Can Mach3 burn my PicStep?

[Cooper]

Dear All,

I just built my PicStep and run a 280 oz-in 3V 3A Keling Step motor. When i was trying to tune my motors in Mach3 i changed these values :

Steps Per : 1500 ->2000
Velocity : 468 -> 500
Acceleration : 7.65 -> 10

Then my LMD's are burnt I am very dissapointed. So can Mach3 burn my chips? My current limiter resistors(R2 and R4) are 8K2 ohm.

Cooper

[daedalus]

Its not likely to be mach3 per se, but a combination of factors. What voltage is your power supply, and what ist the max current it can supply? Have you been using these picsteps for a while, or is this early testing? were the lmd's running quite hot before you changed the values? Do you have heatsinks on the lmds?

IIRC lmd18245 is rated 55v 3A max. That is the absolute most you can get out of them without risking destroying them, and near that power level you should be VERY careful to make sure they are properly cooled, and the power supply voltage never exceeds the rating.

[dtman2]

8K2 is less than 3A. What type of heatsinks were you running? The 18245 has internal thermal protection so I would have expected them to shut down rather than burn. It also has internal clamp diodes but a significant voltage overshoot could do these in.

[daedalus]

dtman: when they are running pretty hot, then the current sense is no longer linear, and the same sense output for 2.5A @30degC is over 3A at 150degC. The thermal shutdown temp is 155degC.

That said i suspect that you are right, and cooper may have been running it very near 55v, and just had a spike in bus voltage.

[Cooper]

Hi,

I'm running these chips at 35V power supply(can supply 10A) and my heatsinks are 40mm x 40 mm fan cooled black coated aluminium type. I'm pretty sure that my coolers have enough capacity.As i said before my current limiter resistors are 8K2.
I can not understand why they burnt. I'm not sure if 2 of them are burnt, the chip, which is near to pcb mount screw terminals, seems ok. The other one is damaged, i can visually inspect it.

Cooper

[pminmo]

If you see visual damage, something happened. Mach isn't the problem, your hardware setup is.

[Cooper]

Hi there,

I bought new LMD's My motors are 3V 3A and i suspect from "starting" current but these ic's have thermal shutdown protection. I thought it is very hard to burn these chips but they burnt easily.I will doublecheck my pcb and try again.

Cooper

[dtman2]

Why dont you try putting some transient protection across the motor leads? maybe even some 40V zeners back to back, or something more sophisticated like a tvs. I was thinking something like this http://ca.digikey.com/scripts/dksear...=46772&Site=CA

unfortunately surface mount - cant seem to find a transient supressor that they stock in an axial leaded package.