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Topic: High current draw causes 7808CT Regulator to shutdown? (Read 404 times) previous topic - next topic

zinxer

I'm using a brushed DC motor if it makes any sense :|


See the L298 datasheet (click !), Figure 6 on page 6.
At the right,a truth table is shown, telling you what happens on which levels at the controlling pins.
See the function of C = D ?

Try that.
It will save some power, as well as other problems.

Code: [Select]
void halt()

{
  digitalWrite(in1, LOW);  //right front and rear wheels
  digitalWrite(in2, LOW);

  digitalWrite(in3, LOW);  //left front and rear wheels
  digitalWrite(in4, LOW);

}


This is where "C=D", but because this only releases the dc motor, the motors still coast. i had to reverse the motors so that it would stop/brake exactly at a point of delay. I understand however that this may draw up to twice the amount of stall current. My only problem now is to find a way to bypass the 1A limiting "Io" from the L7808 as it gets really hot even with the heatsink. I also notice that my 1602LCD dims everytime it brakes, this probably shows that the Voltage regulator is struggling to supply enough current to overcome the load.
Like opening a door knob, our mind does it seamlessly. If i'm a machine, every touch and move is a response. There could only be one try, and once is all I need. AI is my biggest interest, Engineering is my passion(: -MattPrag

MAS3

Did you try to do this:
Code: [Select]

void halt()

{
  digitalWrite(in1, HIGH);  //right front and rear wheels
  digitalWrite(in2, HIGH);

  digitalWrite(in3, HIGH);  //left front and rear wheels
  digitalWrite(in4, HIGH);

}




It shouldn't matter whether you do this by setting them both HIGH or both LOW, but it won't hurt to try this, right ?
You need to have the ENable pin HIGH to have this to work.
Best is to set EN low, change in1 through in4 to whatever you need them to be, and then set EN to HIGH.
Disabling EN will set the free running of your motor.

I'd say create 2 power supplies, 1 for the motor controller, and another one for the other electronics.
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

zinxer

Did you try to do this:
Code: [Select]

void halt()

{
  digitalWrite(in1, HIGH);  //right front and rear wheels
  digitalWrite(in2, HIGH);

  digitalWrite(in3, HIGH);  //left front and rear wheels
  digitalWrite(in4, HIGH);

}




It shouldn't matter whether you do this by setting them both HIGH or both LOW, but it won't hurt to try this, right ?
You need to have the ENable pin HIGH to have this to work.
Best is to set EN low, change in1 through in4 to whatever you need them to be, and then set EN to HIGH.
Disabling EN will set the free running of your motor.

I'd say create 2 power supplies, 1 for the motor controller, and another one for the other electronics.


This is what i have tried to do to perform the brake, but it seems to still coast the motors.

Code: [Select]
void forwardbrake()    

{
  //right motors:
  digitalWrite(in1, HIGH);        
  digitalWrite(in2, HIGH);
    //left motors:
  digitalWrite(in3, HIGH);
  digitalWrite(in4, HIGH);
  digitalWrite(enA, HIGH);
  digitalWrite(enB, HIGH);
}


Anyways i have also carried out some readings on the overall circuit and here are the data i've retrieved:

No load current (booting): 0.21A
Stall current(all motors forced stop) : 0.89A
Operating current( motors running): 0.62A


The current reading was retrieved without the use of the voltage regulator. As for now, my only resort is to add a power transistor to allow more current output and remove some load off my Voltage regulator as it gets really hot very quickly. Could anyone provide any suggestions or calculation for the implementation of a power transistor onto the circuit?

Thanks everyone for the help!
-MatthewPrag
Like opening a door knob, our mind does it seamlessly. If i'm a machine, every touch and move is a response. There could only be one try, and once is all I need. AI is my biggest interest, Engineering is my passion(: -MattPrag

Isaac96

I use UnoJoy and Hoodloader for HID. No Leonardo!
Do not PM me for help.Only links to topics.

CONNECT THE GROUNDS!

zinxer

Try parallel voltage regulators.
If two identical voltage regulators were to be paralled, the regulated voltage will still differ slightly and it will cause one regulator to withstand all the load and it would shutdown followed by the other. It doesnt seem like a solution for this  :(  Will update here later if it works by including a power transistor to take off some load off the 7808reg.

-MatthewPrag
Like opening a door knob, our mind does it seamlessly. If i'm a machine, every touch and move is a response. There could only be one try, and once is all I need. AI is my biggest interest, Engineering is my passion(: -MattPrag

Isaac96

Well, some RC ESCs use parallel 7805s without any problem.
I use UnoJoy and Hoodloader for HID. No Leonardo!
Do not PM me for help.Only links to topics.

CONNECT THE GROUNDS!

zinxer

Update: realised that the Nicd battery caused the sudden shutdown through the voltage regulator. If the voltage regulator was not used, the system can be powered optimumly with direct battery. However, due to the fact that i still need it to produce 8v linear. Therefore, i have managed to use a dc to dc buck converter connected to a power supply for my project. Though there we still some doubts on why the battery paired with the regulator/buck converter would cause reboot during higher current draw situation :/
Like opening a door knob, our mind does it seamlessly. If i'm a machine, every touch and move is a response. There could only be one try, and once is all I need. AI is my biggest interest, Engineering is my passion(: -MattPrag

MAS3

You do not seem to fully understand some important properties of such batteries.
A battery has an internal resistance.
That means it has an unintentionally built in current limiter.

However, the < 1 A maximum you measured might not be enough for this to really cause that problem but that depends again on exactly what battery was used.
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

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