This doesn't fill me with confidence

I have a medical device with a blown globe. I measured 240volts at the globe but the suppliers says it takes a 120V globe. I asked them if they are sure because I measured 240volts at the terminal. Their reply was that they run the 120V globe at 240V but at a lower amperage. They do this to get a better colour temp out of it. Interesting. I'm guessing I measured 240V only because there was no load. Either that or they are breaking the laws of physics.

Reply to
Michael C
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Connect a similar wattage (if practical) 240v globe to the socket in the device and see if the voltage drops.

Unless the bulb is really low wattage, (which I doubt, or they would be running it from a low voltage) I would hate to think they were using a resistor or linear regulator as a voltage drop method !

of course - shoving a 110v globe in a 240v socket might be a really good reason the poor bulb blew in the first place.

Reply to
kreed

I wonder how much the person you spoke to knows about the actual design of the thing. Giving a globe higher voltage than it's design voltage will increase the heat, and hence increase the resistance of the element, but not by enough to reduce the current back accordingly. Running at higher voltage will also improve the colour temperature, but the downside is it will shorten the life of the globe quite dramatically. A blue filter would be a more reliable way of improving colour temperature. I would be very surprised if a globe was able to withstand double it's design voltage for any sustained length of time. My guess is that they have either another globe, or a resistor in series with this globe. This would cause the voltage to read 240V when open circuit, but of course it will drop to something more reasonable under load.

Reply to
Doug Jewell

I know it's sort of unrelated but that bring something to mind...Christmas tree lights, the old ones with 20 series connected 12V lamps. 12V lamps but of course 240v potential if someone (read child) removes a lamp and shoves something in there.

James

Reply to
James
12V lamps but

That makes no sense at all. If there are still 19 lamps in their the most you will get is still 12volts once you actually draw some current.

Reply to
MisterE

You will get ~12V if you draw as much current as the absent lamp would have drawn. Loads presenting a lower current will obvioulsy see a higher voltage, and on OC it will be the full supply voltage. Basic Ohms Law stuff.

Reply to
who where

shoves

have

voltage,

Right, and since you only need ~10mA or so to be potentially lethal, the right amount of skin resistance should do the trick.

MrT.

Reply to
Mr.T

shoves

What if you touch the lamp closest to the cord and ground yourself at the same time?

Michael

Reply to
Michael C

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