[EVDL List]

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

thanks


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Yes, that is the cathode (-) end.


David C. Wilker Jr.
USAF (RET)

---- Eduardo Kaftanski <[email protected]> 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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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

David Wilker wrote:

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

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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" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
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
>
>
>

David Wilker wrote:
>
> > ---- Eduardo Kaftanski <[email protected]> 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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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 <[email protected]> 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

David Wilker wrote:

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

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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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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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From: [email protected]
> 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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