Connect with us

Hall effect with 5 amp draw

Discussion in 'General Electronics Discussion' started by Steve Kaz, Mar 30, 2017.

Scroll to continue with content
  1. Steve Kaz

    Steve Kaz

    10
    0
    Mar 30, 2017
    Hello all! I'm new to this forum and like to say hi and thanks in advance.

    Project details can't be disclosed in full but the circuit is pretty simple.

    I am looking for help designing a circuit that will use a pickup sensor like a reed or hall effect. The trigger is going to be a wheel that can be outfitted with a magnet or can be iron. Space, size and cost will determine what is best to use.

    I have a steady 12V DC supply coming in. I want to use a trigger type sensor that will act as a switch which will stay closed as long as the trigger is in proximity. I was thinking of using a transistor to handle the needed 12VDC 5amp max draw. What I need help with is selecting the correct components that will work together. The ground wire will be the side being switched on and off with the primary hot all the time. I know enough to get me in trouble which is why I thought I'd save the time and money and ask for help.

    I may have up to 16 sensors so if a 16 channel IC is available I can source that for prototypes from the start. If not, I can build the array with transistors to handle my needs. When the trigger is not in proximity the circuit needs to be full open. The size and length of the trigger wheel magnet will determine the duration of how long it's open and closed for.

    The draw will be a 12v 5 amp max motor. The cycle time will vary from 1 second to 5 seconds. Normal draw is 2.5 amps but the max pull may hit 4 amps at startup. So if the circuit can handle 5 amps I think that should be enough.

    I'm sorry I can't be more specific about the project. I'm a mechanical engineer and this is for a product we are working on for a customer.
     
    Last edited by a moderator: Mar 30, 2017
  2. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    If you want a compact solution there is the Honeywell SS400 series proximity sensors, these come in three styles, uni-polar, bi-polar and latch/unlatch types.
    Use a Mosfet on the output to increase the current range to what you need.
    But if really needing to switch from +ve then you may need PNP output devices. although you have an inversion with the Mosfets.
    M.
     
    Steve Kaz likes this.
  3. Steve Kaz

    Steve Kaz

    10
    0
    Mar 30, 2017


    Thanks for the reply.

    What I need help with is choosing the correct parts for the circuit. I know enough about how the circuit will work but not confident I will order the proper supplies. I've only used hall on small loads like small relays and LEDs with small transistors. I would think going to a high load 5 amp draw would require bigger more robust resistors. Will the hall have enough current to satisfy the large mosfet? Also, should a resistor be placed on the motor leads to help stop the current dead in it's tracks when the mosfet opens? Should I care about any possible feed back from the motor as stops spinning?
     
    Last edited by a moderator: Mar 30, 2017
  4. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    It is very hard to recommend components for a system without know anything apart from a few scant details,
    For e.g. the mechanics and the environment they are in will probably decide the physical nature of them.
    AC or DC motor? Size? What is its exact function?
    .Is the unit for use in a domestic or industrial environment?
    One-Off or Many?
    If for a customer, does the unit have to conform to NFPA79 etc?
    M.
     
  5. Steve Kaz

    Steve Kaz

    10
    0
    Mar 30, 2017

    It's a counter for small parts. Max temp would be 120F with some vibration. After looking at the sketch more, it's not a motor it's a solenoid that will open and close a door. A spring will keep it shut and when the trigger will activate the sensor sending current to the solenoid in turn opening the door. The coil specs on the solenoid says normal operating amp draw is 2.5 amps but circuit should be designed to handle double. It's a 12V DC solenoid actuator none latching.

    Hope that helps some.. right now this is a prototype some I'm not concerned with anything other than making it work..We can cross the legal bridge if that time comes later.
     
  6. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    Well are the Honeywell items OK or do you need some other type?
    What is the reason behind :-
    "The ground wire will be the side being switched on and off with the primary hot all the time".
    Any particular reason?
    You say 16 sensors, What and how many trigger the solenoid?
    There are also magnetic latching solenoids that only require a pulse and have 'memory' when off.
    M.
     
  7. Steve Kaz

    Steve Kaz

    10
    0
    Mar 30, 2017
    I can't have a latch style. When all power is off I need to be sure all latches are closed. The ground is being used is the customers request. Alot of time we build things which are only a fraction of the project so I don't ask questions anymore. The Honeywell is great small and easy to use for this application. As for the trigger wheel, it may have up to 16 sensors but on one trigger point is being used. It will rotate and trigger one sensor at a time. The trigger will be unique to it's purpose to allow for different open and close times depending on the magnet length.
     
  8. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    I am still a little confused as to your definition of the ground being switched on/off?
    The SS400 series are NPN output and are termed sink function switching as opposed to source (PNP).
    But these cannot switch the solenoid direct anyway, they need a Mosfet driver.
    Maybe a simple sketch on the nature of the switching you have in mind without disclosing it all.
    M.
     
  9. Steve Kaz

    Steve Kaz

    10
    0
    Mar 30, 2017
    Sorry for the chicken scratch. This is the basics of the design.

    1490902584705777613906.jpg
     
  10. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    The R will go to the base = ~10K. Although if using Mosfet it will be G (Gate) instead of B.
    Otherwise it looks OK in principle.
    M.
     
  11. davenn

    davenn Moderator

    13,808
    1,943
    Sep 5, 2009
    not sure what you think that resistor will do ... nothing that I can see
    ohhh btw its Hall effect not halls

    you need a reverse diode across the coil of the relay .... that is with pointy end up towards supply
     
    Minder likes this.
  12. davenn

    davenn Moderator

    13,808
    1,943
    Sep 5, 2009
    that's what I was thinking it should do for a bit of biasing :)
     
  13. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    Ensure you get the Bipolar version of the sensors, in that case the magnet polarity won't matter.
    M.
     
  14. Steve Kaz

    Steve Kaz

    10
    0
    Mar 30, 2017
    What size diode do you suggest?
     
  15. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    In400x series, I keep 1N4007 as they cover just about all eventualities for the range.
    Although a 1amp rectifier, they take a 30a momentary pulse.
    M.
     
    davenn likes this.
  16. Steve Kaz

    Steve Kaz

    10
    0
    Mar 30, 2017
    Well I take it that the resistor is there to knock the 12v down before going into the mosfet? All the mosfets I see go from 5v with a jump to 600v. And if that's the case, the hall effect will need to match the supply voltage of the MOSFET. I'm very confused
     
  17. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    The resistor is also the load for the open collector SS400 NPN output.
    The Mosfet is voltage controlled, as opposed to a bi-polar transistor, which is a current switched device. so it just requires voltage bias, the gate voltage switches from 12v to 0v when the SS400 operates.
    That may make the logic opposite than you want.
    M.
     
  18. Steve Kaz

    Steve Kaz

    10
    0
    Mar 30, 2017
    Thanks for the help. This is my order for the day. I hope I got it right!??
     

    Attached Files:

  19. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    If you find you have to invert the signal, you could use a 2n7000 between the SS400 and the Power mosfet.
    I see you went with a BJT instead of Mosfet?
    My 1st choice for supplier is Digikey.
    M.
     
  20. Steve Kaz

    Steve Kaz

    10
    0
    Mar 30, 2017
    Not knowing I did go with the BJT..I had a ton in my cart and everything was on back order. I must have deleted the wrong ones. That said, will the BJT work for this application with those other components I ordered? I can't believe I must have looked at 100 MOSFETS today!
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-