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

[Martin Gutkowski <webmaster@xxxx>]

Hi Jim

Do I take this to mean you have the OEM fan fail module? I have had the 
opportunity to take mine apart and I thoroughly concurr with the 
statement (if it's there, throw it away!).

Forgive me if I start talking too techy here... the fan fail module is a 
simple hall effect sensor. It measures the current drawn by each fan and 
if there's an imbalance between the two, the current generated by the 
coil is enough to light the light. Wonderful, if it weren't so badly 
made! I imagine there's a slight imbalance in your two fans - nothing to 
loose any sleep over - but at 13.5v there's enough difference to turn 
the light on.

At the moment mine has a simple 4-way daisy-chain of spade terminals so 
that the fans and the fan-fail light all come on at the same time. This 
is a very simple way of telling you that power has been fired to both fans.

I have designed but not yet built a fan sequencer which restores the 
fan-fail light functionality. I discovered these superb high-side 
switches which have an integrated "status" output which can be used for 
the fan fail light directly. Mine treats each fan seperately and detects 
a short or open circuit.

The circuit diagram is here (duplicate for each fan)

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

to read an explanation, you'll have to join dmc_electrics and read the 
archives :-)

Martin
#1458

jwit6@xxxx wrote:

> I know I could probably just go with one of the fan fail fixes out there but 
> I'd like to understand a little more about what's actually happening. 
> Originally I had a fan fail indication when the spade connectors on the two 
> circuit breakers would heat up and sometimes trip the breaker. Those 
> connections are now fixed for good. No appreciable heat build up, resistance, 
> or current draw.