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What's the difference controlling a 180v PMDC motor to controlling a 12v PMDC motor?

Discussion in 'General Electronics Chat' started by bigal_scorpio, Feb 3, 2015.

  1. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Ron, Yes its a 3 pin connector as is the one on the bottom right that has the legend Inc/Start.

    Al
     
  2. ronv

    ronv Well-Known Member Most Helpful Member

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    Can you find a part number on the other ICs?
     
  3. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Ron, which other ICs?

    Al
     
  4. dave

    Dave New Member

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  5. ronv

    ronv Well-Known Member Most Helpful Member

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    The ones with the yellow line.
     

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  6. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Ron, the very top two 4 legged ones are EL817c 334 that google as opto isolators or photo couplers. All the others are on post #40.

    Should I try a pot across the speed pins and if so which way? The centre pin is at 0v with the outer two at about 0.6v.

    Al
     
  7. ronv

    ronv Well-Known Member Most Helpful Member

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    Sorry, I missed that one. :oops:
    Strange, I don't see a driver IC.
    I'm kind of out of ideas. If I remember correctly you said there were up down buttons for speed, not a pot.
    Maybe 4pyros has some ideas.
    Be careful working on the board. I think the whole thing may be floating at line voltage.
     
  8. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Ron, I assumed that the Megawin IC was the driver (programmable) on the control board and if the other board has a driver it would be the un-named IC which is also programmable, maybe a PIC or Arduino, both have a memory IC beside them so its a safe bet that they are microcontrollers and surely one of them has to be dedicated to driving the motor?

    Al
     
  9. ronv

    ronv Well-Known Member Most Helpful Member

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    Your probably right. The problem is understanding how they talk to each other, then to modify that process. Hard to do I think.
     
  10. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Ron, so failing any workable means of using the original board/s what is the best way of doing the job?

    I did think at first it would be easy but every time I think I have the solution there is a problem.

    For a start I intended just to make a similar circuit to the one posted earlier in the thread but then I realised I would not get any soft start to speak of. So next I thought of using a microcontroller and that does seem to get over most of the obstacles, soft start, A to D conversion from the speed pot and even a number of fixed speeds if I wanted them. Then I began to think that the motor has a largish flywheel and would tend to run on when I turn off, so what about braking?

    Thats where I am stumped with how the original board brakes the motor. With the setup and parts as they are how can the circuit accomplish braking?

    Can braking be done without some kind of H-Bridge setup to short the motor terminals?

    Any thoughts? Al
     
  11. ronv

    ronv Well-Known Member Most Helpful Member

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    Let me see what I can come up with tonight.
    $20 - $25 ok?
     
  12. bigal_scorpio

    bigal_scorpio Active Member

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    Should be ok mate, saying that I may have some or all of the parts even if it means cannibalising an old project. ;)

    Al
     
  13. ronv

    ronv Well-Known Member Most Helpful Member

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  14. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Ron, I'm having problems getting that one. Which characteristic of it is important? I may be able to source something similar if I know?

    Thanks, Al
     
  15. ronv

    ronv Well-Known Member Most Helpful Member

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    It is just a fast opto coupler and FET driver in one package. Pretty fancy. :D
    Let's check one more thing. What is the other part on the heat sink. I was thinking it was a diode, but it may be the driver.
     
  16. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Ron, The silkscreen says D1 and it does have only two legs so I assumed a fast diode but the markings on it come up blank in google NFC25G 560.

    I even tried transposing the 5s with Ss but no joy!

    Al
     
  17. bigal_scorpio

    bigal_scorpio Active Member

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    Hi again ron,

    I just found some MOSFET Driver ICs in my parts! I have some MAX626, 627 and 628's and also some MAX4426 and 4429's. Hope they are useful.

    PS just wondered would ramping down the PWM before off, have a similar slowing effect as shorting the motor? I mean like a reverse soft start.

    Al
     
  18. ronv

    ronv Well-Known Member Most Helpful Member

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    We can make one of those work with one of the opto couplers.
    The switch like in post 22 might be the easiest for a brake. It could also serve as the on off switch with one more set of contacts. Or maybe a relay.
    It might be a good idea to have some resistance in the brake circuit. Lets think about that one.
    Do you by any chance have a couple of little 12 or 15 volt supplies in your parts bin?
     
  19. bigal_scorpio

    bigal_scorpio Active Member

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    Hi mate, Plenty of those!

    Al

    BTW been tampering with the controls and the speed 3 pin connector does change the speed with ANY pot across it but only at full scale either way and then the speed goes up as it would when holding the +speed button down, and same full scale turn starts the motor slowing, so I am tending to think its just a spare connector for a different but still button controlled machine. The pot certainly seems to act like a switch anyway.

    Edit: it is a switch. Touching centre pin to either side momentarily changes the speed by .1kph on the display so the pot idea is off! doh!
    Also I think the brake is essential. With all the load on a treadmill it stops nearly instantly but in the outside world this beast takes about 30 seconds to spin down from full (or full on the controller anyway). double doh!! Al ;)
     
    Last edited: Feb 12, 2015
  20. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Ron, Just did a brake experiment with some resistors. You were spot on that it would need some mate! From full speed a 5w 10r ceramic judders and knocks the motor to a halt in about a second. After more cautious experimenting I think the value needs to be about 50r and a good few watts, maybe 10 or more.

    Anyway its a bit less for you to think about mate, at least the braking resistance is sorted roughly.

    Al
     
  21. ronv

    ronv Well-Known Member Most Helpful Member

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    Hi Al,

    You can always steal the element out of your wife's hair dryer. :D

    I almost had a circuit drawn up, but I didn't save often. :banghead:

    Tomorrow is another day. I think we are close now.
     

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