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Re: What Relay for Adding a Fan

To: <moag@ix.netcom.com>, <spitfires@autox.team.net>
Subject: Re: What Relay for Adding a Fan
From: "James Carpenter" <james.carpenter@jccsystems.swinternet.co.uk>
Date: Mon, 26 Apr 1999 02:06:33 +0100
I have thrown away my engine driven fan and replaced it with an electric
one.  My one was purchased for the sum of £3 from my local scrap yard.  It
was originally from an Austin Maestro, a worthy sacrifice for my car, you
wouldn't want to restore on of those ugly beasts.  Especially when you can
get them in kit form!  This fan has two distinct advantages over normal
fans.  One it's a pusher, if goes on the front of the radiator, and only
leaves three inches of completely uncovered radiator on the left.  Two the
Maestro had plastic radiators, and so needed a lot of air flow this fan is
so powerful that turning on the fan allows will add 3mph to the top speed.

The thermostat was new and designed for a Metro, because the cooling system
pressures are the same and the metro uses an 'A' series engine which I
reckon is pretty close in cooling needs to a Triumph.  I then cut the
thermostat housing from a Rover because this was the only brass radiator I
could find, and had that silver soldered into my Spitfire radiator.  It MUST
be silver solder.

When operating with the thermostat at idle it needs 15 seconds every two
minuets to keep the engine cool.  And when you override the fan it takes 60
seconds to cool from 3/4 to 1/2.  It's so much nicer to tune the carburettor
without a fan inches from your face!

Here are some lesson I learnt about the difference between normal and
automotive electronics.

There a bit long but my whole engine cooling experience thing!

James

1.  Car are quite wet environments, sometimes the water is very conductive
because of substances devolved in it.  This conductive water can get into
wiring causing a fizzing sound and current to flow.

2.  The car battery has a limited amount of energy (potential to supply
current) stored in it.  It can not sustain the fizzing of connections for
long, say a day or two at the most.

3.  Leaving a car battery trying to turn the radiator engine block and
coolant into another battery for a week is not a good idea, especially if
you are depending on the car to get yourself into university to hand in  a
dissertation.  Although thankfully this form of discharge saves the plates
in the battery from buckling, oh and it was a Japanese battery so it wont go
wrong anyway!

What I had done was wired my electric fan direct to the battery via a fused
wire I have for the driving lamps.  The wire went from the battery to the
fan, which then went to the thermostat, and then to ground.  Apon the
thermostat leaking and there generally being really wet weather the contacts
started to fizz and the fan to edge slowly round.

This discharged the battery!

So when you wire your fan bear this in mind.

I have a temporary rig of a switch on a bit of metal that one of the trim
retaining screws goes through in addition to the crash pading.  On the
angled bit of the passenger dash.  This connects the fan to ground when I
want the fan to operate.  The other side of the fan is connected to the
supply mainly because this is fused.

Anyway I am going to fit a relay to it later, so the thermostat takes its
power from the ignition and energises the relay coil.  The other side of the
relay is connected to my fused auxiliary supply I have routed to the front
of the car.  Although I may put a relay on this so that it only energises
with the ignition.  Along with a buzzer for the lights.

The other thing I have learnt, disconnect the battery if you leave your car
for any length of time.


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