[Fwd: Test of DIY-WB]

rr RRauscher at nni.com
Thu Aug 16 23:36:56 GMT 2001


[info forwarded from the gmecm list]

Yes it should be paralleling R4. Only needs to be a 1/2W resistor. The
value of this resistor will vary depending upon the real value of R4 and

the desired warm-up time. The resistor R4 is the current sense resistor
for maximum heater current.

I tend to use easy to obtain parts and fudge from there. I've used a 10%

tolerance resistor for R4 and then find it may need trimming. On the
perf
boarded unit I ended up with a 6.8 ohm across R4. For the PCB unit I
just built I ended up using a 10 ohm resistor across R4. Both times I
used
a 10% 1 ohm main resistor (0.9 to 1.1 ohm)

There is still some dispute as to what the absolute maximum current
should be. On the low side of ~1.3A it has been found that the heater
takes over 2 1/2 minutes to warm up. At that current it sometimes won't
reach the 10.5 V limit required to enable the UEGO controller. In other
words the sensor never reaches full temperature.

Empirical evidence shows that warm up times of 30 to 45 seconds is
common for WB units. In order to obtain this warm up time a higher
heater current is required. Hence the trimmed current sense resistor. I
try to shoot for a current of a little over 1.4A or ~40 seconds warm-up
time from a cold sensor.

BobR.



Flanagan, Steve wrote:

> I am confused why this will not affect the pre made board group. On
that
> board, don't you
> have to still parallel the resistors?
>
> I do not see on the parts list the 6.8 Ohm resistor.  Should we assume
that
> it is also a 5W resistor?
>
> Steve F
>
> -----Original Message-----
> From: Brian L Massey [mailto:blocklm at juno.com]
> Sent: Thursday, August 16, 2001 1:54 PM
> To: gmecm at diy-efi.org
> Subject: Re: Test of DIY-WB
>
> On Thu, 16 Aug 2001 09:40:45 -0400 "rr" <rrauscher at nni.com> writes:
> >
> > Had a chance to do some testing yesterday. Swapped out
> > the perf-board prototype for the PCB version of the WB.
> <.......>
> > This is good. It looks like I didn't miss any traces! <g>.
>
> This won't affect people who use the pre-made pc board, but since I'm
> building to my own form-factor on perf, there seems to be a slight
errata
> needed on the diagram for the heater control.
>
> Bob, in your "Note:" on the right of the heater control drawing, it
says
> "parallel R1 w/6.8 ohm ...". Shouldn't that be *R4*? Just a nit
really.
> Tnx.
>
> Brian
>
> ________________________________________________________________




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