussion in 'General Electronics Chat' started by upendra_p, Feb 26, 2014.

  1. upendra_p

    Thread Starter New Member

    Feb 26, 2014
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    Hello guys!
    I am designing driver circuit for a 3 HP dc motor.I am using the IRF2807Z NMOS
    and DSEI60-10 as Freewheeling diode.
    The power is supplied through batteries connected in series i.e. 60V i/p is available.
    I am currently going just for a simple chopper circuit i.e. class A chopper circuit.
    i have attached schematic.

    please help me correct the design if it has any problems and suggest improvements.
    i dont have many components and they are not readily available so I need the help guys.
    Thanks in advance!
    edit:last time the mosfet blew with sparks thats why need to do it carefully this time.
     
    Last edited: Feb 26, 2014
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    You don't give enough information to get help.:)

    What gate voltage are you using? How big is the heat sink ? And how many mosfets are you using? One mosfet like you say your using won't be anywhere near enough to switch ~2.2kW of power. And the 2.2kW doesn't consider the starting current.

    You might want to look at this link to get a better idea of your mosfet needs -
    http://mcmanis.com/chuck/robotics/projects/esc2/FET-power.html
     
  3. upendra_p

    Thread Starter New Member

    Feb 26, 2014
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    Thanks for the reply.
    I am currently using single mosfet but was thinking of paralleling a couple.
    My vgs=5v
    The motor voltage is rated at 60v so 37 A Will be required
    About the inrush current can u point me as to how can I calculate the same? And limit it if possible?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you have a controlled acceleration or ramp up, there will be no inrush especially if you have current monitor circuit of some kind.
    Max.
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    You will never do it with that mosfet or any number of them paralled, if your only using 5Vgs. At 5V on the gate the mosfet is barely turned on. This makes them a resistor rather than a switch. This type of mosfet needs ~10Vgs to be fully turned on. There is another type of mosfet that works at 5Vgs, it's called a "logic level" mosfet.

    In your first post, you said components are hard to come by. If this is so, you really should spend more time on some more research. Research and understanding of the principles is much cheaper than components.:) I'm not trying to discourage you, just trying to give some hard earned advice. Maybe start with a much smaller motor, like a RC car motor. The parts of what you learn from that can then be scaled up to what you learn from it. Crawl before you walk, and walk before you run. :)
     
    Last edited: Feb 27, 2014
  6. upendra_p

    Thread Starter New Member

    Feb 26, 2014
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    actually i am using PWM using arduino board for firing these MOSFET(s).
    and I am sensing the pot value and controlling the PWM duty cycle.
    So its kind of ramp up, right?
    and I am not sure how I can implement current monitor circuit.
    I was thinking of using a resistor but it can cause losses. I was thinking about using 0.01 ohm resistor and measuring voltage drop across it and using it for current limiting i.e. I will stop MOSFET(s) firing.

    @shortbus:
    I have an optocoupler(TLP350) which I can use to increase the firing voltage upto 25V. But the datasheet for the MOS says Vgs(threshold) from 2-4V. So I was using 5V.
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    This is part of what I was saying in my second post. Research/learn what things do and how they work. The Vgs threshold is the voltage where a mosfet is almost turned off. Thershold Vgs, is used when designing an amplifier, not when using a mosfet as a switch.

    The most important information about any mosfet will be listed on the first page of the data sheet. And the data sheet will lie to you. By that I mean that you can't use the full voltage and amperage values and figure that as the wattage it will handle. The wattage is dependent on what the "package" of the mosfet will accept. Go beyond that and expect to let out the magic smoke.

    Did you read any of the link I gave you? There are many sites that will help you understand what you want to do. I'm 66 years old and still learning this stuff, but it does take time. 2.2kW motor control is not an easy thing to start with.
     
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