[student1616]

Hello all,
Iam a satisfied user of linistepper.i made 3 boards(using posix layout) all of them worked very well.
iam using steppers of step-syn rated @1.2A
mosfets are mounted a big heat sink and are connected to board thru wires.and for power supply iam using Computer SMPS(whose 12v is rated at 20A)

the problem iam facing is,frequent burn out of mosfets.and some times motor gets very hot.and mosfets stay cool.
so isn't possible to make the mosfet part stronger? imean may be by using IRFZ44 instead of TIP122? is this gona effect the microstepping function?

and one more limitation of linistepper is,currently i can only driver motor upto 1.5A max.now i want to driver 2-2.5A motors.can i do this by shifting to IRFZ44's?

[epineh]

How big of a heatsink are you using ?

I had two drives running on a half inch block of aluminium about 8 inches square that had two CPU fans bolted to the opposite side, and this worked well, the whole lot got warm but no burn outs.

Also the IRFZ44 is a MOSFET and is a different beast to the TIP122's which are transistors.

Better to stick to the design and possibly look at bigger heatsinks or better mounting, I used the little rubber like insulators on mine and this seemed to work well. The TIP122's should be able to handle 1.2 amps without problem.

Cheers.

Russell.

[student1616]

actually my heatsink is 12''X8''x3'' thick on which 8 TIP's are mounted.
its not the heat problem is guess.
bcz heat sink stays cool even after continuous running of 4-5Hrs.motor gets little hot.but its ok.once i fix the motor on mechanicals heat will dissipate.
and i have one more doubts.is the PIC protected from the spikes generated by motor?(iam not very good at electronics).bcz my 2 pic's also got burned out.
i wonder where am i doing wrong.

mean while iam planning to build this hack too.
http://www.cnczone.com/forums/showthread.php?t=39770
its not linistepper exactly.but any drive which can do microstepping will work for me.

[James Newton]

Other than heat, connecting and disconnecting the motor leads without removing ALL power will fry power transistors and potentially other components including the PICs.

Also, don't dismiss heat as a possible cause. The fact that your heatsink doesn't get hot means absolutly nothing. It is entirely possible that your power transistors are not transferring heat to the heatsink and are therefor overheating themselves. Check the heat at the actual transistors. If they are significantly hotter, look into better isolators and heat sink goop.

The motor heating concerns me. Typically, the Linistepper will run hot, but the motors will run cool. Are you "pushing" the motors? Running more current than they are rated to take?

What mode are you running the Linistepper in? Half step will produce a little more motor heat (less controller heat) and the microstepping modes should do the opposite (hot lini, cool motor).

Can you check the waveform on any of the motor leads with a scope? If you are micorstepping and you see sharp transition instead of smooth, sine like wave, that would explain the motor heating and possibly the PIC and driver burnouts. It would indicate that some of the capacitors or resistors have failed in the analog part of the drive circuit.

Anyway, let us know how it goes?

[student1616]

i have 4 motors.2 are from step-syn and other too are local made.
the step-syn motors are rated at 1A so iam using 2-0.5 resistors in series.and the other too iam doing same.as there si nothing mentioned over them.the coil resistance from end-end is 13ohms.so for these motors are iam using same 1ohms resistance(0.5+0.5)

and i think heat sink is working ok.bcz along with insulators i used good amount of therml paste.and when i run the system with out the fan,heat sink become warm.that mean transistors are conducting the heat to heatsink.

and iam running the system at 3600 steps.:-)

and i'll try the scope.(where shld i check the wave form.imean between the coil ends or between coil end and center tap.i never used it before :-(

and say if i got the spiky waveform.which part shd i go first to modify.the small transistor(337) or the capacitors or the zeners.

[James Newton]

What voltage are you running the motors at? IOW, what is your motor power supply voltage?

1 amp at 6 Ohms (coil end to center, rather than coil end to end) is 6 volts. With a linear driver, you want the power supply to be about twice the motor supply voltage so 12v would be right. You can go as much as 3 times and get better speed, but that heats the controller. Since the lini regulates the current getting to the motor, it won't burn the motors out (assuming the Lini is working correctly).

Ok, the heat sink sounds good. But again, check the temp AT the power transistors.

Check the shape of the signal between the motor common and each of the coil ends. It may not be perfectly smooth, but if it is really spiky, then try replacing the caps AND the small transistors AND the drivers. Check the Zeners and the resistors. If the coils don't all look the same, you will know which ones to replace.