Re: Best Snubber for Nasty Spikes?

From: Rolavine (rolavine_at_aol.com)
Date: 01/04/05 

Date: 04 Jan 2005 17:43:06 GMT

>Subject: Re: Best Snubber for Nasty Spikes?
>From: "Frithiof Andreas Jensen" >
>
>"Peter Kiproff" <peter@microtrendrobotics.ca> wrote
>> What would be your recommendation?
>
>Buy some of those encapsulated RC networks that clip into the mounting
>system (DIN Rail ... Clip_on_top_of_Relay ... WhatEver) that the controls
>are using; it looks much neater and the site technician can get/install new
>ones, should the need arise. Discrete components are subject to abuse,
>vibration, moisture e.t.c.
>
>The values are not that important - it seems to be a "one-size-fits-all"
>device - shouldn't surprise me they are 47 Ohm, 0.1 uF as you say.
>
>PS:
>
>Diodes across relay coils are Evil:
>
>They are *easily* blown out by one of the many spikes in an industrial
>environment; Especially the wimpy 1N4148 diodes that some designers are so
>fond of. When that happens they will fail short, and then the the wires or
>the controls will be damaged too! RC-Networks, MOV's or Tranzorbs (if one
>absolutley MUST have a diode) will survive much longer!
>
>I prefer to put the voltage limiter across the *driver*,
>contacts/transistor, not the coil, because it is the *driver* and not *the
>coil* that needs overvoltage protection (and some site techies might forget
>it if it is not soldered in ;-)!!
>

Good points. How is a 1N4004 as a flyback eater diode? Is it fast enough? When
I look up the specs they are not very specific about speed, since they are
intended to be rectifiers, however when I test them they seem fast enough, my
100 meg scope shows no transient. If not a 1N4148, what is the stronger
cheapest option? How about a BAW78? Do you think a coil driver really benefits
from a faster clamping device?

Rocky

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