Any electrical engineers here?

[Thomas Rogers]

R Shek,



One of my last jobs we had an engineer that was designing an Internet-based video monitoring systems for daycares, allowing parents to securely go online and see the activities in their child's daycare. The engineer kept bugging me about the need for power to the cameras. They had wireless video feeds, but no wireless power and he felt that was a shame.



I told him that they already invented wireless power and it's called "a battery"....he didn't like that answer.



TJR

 

[Ryan Schaecher]

There is actually a local daycare that has that system. Pretty slick. But as far as the wireless power, it is available as I said in a fashion similar to RFID. Basically it's kinda like microwave (but without the burning and itching). Many electric toothbrushes (see OralB and SonicCare) use it to great effectiveness. Several factories that I have read about us it. It's not that complicated of a system. It can be unidirectional or omnidirectional. These devices usually run at 3.5VDC.



However, I'm sure that there will be some kooks out there that will saw "YOU'RE NOT GOING TO USE MICROWAVE POWER AROUND MY CHILDREN!!".... that own a SonicCare toothbrush....



Another option would be to run all the camera operations over ethernet (power and signal on one line), but that defeats the wireless purpose.

 

[Bill Ellis]

Just so you know, high voltage DC, anything over about 50 volts, is much more dangerous than AC. With an AC shock, you feel it because of the alternating current and your muscles can not "clamp" down. However, with DC, you will not feel a shock and your muscles may "clamp" preventing one from letting go. This was determined many years ago when DC was used in homes. Also, the kitchen pictured above does not meet many building codes which state that there must be GFI protected outlets on the backsplash with minimum spacing requirements depending on the design of the counter top. Outlets under the counter top lip are not allowed in any of the codes.

 

[Thomas Rogers]

R Shek, yeah, we have an OralB toothbrush that is powered that way...but for that appliance, the field is only a few millimeters long, through plastic. I was impressed when I saw it...almost took it all apart, but then didn't.



Yup, Bill-E, as I said, I am aware of the dangers of high DC voltage. That's why I said in my intro on this subtopic:

Now I know the history of DC vs AC in homes, and I know the safety issues associated,

I saw the history channel special that had Westinghouse vs Edison's companies competing for the standards. AC is safer, and transmission is much easier and less costly.



Thanks for brain-farting boys!



TJR

 

[Bill Ellis]

I noticed your point, TJR. However, most probably are not aware of the history since it is an obscure topic. Strange as it may sound, most things are the way that they are for very good reasons and often, due to some very bad mistakes in the past. Building codes are a prime example. Nearly all changes and updates are due to safety and structural integrity issues. Although, meeting current building codes seems like a real hassle when you have to do it for a remodeling project.

 

[Ryan Schaecher]

Building codes.... yeatch... I deal with the NFPA, NEC and UL codes every day (not in home but industrial machines). I do run into cases where the codes contradict themselves, or one code will contradict the other. Our goberment at work (at least UL is private and keep their codes and rules pretty well consistant).



I too am well aware of the dangers of DC above 50V, as well as the transmission problems associated with DC. My point was that the concept was interesting, not necessarily practical.



When "testing" to see if a DC circuit is live, always touch the circuit with the back of your hand. You won't clench onto the conductor should the circuit be live and the protection elements (if they exist) fail.