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mosfet power supply issue

Discussion in 'Power Electronics' started by Tamara, May 3, 2017.

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  1. Tamara

    Tamara

    2
    0
    May 2, 2017
    Let me preface this post by telling anyone kind enough to answer that I am a TOTAL newbie to electronics and am unfamiliar with most of the jargon I see being used in this forum. So PLEASE answer as though you were addressing a rather dense pre-schooler......I'll be gratefull rather than offended. Having said that, here is the issue I'm facing. I am using a DC3v-5v mosfet with a momentary remote transmitter. Am basically using the mosfet as a witch to turn a 1.5v mini hobby motor on and off. The problem is that when I use a 3v battery for the mosfet, it only works for a very brief period of time before the battery drains, and the battery seems to continue draining further overnight, when not in use. I switched to a 6v battery for the mosfet and it's working just dandy. After over 4 total hours of use (about an hour of continuous on/off clicking at a time), the mosfet is not heating up or misbehaving. My question is.....is it safe to continue using the 6v battery, or am I asking for trouble down the line with the mosfet. This whole setup is part of a very small magic prop, and all the electronic components must fit into a 3"x2"x1" project box, so I have very little available room to add other components. Thanks in advance for any advice offered.
     
  2. Cirkit

    Cirkit

    88
    4
    Oct 28, 2015
    Hi Tamara,

    Welcome to the forum :)

    Would you be able to sketch how you have wired up the transistor, battery, motor and output from the remote transmitter?

    Maybe using the MOSFET as a witch might be the issue ;)
     
    Harald Kapp likes this.
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    9,663
    2,019
    Nov 17, 2011
    A schematic diagram is really the first step to help us guide you along.
    Also state the type of mosfet (part number) and of the batteries you use or used.
     
  4. Minder

    Minder

    2,922
    615
    Apr 24, 2015
    So you are using 6v for a 1.5v motor? how are the rpm's doing??o_O
    M.
     
  5. Tamara

    Tamara

    2
    0
    May 2, 2017
    Thanks so much to all responders. I am attaching a copy of the specs for the mosfet and have circled the specifics of theversion we are using. Also included is a truly pathetic diagram of how we have this all hooked up.....Hopefully you'll be able to decipher what I was trying to illustrate. As previously stated, the housing for all this is 3"x2"x1". Again......everything is working exactly as we had hoped for the magic prop....though we may have gone about it all bassackwards. Our biggest concern is whether or not we are going to harm the mosfet by powering it with a 6v battery rather than with the recommended 3v-5v.
    mosfet specs and project diagram.jpg version we are using. Also included is a truly pathetic diagram of how we have this all hooked up.....Hopefully you'll be able to decipher what I was trying to illustrate. As previously stated, the housing for all this is 3"x2"x1". Again......everything is working exactly as we had hoped for the magic prop....though we may have gone about it all bassackwards. Our biggest concern is whether or not we are going to harm the mosfet by powering it with a 6v battery rather than with the recommended 3v-5v.
     
  6. BobK

    BobK

    7,673
    1,684
    Jan 5, 2010
    You are treating this like it is a relay. It is not. The receiver is designed to output it's input voltage directly to the load, not by using a separate battery as you show. Since the receiver outputs the same voltage that is it powered by, and it must be powered by 3-5V, you cannot directly run the motor from the output.

    The first thing you should do is top giving 6V to something rated to run on 3-5V. It has probably survived because the difference is not that great, but who knows.

    After you have provided the receiver with 3 to 5V you have to come up with a way to run your 1.5V motor from 3-5V power. If you use 2AA cells, you could get it down to nearly 1.5V by using 2 diodes in series between the output and your motor. Or you could use an external relay and a 1.5V battery for the motor, wired much like you have your non-relay output wired now. The receiver board would power the coil of the relay and the 1.5V battery would power the motor.

    Bob
     
  7. Audioguru

    Audioguru

    2,726
    614
    Sep 24, 2016
    You show a box instead of a Mosfet symbol. Your box has no part number but all Mosfets have a part number. Your box has 4 wires but all Mosfets have only 3 wires, the gate as the input, the source as the common and the drain as the output. Your box does not have these markings.
     

    Attached Files:

  8. BobK

    BobK

    7,673
    1,684
    Jan 5, 2010
    His box does not represent a MOSFET. It is a wireless receiver with an MOSFET output.

    bob
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,300
    2,737
    Jan 21, 2010
    All of them except for those with 4 wires.

    (Not that you'd want to use a dual gate mosfet here)
     
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