3 ms·

I always cringe a bit when folks approach hardware like they do software Not sure what you mean - was there some terrible mistake in what the author was doing?

astrodust 11y ago
Software doesn't short out and burn down your house, for example. Low voltage systems are a lot safer, but not immune to trouble. Even USB ports occasionally catch on fire if there's a damaged cable or crossed pins.
- linkydinkandyou 11y ago
  Actually, they're not because the current is so high. You can easily start a fire.
  - astrodust 11y ago
    I mean mostly safer from electrocution. The risk of fire is still there.
- cadr 11y ago
  But software might have a race condition that causes you to get zapped by a lot of radiation. https://en.wikipedia.org/wiki/Therac-25 https://en.wikipedia.org/wiki/Therac-25
  - astrodust 11y ago
    Most people don't have one of those in their house. Also a case could be made that it wasn't software that irradiated people, but the hardware. If there was the potential for danger, the hardware should have had a limiter built-in. We have fuses in equipment for much the same reason.
ChuckMcM 11y ago
Consider the following quote, which concludes the discussion on power -- "The wires we use to provide the power also have resistance. Allright, so what do we do? Let's split the four strips into two segments, and power each one in the middle. This makes the situation much more palatable. On one side I used a PC power supply, and on another two parallel 5V15A supplies. They are both well isolated, so there was no potential difference between grounds or signal integrity issues." So I don't doubt this works for the author's setup, but it is by no means the correct solution to distributing power across his lights. There are three problems with this, first the PC power supply (being unspecified) may, or may not, actually regulate the 5V line when the 12V line is unloaded. So someone reading this might spend hours trying to figure out why their supply isn't producing 5V when the answer in the general case is to load the 12V supply with a 15W load (a 12V lightbulb works well for this). Next up he adds two 5V supplies that can provide 15A in "parallel" but the "grounds are isolated". So he is assuming there might be ground cross talk, but what he really should be concerned about is whether or not the power supplies are designed to run in parallel. If supply A produces 5.05V (well within spec) and supply B provides 4.95V, then supply A will try to drive all the LEDS and back drive supply B. Of course in so doing its output will come down, and eventually supply B will get a chance to contribute some power, the supply with the slightly higher output however will run at 100% of its rated output, and can then heat up. This can sometimes cause it to go into thermal shutdown, and suddenly supply B will have all the load. Now it over heats and supply A is called upon again to carry the load. Power supplies that are designed to be run in parallel will have a current mirror which lets each supply see what the other is producing and split the load between them, they are essentially current controlled supplies at that point. Third, there are lots of places that sell 60A 5V supplies if you want one, although a more typical arrangement might be to bus a higher power and then run independent supplies with a common return at each group of LEDs. So perhaps a 48V bus, with 5V step down supplies every 5M. The simplest solution is of course to just use a bus bar. Provide a suitable gauge wire (8M of 8Ga wire will have a resistance of about 10 mOhms. Less than .5V drop over the length. Have the bus wire go 8M along two walls, and then out the other direction 8M along the other two walls. That solves his power supply issue caveat he needs a 300W 5V power supply. Since high power GPU boards are so common, if he wanted to use a PC power supply he could run 12V on one half of the room and 12V on the other half split into two 150W feeds, with 12V->5V supplies to down convert at the LED strips. However since he missed all that (and I think its just missing some of the EE basics) and may (or may not) get a fire in his dual 15A supplies, I cringed.

astrodust 11y ago

Software doesn't short out and burn down your house, for example. Low voltage systems are a lot safer, but not immune to trouble. Even USB ports occasionally catch on fire if there's a damaged cable or crossed pins.

linkydinkandyou 11y ago
Actually, they're not because the current is so high. You can easily start a fire.
- astrodust 11y ago
  I mean mostly safer from electrocution. The risk of fire is still there.
cadr 11y ago
But software might have a race condition that causes you to get zapped by a lot of radiation. https://en.wikipedia.org/wiki/Therac-25 https://en.wikipedia.org/wiki/Therac-25
- astrodust 11y ago
  Most people don't have one of those in their house. Also a case could be made that it wasn't software that irradiated people, but the hardware. If there was the potential for danger, the hardware should have had a limiter built-in. We have fuses in equipment for much the same reason.

ChuckMcM 11y ago

Consider the following quote, which concludes the discussion on power -- "The wires we use to provide the power also have resistance. Allright, so what do we do? Let's split the four strips into two segments, and power each one in the middle. This makes the situation much more palatable. On one side I used a PC power supply, and on another two parallel 5V15A supplies. They are both well isolated, so there was no potential difference between grounds or signal integrity issues." So I don't doubt this works for the author's setup, but it is by no means the correct solution to distributing power across his lights. There are three problems with this, first the PC power supply (being unspecified) may, or may not, actually regulate the 5V line when the 12V line is unloaded. So someone reading this might spend hours trying to figure out why their supply isn't producing 5V when the answer in the general case is to load the 12V supply with a 15W load (a 12V lightbulb works well for this). Next up he adds two 5V supplies that can provide 15A in "parallel" but the "grounds are isolated". So he is assuming there might be ground cross talk, but what he really should be concerned about is whether or not the power supplies are designed to run in parallel. If supply A produces 5.05V (well within spec) and supply B provides 4.95V, then supply A will try to drive all the LEDS and back drive supply B. Of course in so doing its output will come down, and eventually supply B will get a chance to contribute some power, the supply with the slightly higher output however will run at 100% of its rated output, and can then heat up. This can sometimes cause it to go into thermal shutdown, and suddenly supply B will have all the load. Now it over heats and supply A is called upon again to carry the load. Power supplies that are designed to be run in parallel will have a current mirror which lets each supply see what the other is producing and split the load between them, they are essentially current controlled supplies at that point. Third, there are lots of places that sell 60A 5V supplies if you want one, although a more typical arrangement might be to bus a higher power and then run independent supplies with a common return at each group of LEDs. So perhaps a 48V bus, with 5V step down supplies every 5M. The simplest solution is of course to just use a bus bar. Provide a suitable gauge wire (8M of 8Ga wire will have a resistance of about 10 mOhms. Less than .5V drop over the length. Have the bus wire go 8M along two walls, and then out the other direction 8M along the other two walls. That solves his power supply issue caveat he needs a 300W 5V power supply. Since high power GPU boards are so common, if he wanted to use a PC power supply he could run 12V on one half of the room and 12V on the other half split into two 150W feeds, with 12V->5V supplies to down convert at the LED strips. However since he missed all that (and I think its just missing some of the EE basics) and may (or may not) get a fire in his dual 15A supplies, I cringed.