Member Since: 08 May 2006
Location: Bristol
Posts: 16390
Watts, Amps Volts ??
If I have 2 x LED lights each rated at 36 Watts.
what cable amperage do I need ?
is the calculation correct
amps = (36x2)/12v = 6amps
ive got some 33amp thinwall twin core wire - will that do ? and what size relay do I need ?
I was expecting 30amps - not 6 amps !!
Duncan
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If I'd known I was going to be so thirsty this morning I'd have drunk more beer last night.
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depends on how the bulbs are connected - are they separate circuits? can be connected in series or parallel and that will have an effect on the current flow/ratingSi
2016 Disco 4 SE Tech
2019 Fiesta ST3
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on another note - standard brake light bulbs are only 21wattsSi
2016 Disco 4 SE Tech
2019 Fiesta ST3
2021 GBS Zero
11th Apr 2013 5:08 pm
wiggs
Member Since: 03 Sep 2006
Location: Manchester
Posts: 14372
3 amps each light...so 6 amp for the both
33amp cable is more than enough G4 Gone ...but not forgotten
11th Apr 2013 5:16 pm
DiscoDunc
Member Since: 08 May 2006
Location: Bristol
Posts: 16390
I like to make sure
I take it a standard 30a relay will be ok then and I can run both the lights off the same contacts so I only need to run one live cable to the lights and connect the -ve to an earth point on tht vehicle.
perhaps I'll buy some smaller cable
if standard driving lamps are 55w each , why does a pair come with 30a fuses and 30a relays ? Duncan
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If I'd known I was going to be so thirsty this morning I'd have drunk more beer last night.
FFRR Autobiography 4.4 SDV8 MY17
D4 HSE MY13 SOLD
FFRR 3.6 Vogue TDV8 SOLD
D4 HSE MY10 SOLD
D4 SE TECH MY15 SOLD
D4 XS MY12 SOLD
D4 HSE MY10 SOLD
D3 HSE MY06 - Re-Cycled Worldwide
11th Apr 2013 5:40 pm
Tufty
Member Since: 13 Jul 2010
Location: UK
Posts: 481
DiscoDunc wrote:
if standard driving lamps are 55w each , why does a pair come with 30a fuses and 30a relays ?
The fuse is there to protect the circuit more than the lamps, if you use a 30A relay and cable capable of carrying 30A then a 30A fuse is fine.
Don't know what kind of inrush current halogen lamps have?
Also reading he below post most driving lamp kits probably assume wiring from the battery direct to the relay.
Last edited by Tufty on 11th Apr 2013 7:20 pm. Edited 1 time in total
11th Apr 2013 6:54 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
33 amp is serious overkill but if you use it select the correct fuse for the load, not the wire. Whilst a 30 amp fuse would protect the wire it would not protect whatever wiring you are connecting to on the car as that is unlikely to be 30 amp. I'd rather have the fuse blow on the accessory rather than the fuse on the circuit you are connecting to.Land Rover - Turning Drivers into Mechanics Since 1948
I got a wiring kit with a new set of spots and was a bit shocked to find a 30amp fuse with it. As said above, fuse shoud be the next size above your load. I've changed the 30a one out for a 15a one to run a pair of 55w lamps
11th Apr 2013 9:26 pm
DaveT
Member Since: 01 Aug 2005
Location: Cornwall
Posts: 2578
72w of LED sounds like one heck of a lot of light
8)
Can't wait to see the pics of that one Long succession of Disco's since 2001...
SIII Lightweight - neglected & rusting. Bulkhead, A panels, vent panel & outriggers now disintegrated - Next years project!
11th Apr 2013 9:37 pm
DiscoDunc
Member Since: 08 May 2006
Location: Bristol
Posts: 16390
112 watts on the bumper and 72 watts on the roof rack.
let the be light .......... Duncan
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If I'd known I was going to be so thirsty this morning I'd have drunk more beer last night.
FFRR Autobiography 4.4 SDV8 MY17
D4 HSE MY13 SOLD
FFRR 3.6 Vogue TDV8 SOLD
D4 HSE MY10 SOLD
D4 SE TECH MY15 SOLD
D4 XS MY12 SOLD
D4 HSE MY10 SOLD
D3 HSE MY06 - Re-Cycled Worldwide
Last edited by DiscoDunc on 12th Apr 2013 6:47 am. Edited 1 time in total
11th Apr 2013 10:03 pm
Gobbler
Member Since: 28 Jul 2012
Location: Kent
Posts: 116
DiscoDunc,
It's Ohm's Law wot you needs:-
The current I in amps (A) is equal to the power P in watts (W), divided by the voltage V in volts (V):
I(A) = P(W) / V(V
or, made simpler,
A = W / V
(just use the Rules of Algebra wot you forgot from Skool to 'rotate' the equation... e.g. W= V X A etc )If it has TIT's or WHEEL's it will cause you problems!!
Member Since: 08 May 2006
Location: Bristol
Posts: 16390
thanks all.
question now is do I run the cable up the a pillar trim or through the car and out of the boot upto the rack ? I just know if I taker the RAI and A pillar trim off ill break come clips or something.Duncan
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If I'd known I was going to be so thirsty this morning I'd have drunk more beer last night.
FFRR Autobiography 4.4 SDV8 MY17
D4 HSE MY13 SOLD
FFRR 3.6 Vogue TDV8 SOLD
D4 HSE MY10 SOLD
D4 SE TECH MY15 SOLD
D4 XS MY12 SOLD
D4 HSE MY10 SOLD
D3 HSE MY06 - Re-Cycled Worldwide
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