DEFENDER2.NET - View topic - Do I need to fit a relay?

↓ Advertise on Defender2 ↓

Home · FAQ · New Posts · My Posts · PMs · Search · Members · Map · Calendar · Profile · Donate · Register · Log In

Home > In Car Electronics > Do I need to fit a relay?

Page 1 of 1

Print this entire topic ·

Sammyboy

Member Since: 28 Feb 2017
Location: Hampshire
Posts: 121

2012 Defender 110 Puma 2.2 USW Sumatra Black

Do I need to fit a relay?

I am considering fitting either one or two rear LED work lights to my Puma. What determines the need, or not, to include a relay in the circuit? I am only going to connect it to a switch I do not intend wiring it to come on with reverse.

Discovery 4 HSE
Defender 2.2 110 USW XS
Ford Kuga AWD
Discovery 3
Range Rover P38
Discovery - 300 TDI
Discovery - 200TDI

16th Jan 2019 8:32pm

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5707

2006 Defender 110 Td5 USW Zermatt Silver

No relay needed for what you’ve stated.

16th Jan 2019 8:35pm

grafty99

Member Since: 15 Aug 2012
Location: North Devon
Posts: 4785

Re: Do I need to fit a relay?

Sammyboy wrote:
What determines the need, or not, to include a relay in the circuit?

Current draw.

A relay is an electronic switch which can switch higher loads than a normal toggle switch for example. If you are using low current loads (like your led lights for example) they generally aren't required.

Higher current loads which draw more than the switch can handle need a relay to handle the current so the switch doesn't melt

2002 90 Td5 Station Wagon
1990 Vogue SE
Triumph Tiger Explorer 1200
Td5 90 Thread http://www.defender2.net/forum/topic50767.html
Tdi 110 Thread https://www.defender2.net/forum/topic69562.html
RRC Thread http://www.defender2.net/forum/topic54492.html
Instagram http://www.instagram.com/george_grafton

16th Jan 2019 8:43pm

Sammyboy

Member Since: 28 Feb 2017
Location: Hampshire
Posts: 121

Do switches come with a current load rating? The lights I am considering range between 18W and 36W. Using the 36W I would presumably need a switch with a 3A rating?? Discovery 4 HSE
Defender 2.2 110 USW XS
Ford Kuga AWD
Discovery 3
Range Rover P38
Discovery - 300 TDI
Discovery - 200TDI

16th Jan 2019 8:49pm

grafty99

Member Since: 15 Aug 2012
Location: North Devon
Posts: 4785

The current handling capacity of a switch is normally advertised when you buy. If in doubt fit a relay

As battery voltage is actually slightly higher than 12V then current draw is actually slightly less than 3 amps at 36W. A 20A rated switch such as a Carling contoura switch would cope no problem

16th Jan 2019 9:22pm

olivers

Member Since: 19 Jan 2012
Location: Southern Scotland
Posts: 115

2007 Defender 90 Puma 2.4 XS CSW Zambezi Silver

I don’t disagree with previous posters - no relay needed in your case. However, I use relays for all my worklights for a different reason: I have a separate box where the relays are located. This allows me to route the cables from the work lights (six of them, altogether) to that box, and I have thinner multi-core wires running from there to the dashboard where the switches are - much easier than having to route the actual power cables through the dashboard (and fuses, don’t forget).

Finally, if current draw is not minimal, you can also expect switches to degrade a bit over time due to corrosion. Of course a high-quality switch should deal with its rated current for a long time, but using a relay will be easier on the switch - and the relay can be changed more easily later if it should stop working.

16th Jan 2019 9:44pm

Page 1 of 1

All times are GMT

Jump to

< Previous Topic | Next Topic >

Posting Rules

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum