locoboy
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| posted on 16/4/15 at 06:10 PM |
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LED light woes and blowing fuses pls help!
Folks
I have 4 LED lights from Maplin and they all run off a communal feed and a communal earth, I have wired it up with a 5 amp fuse in my fuse box and it
blows it
Put a 7.5 amp in and it doesn't blow it.
I put my multimeter in-line in the positive feed wire with it set on 10A to measure how many amps the 4 of them are drawing and it is showing 0.45 so
why is it blowing a 5 amp fuse??
any help appreciated as I want to get it sorted for bustypes vw show at the weekend :-(
It is wired up as shown in the diagram below
 
wiring issue
Lights I have are here
http://www.maplin.co.uk/p/pack-of-4-warm-white-led-floor-lights-a53lw
Thanks
Colin
[Edited on 16/4/15 by locoboy]
ATB
Locoboy
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russbost
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| posted on 16/4/15 at 06:22 PM |
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First of all are they defo 12V led's, doesn't appear to give a voltage in Maplins ad - link doesn't work BTW had to copy/paste it
into browser
LEDs do have some very strange behaviour see the post I put up a while back
Link
my guess is that they are drawing an initial burst of current which is exceeding the 5A & then settling down to draw the 0.45 that you're
seeing, simple answer is leave the 7.5A fuse in, you're highly unlikely to damage any wiring with a 7.5A fuse to blow first
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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locoboy
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| posted on 16/4/15 at 06:30 PM |
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Hi Russ,
Yeah deffo 12v lights, they come with a 240v ac-12v dc converter and transformer in the plug
The plug states
input 240 0.3A 50/60Hz
12V 0.5A
I also have another set of 4 to wire in off the same power feed..............will that need a 15 amp fuse now? (2x7.5A)
Cheers
COl
[Edited on 16/4/15 by locoboy]
ATB
Locoboy
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digiman
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| posted on 16/4/15 at 06:45 PM |
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Have you shorted the communal feed to the communal earth? from the Maplin catalogue the LEDS are fed by a dual core cable, have you tapped into the
wrong core on one of them?
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locoboy
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| posted on 16/4/15 at 07:08 PM |
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If I had shorted it then a 7.4 amp one would surely blow too??
ATB
Locoboy
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digiman
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| posted on 16/4/15 at 08:23 PM |
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Ahhh fair point.
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theprisioner
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| posted on 16/4/15 at 08:31 PM |
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The Maplin product information is not specific enough to draw conclusions where non linear voltage vs current LED's are concerned. The 12V at x
amps only refers to the maximum capability of the power conveter.
1) Each LED (in it's naked form) is a non linear device and is ideally driven by a constant current. A sort of constant current can be provided
from a constant voltage source by adding a series resistor (to each and every LED).
2) The series resistors can be hidden (in the illustration) in the distribution block for example. In any case you have to define where/how the
constant current is derived.
3) A diode (LED) in series with a fuse will blow without the conversion from constant voltage to a constant current.
I think this has been explained in this forum before.....
http://sylvabuild.blogspot.com/
http://austin7special.blogspot.co.uk/
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bi22le
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| posted on 16/4/15 at 10:14 PM |
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I would say your problem lies with the transformer. It may be drawing current to start with. Have a read about electric coils and EMF.
Back EMF is a massive problem and can spike large voltages. Solved with a capacitor or diode.
As russ says. If your only going to a 7.5A fuse then don't fuss. If you said a 30A solved it, I would be more worried.
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