Cooling fan control

cng1 · Post by **cng1** » Mon Oct 26, 2009 7:46 am

Yes, you can get them in all sorts of temperature ratings, the 70C one was just the first one my search stumbled across

capri_turbo · Post by **capri_turbo** » Mon Oct 26, 2009 9:25 am

the temperature input can be added to the V3 quite easily. I have it on both of mine although I havn't used it on either yet.

Have a read through this whole thread for info

http://www.autosportlabs.org/viewtopic.php?t=2100

Col

stradacab · Post by **stradacab** » Fri Oct 30, 2009 7:07 pm

I reckon the temp sensor stuck to the rad seem loke a simple way to go. What temp should I try to get for the fan to cut in? 70 seem very low seeing as the stat is 91?

Also, on V3 where does the unit get it's temp reading from, it doesn't have any signal cause the thermistor isn't in the loop?

cng1 · Post by **cng1** » Sat Oct 31, 2009 10:05 am

The tanks of the radiator will be a slightly lower temperature than the engine itself. You will find that depending where you measure the temperature on the tanks you will get a certain amount of variation from your engine temperature gauge so you have a little flexibility there to adjust the cut-in point. I would give an 80C switch a go and if necessary swap up a temperature rating if you find the fan is on too much.

Quagmire · Post by **Quagmire** » Sun Nov 01, 2009 9:47 am

If you are not using MJ to control fan, or want something that will allow a second temp sender to be installed neatly then what you really want is one of these:

http://www.x-eng.co.uk/X-Fan.asp

I was going to get one before i installed MJ and decided i could just use the sender already in my inlet manifold...

capri_turbo · Post by **capri_turbo** » Fri Jul 05, 2019 8:22 am

Patriq wrote:I've wired an electrical cooling fan with my V3. And it works like a charm.

But...... it is wired so that the fan is fed directly from the battery, then to the relay controlled by one of the user outputs in MJLJ, and then to the fan.
The battery in return is connected/disconnected to the the whole system via a heavy duty relay.
When I turn on the battery - the fan starts running, then if I turn the ignition key - it stops.

This leads me to the conclusion that the user outputs in MJLJ are earthned until the unit is powered. Is this correct ?

I found the same issue with the fan coming on with the ignition.

There is an issue with the design of the Megajolt unit where if a relay is connected to the user outputs and a permanent supply the megajolt is them permanently powered as the ULN2003 chip has built in protection diodes which dump and stray Voltages down pin 9 which is connected to the input side of the Voltage regulator hence the unit switches on permanently.

There is an easy solution though. disconnect pin 9 from the board (easy as the chip is socketed and pin 9 can be bent upwards), this prevents the diode protection within the chip powering the unit but also disables the protection which is essential. The easy solution is to add the diode protection at the relay... simply add the diode across the relay terminals. Search relay with freewheeling diode and you should come up with the answer or read the following thread where I had the exact same issue.

viewtopic.php?t=5802