Problem with testing WB (heater circuit)

[Crescent Kao]

One thing I noticed when I tested my boards was that you definately need
around 14v for the LED to turn on. I was testing around 12.5v-13v and it
wasn't turning on at all. HTH


Crescent Kao
Director of Marketing and Sales
www.c-speedracing.com


----- Original Message -----
From: "Brian Renegar" <thomas.renegar at nist.gov>
To: <diy_efi at diy-efi.org>
Sent: Monday, January 28, 2002 10:02 AM
Subject: Problem with testing WB (heater circuit)


> Started testing my WB circuit yesterday, and have run into a
> problem.  First a run down of the specs....
>
> US PCB
> Parts kit from Steve
> Power source from battery on running car (13.50V)
>
> The problem is, the sensor heats up and appears to be working, but the LED
> never comes on.  I have been monitoring VOut, and it never deviates from
> 2.50V.  The current to the sensor started at about 1.33A.  Reading through
> previous posts, I see it should be just over 1.4A.  So I added several
> resistors to R4, one by one.  Eventually I got the current up to about
> 1.5A, which I thought was more than adequate to properly heat it.
However,
> within a minute of connecting the power, the current slowly goes down to
> about 1.23A.  Is this supposed to happen?  I'm afraid to add any more
> resistors.  I don't want the current to go too high on initial turn-on.
>
> Can someone please give me some ideas as to what's going on?  I don't know
> where to begin testing.  BTW, I built two boards, and they are both
> exhibiting the same behavior.
>
> Thanks,
> Brian
>
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