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  • cadcoke5 commented on noahw's instructable LEDs for Beginners5 weeks ago
    LEDs for Beginners

    I did a similar project many years ago, before I had any electronics training. It worked, but I was puzzled about some of the behaviors. The issue is that putting a bunch of LEDs in parallel, without individual LEDs will work well, only if each LED has at the same voltage drop. If one of the LEDs have a lower voltage drop, they will steal more current from the others, so that it is prone to failure.If you read the LED's specs from the manufacturer, they will give the voltage drop as a range. Perhaps for a green LED 2.7v to 3.4v. In your parallel circuit, with only one resistor, that 2.7v odd-ball one is going to be brighter, draw more than its share of the current, and die a quicker death.The author of the article has done an in interesting job of learning through experimentation, ...

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    I did a similar project many years ago, before I had any electronics training. It worked, but I was puzzled about some of the behaviors. The issue is that putting a bunch of LEDs in parallel, without individual LEDs will work well, only if each LED has at the same voltage drop. If one of the LEDs have a lower voltage drop, they will steal more current from the others, so that it is prone to failure.If you read the LED's specs from the manufacturer, they will give the voltage drop as a range. Perhaps for a green LED 2.7v to 3.4v. In your parallel circuit, with only one resistor, that 2.7v odd-ball one is going to be brighter, draw more than its share of the current, and die a quicker death.The author of the article has done an in interesting job of learning through experimentation, but he failed to uncover certain details. I think the biggest mistake was that he is treating a LED like it was a incandescant bulb. The 2nd error is in thinking that this "no resistor" circuit actually did not have a resistor. In fact, there was some small resistance in his battery. As long as the battery is fairly small, and the voltage is just a little above the voltage drop of the LED, it may work.

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  • cadcoke5 commented on flywoodkb's instructable Hot Wire Foam Cutter9 months ago
    Hot Wire Foam Cutter

    I know this is some old commentary, but I wanted to correct some mis-information. The old-fashioned heavy type of transformer is the kind you can use with a dimmer to control the output. Buy the High-frequency ,switching type of transformer is NOT compatible with messing with the input voltage.

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