LED indicators..

[zero]

Ello all..

Not sure where to start.. fitting some led's as replacement indicators on a bike, only the front indicators though..

So..

Solution 0: 7 x 2 array uses 14 LEDs exactly

+----|>|----|>|----|>|----|>|----|>|----|>|----|>|---/\/\/----+ R = 56 ohms
+----|>|----|>|----|>|----|>|----|>|----|>|----|>|---/\/\/----+ R = 56 ohms

The wizard says: In solution 0:

* each 56 ohm resistor dissipates 22.4 mW
* the wizard says the color code for 56 is green blue black
* the wizard thinks 1/4W resistors are fine for your application
* together, all resistors dissipate 44.8 mW
* together, the diodes dissipate 560 mW
* total power dissipated by the array is 604.8 mW
* the array draws current of 40 mA from the source.

However i know this will send the indicator into an absoloute mental disco fit, so.... if the original bulb draws 20watts/1.5amps(ish)@~14volts am i right in thinking that 10.7Ω of resistance would fix that problem? say if it were between the end of the array and the earth line?

Does that seem about right or a load of rubbish?

 

[andi]

Despite being an electrical engineer, I have no idea

But, if your buying standard LED indicators, Hein Gericke sell the resistors you need for about £2 each, which should save you some work..

 

[eidolon]

Do it the easy way, check out www.ultraleds.co.uk

 

[zero]

Thing is with the resistors if i can work out the rateing i can get the same things for 20p max..

Think i'll have to experiment a bit, get a big bag...

I'd like to fit one right off the shelf but its no longer got fittings to plug them in (they had been in there for a decade though)

As far as i can fathom to draw roughly 1.4 amps on a 14v system i'll need a resistor of roughly 10KΩ (not 10 as i thought at first )

 

[Sputnik II]

The problem with using a resistor to load the circuit is that it would need to be a power resistor and they get hot as well as being expensive to buy.

The way I would go about this problem is to make or obtain a flasher unit that wasn't current dependant. This way you won't need a resistor to load the circuit to stop it flashing like a strobe light.

The 555 is an excellent unit to use for this application.

 

[zero]

I'd use a 555 but its all got to run off the original relay (for now)

somebody i know did similar and used a 20watt bulb on the return feed of the circuit which worked apparently... (and that was for front and back)

power resistor? stupid question but how are they different to a normal resistor? as normal but with a heat sink?

bear in mind also that it will only be runing wile the indicators are on also there is a 20watt bulb allready in the circuit (the normal original bulbs at the rear)

 

[Sputnik II]

power resistor? stupid question but how are they different to a normal resistor? as normal but with a heat sink?

Yeah, the term power resistor normally is used for high power dissipation types i.e. Wirewounds in either Ceramic/cement or wirewounds in an aluminium heatsink normally anodised in gold. 10 ohms would be somewhere around what you would need.

bear in mind also that it will only be runing wile the indicators are on also there is a 20watt bulb allready in the circuit (the normal original bulbs at the rear)

yep, really you need to know the threshold current draw to stop them flashing like crazy. If its a standard format type flasher relay, then I'd be inclined to do a mod on it. almost all car flasher relays are electronic now and it wouldnt take too much to stop it flashing fast with a low current load.

 

[andi]

Yeah, the term power resistor normally is used for high power dissipation types i.e. Wirewounds in either Ceramic/cement or wirewounds in an aluminium heatsink normally anodised in gold. 10 ohms would be somewhere around what you would need.

Sounds pretty much like the ones Hein Gericke sell.