Fast acting diodes for dc motors, how to ...?...

Thread Starter

Lineout

Joined Nov 20, 2013
64
...how would you identify the ones that are fast enough to protect the controllers & boards ?

Are 'rectifier' diodes in that category ?

What different generic and specific names would I be looking for to know they are the faster ones.

Is there a test function on simple multimeters to be able to identify them ?

In a reversing motor I was told to put two diodes on each side of the motor, could someone point me to a schematic that shows this ?

Thanks/////
 

Thread Starter

Lineout

Joined Nov 20, 2013
64
Ultrafast or fast recovery diodes, shottky diodes will do.
I've asked befor about shottky's and got no reply, is that a brand , a generic tag ?

Also how would you hook them up , I read that zener diodes in series on each terminal would work , how would you do it with any diode,or specifically a shottky , and how do you know when you have a slow diode that won't do any good (not act fast enough) ?



Thanks.
 

tcmtech

Joined Nov 4, 2013
2,867
What type of motor and what exactly you are trying to protect it's circuitry from would be helpful information for us to work with.
 

Thread Starter

Lineout

Joined Nov 20, 2013
64
What type of motor and what exactly you are trying to protect it's circuitry from would be helpful information for us to work with.

Various cheap low watt motors so far.

One that I've been able to identify is a 1 - 2 volt, 50 - 100 mA.

I ran it as a hoist off or a battery and switch, now this motor like others (maybe larger , or steppers) will be integrated with rc modules, so that's why I'm starting to think about protection.

I just brought out my diode pak , they are very hard to read , small and unfamiliar to me, I have my meter and a 1.5 volt battery and am going to start trying to id them the vendor sent them as a pak , not idividually id'd...
 

Papabravo

Joined Feb 24, 2006
15,095
...how would you identify the ones that are fast enough to protect the controllers & boards ?

Are 'rectifier' diodes in that category ?

What different generic and specific names would I be looking for to know they are the faster ones.

Is there a test function on simple multimeters to be able to identify them ?

In a reversing motor I was told to put two diodes on each side of the motor, could someone point me to a schematic that shows this ?

Thanks/////
You identify them by looking at a datasheet. The parameter of interest is called the reverse recovery time(t_sub_rr). It is usually shown as a function of time and involves the change from conducting to blocking and how long it takes for this to happen.

http://en.wikipedia.org/wiki/Diode ; find the section on "reverse recovery effect".


A Schottky diode, named after it's discoverer replaces, one of the semiconductors with metal, gold I believe, to lower the forward voltage drop for a given current and to speed up the switching time from conduction to blocking.

http://en.wikipedia.org/wiki/Schottky_diode
 

tcmtech

Joined Nov 4, 2013
2,867
I don't see why you would need a fast recovery diode for such a small motor.

In any standard brush type DC motor the armature is made from laminated steel sheets and has a rather slow magnetic field reactance speed.
 

THE_RB

Joined Feb 11, 2008
5,438
Agreed. Commercial manufacturers that use small motors like that in VCRs or CD players just put a cap across the motor terminals.
 

Thread Starter

Lineout

Joined Nov 20, 2013
64
I don't see why you would need a fast recovery diode for such a small motor.

In any standard brush type DC motor the armature is made from laminated steel sheets and has a rather slow magnetic field reactance speed.

I was told in this forum to use fast acting, because the reaction time of one style of diode vs another style is too slow to do any good.


Can you draw a schematic for me of how to actually hook 4 diodes into a configuration that would work for a motor that would actually benefit the circuit with the use of diodes? This is for a motor that will be reversing.
 

Thread Starter

Lineout

Joined Nov 20, 2013
64
Agreed. Commercial manufacturers that use small motors like that in VCRs or CD players just put a cap across the motor terminals.
'
Do you have a formula for an acceptable value of capacitor that would work for a .2 watt motor (2 volt 100 mA) , or if I use something bigger like a 1 or 2 watt motor, is there a rule of thumb or formula to determine the right capacitor , or one that's close enough to do some good ?
 

Alec_t

Joined Sep 17, 2013
11,893
Can you draw a schematic for me of how to actually hook 4 diodes into a configuration that would work for a motor that would actually benefit the circuit with the use of diodes? This is for a motor that will be reversing.
Google 'H-bridge snubber diodes'and look at the images on the first page of hits.
 

tcmtech

Joined Nov 4, 2013
2,867
I was told in this forum to use fast acting, because the reaction time of one style of diode vs another style is too slow to do any good.
That doesn't mean the person knew what they were talking about.:rolleyes:

My wife tells me things all the time trying to be helpful. That still doesn't mean she knows what she is talking about. :p
 
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