Re: [DML] Fan Fail Light Without Actual Fan Fail

[Martin Gutkowski <webmaster@xxxx>]

Well, seeing as the subject came up :-)

The problem with all the systems described EXCEPT the Fanzilla (to my 
knowledge - I have never seen one much less taken it apart) is that the 
fain fail light can only tell you when the voltage is going to the fans, 
or when the fans should be on, or when there's an imbalance between the 
fans. None of these solutions actually "know" when a fan is or is not 
drawing current when it should. The only way to do this efficiently is 
with a hall effect sensor - the original fan fail module did it this 
way, but only comparing one fan to the other, and it was appallingly made.

I have been asked about the progress of my little project to make a fan 
sequencer and restore the fan-fail light functionality. I've been really 
busy the past month - 2 weeks filming a TV show in Glasgow (nothing to 
do with DeLoreans), and two joyful weeks of good weather with my 
DeLorean parked outside, so every evening was spent working on it, and 
not sweating over a hot soldering iron! However, as members of the 
dmc_electrics list know, I did produce a design. I found some truly 
fantastic IC's made by Philips which are BUK202-50X 20A high-side 
switches with status pin. They make it possible to build a completely 
solid-state fan sequencer from fewer than 20 components, which gives a 
genuine "fan fail" signal. Here's the design

http://www.delorean.co.uk/electronics/fandelay2.jpg

A drives the fan, B drives the fan-fail light. Two of these circuits 
need to be built, one per fan. R3 sets the delay. For those who are 
comfortable with data sheets, I've put it here

http://www.cix.co.uk/~mgutkowski/20A_switch.pdf

The BUK203 is exactly the same, but will only drive 4A and is cheaper, 
so ideal for the fan fail light. This device has open and short circuit 
detection, overheat protection (negating the need for a fuse) and under 
all these failure conditions, will light the fan-fail light.

NB I have NOT tested this yet, but as the subject came up.... :-)

Martin
#1458

DMC Joe wrote:

> You said :
> ".........Also why not run one additional accessory relay so the
> light only indicates a "fail" condition when there really is no voltage
> going to one of the fans?.."
>
> There is a device that does all of the above and more; it's called
> "Fanzilla"!
>
> DMC Joe
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