For the electrically qualified

[preacherman]

On the mk2 escort I have an electric fan. It has a reputatio  for blowing 25 and 30 amp fuses. As soon as the fan kicks in the fuse blows. There are no relays involved just a fused spur off an ignition live.The fuse only blows when the car is being driven and not when stationery.

I have a dash light that lights up when the fan kicks in at 85 degrees. I have noted that at around speeds of 30mph it lights up yet the fan has not kicked in.

My one theory is that when the car is being driven at certain speeds, it allows the fan to rotate creating a back emf that lights up the led dash light . I think the fan is running in opposite direction. When the fan kicks in it draws a large current to enable the fan to spin in the opposite direction to draw air in.

Theory 2 I need A relay to overcome the initial surge.

Theory 3 a short circuit to ground is present

Theory 4 fan is fooked

I am not an auto electrician and fed up of buying fuses.

[katana]

Relay - yes - always pretty essential for high load switching. Really shouldn't need much more than a 15A fuse.

The fan won't spin 'backwards' with just airflow over it - the blades are efficient in one direction so should spin with air with least resistance. An LED needs very little to light it - a fan motor is just an dynamo when its not powered!

[colr6]

As already stated you could do with a relay in circuit. A relay is not a magic 'thing' it's just a heavy duty switch to take away the stress off a normal switch and to stop you overloading it. Where ever the fault lies you may aswell have it wired up correctly to start with ! I would suggest you purchase a 30amp 5 pin relay 2/3 metres 30 amp wire two in line fuses or one in line and a fused relay. If your fan has a wattage rating on it you can calculate the Amps it needs to run which will give you an idea on the size of fuse required to protect the circuit. I've got a drawing off the net for wiring. Using your existing feed from ign switch would suggest a 5amp in line fuse to be fitted. Your 12v permanent power source for either battery pos or starter motor feed side whichever the easiest with 15/20amp fuse in. This needs to be rated at 30 amps same as feed to fans, this gives you options on fan size apart from twins which can pull more than 35amps on start up.

[preacherman]

So I  wired in a relay with 30 amp fuse and it still blows , tried 35 amp and that went after a short run in the car. As I said when the car is stationery there is no problem the fan kicks on and off, no problem.

I had a rethink and traced it to the same time after i fitted an LED kit car fan light that illuminates when the fan is on.it took a feed from the fan and the other cable was earthed. Disconnected  the led light and all ok. Took it for a good run with water temp up to 90 degrees and fan is good.

Must be a dodgy fan light or how I hard wired it in.

 

Neil

[katana]

LED and fuse blowing is too co-incidential. As LED's only pass current one way (they are a diode) so probably the way its wired is a direct short hence fuse popping time. Don't bother with a light - as long as the fan works, you don't need to know that it is!