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What is the best heat transfer method

Discussion in 'General Electronics Chat' started by kinarfi, Mar 4, 2014.

  1. kinarfi

    kinarfi Well-Known Member

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    If I use the LEM, it adds the 2.5 volt to the mixer that has to be compensated for by the LM317. The Lem starts at 2.5 and adds or subtracts .0125 volts per amp, depending on which direction the current flows.
    OK, I toasted another PFET today, I have not put the totems on the Pfets yet. Can you explain why I'm frying the PFETS, I don' think the current is whats killing them, I killed one with power supply and another on the vehicle, the Nfet survived, the 30 amp fuse did not. I plan to put the totems on tomorrow. If I can understand what's going on, it will probably explain what I've been doing wrong for a couple years.
     

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  2. ronv

    ronv Well-Known Member Most Helpful Member

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    Hmm. I couldn't get things going. I think it's because we have different pots and stuff.
    I'm still confused. I think I understand the hall tells you how far you have turned the steering wheel, but something needs to tell you where the wheels are pointing.
    I played with how I thought it worked, assuming FB told you where the wheels were pointing.
    I suspect the fets are blowing because at some time the top and bottom fets on the same side of the H are on.
    The source of the PFET goes to +14, not the drain like your asc... It will then turn on when the gate is low. The NFET will turn on when the gate is high.
     

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  3. kinarfi

    kinarfi Well-Known Member

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    Try this explanation, top of steering wheel is moved to 2:00 and hall senses the torque and drives the mechanics toward 2:00 and as it gets there and the torque is relieved, the hall returns to 0 (5.2 volts center)
    Pote. lib has one pot changed.
    I still don't see what killing my fets, guess I'll just put the totem in and see what happens.

    On my last posted .asc, there are 3 halls, you can only use one at a time, the first hall (Hall) starts at 0(5.2), goes down, back to 0, then up and back to 0, the next (Hall 2) is short duration, the third (Hall 3) has a long 0 time in the middle so current can drop to 0 before P2 goes high.

    EDIT
    THIS IS THE POT I USE copied from my Pote.lib
    .SUBCKT pot10t 1 2 3
    .param w=limit(SET,1m,9.99)
    R0 1 3 {Rt*(10-w)/10}
    R1 3 2 {Rt*(w)/10}
    .ENDS

    It seems to me, now, that I changed this because this wasn't working the way I thought it should, the following is the stock version
    *.SUBCKT pot10t 1 2 3
    *.param w=limit(set,1m,9.99)
    *R0 1 3 {Rt*(1-0.1*w)}
    *R1 3 2 {Rt*0.1*(w)}
    *.ENDS
     

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    Last edited: Mar 27, 2014
  4. dave

    Dave New Member

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  5. ronv

    ronv Well-Known Member Most Helpful Member

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    OK, I'm starting to get it. So FB is like something to limit the current to a safe level?
     
  6. kinarfi

    kinarfi Well-Known Member

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    Spent the morning tweeking this, the hall input goes from min to max as if turning the steering wheel from hard left to hard right.
    If I am careful in my set up, putting enough dead band in the middle, do you see any problems with 2 drivers, one for P and one for N

    It's interesting how the current lags so far behind the FETS, that's why in one of my sims, I had such a long time at 0, 5.2, input
     

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  7. ronv

    ronv Well-Known Member Most Helpful Member

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    Hi.
    So here is rev 1. I got to thinking about just plugging in a voltage where you had a regulator. Since I don't have a 7810 I used a 317, and sure enough now it needs a power safe circuit like you had in your original. So I added that. Since I think FB is some kind of current limit I stuck in a current limit circuit. It triggers at about 18 amps but is easy to change if more or less is needed. Hope this is correct. The pressure sensitive hall is a neat idea. Do you have a link?
    Anyway, I hope you have a scope.
    I didn't notice any current lag, but I don't have FB.

    Edit
    Maybe in a real early one it was because power on reset was active?
    Edit 2
    Notice I made the cap at the output of the regulator smaller. That's because I was to lazy to rewrite your plw to wait for por. So If you want the big cap after the regulator you might need to make por longer
     

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    Last edited: Mar 27, 2014
  8. kinarfi

    kinarfi Well-Known Member

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    POR??? I looked at your drawing and I like and will use your current limit,
    The lag probably comes from the motor being put in aa 136uH with a 0.0791 parallel resistance, you have been using 1 ohm parallel.
    I posted the data sheet for the LEM current transducer, FB, in post 121.
    My LM7810 is actually a LM7808 or LM7812 and I went into regulators.lib and changed the voltage.
     

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  9. ronv

    ronv Well-Known Member Most Helpful Member

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    Well it's not Power on reset, more like a delay. Should probably add a zener and make it a voltage above 9 volt circuit.
    Yea, I saw the low resistance. That must be the locked rotor resistance? I'm hoping the inductance is much higher.
    Yes I saw that link, just didn't know what it's use was in the circuit. I guessed it was some sort of overcurrent protection.
    I was looking for a link to the hall. There are a lot of applications that could use it. The only thing similar that I have used is pressure sensitive resistors.
     
  10. kinarfi

    kinarfi Well-Known Member

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    Oh yea, forgot to answer the link question, It's home brew, It's similar to a throttle position indicator, but instead of direct coupling, it has a bearing on an arm that is spring loaded against stop that moves up and down a shaft and returns center with no force applied. The hall part of it is similar to an electric motor scooter's hand throttle, except the throttle has ~3/4" travel and this has ~3/16, I ruined the original, rated at 3 volt and I tested it at 10 so I had to make some that worked because I couldn't get another.
    So, no link, maybe I can get a photo for ya.
    I spent some time and brain cells to get those numbers (.0791 & 136uH) see up loads
    Question I used 60Hz for this testing (sine wave), If I try it again with a higher frequency square wave, does the math change?
    here's a link to the motor http://banebots.com/pc/MOTOR-BRUSH/M4-R0062-12
    It's a way earlier thread of mine.
     

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    Last edited: Mar 28, 2014
  11. kinarfi

    kinarfi Well-Known Member

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    AM I looking for trouble by limiting my current from a PWM circuit with another PWM circuit? they both have the same triangle generator involved.
     

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  12. kinarfi

    kinarfi Well-Known Member

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    Changed a few things, a bunch things
     

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