stupid snubber diode question

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stupid snubber diode question

Eduardo K.

        Which way does the banded end of the diode go? negative?

thanks :)


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Re: stupid snubber diode question

David Wilker

Yes, that is the cathode (-) end.


David C. Wilker Jr.
USAF (RET)

---- Eduardo Kaftanski <[hidden email]> wrote:

        Which way does the banded end of the diode go? negative?

thanks :)


--
Eduardo K.           | Some say it's forgive and forget.
http://www.carfun.cl |  I say forget about forgiving just accept.
http://ev.nn.cl      |  And get the hell out of town.
                     |                      Minnie Driver, Grosse Point Blank

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Re: stupid snubber diode question

James Massey
In reply to this post by Eduardo K.
At 09:03 PM 15/08/07 -0400, Eduardo K wrote:

>         Which way does the banded end of the diode go? negative?
>
>thanks :)

G'day Eduardo, All

The band is the end that current flow will go to: put + on the other end
and current flows through it.

As a snubber across a coil you put the banded end to positive, and
preferably a zener diode in series with it, since just a diode is the
slowest way to turn off a coil.

A zener diode/diode combination (the zener in reverse connection) is a
simple no-tests needed way to snubber a coil with reasonable results.

  ____________________ coil+
   _|_
  |___|
  |   |
  |   | diode
  |___|
    |
    |
   _|_
  |   |
  |   | Zener
  |___|
  |___|
___|________________coil-

Hope this helps

Regards

[Technik] James

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Re: stupid snubber diode question

Phil_Marino
I'd like to add to James' response:

A zener/diode series combo across the coil is, as James says, a great
solution.

And, the voltage of the zener that you use is a compromise : the higher the
zener voltage, the faster the relay or contactor will open, and the better
for its contacts.  But, the zener voltage will appear across the switch (or
transistor) that is opening the relay (as the relay opens).  So, if you use
too  high a voltage zener, you could damage that switch or transistor.

People often choose a zener that's about twice the coil voltage.  For
example, for a relay with a 12V coil, a 24 V zener would be a good choice.


Phil

>From: James Massey <[hidden email]>
>Reply-To: Electric Vehicle Discussion List <[hidden email]>
>To: Electric Vehicle Discussion List <[hidden email]>
>Subject: Re: [EVDL] stupid snubber diode question
>Date: Thu, 16 Aug 2007 13:44:08 +1000
>
>At 09:03 PM 15/08/07 -0400, Eduardo K wrote:
>
> >         Which way does the banded end of the diode go? negative?
> >
> >thanks :)
>
>G'day Eduardo, All
>
>The band is the end that current flow will go to: put + on the other end
>and current flows through it.
>
>As a snubber across a coil you put the banded end to positive, and
>preferably a zener diode in series with it, since just a diode is the
>slowest way to turn off a coil.
>
>A zener diode/diode combination (the zener in reverse connection) is a
>simple no-tests needed way to snubber a coil with reasonable results.
>
>   ____________________ coil+
>    _|_
>   |___|
>   |   |
>   |   | diode
>   |___|
>     |
>     |
>    _|_
>   |   |
>   |   | Zener
>   |___|
>   |___|
>___|________________coil-
>
>Hope this helps
>
>Regards
>
>[Technik] James
>
>_______________________________________________
>For subscription options, see
>http://lists.sjsu.edu/mailman/listinfo/ev
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Re: stupid snubber diode question

Paul-253
In reply to this post by David Wilker
I still think of it this way - I diode diagram is an arrow and bar.  
Electrons in a wire flow from negative to positive. If they run into  
a diode the arrow and bar mark out "this way - NO." (>|  electrons  
cannot follow that from left to right.) The band on a diode is the  
bar and the arrow is not shown.

To use it as a snubber you want the diode installed so it doesn't  
short out the power to the coil. In other words, the band to the  
positive side of the coil.

Most Albright contactors come with a regular diode as a snubber. When  
my Curtis shorted ON an Albright SW200 with a diode slowing the coil  
opening still had no problems disconnecting my 10 Optimas from my  
Prestolite motor. Its not the best solution but if you are not  
working your relay or contactor to close to its limits it can be a  
fine solution.

Paul Gooch


On Aug 15, 2007, at 7:24 PM, David Wilker wrote:

> ---- Eduardo Kaftanski <[hidden email]> wrote:
>
> Which way does the banded end of the diode go? negative?

