So last year I did a Christmas lights project and learned that cutting off a couple christmas bulbs off a $2 string of 100 bulbs is not so straightforward, it's practically rocket science. Maybe not "rocket science" per se but it takes some serious knowledge of things like ohms and voltage and resistors and diodes etc - which if you don't have a formal engineering education may be challenging to grasp without learning the fundamentals first.
You can't cut even a few bulbs off because if you do it will increase the load on all the remaining bulbs which will significantly shorten their lifespan, and potentially increase fire risk due to overloading voltage on each bulb. This is because each bulb effectively functions as a resistor and the whole string is designed with the bulbs as resistors, specially made so the string works. But it isn't so easy to shorten or lengthen.
I learned about using resistors and successfully used some, however resistors get extremely hot and for that reason I decided to take down the shortened strings.
It was suggested that I could use diodes to step down the voltage rather than use resistors to "soak up" (my term) the excess heat and voltage from the missing bulbs.
However I still didn't really understand what diodes are or why they don't get hot or how I can actually use these, in for example a string of christmas lights to remove say 15 bulbs from a string of 100.
I previous asked this question last year: Is a diode an effective way to replace a resistor in an application where heat should be avoided? for which I accepted an answer however I still don't fully understand diodes and if and how to use a diode in such a project.
For example, the answer given was:
Using the diode however switches off the voltage and power by 50% If this reduced power is acceptable consider reversing the diode in one string to balance the load current.
However, I don't really understand this. So here are my questions:
======= Questions ========
- How does the diode reduce the voltage without getting hot while the resistor gets extremely hot?
- In what way can I use a diode in such a project? It still isn't clear to me how to use a diode in this kind of project.
- What are some other practical usages for small projects in which a diode can be used (for a beginner)?
Christmas is over again but for purely educational reasons I would really like to have a comprehensive grasp of the best solutions for such a project. I would like to try more projects in the future.
I understand it more now (although not entirely). With the answer below and the following two youtube video I just watched now I understand a little better.
Basically, a resistor is more like a sponge whereas a diode is more like a wall. While a resistor absorbs current and releases it as heat, a diode on the other hand will simply reject all the current going in one direction (up to the capacity of the diode).
If you use a diode too small, it is like driving a car into a wall made of 2x4. The car will go through because it has more power than the wall (actual diodes will explode when the current is too high for it, as can be seen in various youtube videos). Likewise, a diode that is big enough is like a large brick wall. A car hitting it will be stopped and the wall will be pretty much unaffected.
This isn't a perfect analogy but it's helpful to me (I just made up this analogy).
Here are the two videos on diodes I watched which helped:
These don't answer all my questions but they do mostly answer why a resistor heats up but a diode does not. A diode doesn't absorb the energy it simply blocks it. A resistor absorbs the energy which is then released as heat.