[Stickman_Dave]

Hi all.

I'm using L298's to drive my stepper motors. I'm not using the 297 chip; just sending the 4 individual line values from my I/O card in my computer directly to the 298.

I'm driving the steppers with 24V (theoretically; it's actually more like ~21V) that i get from 2 daisychained 12V car battery chargers. The 5V logic signal comes from the I/O card.

I have 4 circuits on a single board. During testing, things were fine for a while, then all of a sudden all 4 L298 chips went snap, crackle and pop, burst into flames, and blew chunks off the chip face right above the 24V pin. The sound and light show would have been quite enjoyable had it not been my own time and energy going up in flames.

All 4 chips were enabled. Only 3 were hooked to motors, and only 2 of the motors were in use. The other motor and the unconnected circuits had all the lines set to zero.

All 4 chips have big-ass heat sinks that hardly even got warm before the blow up occurred.

After a little investigating, i found that while the the wall plug I'm using has 3 pins, the ground pin is not attacked to anything. (damn my old house and various incompetent renovators!) This means that not only are the battery chargers and my computer not grounded, but the 24 volt driving voltage and the 5 V logic are probably not relative to the same ground.

Is this likely the problem? Or is it probably that the voltage I'm getting from the battery chargers is too rough or something? Is the 100nF capacitor in the circuit insufficient?

I really have no idea what's going on here. I might be able to figure it out via trial and error, but I'd really rather not blow up any more cards, ya know?

Any thoughts on this would be appreciated. Thanks in advance.

[chepot]

I pray your pc or i/o card are not damaged.

driving L298 directly with your pc will require a sophisticated program.
so far I haven't see that program around.
and if you planning to code that program by your self, i think it need quite a long time & effort.

to save time, you need a stepper motor controller, L297 is one of them and best match with your L298.

or you can build your own stepper controller using PIC/AVR/8051.
building a stepper motor is harder, but you can customize how you want to drive your L298.

[Stickman_Dave]

I pray your pc or i/o card are not damaged.

they don't seem to be, so far. Fingers remain crossed, though.

driving L298 directly with your pc will require a sophisticated program.
so far I haven't see that program around.
and if you planning to code that program by your self, i think it need quite a long time & effort.

Are there considerations I need to be aware of beyond simply sending the right bits down the 4 control lines? I've already written the program, and it's nothing too complicated. I couldn't use an off-the-shelf program anyway, as what i'm working on isn't really a CNC machine. It's a computer controlled machine for tie dying T-shirts; sort of a plotter tied in to 8 stepper motor driven pumps.

I have a lot more experience in programming than in electronics. If i can do something with software rather than hardware, I'm more comfortable with that. Thanks for the advice, though.

[chepot]

for your project, the program will be less complex.

this is the link for information how H-bridge work and control it.
http://www.cs.uiowa.edu/~jones/step/circuits.html

[jeffs555]

You will probably need much more than 100nf. If your car battery chargers are the simple transformer/rectifier chargers they will not have any filtering on the output so you will need 10,000 uF or more.

Also, if they are the typical transformer/rectifier chargers, the peak voltage of two in series will be much higher than 24 volts, possibly exceeding the exceeding the 46volt rating on the L298. You need to attach a 10,000uF cap and measure the DC voltage.

Also, do you have the protection diodes wired on the outputs as shown on the L298 data sheet?