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Author Topic: Motor driver problem, do I need more capacitors?  (Read 549 times)
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I have a custom Arduino 2560 based board with 3 of these motor drivers. http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00134336.pdf

If I turn the motor full speed forward and then stop it it's fine. If I go full speed forward and then full speed in reverse it will temporarily kill the power supply (restart it). I'm using a decent 850W ATX power supply to power it. The motor is 150W so I shouldn't be exceeding it. The chip didn't feel hot to the touch.

I have a 560uF capacitor on it, would going larger help or is it fundamentally bad to send a motor in full reverse from full forward?
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is it fundamentally bad to send a motor in full reverse from full forward

Ouch, Yes. I don't think you would do that to the gearbox of your car? Full speed forwards then slam it into reverse!

Stop it, then reverse it. The capacitor is not going to store a significant amount of energy in comparison to the kinetic energy of a 150W motor!
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http://www.4qd.co.uk/fea/rev.html
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Thanks, that link helped.

Looking further at the datasheet I need 500uF per 10A. At peak I'm going to see over 10A for sure. Looks like I need to bump the size of the capacitor up a bit and make sure I'm doing a full stop first.

Haven't you ever tried a j-turn in your car. Full speed reverse, full lock of the wheel and jam into drive. Totally normal! ;-)
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Haven't you ever tried a j-turn in your car. Full speed reverse, full lock of the wheel and jam into drive. Totally normal! ;-)

Ha - no, not tried that.

But then thats fine because engine and momentum are in agreement by the time you lift your foot off the clutch.
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Lucky you didn't let the magic smoke out of the power supply supervisory circuitry .... That could well have let the magic smoke out of Everything else connected to the power supply too. It's usually the 5V source that supervises everything else, If the math behind the transformer design is right all will be fairly well controlled by controlling the 5V high current output. As to Capacitors I'd use the biggest one that fit 10KuF or .01F would not be out of line... At least on something I would build. a 10,000 uF cap isn't really very big even at 35V working voltage.

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I have a PC connected to the same power supply, Arduino and PC power up but I can't get the motor drivers to work. I think I blew out a gnd trace on there after poking around with a voltmeter.

Oh well, am finishing up a new board design.

Note to self: don't put car in reverse at highway speeds.
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