Led Car Capacitor
2009
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How to step up Voltage Quickly? Trying to make LED brake lights for my car.?
I am trying to create a string of LEDs that are normally at a certain voltage, say 1.7v, when the brake lights are not in use, but quickly steps up to a different voltage, say 2.1v, when the brake is applied (capacitors?). I say quickly because i tried some setup with resistors and it looks like it comes on and goes away gradually, which defeats the point of the LEDs. Clearly, there will be two different power input.
And how would I be able to string more then 6 LEDs together? For example, i want to string 30 together, that'll need like 60 volt input...
I am interested in electronics, i know how to soilder/troubleshoot some electronics with volt meters etc. but don't know the mechanics behind it. Can someone give me a dumbed down answer and suggest some circuitry books/websites for a newbie like myself?
Parallel vs Series: I am aware of the difference, but I read somewhere the LEDs should be in series and not in parallel, was i misinformed?
The voltage across an LED will try to stay constant. Any excess voltage applied to the LED will cause high currents to flow unless there is a resistor placed in series to limit the current.
Most LED's are limited to 25milli Amps (ma) or 0.025 Amps. A low glow will appear around 10ma.
To compute the value of series resistance you take the applied voltage and subtract the LED voltage. The difference is the amount of voltage that need to be dropped across a resistor. To compute the resistance value simply divide this voltage by the current you want flowing through the LED.
Since most cars alternators produce 13.8Vdc
13.8 - 1.7 = 12.1 Volts
12.1 / 0.010 (10ma) = 1210 Ohms
A 1210 Ohms resistor will produce a small glow.
12.1/0.022 = 550 ohms
THis smaller resistance will produce a larger glow.
1210 ohms - 550 Ohms = 1210 Ohms
If you place Two resistors (550 & 660) in series with an LED you will have a small glow. Short out the 660 ohm resistor with the contact of a brake switch and suddenly the series resistance will be 550 ohms giving you a brighter light.
LED's should not be connected in parallel if there is a single series resistance. LED's are not closely matched so different current draws will ocurr in parallel LED's . The mismatch can cause the LED to burn out as it may be operating at a lower voltage than its mates and thereby drawing more current. You can connect LED's in parallel if each string of LED's has its own series resistor. A single resistor added in series to the combined parallel circuit can still be used to dim as the individual series resistor in each leg limit the maximum current.
You can safely put LED's in series in which case there voltage add up. You would then recompute your series resistance values. (6 x 1.7V LED's = 10.2V)
13.8 - 10.2 = 3.6V
3.6 / .01 = 360 ohms A smaller resistor to drop less voltage when using 6 LED's in series.
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