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Author Topic: Flyback diode on DC motor schematic please  (Read 3564 times)
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Hi All

I wonder if anyone could point me to a source which maps the way to wire flyback diodes on a DC motor, and on how to decide which diodes to use.

Further, given the cost of shipping, I wonder if anyone would provide me with a usefull shopping list regarding diodes which I could add to my stock of other electronic components.

Thanks
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I don't think you connected the grounds, Dave.
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Cathode to most positive part of the circuit.
Voltage rating should be about four times the voltage rating of the motor, minimum, IIRC.
For most low voltage work, a 1N4001 should do the trick
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Hi Awol

Given the DC motor may run in both directions, each wire to the motor may be the most positive as you mention.

That leads me to think I need 2 diodes, each one running from a motor wire to GND. Is this correct?
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I don't think you connected the grounds, Dave.
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Given the DC motor may run in both directions, each wire to the motor may be the most positive as you mention.
So, put the snubber on the supply.
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I probably don't understand how the flyback diodes work then, but if it is on the supply, the driver chip will be between the diode and the motor, so if a high voltage is created the motor, will the motor driver IC not get burnt out anyway?

I thought the flyback diodes were to prevent any huge voltage spikes created by the motor from toasting the IC.

Cheers
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If it is decent controller (you haven't said what you're using) it will have diodes built-in.

See here
http://www.robotroom.com/BipolarHBridge.html
for a guide to H-bridges and snubber diodes.
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Hi AWOL

Thanks for the link. That was exactly the sort of thing I was looking for.

I am currently using the SN754410NE quad half h-bridge driver to learn how to drive motors....

Looking at the schematic of outputs it looks like it has diodes...

Again, thanks for the link. I understand now that a diode has to run from each motor wire to Posative and from GND to each wire, making a total of 4 diodes per motor.
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The SN754410NE's internal diodes are NOT flyback diodes - they're incapable of sinking the required current.  You'll need to add external ones as well.
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I didn't read all the posts here, but I want to point you out to my website were I made instructions for how to run a dc motor. Here's the link: http://aksoapy29.comoj.com/dcmotorcontroller.html
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I didn't read all the posts here,
Specifically, you didn't read the bit about reversing the motor.

Interesting circuit diagram - remind me again, which is the base, the emitter and the collector?

Code:
int potpin = A0;
int val;

void setup() {}

void loop() {
val = analogRead(potpin);
val = map(val, 0, 1023, 0, 225);
analogWrite(3, val);
delay(15);
}

Don't you ever want to run the motor at full speed?
« Last Edit: May 22, 2011, 01:30:02 pm by AWOL » Logged

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