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Offline bloodlineTopic starter

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Electronics help :)
« on: August 18, 2009, 07:18:53 PM »
Hi all,

I have replaced my internal car lights with blue LEDs. They look great, and as so much brighter than the original lights, they are actually useful.

But I have decided I want the lights to not switch off the moment I shut the door, but instead fade down once the power is cut.

This is an easy mod, done by simply putting a capacitor in parallel with LED unit... but it has been years since I got my hands dirty with analogue electronics... can someone help me spec out what capacitor I would require?

Cheers!

Offline Karlos

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Re: Electronics help :)
« Reply #1 on: August 18, 2009, 08:07:12 PM »
OMG, you put wanker lights inside your car?
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Offline Speelgoedmannetje

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Re: Electronics help :)
« Reply #2 on: August 18, 2009, 08:09:38 PM »
I know I used at school "Crocodile clips" to experiment with this kind of things.
And the canary said: \'chirp\'
 

Offline bloodlineTopic starter

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Re: Electronics help :)
« Reply #3 on: August 18, 2009, 08:14:53 PM »
Quote from: Karlos;519796
OMG, you put wanker lights inside your car?


Um... yes... the original bulbs were the horrid festoon types... that got very hot and didn't really light up the foot wells... so 4 3volt superbright leds were installed into each socket in series, to take the 12volt supply...

Anyway, what size capacitor do I need?

Offline Karlos

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Re: Electronics help :)
« Reply #4 on: August 18, 2009, 08:24:32 PM »
Poor MX5, you've totally killed any sense of class it had.

Are the LED's pre-resistored up for 12VDC?

-edit-

Never mind. Series wiring. Just keep sticking 1500uF 16V capacitors in parallel to the array of three diodes until you get the delay you want. Note that you'll probably have a fade on too since the capacitor charging will divert a lot of the forward current initially as they charge.
« Last Edit: August 18, 2009, 08:30:27 PM by Karlos »
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Offline bloodlineTopic starter

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Re: Electronics help :)
« Reply #5 on: August 18, 2009, 08:26:47 PM »
Quote from: Karlos;519805
Poor MX5, you've totally killed any sense of class it had.

It's an MX5!!! It is hardly classy :D -Edit- but it is fun!

Quote
Are the LED's pre-resistored up for 12VDC?

Yup, they can't be overcurrented!

Offline F0LLETT

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Re: Electronics help :)
« Reply #6 on: August 18, 2009, 08:30:32 PM »
Quote from: bloodline;519807
It's an MX5!!! It is hardly classy :D -Edit- but it is fun!



Yup, they can't be overcurrented!

LMFAO, you aint my brother are you?
He wired his calibra up with blue neons inside and out.

He always calls me Grandad, cause I have always chosen family cars.
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Offline bloodlineTopic starter

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Re: Electronics help :)
« Reply #7 on: August 18, 2009, 08:38:42 PM »
Quote from: Karlos;519805
-edit-

Never mind. Series wiring. Just keep sticking 1500uF 16V capacitors in parallel to the array of three diodes until you get the delay you want. Note that you'll probably have a fade on too since the capacitor charging will divert a lot of the forward current initially as they charge.

Cheers Karlos! I now know what spec capacitor I want, so I can experiment and get it right!

The harsh On/Off nature of LED is quite distracting when compared to the more organic fade up/down of incandescent bulbs

Offline Karlos

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Re: Electronics help :)
« Reply #8 on: August 18, 2009, 08:43:42 PM »
I'm not sure a simple capacitor based mechanism is your ideal solution though. Charging and draining capacitors with a load like that isn't good for them in the long run. You'd probably want to limit the maximum current into the caps.
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Offline bloodlineTopic starter

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Re: Electronics help :)
« Reply #9 on: August 18, 2009, 08:48:52 PM »
Quote from: Karlos;519811
I'm not sure a simple capacitor based mechanism is your ideal solution though. Charging and draining capacitors with a load like that isn't good for them in the long run. You'd probably want to limit the maximum current into the caps.


Hmmm... I can't find any caps with 1.5kuF caps with a 16v spec either :(

Offline Karlos

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Re: Electronics help :)
« Reply #10 on: August 18, 2009, 08:52:49 PM »
Higher voltage ratings would be OK, if you can find those. Just not less than the supply voltage.
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Offline bloodlineTopic starter

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Re: Electronics help :)
« Reply #11 on: August 18, 2009, 09:09:52 PM »
Quote from: Karlos;519817
Higher voltage ratings would be OK, if you can find those. Just not less than the supply voltage.


Ok, I've not played with analogue electronics for 10 years :(

I think given the amount of time the lights are on, this simple capacitor system should be fine... how long does it have to last? I think I can afford a new 20p capacitor every year or so ;)

Offline the_leander

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Re: Electronics help :)
« Reply #12 on: August 19, 2009, 02:51:01 AM »
Quote from: Karlos;519796
OMG, you put wanker lights inside your car?


You know, it's just as well I was using the eeepc to read this - it meant that when I spat out my tea I'd already lifted the thing away from the likely trajectory :lol:

I seriously have to stop drinking anything reading this place :D
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Offline Tension

Re: Electronics help :)
« Reply #13 on: August 19, 2009, 01:28:22 PM »
Quote from: F0LLETT;519808

He always calls me Grandad, cause I have always chosen family cars.


Ha, i`m about to buy a Volvo 850.  People think i`m mad.

But it`s a T-5 so I think i`ll have the last laugh!!

Offline zipper

Re: Electronics help :)
« Reply #14 on: August 19, 2009, 03:17:14 PM »
..until you notice the fuel consumption...if you have a heavy foot on gas pedal.
(V50 T5 owner)