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Sammyboy



Member Since: 28 Feb 2017
Location: Hampshire
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United Kingdom 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. Bow down Discovery 4 HSE
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Post #751777 16th Jan 2019 8:32pm
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
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2006 Defender 110 Td5 USW Zermatt Silver
No relay needed for what you’ve stated.
Post #751779 16th Jan 2019 8:35pm
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grafty99



Member Since: 15 Aug 2012
Location: North Devon
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United Kingdom 2002 Defender 90 Td5 HT Caledonian Blue
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 Thumbs Up 2002 90 Td5 Station Wagon
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Post #751780 16th Jan 2019 8:43pm
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Sammyboy



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

United Kingdom 2012 Defender 110 Puma 2.2 USW Sumatra Black
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
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Post #751781 16th Jan 2019 8:49pm
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grafty99



Member Since: 15 Aug 2012
Location: North Devon
Posts: 4784

United Kingdom 2002 Defender 90 Td5 HT Caledonian Blue
The current handling capacity of a switch is normally advertised when you buy. If in doubt fit a relay Thumbs Up

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 Thumbs Up 2002 90 Td5 Station Wagon
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Post #751790 16th Jan 2019 9:22pm
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olivers



Member Since: 19 Jan 2012
Location: Southern Scotland
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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.
Post #751796 16th Jan 2019 9:44pm
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