Re: (ET) 36vdc relays

["RJ Kanary" <rjkanary nauticom net>]

        In the automotive field, where I've been for the past 30 or so 
years, {EGAD!}, the common practice is to have the clamping diode 
incorporated into the solenoid or relay coil.
     The Blue Oval Camp, never one to be restricted by convention enjoys 
placing them in more   'innovative'  locations.
     On the Bordeaux France built A4LD transmission, popular in the Ford 
Stranger truck and the Exploder sport ute, the clamping diodes are found in 
the case connector itself. Not where most techs would expect to find them.
         With the E4OD units, a game of hide and seek was held, depending 
on model year. From 1989 until some arcane time in the 1995 model year, the 
clamping diodes were found on the PC board of the solenoid pack , inside the 
transmission pan.
         Later they were eliminated, as the Wizards Of Dearborn utilized 
inductive signature diagnostics to monitor solenoid performance. That was 
all well and good, until the later solenoid bodies found their way into 
earlier vehicles, and PCMs started showing up exhibiting symptoms as if they 
had been struck by lightning,{ Which, for all intents and purposes, they 
HAD. }

----- Original Message ----- 
From: "steves" <ssawtelle erols com>
To: "et" <Elec-trak cosmos phy tufts edu>
Sent: Monday, August 07, 2006 10:27 AM
Subject: Re: (ET) 36vdc relays


> The coil is also an inductor, which means it stores energy. When you
> disconect the coil the energy will be released. It's a spike of opposite
> polarity from the drive signal which can play havoc with the coil drive
> circuit (esp. if it's electronic). The diode routes this back EMF
> (electromotive force) back through the coil to dissipate the energy in a
> safe way. This is very common practice, though usually the diode is in
> the external circuit.
>
> - SteveS
>
>
> Michael S Briggs wrote:
>
> > > I retested the relay and it worked so the blown diode did not ruin the
> > > relay.
> >
> >
> > Hm, interesting. Still, why put it in there in the first place?
>
>
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