Technical direct replacement?

[SgtRich]

ok, so i decided to replace my speedo cluster bulbs with LED direct replacements, and now it keeps fusing the instrument illumination... any help guys?
many thanks

 

[bredsticz]

I presume you mean keeps blowing the fuse, get a bigger amp fuse then!

 

[SgtRich]

doesnt that defeat the direct replacement.. nothing was mentioned about bigger fuses but its the standard fuse thats meant to be there :S

 

[bredsticz]

The resistance of an LED is less than a bulb, so therefore more current and the standard fuse will blow with the larger current so needs a higher amp fuse so as not to blow.

I think I'm right but not done a physics lesson for over 2 years now

 

[paul12345]

Dont use a bigger fuse. The fuse will be blowing due to short circuiting i.e. not enough resistance. adding a bigger fuse would either burn out the leds or a wire somewhere down the line.

Bigger fuses would be needed if you were using more current. Leds will be less then the bulbs.

Dont help when you dont post whats leds you've put in.

 

[bredsticz]

Dont use a bigger fuse.

Bigger fuses would be needed if you were using more current. Leds will be less then the bulbs.

Dont help when you dont post whats leds you've put in.

Aren't I right in thinking less resistance in a circuit creates more current though?

So if the resistance of the LED is less than original bulbs then there will be more current

 

[SgtRich]

these arethe LED's that were supplied... http://www.ultimatemods.co.uk/286-led-bulb.html
and i believe a bigger amp would just set a wire on fire or the LED's or something :s

 

[bredsticz]

Not talking THAT much big of an amp difference but enough to blow the fuse. Wires have to be safe still!
Fuses are designed to blow if the current goes up at all

 

[paul12345]

Aren't I right in thinking less resistance in a circuit creates more current though?

So if the resistance of the LED is less than original bulbs then there will be more current

Yes, more current going back through the wire.

The fuse rating goes higher when you are USING more current through devices etc adding resistance etc.

Look at it this way if you remove the led and short the contacts you'll have lot more current going through the wire - i.e. short circuit. this will blow the fuse add a bigger fuse untill it stops blowing you're going to burn out a wire or blow up the battery

 

[paul12345]

Look at the led - is there a resistor in the end.

should be like

http://www.autobulbsdirect.co.uk/286-T5-LED-Dashboard-Bulbs-286LED.html

 

[paul12345]

Not talking THAT much big of an amp difference but enough to blow the fuse. Wires have to be safe still!
Fuses are designed to blow if the current goes up at all

2 ways to blow the fuse;

1- to much current through it - i.e. short circuit

2- hooking up devices that use more amps then the fuse rating

you kind of got ur wires crossed your trying to do the solution for case 2 for case 1

 

[bredsticz]

like I said it's been a while since I've done any physics! Never did like electrics too much! Mechanical is far easier and more logical

 

[SgtRich]

so i got the LED's in place.. And thy are working fine... But they are really dull and not very blue... More.. Greeny blue :/.. I hear some cars have filters on the speedo clusters... Is the mk1 punto one of them! Is so... Where is the filter and how do you remove it? Many thanks

 

[DaveMcT]

LEDs are very directional. Bulbs throw light all around. Maybe LEDs are just not suitable for the job. Maybe the cluster has coloured plastic over the bulbs that's affecting the LED colour.

 

[MikeSalt]

LEDs should pull less current than the filament bulbs, so do not increase the fuse rating. LEDs are solid-state devices, so A-level physics goes out of the window.

Clearly, one of these bulbs is pulling too many amps. Grab yourself a multimeter and set to 'resistance' to measure each bulb. You should find one with stupidly low resistance compared to the others. Fitting both an LED and resistor in such a compact package leads to the possibility of an internal short due to dodgy soldering.

 

[DaveMcT]

A diode is a one way valve.

I'm not sure about Light Emitting Diodes but I suspect when connected the wrong way they become a short circuit. IIRC they light up when run in the reverse direction.

 

[MikeSalt]

Indeed, if an LED is run backwards, one of the effects can be to allow the doping to cross the boundary, resulting in a short-circuit.

 

[DaveMcT]

Now why did that fuse blow