Rear light LED on Givi Top Box

[davsato]

instead of tape would the reflective stripes from a workmans waistcoat do just as well?

[davsato]

Originally Posted by Lutin

I got my LEDs from this crowd in China -

eBay Store - Sure Electronics: LEDs, Tools, Components

Delivery was not too long and the prices are very keen - much better than Maplin.

Like I said earlier with my series / parallel combination circuit I think the total current draw is around 80 mA as compared to the original 2 Amps.

they are doing 100 5mm superbright red LEDs, including 200 resistors to make them work on 5v or 12v, for £4.80 free delivery, which beats maplins by a few hundred percent even if you have to wait for them to come from china!

just one question, i assume i have to put a resistor on each LED? and it goes on the pos leg? thats two questions, sorry. alright, three, is it best to put the LEDs in series or parallel or dont matter?

[Lutin]

Originally Posted by davsato

they are doing 100 5mm superbright red LEDs, including 200 resistors to make them work on 5v or 12v, for £4.80 free delivery, which beats maplins by a few hundred percent even if you have to wait for them to come from china!

just one question, i assume i have to put a resistor on each LED? and it goes on the pos leg? thats two questions, sorry. alright, three, is it best to put the LEDs in series or parallel or dont matter?

First off, you can put the resistor in either leg as it doesn't matter at all.

Second, and this is where it gets technical, the voltage drop across an LED is of the order of 2 Volts. So, on a 12 Volt supply there's 10 Volts to drop across the resistor - which is basically wasted energy. At an LED current 0f 20 mA (which is what the LEDs are rated at) the resistor will need to be 500 Ohms and needs a power rating of 0.2 Watts.

So, what you do with a 12 Volt supply is put at least 3 LEDs in series (one after the other) - the effective Volt drop is now 6 Volts and the resistor only needs to be (6 Volts / 20 mA ) or 300 Ohms and needs a power rating of 0.12 Watts (about an eighth of a Watt). Less wasted energy.

On a 12 Volt supply you could put more LEDs in series, but I stuck with 3 as it made my wiring simple. However, I did put two groups of 3 LEDs in parallel.

Confused yet?

The total power consumption of my system is 100 mA, which is 1/20th of the original 2 Amps with the filament lamps.

If you want I can knock you up a drawing which will make the above much easier to understand. Picture / thousand words scenario.

I don't think the LEDs took that long to arrive, I can have a root about and see if I can come up with time scales, if you like.

[Kymmy]

Personally If using a proper PCB (or veroboard) dump the resistors as supplied and get some SIL resistor arrays, they're a lot more neater

[Lutin]

Originally Posted by Kymmy

Personally If using a proper PCB (or veroboard) dump the resistors as supplied and get some SIL resistor arrays, they're a lot more neater

True, but there is the extra expense. And I bet there's not a lot of people would know an SIL resistor array if they stood on one in bare feet.

[jarl]

Originally Posted by Lutin

the voltage drop across a red LED is of the order of 2 Volts.

Fixed. White LED's tend to run at 3 to 4V, all other colours somewhere in the middle.

But yeah

[Farky]

Snaphappy & Lutin... youve sold me on that idea, cheers for the pics!!

By far the easiest and most effective idea just adding tape underneath the reflector...which as you say, doesnt reflect dirt, why doesnt Givi see this?

Cuz theyre Italian???

Also looking to add some visability to the side of the bike so might use some of this in places it wont effect styling.... wrap around the pannier tunes and crash bars for example, just not sure how it will stick to metal but thin strips may do well if this stuff cuts easy.

Anybody find those led valve caps that light up when spining anywhere? Edit..scrap that, just remembered they break the valve in some instances.

Found some nice Black Diamond reflective sticker sheets which can be cut to shape...black in daylight = no loss of style + very reflective Scotch White at night. On order now! http://www.wiggle.co.uk/mc/cycle/7/Respro/Reflectives/

[Lutin]

Originally Posted by jarl

Fixed. White LED's tend to run at 3 to 4V, all other colours somewhere in the middle.

But yeah

You are absolutely right but, as we were talking about a brake light, I assumed that the "red" would be taken as read, as it were.

That, or me being slap-dash.

[Grendel]

I tend to get reflective Tape & Stickers from here:

Cyberglow

As you can see from pics the boxes are covered in the stuff and it works a treat at night







Must admit i like the idea of putting reflective tape behind the rear lights but surely it would melt with the heat from the bulb?
Also Would you use Red Or White reflective tape behind the filter?

[Lutin]

Originally Posted by Grendel

Must admit i like the idea of putting reflective tape behind the rear lights but surely it would melt with the heat from the bulb?
Also Would you use Red Or White reflective tape behind the filter?

The idea was not to fit the reflective tape behind the lights but behind the red lenses fitted to the top-boxes or side cases.

The red lenses on Givi boxes can be removed as they are held on by very small screws. Behind the lenses is white tape stuck over the black plastic of the boxes. It is this tape that is being talked about, as it is not great reflectivity wise.