Flyback Diode question/selection?

Thread Starter

SS2017

Joined May 23, 2017
7
Hello,
I have question regarding using flyback diode for 12/24 VDC motor. The motor will be selected to run on 12VDC or 24VDC via mechanical toggle switch. The motor current will very depends on the load from 2A up to 40A. The switch is rated for 80A. The motor will be running in one direction only.
I want to install a flyback diode parallel to the motor to protect the switch contacts. I have FR307 diodes, reading the FR307 datasheet shows to be OK as flyback for my project? 3A continuous current, 150 peak current, 1000V and fast switching Trr 500nS.
Did I make a good choice on the flyback diode? or should I using something else?
Any input is appreciated.
Thanks
 

Dodgydave

Joined Jun 22, 2012
11,284
Usually rule of thumb is 10X supply voltage, your choice will be good, the faster the speed of recovery the better, try MUR120,UF5400 series..
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
If using a simple on/off switch, does the motor have a relatively long wind down or rapid stop due to load etc?
If the former, there is relatively low to no high BEMF due to the generating effect of the motor.
Max.
 

Thread Starter

SS2017

Joined May 23, 2017
7
Thank you guys for the reply,
The motor will stop different and it depends on the load or no load, The switch is Toggle ON/OFF/ON mechanical. The switch actually has 4 pols rated for 20AMP @ 110V each and I am just paralleling them. They may not turn ON or OFF all at the same exact time? That is why the flyback diode is important in my opinion.
Should I be OK with the single FR307 or do you guys suggest something else?
Thanks
 

ian field

Joined Oct 27, 2012
6,536
Hello,
I have question regarding using flyback diode for 12/24 VDC motor. The motor will be selected to run on 12VDC or 24VDC via mechanical toggle switch. The motor current will very depends on the load from 2A up to 40A. The switch is rated for 80A. The motor will be running in one direction only.
I want to install a flyback diode parallel to the motor to protect the switch contacts. I have FR307 diodes, reading the FR307 datasheet shows to be OK as flyback for my project? 3A continuous current, 150 peak current, 1000V and fast switching Trr 500nS.
Did I make a good choice on the flyback diode? or should I using something else?
Any input is appreciated.
Thanks
Most people don't bother unless the motor is switched by semiconductor devices. If the arc as the contacts break is getting into other circuitry, a 1n5404 would probably be sufficient. If for some reason you need fast Trr - use a Uf5404.
 

crutschow

Joined Mar 14, 2008
34,280
There seems to be a common misconception that a diode with a fast turn-off recovery time (Trr) is somehow better for inductive spike suppression in low frequency switched circuits. Not so.
All diodes turn on rapidly, whether they have high or low Trr, and it's the turn-on time that's important is spike suppression, not turn-off.
So you can use a fast Trr diode for that purpose if you like but it will work no better than a standard diode.

The place where a fast diode Trr has an advantage is when an inductor is being rapidly switched, such as in a SMPS, where a long Trr can reduce efficiency.
 
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