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Topic: Flyback diode on DC motor schematic please (Read 4 times) previous topic - next topic

AgeingHippy

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

AWOL

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
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

AgeingHippy

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?

AWOL

Quote
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.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

AgeingHippy

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

AWOL

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.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

AgeingHippy

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.

Aeturnalus

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.

AKSoapy29

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
Andrew K.

AWOL

#9
May 22, 2011, 08:19 pm Last Edit: May 22, 2011, 08:30 pm by AWOL Reason: 1
Quote
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: [Select]
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?
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

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