Making light shorter

[dcphipps]

I am doing faces of Alvin and the Chipmonks, how does one make lights shorter to accomidate the mouths? Can I cit regular Christmas lights and wire a power cord, talking about the 1/4 round lights 120 volts, or can I do this to LED lights.

I posted this question before but forgot where Sorry

 

 don

[LightORamaDan]

Usually people just "clump" up the unused wire. When making things with coro the wire just hangs all over the place in the back. 

 

Dan

[bwhitehead]

Christmas LED had black out caps too that helps as well.

[caniac]

I am doing faces of Alvin and the Chipmonks, how does one make lights shorter to accomidate the mouths? Can I cit regular Christmas lights and wire a power cord, talking about the 1/4 round lights 120 volts, or can I do this to LED lights.

I posted this question before but forgot where Sorry

 

 don

I am sure I will be corrected if I am wrong BUT I think you can with ican's not with LED's.  Don't know the electronics behind it but ALL LED lights have what looks like a resistor in the wire and it is specific to the length/voltage/etc.   Where you might be able to make your strands custom lengths with icans not so lucky with LED (or rope lights).

[basis21b]

Typically a string of 100 incandescent string of lights is two strings of lights wired together.  You can split the string into two lengths of 50 without issue.  If you were to take a string of fifty and split it into a string of 25 you now are doubling the voltage across each bulb.  They will work - and be very, very bright - for a short time.  After that you have a nice string of burned out bulbs. 

[caniac]

Typically a string of 100 incandescent string of lights is two strings of lights wired together.  You can split the string into two lengths of 50 without issue.  If you were to take a string of fifty and split it into a string of 25 you now are doubling the voltage across each bulb.  They will work - and be very, very bright - for a short time.  After that you have a nice string of burned out bulbs. 

roflmao, I needed that 'cause this Monday has sucked.

[Steven]

Don't know the electronics behind it but ALL LED lights have what looks like a resistor in the wire and it is specific to the length/voltage/etc.

 

You can replace the resistor with a bigger one. For example, let's say you want to make your own custom string of 10 white LED bulbs. A white bulb has a voltage drop of about 3 volts, so 10 bulbs will be 30 volts. Assume a typical LED is about 20mA. Line voltage is 120v. So the resistor will need to pass 20mA at (120 - 30) = 90v, which is about 4.5kΩ. The nearest standard value is 4.7kΩ. At this voltage and current, the resistor will dissipate over a watt(!), so your best bet is to get 4 1/2-watt resistors and wire them in series-parallel.

 

The above calculations are using basic DC (or RMS) rules, which need a bit of a modification depending on if they are full or half wave. Unless someone has a better method, you may end up experimenting. I built my own 50-bulb red LED "Tune Radio" sign and experimented a bit until I found the correct resistance, which I have forgot by now.

[Max-Paul]

As Steven has pointed out. Start working with standard DC Ohms law and Kirtchoves (SP?) laws. But take those RMS values and convert to Peak values.  I use 15mA instead of 20mA. And I use 150 Volts instead of 120V. I also put a amp meter inline and tweak the finial resistor value so I have that 15mA reading. Remember the meter is reading RMS values. The reason for this that even though you have a diode rectifier in the circuit. This only creates a dirty D.C. that goes from zero volts to the peak voltage. Where as filtered D.C. goes to a given voltage and stays there. Just got to remember the meter reads RMS while in the real world the voltage is going to peak.  RMS is .707 of peak.

[dcphipps]

1. I like the idea of capping off lights, I have some black shrink tubing used on electrical wires I believe this will work.

Thanks