Stack water temp gauge - switching electric fan - how?

[Weslake-Monza]

I want to use a Stack water temp gauge to switch an electric fan on and off and am puzzled by the drawing that Stack provides.

Terminal 85 on the relay needs a live/positive.

Terminal 86 must be the earth/switched ground from the gauge via the gauge sensor

However, I don't understand what I'm supposed to connect to 87, 87A and 30 to?

Is terminal 30 the live feed to the fan?

Is terminal 87 an ignition live?

What is 87A for?

Also why are 2 relays shown or is this where you want the gauge to switch more than one device or fan - eg 2 fans?

Thanks

[stevieturbo]

Pictures always help....some more than others.

A relay is simply a remote switch. The relays you have shown are changeover relays, so will have an additional terminal over some other relays. Same layout and wiring though, you'd just ignore one terminal.

In your case the "fan switch" will be your stack gauge. Up to them whether it switches the coil via 12v or ground.

[Weslake-Monza]

So the relay isn't polarity sensitive across terminals 86 and 85 so it won't matter that I'm switching with the earth rather than the live?

The Stack drawing isn't helpful because it shows a 5 pin changeover relay when a 4 pin relay make or break relay is all that's required?

[GreenV8S]

Weslake-Monza said:

is this where you want the gauge to switch more than one device or fan - eg 2 fans?

Yes.

[anonymous-user]

Watch out, some relays have a reverse biased diode across the coil to prevent inductively induced high voltage kick back as the contacts are opening. If you fit these backwards then bad things happen!

[stevieturbo]

Weslake-Monza said:

So the relay isn't polarity sensitive across terminals 86 and 85 so it won't matter that I'm switching with the earth rather than the live?

The Stack drawing isn't helpful because it shows a 5 pin changeover relay when a 4 pin relay make or break relay is all that's required?

In general no, not polarity sensitive, other than what Max is saying. It isnt hard to crack it open to see if there is a diode in there though.

It wont matter which you switch with, but may as well keep it as per drawing with 85/6 connected to live or ground as per the drawing you've been given for that relay

[Mroad]

It looks like there are two relays shown as there are two options on switching, one output switches on at 'low' Output and the other on at 'high'. Without looking at the instructions I would assume the levels are user adjustable, in which case you could run a two stage fan (or two fans) if you wanted, stage one kicking in at a lower temperature (Low Output) and then a higher speed kicking in at the higher temperature (High Output).

Edited by Mroad on Thursday 2nd February 09:08

[Weslake-Monza]

How will I know if I have fitted my relay that has a diode, backwards? What is backwards in this sense?

Does this drawing look Ok? I want a manual fan switch to switch the fan on whenever I want to switch the fan on manually. I want the radiator sensor to switch the fan on and off when my manual switch is off. I want the gauge to switch the fan on when the radiator sensor is off, or if the radiator sensor fails in teh off position - this action to be using the gauge set high point - as a kind of fail safe.

[GreenV8S]

Weslake-Monza said:

How will I know if I have fitted my relay that has a diode, backwards? What is backwards in this sense?

The purpose of the diode in the relay is to absorb the EMF spike when the coil is turned off. The diode is connected in parallel with the coil and oriented so that it does not pass current when power is applied to the coil. The standard ISO/DIN automotive relay layout is with the coil connected between terminals 85 and 86. If the relay includes a diode, you should apply +12V to 86 and ground to 85.

If the relay doesn't include a diode, the polarity doesn't affect the relay. It's still good practice to ground 85 anyway, since that's the standard polarity which will help electricians working on your car in future understand how it's wired, and will also mean nothing bad happens if somebody swaps in a relay with an integral diode in future.

If you were to wire the coil terminals backwards and fit a relay with an integral diode, the diode would short out the coil supply when you turned the relay on. That would burn something out - probably the diode.

[stevieturbo]

Open the relay to see if there is a diode.

What are you referring to as "sensor" on that drawing, I can think of no sensor that would hook up to a relay.

As for the switch ?

And why are you running 2 relays for only 1 fan ?

You will not be using terminal 87A

Your fan live will connect to terminal 87.

Battery or an ignition based live will go to terminal 85 ( via a fuse if you wish. If ign source the fan will only be able to run when the ign is on )

Good battery cable via appropriate fuse for load to terminal 30.

Terminal 86 will be from whichever output you are using from the Stack unit to energise the relay via ground which will turn the fan on.
If you want a manual switch to run the fan, install a switch between battery/chassis ground and terminal 86.

Again taking note of whether terminal 85 is given a permanent live or an ignition switch based live. Up to you whether you want the fan to run or not when the engine/ignition might be off.