Fan Control and Trans Control Cct Discussion

[37Pickup]

Hi

Attached is basic diagram of what I am thinking of doing for fan control and Transmission Control. I haven't put in a lot of detail.
Idea is to prevent fan from operation under 80 deg, switch on at 93 deg or when boost is over say 4PSI. And at 4PSI force TCM into power mode (trans uses different map and drops out of overdrive).
Any thoughts?

Rob

Added: termostat is 90deg.

[NITROPIXIE]

Rob

Here is my idea on the circuit.

Normally a fan switch will come on at about 102 degrees (approx) but obviously you can change this in the software. I have used 2 outputs for the 4 PSI output otherwise the auto trans will be effected by the 93 degrees aswell so that seperates the circuit by using an extra output from the mjlj set the same as the other.

There should be a relay around which will have a fixed time delay. I have found 2, one is a relay that lasts 10 secs and acts as a internal light delay. The other is a fan control delay (possibly by landrover) but as yet cannot find any solid details. Believe it lasts 10 minutes. I did find this though http://www.velleman.eu/downloads/0/illu ... _k2579.pdf which you may be able to get. They cost us £8 from maplin. If not it has the circuit diagram so you could make one and it can be adjusted a little to suit your requirements with a little redesign.

Hope this helps a little

Ryan

[37Pickup]

Hey yeah

I was thinking diodes to prevent crosover problems, the idea of the 80deg output is so the fan does not come on in response to 4psi when the engine is cold, and here is a link to a timer avalable over here (Australia).

http://www.jaycar.com.au/productView.as ... eyword2=KC

Rob

[NITROPIXIE]

Ah i see, in that case you may need a circuit like this with 2 relays. Obviously it doesn't matter which way round the relays are put in a circuit with each other.

What might be even more advantagous and discrete is a little circuit board with small components driving just a single larger relay. It wouldn't take that much design and could be produced on some simple circuit board available from most electronics hobby stores.

[37Pickup]

Cool that's it, I'll do it that way. I originally didn't understand that the MJLJ only O/P earth and thought inverting inverted the O/P (wrong). I now get it!

Another thought I will investigate is that maybe the timer could be held "reset" (if there is one on the timer)by the >80 o/p (when its under 80) and so eliminate the second relay or the timer has a relay so maybe modify the tracks so the >80 operates it.

[NITROPIXIE]

There is one problem i think we are going to have and that is how to reset the timer everytime we need too. Let me think about it some more and i will get back to you.

I think a change over relay will do it but need to think more on how to improvise this.

[NITROPIXIE]

Some more info on the 555 chip used in the link to the circuit i provided http://www.kpsec.freeuk.com/555timer.htm#monostable

As we are using it as a monstable if you scroll down the page a little then we can use it as a power on monostable it describes, which auto resets itself on power off. This could easily be incorporated on to the circuit board with a small bodge and may require putting in a different place of the original fan circuit.

However i do think this could be long winded and there maybe an easier solution in the form of a fixed timed relay already in production. We will have to do some more research into this to come up with a final solution.

[DannyP]

The 555 is one of the most useful linear chips ever produced. I used to make timers attached to relays for auto alarm functions. Headlights on for 30 seconds, interior light on after door close, or even a one-touch window/sunroof close. Easy to put a potentiometer in, then adjust it until you get the right time delay. Then you can substitute a fixed value if you'd like, or just put some paint on the adjuster. I like the micro pc-mount potentiometers, they are tiny.

[37Pickup]

Hi
Ryan I have bought a timer kit, it can be set to start timing on a falling trigger. So by moving the timer to be inbetwen the relays, strategicly fitting some diodes and altering the cct so that the O/P of the second relay latches the relay via the NC contacts in the timer, when the first relay drops out the second stays operated via the NC timer contacts until the timer (which is now triggered to commence timing) times out.

I'll draw it later.

