Cooling fan control

stradacab · Post by **stradacab** » Fri Oct 16, 2009 7:27 pm

Help please as I've not had this all up and running and had a fiddle with the software.

I'm installing the megajolt jr on a c20xe.

1. I am including the signal from the coolant temp sensor. Can I configure one of the user outputs to trigger at a defined engine temperature and control the cooling fan relay?

2. Can I configure another output to provide a constant signal at power-up irrespective of engine RPM, but to turn off if RPM drops below, say, 100 rpm when running. I am using bike carbs and hoped to use the output to operate a fuel pump relay. (fuel pump would shut off if enging stalled or in the event of an accident)

Thanks for your help!!

NITROPIXIE · Post by **NITROPIXIE** » Fri Oct 16, 2009 10:32 pm

welcome ot the site stradacab, what vehicle do you have? Get some pics up.

1. Yes you can but you will need to calibrate your temperature sensor to the megajolt unit. Then choose a level for the fan to come off and on. Does your radiator not have a thermo switch to control the radiator fan? as this is normally an easier setup. Most thermo switches all operate at a similar certain temperature anyway.

2. You can set an output to come on above a certain limit of RPM and it will turn off below that limit with a little hysterisis of 100rpm, but that is it. It can't do what you ask at the moment. What you could use is a tachyometric relay like some fuel injection cars use. This turns the pump on for a short time to prime the fuel system when you turn on the ignition and then when the engine is started, it recieves a constant pulse from the coil to keep the pump on. Once the engine stops and there are no further ignition pulses then it will shut off. In the case of an accident you can add a motion switch, which again most modern cars have, which breaks the circuit when a sudden impact is felt. It requires it to be physically pushed to be reset and for the pump to work again but don't forget you will have fuel left in the float chamber so wont cut the engine off straight away. You could add this to the ignition circuit then the engine will be killed instantly.

Hope this answers your questions

stradacab · Post by **stradacab** » Sat Oct 17, 2009 7:54 am

Thanks for the quick answer.

I have just bought a Cavalier Mk1 200GLS with a xe in it. It has the megajolt (obviously!) and R1 carbs, will get some piccies up this weekend!

I'm a bit of a tw*t cause now I have started soldering I have realised it is V3 so it has less connections and omits the coolant temp ones- that's the fan idea scuppered!

Thanks for the fuel pump answer too, I think I'll just fit the relay as a separate circuit, perhaps I was trying to be too clever, no need to over complicate.

Can you tell me the best place to take the coil pulse signal to go to the fuel pump relay?

Thanks again

Cheeze · Post by **Cheeze** » Sat Oct 17, 2009 10:30 am

Alright stradacab, this is the same set up that i will be using also, just a quick one but do you have a pic of the vr sensor fittings as its causing me a bit of a problem,

Also are you using a map senosr of the tps thats is on the carbs

NITROPIXIE · Post by **NITROPIXIE** » Sat Oct 17, 2009 10:46 am

There are a number of ways to get a pulse to the tachyometric relay. Take a look at this page.

http://www.autosportlabs.net/MJLJ_V3_ve ... achometers

I'd try the diode method personally omitting the zener diode.

stradacab · Post by **stradacab** » Sat Oct 17, 2009 6:06 pm

Thanks Nitropixie, I'll do that then!

Cheeze- what do you want photo's of, I'll grab some for you tomorrow.

James

stradacab · Post by **stradacab** » Sat Oct 17, 2009 6:50 pm

Here it is!

I've made some changes to the setup already, put the heater back in, relocated the coil pack and edis to the inner wing and made up a new loom for the Megajolt.

Have to rewire the fan, probably go for manual op for now. I'll put up some bay photo's when it's done and the cooling system works properly.

Cheeze · Post by **Cheeze** » Sat Oct 17, 2009 8:04 pm

How the sensor for the toothed timing ring is mounted mate if you can, lovely looking car btw

Also you got a copy of your map i can steal or borrow lol

Post by **brentp** » Sat Oct 17, 2009 8:23 pm

Looks great! Please add a quick writeup in our "Powered by" section of the forums!

NITROPIXIE · Post by **NITROPIXIE** » Sat Oct 17, 2009 8:29 pm

Very sweet looking car indeed. I'm sure we must have enough people in England for a small meet. Would be good to see what else turns up.

Post by **brentp** » Sat Oct 17, 2009 9:56 pm

If there was a meet that would be a great reason to plan a trip!

NITROPIXIE · Post by **NITROPIXIE** » Sat Oct 17, 2009 10:39 pm

Road trip anyone??????? lol

Patriq · Post by **Patriq** » Sun Oct 25, 2009 5:35 pm

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 ?

cng1 · Post by **cng1** » Sun Oct 25, 2009 9:27 pm

In the past I have found these useful for fan control: http://search.ebay.co.uk/120474052758

A blob of JBweld/epoxy on the radiator end-tank, press the thermostat into place and hold it in place with tape until the epoxy sets. Cheap, completely self-contained and non-invasive. What's not to like?

Yvan · Post by **Yvan** » Mon Oct 26, 2009 6:03 am

This is interesting, but isn't 70 deg Celsius a bit low for auxiliary fan to kick in? Can you get 80 or 90 deg Celsius versions?