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Arduino Duemilanove with Adafruit motor shield causes piggybacked motor drivers to overheat- even with no load. Ideas?

I have an Arduino Duemilanove and an Adafruit motorshield. Both work fine, but the motors I want to run require more current than the available 0.6 amps. I tried piggybacking two more drivers on top of the existing ones, but now when I turn it on one set of chips overheats immediately. It's not a soldering error, because I've tried it with many different chip configurations and the same problem occurs. The only thing I've noticed is that the new drivers I purchased have slightly different numbers under the customary L293D- but isn't that just when and where it was made? Any ideas?

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Just try a series resistor from EACH driver to the load and see what happens. No guarantees. Paralleling, unless these things are specifically designed for it isn't likely to work.

Steve
loki17 (author)  steveastrouk5 years ago
Good idea...I'll try it. Oh, and the instructions on ladyada's website say that chips CAN be piggybacked to increase the potential current.
Yes, well, what LadyAda says ain't always right. The 293 is a bipolar design: Bipolar transistors don't current share unless forced. Sure, it might work, but then, as you've found, it might not.....

Steve
loki17 (author)  steveastrouk5 years ago
Ok, I still can't get it to work, so I guess I'll have to order some SN754410 drivers. But thanks for your advice. I appreciate it!
Out of interest, did you get chips with in-built diodes, or did you put external ones in ?????
loki17 (author)  steveastrouk5 years ago
The diodes are built in.