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Topic: DC motors power supply (Read 648 times) previous topic - next topic

Sajuuk

Hello,
I recently bought a Tamiya 70097 gearbox and I'm trying to build a small line following robot.
As a driver for the motors I used a L298. The motors are rated at max. 3V.

I am using an LM317T to power the motors at 3V and it's working fine, except for the fact that the LM317T
gets extremely hot even with a small heatsink on it(can't keep my fingers on it!!).
The L298 has a bigger heatsink and it's fine.

As a power source I am using 6 AAA (1.5V) batteries connected to the LM317T and then to the L298's motor Vin.

Is there a way to increase the maximum 1,5 A limit of the LM317T or is there another voltage regulator IC that delivers more than 1.5A ?
Should I use a MOSFET? If yes, how ? I never used MOSFETs before.

Thank you.

James C4S

Why not just use two AA, of the six, to power the motors?
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

dc42

The L298N has a voltage drop of between 1.8 and 3.2 volts @ 1A, so you're going to need more than 3V drive to the L298N motor supply anyway. There's not much point in using a regulator for the motor supply. I would use 3 or 4 AA cells and no regulator to provide power for the motors, and a separate supply for the Arduino.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Sajuuk


The L298N has a voltage drop of between 1.8 and 3.2 volts @ 1A, so you're going to need more than 3V drive to the L298N motor supply anyway. There's not much point in using a regulator for the motor supply. I would use 3 or 4 AA cells and no regulator to provide power for the motors, and a separate supply for the Arduino.


Doesn't the L298 gets it's power from logic 5V supply?
As far as I know, the L298 does not draw power from the motors Vin. I measured the Vout for all outputs and I get 3.10 - 3.20  V (@ 3.2 ~ 3.3V input) so as far as the measurement went I didn't notice any voltage drop.
So... is there something that I'm missing ?
I have a separate 9V battery to power the Arduino.
My point to using a 3V regulator is to not kill the motors ahead of their time... at least that made sense for me when I chose this path.

@James C4S: using only 2xAA is not a viabile option because the 2 batteries don't provide the necessary current to drive the motors... (tried this option:D )

James C4S


@James C4S: using only 2xAA is not a viabile option because the 2 batteries don't provide the necessary current to drive the motors... (tried this option:D )


Batteries in series do not provide more current capacity, batteries in parallel do.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

dc42

#5
May 22, 2012, 08:26 pm Last Edit: May 22, 2012, 08:28 pm by dc42 Reason: 1

I measured the Vout for all outputs and I get 3.10 - 3.20  V (@ 3.2 ~ 3.3V input) so as far as the measurement went I didn't notice any voltage drop.
So... is there something that I'm missing ?


You must have been measuring the output with little or no load. Try measuring the output with the motor connected, and measure it directly across the motor terminals (i.e. between the two H-bridge outputs).

Running a motor above its nominal voltage under light load will not harm it. What you need to avoid is prolonged running with the motor stalled or under heavy load, because this will burn out the motor or the H-bridge.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Sajuuk


You must have been measuring the output with little or no load. Try measuring the output with the motor connected, and measure it directly across the motor terminals (i.e. between the two H-bridge outputs).

Running a motor above its nominal voltage under light load will not harm it. What you need to avoid is prolonged running with the motor stalled or under heavy load, because this will burn out the motor or the H-bridge.


You were right, the measurement was made with no load. I measured acros output 2 and 3 (the ones that go to the first motor...) I got 1.6V with the voltage regulator....
I used 4xAA batteries and got 2.6 V on the motors. With no load the batteries showed 5.6V (guess they're a little used ?).

If the L298 has a 1.8 to 3.2V drop... isn't that going to deliver between 2.8 and 4.2V to the motors ? While 2.8 is acceptable.. 4.2 does not make me verry comfortable...
By using 4.5V I get the same 1.6V on the motors... So ... this means I get 2.8 - 3V drop on L298?

I should've paid more attention to the voltmeter... :(

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