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Motor Shield Overheated
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Motor Shield Overheated

by Trackonaut on Wed Jun 10, 2009 10:34 pm

Hey Lady Ada,
I know for fact that I have overpowered my shield with a 24v Stepper that programs at 1amp and peaks at 2amps. I heard a loud crackle, turned off the arduino decimilia immediately and found that the shields LED to be blinking. I now realize that stacking driver chips will allow more current flow preventing this from happening again. However, I'd like to know if this board is still useable and if I replace the chip with a new one, stacked, will it still work? The driver chip itself was smoking and has a mildly melted core. Everything else seems to look fine.

I have three questions:
1. What does the blinking LED mean?
2. Will replacing the chip do the trick?
3. Can I stack(piggy) 3 chips high (instead of just 2) on either side so that everything runs cool?

-The Trackonaut

(Because I'm in a rush to finish this, I have ordered another board via adafruit (nextday air). Can you make sure my order makes it out tomorrow?)
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Re: Motor Shield Overheated

by adafruit on Thu Jun 11, 2009 12:08 am

whee!
yup the chips have mild temperature protection but if you -really- overdo it they'll let'cha!
you might not be able to just solder new chips on top because the transistors inside have fused
24V 2Amp steppers is a hell of a lot to ask these chips to do. you -may- want to check the more-hardcore steppers from pololu
for shipping help email support@adafruit

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Re: Motor Shield Overheated

by adafruit_support_bill on Thu Jun 11, 2009 6:56 am

As the Lady says, that is more motor than the shield was designed for. But if you are in a rush (school project?) and don't have time to start over with a different controller, there are a few things you can do to squeeze more out of it. Just understand that the device will probably have a limited lifetime.

* Replace the L293D's with SN754410's. These can handle roughly twice the current.
* Both types of chip can be piggy-backed to handle more current. You can even mix and match. (e.g. a SN754410 on top of a L293D)
* Add some heat-sinking to the chips to help dissipate the heat.

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Re: Motor Shield Overheated

by Trackonaut on Thu Jun 11, 2009 2:15 pm

Thanks for the quick reply friends!

I thought it wasn't confirmed that the SN754410's were compatible unless hacked or with the addition of a transistor. If it works without being hacked or knowledge of how and where to add the transistor, I'd go with those forsure, otherwise, I think i'll triple stack L293D's... Thoughts?

-The Trackonaut
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Re: Motor Shield Overheated

by adafruit_support_bill on Thu Jun 11, 2009 4:09 pm

The SN754410's are plug compatible. I run them on two of my motor shields with no problems. In theory, they might benefit from some additional diode protection against kickback, but I haven't had a problem with the device as is.

Two devices stacked will nearly double your current handling ability. Three will probably give you somewhat less than 3x. The more you stack, the less effective the heat dissipation will be.

The stock shield dissipates heat to the board via the innermost 4 pins on the chip. You can get heat sinks that glue or clip to the chip to improve dissipation. The clip style have an aluminum tab that goes under the chip, so if you stack them, you can sink some heat from the chip underneath too. A dab of thermal grease on all contact surfaces will help.

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Re: Motor Shield Overheated

by adafruit on Thu Jun 11, 2009 4:58 pm

the SN75's are -basically the same- except that they are not guaranteed to protect against kickback. /for the most part/ i dont think this has been a problem. however, id rather not have 'em in the kit cause even though they are cheaper i'd rather provide a 'guaranteed' thing :)

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Please be positive and constructive with your questions and comments.