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Re: stupid snubber diode question

Roland Wiench
Instead of a standard diode, use a Zener Overvoltage Transient Suppressor
Bidirectional type.  Does not matter which direction you install them.  NTE
4933 which is rated for 36 volts that is use on 12 volt circuits.

These Transient Suppressor are listed from NTE 4933 to 4999 depending on
voltage.

I use them on all my contactor 12 volt coils and some on 180 volt coils on
my safety contactors.

Roland


----- Original Message -----
From: "Paul" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Thursday, August 16, 2007 4:14 PM
Subject: Re: [EVDL] stupid snubber diode question


> I still think of it this way - I diode diagram is an arrow and bar.
> Electrons in a wire flow from negative to positive. If they run into
> a diode the arrow and bar mark out "this way - NO." (>|  electrons
> cannot follow that from left to right.) The band on a diode is the
> bar and the arrow is not shown.
>
> To use it as a snubber you want the diode installed so it doesn't
> short out the power to the coil. In other words, the band to the
> positive side of the coil.
>
> Most Albright contactors come with a regular diode as a snubber. When
> my Curtis shorted ON an Albright SW200 with a diode slowing the coil
> opening still had no problems disconnecting my 10 Optimas from my
> Prestolite motor. Its not the best solution but if you are not
> working your relay or contactor to close to its limits it can be a
> fine solution.
>
> Paul Gooch
>
>
> On Aug 15, 2007, at 7:24 PM, David Wilker wrote:
>
> > ---- Eduardo Kaftanski <[hidden email]> wrote:
> >
> > Which way does the banded end of the diode go? negative?
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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Re: stupid snubber diode question

David Wilker
In reply to this post by Paul-253
Good example, Paul! May I use that?
I teach my students that a Zener Diode is like a teacup. It is designed to be used in the reverse bias (Breakdown) zone. As long as you pour less tea into it than it can hold, nothing happens. But if you overfil it, any amount above its capacity spills over and is wasted. So using a Zener across your output in reverse bias mode will not allow your output to excede the Zener's breakdown voltage limit


David C. Wilker Jr.
USAF (RET)

---- Paul <[hidden email]> wrote:
I still think of it this way - I diode diagram is an arrow and bar.  
Electrons in a wire flow from negative to positive. If they run into  
a diode the arrow and bar mark out "this way - NO." (>|  electrons  
cannot follow that from left to right.) The band on a diode is the  
bar and the arrow is not shown.

To use it as a snubber you want the diode installed so it doesn't  
short out the power to the coil. In other words, the band to the  
positive side of the coil.

Most Albright contactors come with a regular diode as a snubber. When  
my Curtis shorted ON an Albright SW200 with a diode slowing the coil  
opening still had no problems disconnecting my 10 Optimas from my  
Prestolite motor. Its not the best solution but if you are not  
working your relay or contactor to close to its limits it can be a  
fine solution.

Paul Gooch


On Aug 15, 2007, at 7:24 PM, David Wilker wrote:

> ---- Eduardo Kaftanski <[hidden email]> wrote:
>
> Which way does the banded end of the diode go? negative?

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Re: stupid snubber diode question

drdhdmd
In reply to this post by Eduardo K.
 
 
As an extension of this question, how does one  determine the Voltage and
current rating of a snubber, or freewheeling diode  used in a large DC motor
application?  

Dave  Delman
1981 Electric DeLorean  Project






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Re: stupid snubber diode question

Al-57
In reply to this post by Paul-253
What about TVS's? I think they are pretty fast and available in many
voltages and wattages. Are they basically just a zener diode?

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Re: stupid snubber diode question

Lee Hart
In reply to this post by Eduardo K.
From: [hidden email]
> how does one determine the Voltage and current rating of a snubber,
> or freewheeling diode used in a large DC motor application?

If the diode is connected straight across the motor, the maximum (theoretical) voltage it sees is your pack voltage. The maximum (theoretical) current it sees the your maximum motor current. For example, if you have a 120v pack, the diode sees 120v max. If peak motor current is 100 amps, the diode sees that 100 amps.

In practice; noise, wiring inductance, heat buildup, the degree of matching between paralleled parts, and other factors require a higher voltage and current rating to be reliable. Extra voltage is usually cheap, so a 2:1 safety factor is reasonable. Extra current ratings are expensive, so people tend to skimp.


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