Horn and cooling fan relays

Talk about the E-Type Series 1

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Robbiee
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#1 Horn and cooling fan relays

Post by Robbiee » Tue Nov 02, 2021 12:00 pm

Hi again
I’m a little confused as to which of these is which!!
The Horn relay appears to have 4 inputs/outputs C1/2 and W1/2 (C1 with 5 spades)
The engine cooling fan relay has 3 (C1/2 and W1)

I have part Srb111 from sng (for the horn I believe) with the correct number of connectors
However the same part is listed by them as being for the engine fan motor!!!

Is it okbto use the same relay for both or is there a specific 3 way relay for the fan ???

Robbie
Robbie 1962 3.8 Coupe OSG 1962 OTS ODG

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MarekH
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#2 Re: Horn and cooling fan relays

Post by MarekH » Tue Nov 02, 2021 2:20 pm

What contacts you have and what you want to use them for is easy to explain.

W1 and W2 are relay contacts and pull very little current. When a relay has no W2 contact, it is because the C2 contact doubles up as the W2 contact.

Whether the source of the 12v is a fused green wire carrying little current or a big fat unfused brown wire makes no difference to the relay winding - the relay itself still draws only ~150mA.

The relays with the missing W2 contacts are usually set up so the 12v supply that needs passing to the component is switched by a grounding contact on W1. If W1 is not grounded, then the C2 connection never gets passed on to the C1 terminal, so the component never sees its 12v supply.

A five terminal 6RA relay has separate W1 and W2 contacts, so the circuit to be switched is kept totally separate from the relay circuit. When the relay is "off" C2 is connected to C3 and when a circuit is made using W1 and W2, the C2 to C3 link breaks and C2 joins to C1.

Using the 3pole 6RA with the missing W2 contact is usually inappropriate for a high current application if the power is being supplied by a green wire to C2, as although this is fused, it is a much smaller gauge wire than a thick brown wire. You should consider horns and radiator fans to be high current components.

The wiring diagram lists the relay contacts being used.

kind regards
Marek

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Robbiee
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#3 Re: Horn and cooling fan relays

Post by Robbiee » Tue Nov 02, 2021 11:27 pm

Thanks Marek

Very detailed description

However :

I’m afraid I’m still not sure whether to use the 3 terminal relay for the horns or not though…you seem to suggest not but then say to check the wiring diagram!

Can you put it more simply in lay man’s terms please?

Thanks
Robbie
Robbie 1962 3.8 Coupe OSG 1962 OTS ODG

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mgcjag
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#4 Re: Horn and cooling fan relays

Post by mgcjag » Wed Nov 03, 2021 9:03 am

Hi Robbie..the fan and horn relays are different...the srb111 is a 20amp single contact relay. .i can see no problem in you useing it for both if wired correctly. The problem you may have is for the horns you will have 4 wires but for the fan 3 wires...have a look at this thread.....the first post has a link to the Lucas details, pinouts, etc.....Steve viewtopic.php?f=3&t=17120
Steve
69 S2 2+2 (just sold) & Building a C type replica, 1960 xk150fhc

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Robbiee
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#5 Re: Horn and cooling fan relays

Post by Robbiee » Wed Nov 03, 2021 9:54 pm

Thanks v much
Robbie 1962 3.8 Coupe OSG 1962 OTS ODG

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Norton
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#6 Re: Horn and cooling fan relays

Post by Norton » Tue Jan 18, 2022 9:12 am

Lucas relays.
Shows relays in relaxed position. W2 is normally earthed, when W1 is powered, relay is switcing. Relay may also be operated by switching earth in/out. May also be done by another relay etc. Playing with relays can be fun, and here you see how they switch. As long as it is a basic relay, without diode or condensator it doesen’t matter if W1 or W2 is earthed.

When my a/c switch started playing up, I put relays into the circuit to take care of high current switching. As the switch was suffering from heat damage. Old corroded / dirty contacts + high current = heat.

Harald
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