Friday Night Engineering

[Syko_]

How about some stories or images of things that were probably engineered at 4:58 pm on a Friday? Here goes:

[T3sl4co1l]

Heatsink connected to line?  Pah!  Back in, well, not in my day, but proverbially so: open the HV cage of a tube TV and you'll see more than a few bits of uninsulated metal floating at 10 to 30kV.  And if you're lucky, some x-ray exposure to boot!

Tim

[Syko_]

Haha, can't say I've much experience in the EE world, the image was just handy so I used it 

[NiHaoMike]

Pretty much every good sized switching power supply will have some heatsinks connected to mains.

[denelec]

Heatsink connected to line?  Pah!  Back in, well, not in my day, but proverbially so: open the HV cage of a tube TV and you'll see more than a few bits of uninsulated metal floating at 10 to 30kV.  And if you're lucky, some x-ray exposure to boot!

Tim

Some old TV sets really produced x-rays.
http://books.google.ca/books?id=kyYDAAAAMBAJ&pg=PA88&dq=popular+science+x-ray+television&hl=fr&sa=X&ei=TtleU9P1NMKiyAHXpoDwDg&redir_esc=y#v=onepage&q&f=false
When I was a kid I was told that you should not sit too close to the receiver because of the radiations.
There was some truth in it.

I wonder how much radiation our old Zenith from the early 60's emitted...

[Tinkerer]

Pretty much every good sized switching power supply will have some heatsinks connected to mains.

Yep, I touched the two heatsinks in a SMPS once with one hand(I wanted to feel how hot they were) and wondered why the heck it felt funny. haha Nope, didnt hurt. Its kinda a peculier thing, the only time a shock actually causes me pain is when it jumps a gap to me, direct contact has never 'hurt' me.

[Phaedrus]

We've stopped connecting heatsinks to line voltage in ATX PSUs... Too many liability issues when someone sticks their finger or a screwdriver in. Generally speaking there's no uninsulated line voltage on the topside of the unit, there's at least a layer of solder mask on the PCB or enamel on a coil. If you take it far enough apart to take the PCB out and kill yourself from the charge in the primary caps, well, that's your fault for ignoring the five or six warnings telling you not to do that. Legally speaking.

[lewis]

Yep, I touched the two heatsinks in a SMPS once with one hand(I wanted to feel how hot they were) and wondered why the heck it felt funny. haha Nope, didnt hurt. Its kinda a peculier thing, the only time a shock actually causes me pain is when it jumps a gap to me, direct contact has never 'hurt' me.

Are you running off that watered down American rubbish? It's like 10 volts or something isn't it?

Get some proper mains into you lad! 

[SeanB]

Capacitive voltage coupling into the heatsink from the 2 collectors of the switchers via the isolation pads or the isopak transistors, with the one being connected to 300V from the input doubler and the other to the switched input to the transformer. You probably had 1mA at whatever the switching frequency was flowing through your skin. If your skin was damp, like from humidity or just washing your hands, then it would have stung a lot more. As you were touching the grounded secondary heatsink ( often unintentionally, as they leave a silpad off on one diode to save cost, commonly the 12V rail) the current only flowed through the same hand.

[jlmoon]

Yep, I touched the two heatsinks in a SMPS once with one hand(I wanted to feel how hot they were) and wondered why the heck it felt funny. haha Nope, didnt hurt. Its kinda a peculier thing, the only time a shock actually causes me pain is when it jumps a gap to me, direct contact has never 'hurt' me.   

bahh hah hah.. you just have not found a good enough return path with your feet or other hand.. yet!

[Joule Thief]

I wonder how much radiation our old Zenith from the early 60's emitted...

When I was a kid in the 50's, we used to get our feet X Ray'd to check for proper fitting shoes. Then off to the dentist that used a drill powered by leather straps bonded by a small metal clip. One day a clip broke and I got wacked in the eye with it. Off to the eye doctor!  Eye doctor puts my head in a vice to steady it so he can drill a hole in my cornea and remove a fragment of embedded metal from the rusty dentist drill drive belt. For a reward, mom took me to Woolworth's to buy a pet alligator and then it was back to sitting in front of the unshielded TV.  Precious memories all (not one of them made up - all true).

These days I do get a pain or two from old age. My wife says "go see a doctor". I feel this cold chill go down my spine. 50 year old childhood memories tell me to stay home and tough it out.