WBO2 testing ... (What I see)

[Jay Wallace]

Glen,
Be aware that the resistivity of a tungsten filament (and most pure 
metals) changes strongly with temperature. Literature values are 
5.5 at 20 C and 65 at 2000 C (units: micro-ohm cm) whereas the 
resistivity of the heating element in the sensor probably doesn't 
change more than a few percent from room temperature to operating 
temperature. Bottom line: if you get a light bulb with the proper 
high temperature resistance you'll probably draw too much current 
at room temperature.

HTH,
Jay

At 06:23 PM 12/18/2001 -0600, you wrote:
>Glen:
>
>I've just finished testing my heater section for the first time and
>here's what I found. My regulator is mounted to the ~0.040" aluminum
>cover of the same Radio Shack box others are using.  I first used a T906
>dome light bulb (~1.8 ohms cold). With that I saw a peak current of
>~0.59 amps (had a nice soft ramp-up) and about 6 seconds for the LED to
>come on.  The regulator didn't heat much if any.
>
>Then I tried an 1156 bulb (~0.5 ohms cold). I got a soft ramp-up to
>~1.27 amps and I shut it down after about 1.5 minutes without ever
>getting the LED to light.  The regulator did heat up markedly but not to
>the point of being untouchable.
>
>I then realized it's not going to work exactly right unless the bulb
>resistance matches the O2 heater resistance (~3.3 ohms cold). I gave up
>looking for the perfect bulb and since it was exhibiting a soft current
>ramp-up, I decided to just try the real thing. (Sometimes I'm
>dangerous:) With the real heater, it ramped-up to ~1.27 amps and the LED
>came on at 64 seconds. The current settled to ~1.18 after 3 minutes of
>on-time in free air. The regulator was merely warm at that point.
>
>Try a bulb closer in cold resistance to the heater resistance the
>circuit is designed for and see if it doesn't behave more like it
>should.
>
>
>Glen Beard wrote:
> >
> > OK, I've gotten everything soldered up, and I am testing the
> > heater circuit using a tail lamp.  The lamp turns on nice
> > and bright building its current to 1.003 Amps.  Is the LED
> > supposed to turn on after a while?  Is the LT1086 (VR)
> > supposed to get sizzling hot even with a 2x3" Al heat sink?
> > With the smaller heat sink I had on it, the bulb would light
> > up and then start to dim again.  If I blew across it and it
> > got brighter.
> >
> > --
> > Glen Beard  95 T/A conv M6
> > 355, Vortech, heads, cam...
> > http://home.nycap.rr.com/gbeard1/TransAm.html
> > http://home.nycap.rr.com/gbeard1/Impala/Impala.html
> >
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