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

[Mike Sylvester]

Scott,

The one part I disagree on is your comment about not needing the diode
protection for a lighting circuit.
The diode has nothing to do with the load as it is on the coil.

It is meant to shunt the voltage spike caused by the collapsing magnetic
field of the coil when the switch is opened.



Mike

> -------- Original Message --------
> Subject: Re: [urq] High beams/Relays... sigh.
> From: Scott Justusson <qshipq at aol.com>
> Date: Thu, June 28, 2012 8:51 am
> To: mike at urq20v.com, djdawson2 at aol.com, urq at audifans.com
> 
> 
> 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
> > 
> > 
> >