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Topic: Controlling high current DC motor l298 (Read 3041 times) previous topic - next topic


I'm in quite a pickle. Yesterday I got my 12V DC motor for my project and as in many cases there was no current characteristics on the page.

After quick testing with my previously ordered (2A) power supply and l298n module I discovered that the motor on lowest speed takes around 2A, on no load full speed 4.2A and in some load on full speed around 7A. I ran this setup for 2 minutes and the l298 got a little warm, not super hot and power supply was cold (I will do more testing today, as I have thermocouple).

The use case is that the motor will run for 30 sec max per 8 hours.

What I'm considering is to ditch the motor controller and use 10A relays module and computer power supply.

My questions:
Could I use the setup with 2A power and l298 (I like it because of its 5V robust regulator) if it will only work for 2 minutes per day, if no
I should be able to remove the fan from the PSU if it's load will be so small?

If that's not viable what is a good setup (that doesn't cost more than 10$, I already have the PSU on hand and the relay module costs around 2$).


Jun 21, 2017, 11:30 am Last Edit: Jun 21, 2017, 11:34 am by septillion
I would not bed on it the slightest. If the no load current is already twice the rated current of the supply you may price yourself happy it even survived now...

And because it's DC a relay might even be harder then mosfets. Do you need both directions? If so, I would or grab a suitable H-bridge or make a hybrid. That is, use a single n-channel mosfet to drive it and a relay to change the motor polarity. This way you do the real switching with the mosfet and you can switch the relay when there is no current which will prevent arcing / welding of the contacts. Otherwise you would need a pretty beefy relay to switch. A 10A DC relay will just weld itself together with 10A DC.

And yes, although I would not call 10A @ 12V really low. What I would do is switch the PSU with the Arduino as well (just use green PSU wire) and power the Arduino from the 5V standby. The 5V standby will have power even if the PSU is off and fan is not running. That way you can turn on the supply if you want to run the motor and only have a fan then, just to be sure.
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Songle SRD-05VDC-SL-C is rated 10A @ 28VDC, that should handle 10A, 12V.

When looking for DC driver motors that don't cost as much as the whole project I only find 4A ones, I don't need PWM but it'd be nice, and I need both directions.

only this one seems to be capable and not cost a leg, but still I'd rather use relays.

I have 1N4001 (I have 1s only atm, but will replace them with 7 later) should be enough for flyback managment, but I'm not too sure how to install flyback diodes when you need both directions


l298 (I like it because of its 5V robust regulator)
You mean the Vss regulator?- you're still limited to 7V there


I have 1N4001 (I have 1s only atm, but will replace them with 7 later) should be enough for flyback managment, but I'm not too sure how to install flyback diodes when you need both directions
Since you mention speeds, are you PWMing the motor? All of the 1N400X series of diodes have an average forward current limit of 1.0A, too little to be used for PWMing this motor. Increasing the number (4001 -> 4007) just changes the reverse voltage spec, all the other ones (that you care about at least) are identical.

For an H-bridge circuit, you need flyback diodes arranged in parallel with the transistors. MOSFET-based bridges have it easy, since most MOSFETs have a body diode already built in as a side-effect of their construction. A pleasantly useful application for a parasitic structure.


78M05 is up to 35V regulator.

The more I research about the DC motors the less I know. First the flyback, now the inrush.

About inrush current, from reading I should get MOV/NTC/VDR but there isn't too much concrete info about usefullnes etc.

My current plan for setup:

No PWM. Both directions

PC PSU, 5VSB for arduino, NPN transistor for PS_ON, 12V for DC motor, 5V for relay module (2 SPDT, NC1-2 GND, COM motor cables, NO1-2 12V), 1N400X diodes as flyback and ?VRD?

Where should I put the diodes? If I should get VRD, where should I put it, what specs?



Four diodes just like for any H-bridge across every switch to stop arcing.
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