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Motor driving

  1. Sep 18, 2006 #1
    I have quite a monster motor for a mini-hover craft. It requires quite much power. As a motor driver, i'm using a L298. The problem is it's output limited 2A, according to datasheet, while the driving voltage can be up to 50V.
    I'm using a 12V 6A lead-acid battery.

    When I turn it on, it turns a very little angle, but not enough to beat the first bump. I wind it by hand, it starts turning like mad, I let it go for a few seconds, and the resistor connected to L298's current sensing (which was about a few ohms) gets very hot, and it stinks. Plus L298 get very very hot! I tried to lower the current by connecting a resistor that is a few megaohms, but then motor didn't work anymore.

    I came up with a solution, but i'm not sure if it's gonna work. I'm planning to connect a higher voltage battery (such as 40V) and lower the currect by connecting a huge resistor to current sensing pin. In hopes that L298 won't get so hot and motor will run.

    Do you think it's going to work?
    Any other solutions?
  2. jcsd
  3. Sep 18, 2006 #2


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    Staff: Mentor

    a) What voltage and current are the motor rated for?

    b) Drive the motor with that voltage and current.
  4. Sep 18, 2006 #3
    a coincidence?

    gulsen>> that's sounds crazy coz i just did a project where we had to reconstruct a toy hovercraft so that it can hover through a maze!!! what varsitiy you at?
    I also used the L298 and had the same problem and guess what??!! there's a SOLUTION!!!!:

    check out the L298 data sheet - there is way to configur the chip so that you can draw max 4A. the downfall to this , is that you it becomes a single channel H bridge - so you'll need one for each motor!!!

    as for the heat problem: the H bridge can withstand very high temperatures, however, you don' want to risk burning other components!!! to solve this just attach a heatsink to the H bridge - you can't believe how effective it is!!

  5. Sep 19, 2006 #4
    berkeman, if I knew the model, I'd do accordingly! So I have only trial-error. Do that didn't help much.

    LM741, it seems it's indeed a coincidence, I'm a physics undergrad in holiday and and I'm doing this for personal fun, not for any sort of robot competition. I learned to control PIC a bit, but switching LEDs are quite boring, so I decided to start a project like this.

    I already have heat-sink in L298, and already tried parallelling the outputs, but problem remains as is. L298 gets quite hot, but the problem is current sensing resistors burns! I wasn't sure heat-sink was such effective... L298 sheets says 150 C for max temperature, that is why I'm so tedious.

    Do you think higher voltage and lower current will help me about the heat problem?
  6. Sep 21, 2006 #5
    . Sorry bout late reply!! been a bit busy! you need to use very high power resitors to prevent them from going up in smoke. Find it very strange that it still gets hot with the heat sink...maybe try using some thermal paste to attach it (but this is quite expensive and im not sure to what extent it will help). As for high voltage, low current aspect - that's what we were going to do before we decided to configure the H bride. P=IV. if you decreasing your curent your heat generated should decrease...
    good luck
  7. Sep 23, 2006 #6
    So you think it's gonna work. Thanks! :) I couldn't find a high-voltage -more than 24V- battery -preferably lead-acid- yet, but I'll write the result when I get it done.

    If that white jelly-thing is called "thermal paste", it was about $5. A friend told me that it won't make a miracle -since what I need at that moment was quite a miracle!- As for the heat sink, it just decreased the rate of heating. I thought of a cooler fan, but then, it seemed to be too much adventure for a single IC :D

    My resistor was supposed to be a high power resistor, but I noticed that it's just ~5 watts! I should go find a better one...

    Thanks again!
    Last edited: Sep 23, 2006
  8. Sep 25, 2006 #7
    try it - let me know how it goes... :)
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