troubles with my stepper motors...

Discussion in 'The Projects Forum' started by kutalinelucas, Aug 22, 2011.

  1. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    Hey Guys...it was some time ago and didn't expect the same to people to be available to help...and I also thought people wouldn't want to read through 2 pages of back story...but I am sorry about that, to be honest it is a similar post, just edited according to some progression which I know is pretty cheeky.

    Do you guys know how I could go about this? with my DC motors (for example) I can run bewteen 1 and 4 on the same 12v rail (again using 2 L293D's) and start, stop, switch direction, speed...whatever I fancy without any shorting...is there any way I can get similar functionality from 5 steppers?
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Can you post a schematic of the driver part?
    If you draw more than 1A from a power supply that can provide 1A at most, then it's output voltage will drop. According to your motor datasheet it draws 0.6A. 2x0.6A = 1.2A
     
  3. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    I've attached a sketch of the driver parts for my circuit...the only thing left out is I would like pin 8 of the driver being driven by the lower power supply...I see where you are coming from, but is there any way around this? Can I get a 6v, 3A AC/DC converter?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Wait a moment - you say your adapter is 6v, yet your motors are rated for 0.6A @ 3.9v.

    You really need to post a schematic. If you are not using the chopper function, you'll be feeding too much current through your motors - AND the L293. [eta] Oops, forgot - the L293 doesn't have a chopper function. You're probably dropping between 2v and 3v across the L293; which means you'll have about 3 Watts of power dissipation in it; that is a LOT for an IC.

    Schematics are worth a thousand words; only better. It's far easier to take in a schematic quickly than a large block of text, and a properly & accurately drawn/documented schematic leaves few questions to be asked.
     
    Last edited: Aug 30, 2011
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  5. kutalinelucas

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    Nov 20, 2007
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    Fair comment. Ok, it'll probably take a while but i'll draw the circuit up now on proteus, i've just been putting it off for too long!
     
  6. SgtWookie

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    I edited my post after you'd already replied. Looks to me like you're really pushing the thermal limits of the L293 IC, particularly if you don't have it on a PCB with a large heat sink area.
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have merged the three threads.
    The post will show up in the time line.

    Bertus
     
  8. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    oh...I wouldn't even have thought of that...but i've just been switching a motor for over a minute and there was no noticible rise in the surface temp of the driver chip...I'm planning on drawing up the pCB's in the next day or so and I will fit a heat-sink over the board, as I know it will be an issue, but for now do you think it is just a case of trying to draw too much current from the supply? and if so, could I use a 3v ac/dc adapter? I have an old laptop charger that is 3a @ 19v...but will this be a little too dodgy to use on a breadboard?
     
  9. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    Sorry, completly lost you!...would a schematic help? I'm sorry, this is only the second circuit I've designed and think I may be in well over my head!
     
  10. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    As Sgt said, the power supply/motor voltages do not match, but just to know if the problem IS your power adapter, put a more powerful on the input.
    However if you are passing this current (1.2A) through the 5V regulator (is this a common 7805?), it is going to dissipate lots of energy, especially if the input voltage is much higher than 5V....make sure it's mounted on a heatsink.

    However this can't be the final solution. It's just to test if the problem is the power supply.
     
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  11. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    How are you guys so good???

    Think that may have solved it...the driver Vss power supply comes through a 5v regulator which is always hot, so I curled around some copper sheet and bolted it to the rear of the regulator, and now I know why my propeller chip burned out yesterday (which runs on 3.3v!)

    so now I have 2 motors running just fine. three seems to be pushing it but when the third is run, the other 2 hold torque, so as sgt said, the driver probablly had too much power to dissipate.

    SO...tomorrow I get a 3A AC/DC converter...just one more question (for now at least!), I believe the max output current for the v-regs is 1.5A, so can I just put two of these in parallel, on the same (new 3A; 4.5v) voltage rail?

    Thanks again guys
     
  12. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    You just put a "heatsink" on the regulator, and it worked? This would mean it went near thermal shutdown, thus lowering it's output voltage.

    I don't think they will share current equally. One regulator will always have a voltage a bit higher than the other, this will be the one where most of the current will be drawn from.
    Also, I would be worried about reverse current into one of the regulator's outputs.
    You could use two diodes at their outputs to overcome the paralleling/reverse current issue, this would also lower your output voltage a bit. Still, they wouldn't share current equally.
    Actually I never did it, so if you find matched regulators it might even work more or less.

    Why not use 1 regulator that can provide more current. Example: LM123, although this one needs at least 7.5V at the input: http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXvzvu.pdf

    There are many other options too. Especially a device in a TO-3 package may be better for you.
     
  13. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    Hey guys, I'd really appriciate a bit more advice on how I could go about powering my circuits...

    just to re-cap, I'm controlling 5 stepper motors and 4 DC motors using a propeller chip and five basic stamp chips, driven through 7 L293D H-bridge drivers.

    The stepper motors are rated at 600mA @ 4.6v, the DC motors 12v, 0.1A no-load.


    Through development, I've been using a seperate 12v wall supply again divided by two voltage regulators to provide the 4.6v and 12v voltage levels nessesary to drive the motors (plugging into pin 8 of each L293D and all sharing a common ground).

    The problem is I can only realistically run 3 steppers at a time and they have little torque...I can run all four DC motors but presumably only because I have not tested them with any attached load.

    I've found a pretty cheap variable AC/DC wall supply (http://www.maplin.co.uk/ac-dc-multi-...-226)providing 6A and I was wondering if this would be suitable for the task...

    So, this is what I could really do with some help with...

    1. if I bought the above supply, could I use two voltage regulators to divide the voltage into 12v for the DC's, and 4.6v for the steppers?

    And how would the current be divided over the two voltage drops?

    Thanks
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    Your Maplin link doesn't work; the middle of the link got chopped out and replaced with "..." - would you try again using the "Insert Link" button? (button that looks like planet Earth with chain links under it)

    [ETA]
    Never mind, I found it:
    http://www.maplin.co.uk/ac-dc-multi-voltage-6w-power-supply-226

    That's a 6W supply, not 6A. Current = Power(Watts) / Voltage, so if it's 12v out, you only get 0.5A current.

    Go fish!

    BTW, a common and inexpensive ATX-form-factor PC supply can be inexpensively converted into a "bench" supply. You being a computer person will probably have access to a number of obsolete PCs that have power supplies ripe for the plucking.
     
    Last edited: Sep 3, 2011
  15. shortbus

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    Sep 30, 2009
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  16. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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  17. SgtWookie

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    Jul 17, 2007
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    On the main page, it simply says "up to 4.0A output", so that bore more research.
    If you click on the "Specification" tab, you will see that it has a 60W rating.
    60W/15V = 4 Amperes. So, it appears that even at the highest selectable output voltage, the power supply is capable of supplying up to 4.0A output.

    That should take care of your immediate needs.
     
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