Page 1 of 2

Relay source wire

PostPosted: Fri Aug 16, 2019 12:18 am
by lightwait26
Looking to add a cooling fan relay to an S3, where be the best place to connect the permanent, unswitched hot lead?

Re: Relay source wire

PostPosted: Fri Aug 16, 2019 8:15 am
by lotusfan
Probably the best place would be the main battery connection on the starter solenoid on the firewall behind the carbs. There should be a spare tab on there. I think the solenoid connections point downwards on an S3 so may be difficult to get at. Don't forget a fuse!

Re: Relay source wire

PostPosted: Fri Aug 16, 2019 8:22 am
by MarkDa
If you don't mind it being unfused you could use the battery side of the starter solenoid.
Which doesn't preclude you using an inline fuse of course.
It's a good source for a highish load on right side of the car.

Re: Relay source wire

PostPosted: Sat Aug 17, 2019 6:31 am
by alan.barker
I use relays which have a fuse
Alan

Re: Relay source wire

PostPosted: Sat Aug 17, 2019 11:08 am
by elanner
It terms of neatness wouldn't it be better to power it from the F connector on the RB340 control box? Electrically it's the same place, but would avoid a stray "what-the-heck's-this?" cable hanging off the solenoid, and could be tidily integrated to the rest of the wiring system.

(Not that I even have a control box, the PO removed it when fitting an alternator and made a up a small distribution panel to replace it. My fan is powered from the panel.)

Nick

Re: Relay source wire

PostPosted: Mon Aug 19, 2019 1:03 am
by lightwait26
elanner wrote:It terms of neatness wouldn't it be better to power it from the F connector on the RB340 control box? Electrically it's the same place, but would avoid a stray "what-the-heck's-this?" cable hanging off the solenoid, and could be tidily integrated to the rest of the wiring system.

(Not that I even have a control box, the PO removed it when fitting an alternator and made a up a small distribution panel to replace it. My fan is powered from the panel.)

Nick



I have essentially the same setup with my alternator. This would certainly be the easiest method.

I assume that you are referring to the terminal for the heavy output wire from the alternator ?

Re: Relay source wire

PostPosted: Mon Aug 19, 2019 9:44 am
by lotusfan
art

If you have an alternator, not standard on an S3, then the heavy output wire is a good choice and is very close to where you need the supply.

Re: Relay source wire

PostPosted: Mon Aug 19, 2019 12:44 pm
by elanner
lightwait26 wrote:I assume that you are referring to the terminal for the heavy output wire from the alternator ?


Yes. There's nothing wrong with using the solenoid, of course. But for neatness and future maintainability I'd be keener to connect the fan closer to the main wiring hub rather than string a stray wire over from the solenoid. Depending on your fan controller you may also need to run an "enable" wire from the switched power, so that the fan will only run when the ignition is on. In which case it's tidy to keep both wires close together.

Nick

Re: Relay source wire

PostPosted: Mon Aug 19, 2019 1:41 pm
by MarkDa
Deleted double post

Re: Relay source wire

PostPosted: Mon Aug 19, 2019 2:04 pm
by MarkDa
The OP wants a permanent live supply - so wherever it comes from it can provide the feed to thermal switch from the relay end of the wire.
I used the same main feed wire for the air horns as well which with a double relay brought an added lightness to the wiring!
As well as having less wires to tie in or trace in the future.

Re: Relay source wire

PostPosted: Mon Aug 19, 2019 2:36 pm
by elanner
MarkDa wrote:The OP wants a permanent live supply - so wherever it comes from it can provide the feed to thermal switch from the relay end of the wire.
I used the same main feed wire for the air horns as well which with a double relay brought an added lightness to the wiring!
As well as having less wires to tie in or trace in the future.


Yup, right. But with my fan controller (a Derale 16759) there's a permanent live supply to the fan (which draws a high current). Then there's another low current wire from the switched (ignition) 12v that "enables" the controller. The controller monitors the thermal sensor and an under-the-dashboard override switch. The fan doesn't run when the ignition is off. Picture attached - there are lots of way to do this (note that the controller is on the ground side of the circuit, not the supply side, per Derale instructions).

Nick
Elan_FanWiring.pdf
(25.32 KiB) Downloaded 36 times

Re: Relay source wire

PostPosted: Tue Aug 20, 2019 1:27 am
by lightwait26
Thanks to all who have responded!

Re: Relay source wire

PostPosted: Tue Aug 20, 2019 5:37 am
by Andy8421
elanner wrote:
MarkDa wrote:The OP wants a permanent live supply - so wherever it comes from it can provide the feed to thermal switch from the relay end of the wire.
I used the same main feed wire for the air horns as well which with a double relay brought an added lightness to the wiring!
As well as having less wires to tie in or trace in the future.


Yup, right. But with my fan controller (a Derale 16759) there's a permanent live supply to the fan (which draws a high current). Then there's another low current wire from the switched (ignition) 12v that "enables" the controller. The controller monitors the thermal sensor and an under-the-dashboard override switch. The fan doesn't run when the ignition is off. Picture attached - there are lots of way to do this (note that the controller is on the ground side of the circuit, not the supply side, per Derale instructions).

Nick
Elan_FanWiring.pdf


Nick,

I wouldn't consider that circuit to be best practice. Fuses can be used effectively in many places in a circuit, but in a car application, it is best to have the fuse upstream of the device and wiring being protected. In your attached diagram, the fuse will protect against an over-current event in the fan, but parts of the circuit and the fan itself are unfused in the event of a short to earth. Not as likely in an Elan as a normal metal bodied car, but still possible. It would be better to have the fuse as close to the point of supply as possible.

Andy.

Re: Relay source wire

PostPosted: Tue Aug 20, 2019 8:51 pm
by elanner
Andy,

I agree, your suggestion is what I would do if starting from scratch. However the controller that I've been referring to comes with a good quality, nicely built loom that is set up per my previous diagram. So I had the choice of ripping it apart and putting the fuse nearer the power source or just trusting the folk at Derale. I chose the easy option!

I have to say that I like the idea of running 12v directly to the powered device and then having all the unreliable stuff - connectors, fuse blocks, relays - controlling the ground.

Anyway, for completeness, here are the Derale installation instructions and installation kit.

Nick
derale1.jpg and

derale2.jpg and

der-16759_xl.jpg and

Re: Relay source wire

PostPosted: Tue Aug 20, 2019 10:36 pm
by MarkDa
It's certainly an impressive product.
Whilst I agree that in principle fuses should be as early in the run as possible if presented with a prefabricated kit I too would go with it as standard overload conditions are catered for.