Lotus Elan

Relay supply

PostPost by: Robbie693 » Mon Sep 15, 2014 10:21 am

Hello,

I need some ideas or tips on fitting a relay to the cooling fan, specifically where would be the best place to pick up a live feed from in a '72 +2S/130 (fuses in the dash model).

My only previous experience with relay fitting was when I did the headlights and for this I picked up the live feed from the starter solenoid which was probably not ideal. Obviously I can't keep using this point as a supply so I was wondering if anyone could help with a more professional way of doing this.

It also needs to be a switched live as I don't want the fan to keep running once the ignition is off. Basically, because of my limited electrical knowledge I could do with someone saying "pick up your feed from here " please!

Hopefully,

Robbie
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PostPost by: billwill » Mon Sep 15, 2014 1:43 pm

You don't really want the current for the fan to be passing through the ignition switch, so to achieve your aims you can feed the live to the SWITCH part of the fan relay from that feed point on the solenoid, preferably through a fuse, but you want the feed to the RELAY Coil (activated or earthed by the fan's temperature sensor switch) to be coming from a source that has passed through the ignition switch.

This means that although you have unswitched power to the contacts of the relay, when you turn the ignition off, the relay will open and stop the fan.

I don't know the Plus 2 layout well enough to give you exact pickup points.
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PostPost by: mbell » Mon Sep 15, 2014 6:12 pm

When I added some additional wiring/relays for the lights, light motors, fan and horn on my 73 +2/130 I took the main +12v from the alternator by adding a wiring post on the inner wing, I used a fusible link from the post to the alternator and connected the new feed and original alternator wire to the post. Not very original but improved safety and easy to undo.

I then used the standard fan supply wiring as the switched live to control a large relay. I powered the revotec fan controller, with its own relay, from this relay output with it's own fuse.

All the wiring is in one box on the inner wing just in front of the radiator. This box also includes fuse and relays for the headlights and horn. All these run off the switched large relay.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: Robbie693 » Tue Sep 16, 2014 9:52 am

Thanks both, I must admit I don't completely understand what you're saying but It's probably one of those things I'll grasp as I'm going along.

What I was also wondering was if there was any way I could use any of the fuse box connections on the back of the dash to get a live supply?

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PostPost by: billwill » Tue Sep 16, 2014 3:12 pm

Robbie693 wrote:Thanks both, I must admit I don't completely understand what you're saying but It's probably one of those things I'll grasp as I'm going along.

What I was also wondering was if there was any way I could use any of the fuse box connections on the back of the dash to get a live supply?

Robbie



The answer is yes, but you need to know what each fuse does so you ideally need some sort of diagram..

Do you have a multi meter? If not then get one, they are inexpensive nowadays.

To make your own chart of what fuses do what:

Draw an unannoted diagram of the fuses first

With ignition switch off:

Measure the voltage between each fuse and a good chassis ground.

Write down the fuse pins that are at 12v (i.e the permanently Live wires)

Turn on the ignition switch and note down which extra pins became live, these are the ones controlled by the ignition switch)

Again with ignition off, remove the fuses that were permanently live and measure the voltage at each side of the empty fuse location, one side will be live (connected to the battery) the other side will be off, showing that that side is the circuit protected by the fuse.

Replace those fuses (one at a time if there was more than one permanently live fuse) and work out which parts of the car electrics are now operational. i.e try Lights, Horn, ignition, window, heater-fan, wipers etc etc.

Write it all down!

With all the permanently live fuses back in place.

Remove the fuses that were activated by the ignition switch and with ignition switch on, use the voltmeter to see which side of the fuse is now live and which side of the fuse is the protected circuit.

Replace those ignition controlled fuses one at a time and find out which parts of the car electrics are controlled through each.

Write it all down for future reference.

You should now be able to choose suitable connection points for your engine fan relay
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PostPost by: Robbie693 » Tue Sep 16, 2014 3:51 pm

Excellent, understood and I have a multimeter :) - thanks Bill.

