# A 25W Light Bulb Married a GE Clock/Radio

Discussion in 'LEDs and Optoelectronics' started by Dummycorp, May 16, 2012.

1. ### Dummycorp

2
0
May 16, 2012
I'm wiring a 25W Edison bulb to an old GE clock/radio.

The radio is 120V/60hz 8.5W input.

Basic calculation I = P/E would mean the current is 0.07A

If I wire the bulb in parallel between source and the clock/radio, there's now 0.2A for the bulb branch and 0.07A for the clock/radio branch making Current Total about 0.3A (300mA) correct?

In doing so, however, I haven't actually made any change to the current flowing through the radio, right? It's still 0.07A?

So if the power cord which goes from the source to the bulb branch (first) and then to the clock/radio branch is the only thing carrying 0.3A and is rated well above that, I'm not in any danger of burning up the clock/radio, yes?

My concern is safety (obviously) so any help is appreciated.

Last edited: May 16, 2012
2. ### timothy48342

218
0
Nov 28, 2011

If you plug the clock into the wall and plug the bulb into the wall. That's parallel. You could plug them in in different rooms or different houses, and it's still parallel.

If you expose both leads to the clock and attach the 2 leads from the bulb to those 2 expposed spots.... still parallel.

In all these cases the bulb and clock should function as normal. (Except the danger of exposed wiring.)

If you snip just one lead to the clock and attach the lamp between those to loose ends from your snipping, then finally that is a series connection. ie. the lamp is in series with the clock. You said "parallel" and I think that was misleading. I couldn't tell for sure what you were planning, so post a diagram. (A quick hand-drawn scan would be fine.)

Assuming that you are connecting them in series:
The clock only pulls 8.5W, and that is going to limit the current and wattage to the bulb. The bulb will limit the current/wattage to the clock a bit as well. Treating them both as ideal resisters there will only be about .05A current running though the both of them. (It is a stretch to treat them as ideal resisters, but for sure there won't be any more than .07A running through, because that is what the clock can draw. I suppose there might be some weird circumstance where the clock actually pulls more current under brown-out conditions, but it is unlikely.)

The bulb will get a current that is about 1/4 to 1/3 normal, so it will not be very bright. The clock might work... might not.

Still assuming this is a series connection, rememebr that current if a flow. A flow through one thing into another thing requires that the other thing must have the same flow. (Usless there is somewhere else for the flow to go.)

Is this youre set-up?

If so then the clock and lamp both have the same current and it will most likely be close to but slightly less then the clock normally pulls.

--tim

Last edited by a moderator: May 17, 2012
3. ### Dummycorp

2
0
May 16, 2012
Hmm. Can't upload image from my iPad any easy way! I'll take care of that tomorrow and respond. Thanks for your help on this. Just making sure I still understand principles, etc.