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Home Forums General Discussion AC or DC? Re: AC or DC?

#65735
elnav
Member

Yes it is possible to have both AC ande DC. I have been designing multi-voltage systems since 1996. Northern person made the comment that there are plenty of 12V devices and they last forever. This is one statement I will challenge on technical grounds. I once worked for a charter company and was forever replacing 12V flourescent lights. When I had a dozen or so lights in the junk bin I would try and repair them by either swapping parts or getting repair components. Failure was invariably caused by over heating. 12V products are mostly made for a market place that is very cost conscious. Very few people are willing to pay $129.95 for a light fixture But they will pay $29.95

Volume production also means the unit cost is lower than limited volume production. This explains why 120V AC appliances are comparatively cheaper than their 12V DC equivalent.

Lastly it takes power to do work. If you compare 10 watt devices the 12V product will use 10X as much current as the 120V product doing the same function. Current is what produces heat. This increased current results in more heat internally in the 12V device which typically leads to failure sooner rathe than later. This is equally true for lights, fans and coffee makers. I spent a lifetime working in the manufacturing industry including 4 years as a Quality Assurance Manager. Analyzing product failures wa a daily job function. In addition, as a repair technician, I saw first hand what worked and what did not. I agree new advances in LED technology can make DC lighting feasible. It is too new for us to have any statistical database on what if any effects, LED light will have on eyes over many years exposure. I do know LED lights gives me eye strain in as little as one hour.

I also know normal electrical connectors commonly used in all appliances tend to overheat and fail sooner in 12V DC appliances. Sometimes they even start fires.

Someone in another thread proudly declared that they were using 26Ga cat5 data cable for power wiring. Evidently this person has over looked the fact you can start a fire with 12V. Think about the cigarette lighter in your car. That outlet is fused at 8 amps. Not exactly high power but when something is high resistance it will reach hot enough temperatures to start a fire.

I have done my share of bitching about stupid standards but I also recognize when a standard is there for a good safety reason. I have the education, training, and experience to judge when a short cut is safe and when it is not.

What scares me is when people lacking this background blithely assumes something is safe just because it looks like it might work. Low voltage DC is a case in point. Someone runs telephone wire for one LED light. No problem but later on someone decided to add another or maybe two 12V devices to this light power circuit. How often do you think they bother to make a power calculation to ensure it is safe. For that matter how often do you see people running 12V wiring without fusing?

You do not have to take my word for it. There are plenty of books out there that will tell you the same thing. I am guessing people are asking questions here because they haven’t the time or inclination to read all those books.