Rob

[37Pickup]

A second Question:

Could I eliminate this timer by somehow fiddling and setting the MJLJ hysteris settings to give a wider range of O/P thingies.

Rob

[NITROPIXIE]

Hey rob

If you can draw the diagram out that would be ideal. Picture paints a thousand words, lol. Does the timer also require a reset function? If you have a link for its wiring diagram then i can have a look at it aswell.

For your second question, megajolt only has a hysteresis factor of 1 degree i believe, but yes if it could be programmed for an adjustable hysteresis it would make it much more flexible.

[37Pickup]

OK

The water pump runs at 6-8v default.
At around 90C O/P A increases the voltage, via the motor controller, to 8-12V.
At around 95C O/P B operates the water pump relay and applies full available power eg 14V.
O/P also applies operates a relay that applies + to the timer trigger the trigger is looking for a falling trigger.
At around 98C O/P C operates the fan relay, the fan relay self locks via the timer and also locks the pump motor relay.
Once the engine drops below 95C O/P B drops out the trigger relay and the timer begins timing. Fan and Pump are held via the timer cct.
Once the timer finishes the NC contacts open and both relays drop out.
O/P D will bring in both Fan and Pump immediately and when drops out the timing starts. Could add another relay so this only happens if O/P A is triggered.

I just relaised that O/P B doesn't time by itself, I'll fix that.
Rob

[NITROPIXIE]

Wow this is getting complicated.

The problem with using diodes is they have a potential difference of 0.7v across each one which will cause us problems. I'm afraid they don't work quite like one way valves. What we will need now is a logic circuit using a selction of 'and, or, not, nand, nor,xnor, etc' gates. I have the day off tomorrow so will come up with a solution then.

How does the water pump motor speed control operate. Does it have Pulse Width Modulation (PWM) or using a selection of high power dissapating resistors??

For a water pump i would recommend PWM as the motor will keep its torque at low speeds and has a better control of the motor but that then will cost more and could be done with some large (physically) resistors.

[37Pickup]

Hi

A logic cct is a cool solution.

O/P A simply alters the earth (via resisters) in the PCM cct that regulates the PW

The water pump is PWM (Jaycay 10A/20A motor control kit).

Are the diodes a problem if they are driving relays off the O/Ps?

I would like to make it simple, hysteresis on each O/P would solve everything I think, this is what my diode and timer cct is actually sort of doing.

Regards Rob

PS the two main relays are standard auto relays that the car uses with or without the above cct and would normally be operated manually or via a engine sensor. The pump can be used without the controller but this is a waste of power and wear.

[NITROPIXIE]

Hey Rob

I'm going to break this down into two main parts. Firstly water pump control. I'll do fan motor control when i can get my head around what we are trying to achieve a bit more clearly.

I have changed quite a bit of your original circuit on this. I have used a regulated voltage on this circuit to give a continuous regulated voltage, therefore the input signal and speed output will not change due to voltage changes in the cars electrical system. 10.5V I used from the voltage regultor of the dash gauges (petrol and temperature gauges) or you could use a regulated supply from the speed controller itself.

Now to work out V1, the voltage input to the speed controller. I have inverted the 90 deg output of megajolt hence the line above it. Under normal running (below 90 deg) the output to megajolt is earthed. This will mean that the potential difference is controlled through the single potential divider (pot), which you can set to what ever voltage you want, obviously you want it small.

Above 90 degrees the megajolt output is floating and so now V1 is worked out as a component of where ever the pot is set plus the variable resistor underneath it. This greater total resistance bewtween the input of the speed controller and ground will cause a greater potential difference across it and therefore increase the voltage. Having a variable resistor means again you can set it to what you want.

I'm sure the speed controller will have a variable speed control so you can set it by another dimension here too, this would also set the max speed input threshold so you will have to play with 3 variables to get the speed you want. Obviously changing one could affect the others.

I have accidently omitted the full power relay which was fine how it was, except it might be better using a changeover relay so the motor is either connected to the speed controller or direct to 12V and not both.