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Im trying to power a brushless DC Motor (Tamiya 300054358) through the l298n attached to an Arduino.

The l298n is powered by an external 9V source and the logic of the l298n is powered by the Arduinos 5V, wich is also powered by the 9v.

Both components using the same ground.

The code looks good and i can successfully adjust the power-output for the motor between 6-9V.

As soon as is attach the Motor, the volage drops do somewhere around 0-1V and the motor isnt turning.

When i attach the motor directly to the power source, it runs fine, so the power should be enough. (in the original RC car its powered by an 7V battery).

I tried some smaller motors just to be sure and the problem is similar. The motor is turning, but very slowly.

I also tried to connect the batterypack instead of the extern power source just ending up with the same result.

Do you have any ideas, where the problem could be at?

Thanks in advance

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2 Answers 2

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The problem is in the H driver. You lose about 1.4 volts on each leg so your loss from the battery is about 2.8 volts. The internal driver transistors are in a darlington configuration. If the bridge were Power MOS instead of bipolar transistors your voltage would be dependent on the resistance of the MOSFETs. Typically a few tenths of a volt in total. If your 9V source is a battery you probably are not getting the 9V you are expecting.

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From an L298N datasheet:

TOTAL DC CURRENT UP TO 4 A

From motor's "datasheet":

Motor datasheet graph showing current usage up to 150 Amps

I'm no expert in electric motors and driving them, not even sure I'm novice level, but I just don't see you driving a motor anything near this current draw with this part. If by some miracle you can, it will be horribly inefficient owing to the losses associated with the voltage drops that Gil mentions.

For a motor that operates with this much current I would expect a practical h-bridge setup to have discrete mosfets, perhaps mounted to a heatsink.

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  • ah okay. So if im getting this right, i need a Mosfet witch is capable of handling 150A. So something like this? reichelt.de/… As you can see im quite new to this and im just not sure with these numbers. Thanks for your help!
    – Alex
    Jan 2, 2021 at 8:25
  • I would like to address some of this, but I really can't answer it well, less so in a comment. Probably the best thing to do is to ask about appropriate driving circuity for that motor on the electronics SE. If you want to try to ask here, it would probably be similar, but less open ended, e.g. "is there an Arduino-friendly shield/module that can handle this motor's current requirements?"; I don't know how well that will go though.
    – timemage
    Jan 2, 2021 at 13:54
  • I will just caution you that there's a lot more to it than picking a FET by datasheet where the large current shown in the datasheet is greater or equal to your motor current. That number is often a maximum current for some pulse usage scenario which may not match how you're actually trying to use the FET. And I'm sure there are other factors to consider.
    – timemage
    Jan 2, 2021 at 13:59
  • thanks for your advice! I really should try to get into these things deeper first.
    – Alex
    Jan 2, 2021 at 15:53

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