12 into 240? theoretically?

[AndyPRK]

removed

 

[slup]

You think that chandelier is bad?

Check this out... by the same guy

It follows that the device should only be used when someone capable of giving CPR (Cardio-pulminary-resuscitation) is present, and should not be used on anyone who declines it's promised treasures.

(!)

 

[electronicsuk]

You think that chandelier is bad?

Check this out... by the same guy

It follows that the device should only be used when someone capable of giving CPR (Cardio-pulminary-resuscitation) is present, and should not be used on anyone who declines it's promised treasures.

(!)

The author clearly isn't stupid, he just enjoys a little bit of electronics in his spare time as a hobby, and there ain't nowt' wrong with that. If you were reading his site and considering constructing anything you found there for yourself, you'd already be well aware of the dangers involved, otherwise you would have been unlikely to be interested in the first place!

 

[ricicle]

If they are Electricians then I am a Dutchman......tossers !

 

[slup]

It's a fantastic site - his LED controllers are brilliant, and the writing is amusing.

I know there is nothing wrong with the little self electrocution device - it's probably no more dangerous than the touch dimmers I have in my house.

It's just the thought of deliberately assembling something into a metal box and connecting it to the mains with the sole intention of giving yourself a shock. The potential for something to go wrong due to careless assembly is there though...

 

[slup]

My favourite picture on his site is on the Jacobs Ladder page.

Someone at the BBC has affixed a PAT test sticker to the side of an 18kV neon transformer which is connected via uninsulated terminals to the large and completely uninsulated jacobs ladder.

 

[ban-all-sheds]

You'd also see 230v across the lampholder with the blown lamp, or across the lampholder should one lamp be removed from a healthy circuit.

Until you tried to draw any current...

 

[sparkyspike]

1 Shepherd x 2 Sheepdogs = 54 sheep ( rounded up ).

http://www.youtube.com/watch?v=D2FX9rviEhw

I enjoyed that. I always wondered what the Welsh were up to....

 

[electronicsuk]

You'd also see 230v across the lampholder with the blown lamp, or across the lampholder should one lamp be removed from a healthy circuit.

Until you tried to draw any current...

I expect it would still be enough to give a nasty shock. Negating any effects of heating on the filament, a 12v 20w lamp will have a resistance of about 12v / (20w/12v) = 7.2 Ohms. Best case scenario is that you get a shock from the lasmp furthest from the live terminal, in which case you have 19 lamps x 7.2 Ohms = 137 Ohms between yourself and 230v AC.

If you were then to take a resistance across your body of 1000 Ohms (admittedly this may be a little on the low side, but for arguments sake) then you have the potential for 230v / (1000+137Ohms) = 202mA of current there, assuming you're looking purely at resistance rather than worrying about impedance. That would also mean a voltage across your body of 1000 Ohms * 0.202A = 202v.

Although very little current in electrical terms, it's still enough to kill.

 

[ericmark]

Although it would work "theoretically", in theory, there would be the potential for 230v across a 12v lampholder if there was a break anywhere in the series circuit.

If it goes open circuit there will be 0v across each lampholder.

if a lamp or number of lamps were to fail short circuit

Do they ever do that?

Yes it is common for lamps at moment of failure to have ionisation and often there is a built in fuseable link which should blow first to stop main fuse blowing. I am sure you have seen lamps blow with a bright flash and leave glass blackened inside.

As to voltage at lamp for the lamp closest to line connection 230v with only protective device (fuse etc) that will open circuit.

OK we may do daft tricks in Algeria I used a string of 12 volt side lamp bulbs and florescent lamp starter to make them flash nothing went wrong still does not make it right!

To use any equipment for purpose it is not designed for can introduce danger and to have a lamp designed for SELV connected to LV is asking for problems.

 

[ban-all-sheds]

I expect it would still be enough to give a nasty shock. Negating any effects of heating on the filament, a 12v 20w lamp will have a resistance of about 12v / (20w/12v) = 7.2 Ohms. Best case scenario is that you get a shock from the lasmp furthest from the live terminal, in which case you have 19 lamps x 7.2 Ohms = 137 Ohms between yourself and 230v AC.

If you were then to take a resistance across your body of 1000 Ohms (admittedly this may be a little on the low side, but for arguments sake) then you have the potential for 230v / (1000+137Ohms) = 202mA of current there, assuming you're looking purely at resistance rather than worrying about impedance. That would also mean a voltage across your body of 1000 Ohms * 0.202A = 202v.

Although very little current in electrical terms, it's still enough to kill.

Now envisage the same scenario with a regular LV lampholder, and show why that one is of no concern.

 

[electronicsuk]

I expect it would still be enough to give a nasty shock. Negating any effects of heating on the filament, a 12v 20w lamp will have a resistance of about 12v / (20w/12v) = 7.2 Ohms. Best case scenario is that you get a shock from the lasmp furthest from the live terminal, in which case you have 19 lamps x 7.2 Ohms = 137 Ohms between yourself and 230v AC.

If you were then to take a resistance across your body of 1000 Ohms (admittedly this may be a little on the low side, but for arguments sake) then you have the potential for 230v / (1000+137Ohms) = 202mA of current there, assuming you're looking purely at resistance rather than worrying about impedance. That would also mean a voltage across your body of 1000 Ohms * 0.202A = 202v.

Although very little current in electrical terms, it's still enough to kill.

Now envisage the same scenario with a regular LV lampholder, and show why that one is of no concern.

Because we expect to see 230v on a LV lampholder, we don't expect to see it on an ELV lampholder.

 

[Spark123]

To be pedantic - the 12v 20W lamps will only have a resistance of 7.2 ohms when they are hot. When they are cold owing to the filament which has a positive temperature co-efficient the resistance at room temperature will be lower.

 

[Spark123]

You'd also see 230v across the lampholder with the blown lamp, or across the lampholder should one lamp be removed from a healthy circuit.

Until you tried to draw any current...

It depends how much current you mean, if the circuit is open circuit then the full voltage will be measurable with a dvm.

I'd expect shock current to be a majority of what it would be for direct contact to the line conductor with the lamps having a small effect on the overall current. It could also depends on how many lamps are upstream of the point of contact however as the lamp resistances are in ohms and body resistance is generally Kohms the potential difference across the human body will be similar.

 

[Space cat]

The start up current on a quartz halogen lamp is many times its run current and it is unlikely they would all take same current on start up

For this reason, I would suggest using lamps that are, as near as possible, identical. That means buying the same make as well as the same power. While you're at it, and especially if you're planning to use 50W lamps, think about the switch-on surge current. For halogen lamps this is about sixteen times the running current (thirteen for standard lamps).

And finally ---

Remember that fittings for 12V lamps are not expected to operate at mains voltages. Convince yourself that their insulation is up to scratch. Do they have earth terminals?