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]

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

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]

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?

If I had shorted it then a 7.4 amp one would surely blow too??

Ahhh fair point.

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.....

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.