Overdrive Relay

[exint2]

Hi does anyone have the specifications for the Overdrive Relay (TR4A)?

 

Ideally with a link ;-)

 

Thanks

[Kevo_6]

Lucas 6RA 20 amp, I believe.

 

http://www.moss-europe.co.uk/relay-6ra-type-142169a.html?assoc=114915

[exint2]

Thanks Kevo

 

Nick

[exint2]

Can this be substituted for a more modern alternative relay? (if so which)

 

as I assume that progress in electronics would make newer models more reliable?

[kob666e]

Easy to fit a modern relay, but they are no more reliable, it's just easier and cheaper to have a bunch of them in the tool box. http://www.gsparkplug.com/durite-relay

[exint2]

Thanks Justin -

 

Final dumb question - Latching, normally Open, or normally closed type?

[stillp]

Normally open.

 

Pete

[kob666e]

Thought it would show the correct relay, try again: http://www.gsparkplug.com/durite-relay-mini-make-break-a-term-30-amp-12-volt-cd1-0-727-62.html?___SID=U

[AndrewP]

If I remember correctly, one way of ensuring the relay lasted longer was to fit a flyback diode across the solenoid.

As you are switching on/off an inductive load (the O/drive solenoid) it induces a large back EMF voltage when the contacts are pulled apart (similar principal to your ignition coil).

 

I used a bog standard 30A automotive coil after my original Lucas went belly-up and never had an issue after that.

 

https://en.wikipedia.org/wiki/Flyback_diode

 

Keep a few handy, but this should at least prevent the coil in the relay copping the full brunt of the high voltage as it opens/closes.

 

Andrew

[exint2]

Thanks guys

 

Really appreciate the help form all of you

 

Nick

[RogerH]

Hi Nick,

it is a simple single pole single toggle (SPST) relay - nothing special

 

http://www.vehicle-wiring-products.eu/product.php/642/12v-4-blade-relay this is a what you need

 

If you get the relay socket then fitting a replacement (never needed) is easy.

 

You can have the same relay for the headlight mod, leccy Rad Fan etc etc - so carry a couple of spares.

 

Roger

Edited April 14, 2016 by RogerH

[RAHTR4]

Hi Roger,

 

Car electrics are certainly not my strong point, so forgive me if I have got the wrong end of the stick, but I am puzzled that the relay in the link that you posted, has a description as follows :

 

"This is the most common relay. Use for single circuit on/off applications such as spot lamps, horns, rear screen heater etc."

 

Your inference is that this relay would be suitable for use with the overdrive, headlamps, fans, etc, basically this same one relay for every application on the car.

 

The Lucas catalogues state that a 6RA 33213 relay was originally used for the overdrive on the TR4 and TR4A's and this has four connections - C1, C2, W1 and W2.

 

The TR4A had a relay added for the horn circuit which was a 6RA 33188 and this has three connections - C1, C2 and W1.

 

Now to me these two relays look like totally different animals.

 

Has technology now moved on and thus one relay does everything?

 

If so then the wiring for each application may well be different?

 

Any clarifications would be most welcome.

 

Regards, Richard

[RogerH]

Hi Richard,

I haven't studied the Lucas R6 relays but the three terminal relay must be grounded through its metal case.

+12V to W1 and out through the case. W is the relay winding.

C1 & C2 are the contacts. For both relays Normal Open (NO) - thus no power flows unless energised with 12V on W1.

 

The OD relay does not have a grounded case - hence W1 and W2.

I think that W2 is present because the column switch and the GB inhibit switches are switching earth. If the relay case was earthed then that would bugger up everything.

 

Now, the modern relay above is a reasonable quality product (Durite) and is heavily rated at 30amps.

The earth is separate mimicking the OD relay.

If you wanted to use it for the horn then a separate earth wire would be needed.

 

If I had a choice between a new 'Lucas' R6 (made in some strange place overseas or a Durite I would go for the Durite.

At present I am still using a very old original (49 years old) R6.

 

Roger

[RAHTR4]

Hi Roger,

 

Thank you for the clarifications, I have made notes......!!!

 

However as using Durite relays means messing about with the wiring, I think I will stick with the Lucas 6RA relays as I have a number which are period new old stock.

 

Regards, Richard

[RogerH]

Hi Richard,

indeed, stick with what you are happy with. The original Lucas relay has a good track record.

I still have the OD and horn R6 relays. They will be swapped over if and when needs must.

 

Roger

[peejay4A]

From memory Roger the horn relay isn't wired like you suggest. It has +12v permanently on one of the C contacts. That's internally wired to the missing W terminal. The other W terminal receives an earth from the horn push to operate the relay which sends +12v to the horns. The horn relay case isn't grounded.

Edited April 18, 2016 by peejay4A

[RogerH]

Hi Pete,

that sounds about right.

I didn't look at the wiring diagram with my above answer just the fact that it has three tags means something doubles up.

 

Roger