[T3] Lights

[Dave Hall]

Yes, it was a revelation to me when I discovered the cold resistance of a flasher bulb was maybe an ohm, yet the power on 12V was, say, 21Watts.  It didn't take much deduction to work out its resistance at 2000 deg C must rise to around 6 or 7 ohms.

Dave.
UK VW Type 3 and 4 Club.

-----Original Message-----
From: "Jim Adney" <jadney at vwtype3.org>
Sent: ‎04/‎11/‎2017 21:43
To: "type3 at vwtype3.org" <type3 at vwtype3.org>
Subject: Re: [T3] Lights

On 4 Nov 2017 at 17:21, Dave Hall wrote:

> Thanks, Jim. I wondered how the bulb failure system worked. Further
> research is indicated.

Yeah, this was always a mystery to me, part of which was that there is a 
second relay in our TS flashers that I couldn't explain. it didn't occur to me 
until a few years later, when I was looking at SCR phase control switches 
that I saw that they make special versions "for tungsten loads." I didn't 
understand what that meant, until I remembered that light bulbs have huge 
inrush currents, so the SCRs have to be rated for that. And that inrush 
current would trigger the 2nd relay in our flashers.

I rebuilt a TS relay for someone on this list a few years ago, and I could 
never get it to work right on the bench, because I was just loading it with a 
resistor. I never heard how it worked on the car. If that person is reading this, 
let me know how that worked. If there was/is a problem, I think I can improve 
on it now.   

If it worked, that would be good news, too.

-- 
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************

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