[urq] High beams/Relays... sigh.

[Scott Justusson]

Again, I agree with this Mike, about the only logical explanation I could come up with too, but I wasn't quite ready to move on to that yet.  At least my amusing beer napkin drawings appeared to be correct...  

Dave, no one is arguing your observations, only the conclusion you drew.  Bottom Line:  If there is a problem in your lighting circuit, the root cause is still there.  And, I will try to grab a diode relay this week and put 12 volts (+ serious amps just to make sure it smokes properly), and make my office desk view look just like the view of Pikes Peak these days. Bet I will fail to replicate your observation or conclusion......

Bottom Line:  The diode protected relay is hardly necessary for a lighting circuit (non protected is fine) and with a properly functioning lighting circuit, hooking the diode up with 85 to ground, could cause some smoke as the diode pops, but the relay will still work before and after that event.

Thanks for sticking this out...  (hehe)

The artist formerly known as Torsen Boy 




-----Original Message-----
From: Mike Sylvester <mike at urq20v.com>
To: Scott Justusson <qshipq at aol.com>; djdawson2 <djdawson2 at aol.com>; urq <urq at audifans.com>
Sent: Thu, Jun 28, 2012 6:36 am
Subject: RE: [urq] High beams/Relays... sigh.


Scott,

I think he has a bad ground.
There must be a common grounding point (relay coil and something else)
that is bad and is sitting at something higher than 0V from path to 12V
through something else that is connected to the same point.  When the
relay is in backwards there is a voltage at the relay with current path
to ground the wrong way through the coil an then the indicator light. 
Just enough current to activate the relay.  Fix the ground and the
backwards relay will not stick.

Mike

> -------- Original Message --------
> Subject: Re: [urq] High beams/Relays... sigh.
> From: Scott Justusson <qshipq at aol.com>
> Date: Thu, June 28, 2012 12:45 am
> To: djdawson2 at aol.com, urq at audifans.com
> 
> 
> Not full of crap, only the possible wrong conclusion?  How bout some Napkins?  
Here's how a Bosch/Hella single reverse-bias diode works.  First let's look at a 
properly hooked up (Pin 86 12v+/Pin 85 12v-) Hella/Bosch single reverse-bias 
diode relay
> http://forums.audiworld.com/picture.php?albumid=166697&pictureid=236800
> If you look at C, when switched on, all current flows through the relay coil 
because the diode blocks current flow through the other parallel path.  If you 
look at D, switching off your high beams, you get a back EMF load in the 
opposing polarity.  The diode 'gate' is now open, and the load becomes the 
actual suppression device (in the form of heating the coil for milliseconds), as 
apposed to the headlight switch contacts (Note: NOT the pin 30>87 contacts, they 
have nothing to do with this phenom)
> 
> Now, let's take a look at an improper hooked up (Pin 85 12v+/Pin 86 12v-) 
Hella/Bosch single reverse-bias diode relay
> http://forums.audiworld.com/picture.php?albumid=166697&pictureid=236801
> If you look at A, when switched on, current flows through both the coil and 
the relay, the relay will function normally.  If you look at B, this is where 
the trouble starts.  With the sudden switching off, you get the same back EMF 
load reverse polarity, but now the diode is blocking that spike.  In the common 
1N4001 (standard relay diode app), the Peak Inverse Voltage spike is ~50volts, 
so chances are good that diode won't last very long until failure. The EMF 
voltage will now bleed to the headlight switch just before release, and to the 
board mount (in an electronic circuit).  
> 
> What happens when the diode blows in a euro light conversion application?  
Nothing. Because it's hooked in parallel, so it's the exact same thing as a non 
polarized, non diode equipped relay that is used more commonly on the exact same 
application.  And those of us with non-diode equipped relays running for the 
last 20 years on our euro-lights installs without a relay or a switch failure 
can attest that diode doesn't really do anything in a Automotive lighting 
application.
> 
> So.....  What I'm trying to understand is how a diode equipped relay hooked in 
reverse then, can cause relay sticking.  I claim whatever is going on, the 
installed *diode* can't cause that, because it's not a possible diode function.  
And further, in 'failure' mode, the circuit will operate like any other non 
diode relay.   And, it's possible I have this very wrong too.....
> 
> My apologies in advance to a certain rocket scientist I know out your way, who 
uses really cool visio programs to draw his circuits, where I prefer the 
napkin/marker method.....
> 
> 
> Cheers
> 
> SJ
> 
> 
>