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PostPost by: billwill » Tue Sep 16, 2014 6:44 pm

PS: do not leave the ignition switch on with the engine stationery for a long time, because if the distributor contacts are closed you will be putting an uninterrupted current through the spark coil and it will get very hot and might get damaged.

You can, of course, disconnect the spark coil during the above measurements.
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PostPost by: Robbie693 » Wed Sep 17, 2014 3:53 pm

Thanks Bill, I knew about the coil getting hot if you leave the ignition on but no harm in a reminder :)

Ok so I've been looking at the wiring diagram and now I'm really confused!

The power supply for the existing fan already comes from the fuse box (35A fuse) to one of the 3 connections on the fan, the other connections on the fan are Earth and then a wire for the Otter switch.

Where do I put the relay? As the idea is to protect the circuit for when I fit an upgraded fan can I use the existing power wire for the relay?

Thanks again

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PostPost by: billwill » Wed Sep 17, 2014 5:15 pm

OK this diagram should help.

The top half shows what you probably have now according to your description. The third wire going to earth on the fan motor is probably merely a grounding of the metalwork of the motor to reduce radio interference. You can test this with your ohm meter, with nothing connected to the fan motor you will probably find that there is no connection between that ground wire and either of the other two wires; whereas the wires that I labelled + and - have a measurable resistance between them.


CoolingfanRelayCircuit.jpg and
Cooling Fan Relay Circuit


The lower half of the diagram shows what you want to achieve. The fan is now switched by the relay, not the otter switch and the relay coil is switched on by the otter switch. The main power for the fan comes from its original circuit (If it is on one of the ignition switch controlled fuses, move it to one of the permanently on fuses).

The power for the relay coil should be taken from one of the ignition switch controlled fuses. This will mean that when ignition is switched off the relay coil will have no supply, So even if the otter switch is still hot and closed, the relay will open and cut off the power to the cooling fan.
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PostPost by: PeterK » Thu Sep 18, 2014 11:01 am

My minimal wiring changes approach would be ....

Make a note of which wire goes where on the fan motor. You're especially interested in the Yellow/ Green and Black/ Green wires.

Disconnect the Black / Green wire (from the fan to the Otter switch) from the fan motor
Disconnect the Yellow / Green wire from the fan motor (comes from the fuse box and is switched by the ignition).

Wire this the Yellow / Green wire from the fusebox to pin 86 of your relay.
Connect pin 85 of the relay to the Black / Green wire to the Otter switch

Connect a new high current wire to pin 30 on the relay. To avoid having to pass wires through the bulkhead, this can come from the solenoid, but fit a fuse in circuit.
Wire pin 87 to the fan, where the original Yellow / Green wire went.

Connect the last connector on the fan (where the Black / Green wire came from) to earth.
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PostPost by: Robbie693 » Thu Sep 18, 2014 4:41 pm

Brilliant - thanks both.

Need to look at relays now, may be back with more questions if there is a confusing choice!

Cheers

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PostPost by: Robbie693 » Tue Sep 23, 2014 7:46 pm

Right, I've looked a relays and cable and I've decided to use the same as I did for the headlamps - 40A relay and 17.5A cable, probably overkill but I Can't see any harm in that(?).

Next to decide on the fuse rating for the supply lead, information is scarce but I notice on Demon Tweaks website that a 9" Kenlowe (for that is what I'm getting) draws 5.3A. I have however heard that these things can peak a bit on startup so I'm wondering what fuse I should fit?

Cheers

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PostPost by: billwill » Tue Sep 23, 2014 10:47 pm

You have your multimeter, use the 10 amp range to measure the current through the fan when running normally; then do the same (for just a few seconds) starting the current but holding the fan from turning. i.e stalled.

Suggestion: Use a fuse next biggest standard fuse above 1.5 times the stall current.
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PostPost by: Robbie693 » Wed Sep 24, 2014 3:20 pm

Ah yes - never thought of that!

Cheers Bill

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