[gavztheouch]

I have been running a small cnc router for 6 month as part of a prototyping business. The machine has really only been running maybe 40 hours in total. So far I have blown 3 stepper drives. The problem seems to be the mosfets are blown in all cases. Are there any simple tests I can make on my system to hopefully remedy the situation.

[ger21]

What kind of drives?

[gavztheouch]

Hi Gerry

This was one of the drives,

Motion Control Products | Stepper Drivers | MSD542 Microstepping Driver

The other two were similar from a different manufacturer. These where supposed to have mosfets rated for a higher voltage.

Im using a 24v supply.

Steppers are wired in parallel

[p38nut]

Hi Gerry

This was one of the drives,

Motion Control Products | Stepper Drivers | MSD542 Microstepping Driver

The other two were similar from a different manufacturer. These where supposed to have mosfets rated for a higher voltage.

Im using a 24v supply.

Steppers are wired in parallel

What do you mean by "Steppers are wired in parallel"?

[Larken]

Ive opened one of those drives up, and they use 55 volt mosfets , (close to the limit) It uses P-channels for the upper and N for the lower, that way you don't need a driver chip to save money.
Which mosfets blow ? Do you have part #s ?

BTW, are you running short power wires to the drive ?

And do you have an Estop relay interupting the DC power ?

[gavztheouch]

What do you mean by "Steppers are wired in parallel"?

Sorry im going to have to check my wiring again but I was referring to how my coils are wired in the motors. I have 8 wires motors, so they can be wired in parallel, series, or half coil.

Ive opened one of those drives up, and they use 55 volt mosfets , (close to the limit)

Correct, the other suppliers stepper drivers have much higher rated mosfets. They are using roughly the same board but the beefed up mosfets was one of their main chages.

What would be causing mosfets to blow?

Would measuring the resistance of the coils tell me anything usefull?

[Larken]

What would be causing mosfets to blow?

Are you running short power wires to the drive ?

And do you have an Estop relay interupting the DC power ?

What is the resistance of the parallel windings

[gavztheouch]

Are you running short power wires to the drive ?

Drive power wires are about 600mm long, I didn't give much thought to the drive power wires and they are a mismatch of different wires I had lying around the shop. Some are quite thin.

And do you have an Estop relay interupting the DC power ?

Nope

What is the resistance of the parallel windings

6 ohms
5.8 ohms
5.5 ohms
5.7 ohms
5.6 ohms
5.5 ohms

[Larken]

600 mm is much too long. Download Gecko's stepper manual, or mine (Viper) and the longest you should run wires is 10" (250mm) without adding a 470-1000 uF capacitor at the drive. The long wires act as an inductor and allow large voltage spikes to the drive.

5-6 Ohms in parallel .. Are you sure ? I would say toss that motor and get something with much lower inductance.

Its possible your motors inductance is so high the chopper circuit can't even work !

[leorme]

I have been running a small cnc router for 6 month as part of a prototyping business. The machine has really only been running maybe 40 hours in total. So far I have blown 3 stepper drives. The problem seems to be the mosfets are blown in all cases. Are there any simple tests I can make on my system to hopefully remedy the situation.

after you repair the unit(change the mosfets n-channel)must be the same impedance for all ok)install and adjust the amp.turn the compensate pot ccw all,them back 1and half you gone a hear the servo noise(vibration),adj the signal gain to 595,ok and the balance to cero,do this to all the amps....good luck

[James Newton]

Did the manufacturer not support it?

I guess they can't afford to if the quality is that low...

Why not switch to a better quality driver? You might pay more, but you will only pay once.