cnc problems

[kosacid]

i have a few problems with it, the motor is a M42SP-6TG 10ohm im running them of a 1A 12v as far as i know that is fine but im not sure, the H-bridge im using is a L293D as you can see from the heat sinks they are getting hot, i want to know if that setup is fine ?

[janoc]

i have a few problems with it, the motor is a M42SP-6TG 10ohm im running them of a 1A 12v as far as i know that is fine but im not sure, the H-bridge im using is a L293D as you can see from the heat sinks they are getting hot, i want to know if that setup is fine ?

That's not fine.

Look in the datasheet for L293D:

Output Current 1 A Per Channel (600 mA for L293D)

(emphasis mine)

It has 1.2A peak current capability, but you are using 1A full time, not peak. So no wonder it is overheating. You need a beefier driver than this. I am surprised that it didn't fry yet.

Even if it was L293 (the non-D version) which can handle 1A, that is a very poor design, leaving no safety margins at all. You should never use a part up to its maximum ratings - all it will take for it to blow up is a current spike or a temperature change.

[kosacid]

so what is the minimum for them motors i cant find no data on them

[janoc]

so what is the minimum for them motors i cant find no data on them

Well, you have measured that the motors take 1A at 12V, no? Or how did you determine that? Or what did you mean by "im running them of a 1A 12v "?

If its coils have 10\$\Omega\$ resistance as you have mentioned, then at 12V you end up drawing 1.2A when the motor is standing still.


It is a Mitsumi motor, likely a custom variant made for some printer or copy machine. The closest part seems to be their M42sp-6k:

http://www.mitsumi.co.jp/latest/Catalog/compo/motor/m42sp6k_e.html

There you can see that it is both rated for 21-26V operation and only 550mA peak current, with 8\$\Omega\$ winding resistance. And it also says that the drive method is "constant current". So you need a driver that can do this.

The L293D will not limit the current in any way and you end up either destroying the driver or the motor (or both). With L293D you could probably drive the motors from 5V max - that would give you 5V/8\$\Omega\$=0.625A current, but likely less due to the losses in the L293D itself. However that will cost you in the torque of the motor and it will still be running hot, potentially burning itself out over time.

There is a reason why chips like the Allegro A4983/A4988 stepper drivers (used in the popular Stepstick modules) have an adjustable current limit!