Replaceing a 250v bulb with a 120v bulb
Replaceing a 250v bulb with a 120v bulb
(OP)
Hi,
This is my first post here so please go easy on any mistakes I might make. :) My question is simple.. I have been trying to come up with a way to wire a 120v bulb to a 250v circuit. I'm very new to EE and I was doing some research on the issue and came up with this...
I bought an LED I found at my local radio shack and the only thing I could find that would fit and had the highest voltage rating was a 120v 1.5mA. I'm replacing a bulb and wanted an LED instead.
R=(V1-V2)/I
R=(250V-120V)/1.5mA
R=130V/0.0015A
R=86,666.6667ohms (wow big resistor!)
Now... I'm more then likely not going about this the right way but from what I have read into this was right... So is is possible to wire my 120v 1.5mA LED to a 250v 1/3w circuit?
**Notes
The 250v 1/3w is all I have to go by off the bulb harness I'm replacing...
This is my first post here so please go easy on any mistakes I might make. :) My question is simple.. I have been trying to come up with a way to wire a 120v bulb to a 250v circuit. I'm very new to EE and I was doing some research on the issue and came up with this...
I bought an LED I found at my local radio shack and the only thing I could find that would fit and had the highest voltage rating was a 120v 1.5mA. I'm replacing a bulb and wanted an LED instead.
R=(V1-V2)/I
R=(250V-120V)/1.5mA
R=130V/0.0015A
R=86,666.6667ohms (wow big resistor!)
Now... I'm more then likely not going about this the right way but from what I have read into this was right... So is is possible to wire my 120v 1.5mA LED to a 250v 1/3w circuit?
**Notes
The 250v 1/3w is all I have to go by off the bulb harness I'm replacing...





RE: Replaceing a 250v bulb with a 120v bulb
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If we learn from our mistakes I'm getting a great education!
RE: Replaceing a 250v bulb with a 120v bulb
1) I can't find anyone around here that sales a 250v 1/3w bulb or led that is small enough for this application.
2) I love doing things the hard way because I learn a great deal more with my hands on with the project!
In saying that, I was so stupid when talking about the resistor size... I was looking a a 270ohm resistor at the time and didn't even think about the k in 87k hehe.
Ok so here is what I have to work with unless I go back out to the store... :)
Could I use the 120VAC 1.5mA LED with a 100k-Ohm 1/2 watt resistor?
Arvo Bowen III
http://xeonics.net
RE: Replaceing a 250v bulb with a 120v bulb
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Replaceing a 250v bulb with a 120v bulb
But my plans were to ADD a 100k-Ohm 1/2 watt resistor to the circuit... just to check, do I need to add a cap to it? I thought caps were just used to store power or regulate it...
I definitely want to NOT have a hot led if I can avoid it.
Arvo Bowen III
http://xeonics.net
RE: Replaceing a 250v bulb with a 120v bulb
My suggestion is to just buy one too.
http://www.ledtronics.com/Products/Default.aspx
Keith Cress
kcress - http://www.flaminsystems.com
RE: Replaceing a 250v bulb with a 120v bulb
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RE: Replaceing a 250v bulb with a 120v bulb
RE: Replaceing a 250v bulb with a 120v bulb
RE: Replaceing a 250v bulb with a 120v bulb
RE: Replaceing a 250v bulb with a 120v bulb
Don't even think of what?.....There have been a half dozen suggestions.
Wisdom comes from knowledge
Knowledge comes from experience
Experience comes from bad decisions
RE: Replaceing a 250v bulb with a 120v bulb
"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)
RE: Replaceing a 250v bulb with a 120v bulb
I saw the diode and resistor only used on HV AC more than 20 years ago and thought of it as one of those cost saving Chinese engineer tricks. I tested it then and just about a year ago with line voltage. I didn't get any measurable reverse voltage leakage at 150V.
I knew there just had to be a limit so I ran the test again this time using my Sencore LC101. I have come to love this instrument for the leakage tests it can do up to 1000V. The LED was tested for leakage at 50V, 100V, 200V. Not a uA was seen. When switched to 300V it failed and never recovered.
If a resistor is added, a diode will also be required in series. Stupid engineer tricks only get you so far!
RE: Replaceing a 250v bulb with a 120v bulb
You had to have realized the breakdown/gap voltage of the cap would be reached eventually... the concept is still sound, you just need a different style of cap (i.e., more expensive) for the higher voltage.
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Replaceing a 250v bulb with a 120v bulb
If just a resistor is added in series the LED will breakdown from higher reverse voltage and be destroyed. It is obvious that some manufacturers understand that a LED can withstand normal 120V line voltage. Adding a diode in series with the 68K resistor will prevent reverse voltage breakdown when voltage goes from 120 to 250V.
RE: Replaceing a 250v bulb with a 120v bulb
Arvo Bowen III
http://xeonics.net
RE: Replaceing a 250v bulb with a 120v bulb
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Replaceing a 250v bulb with a 120v bulb
20mA and produces about a 2V voltage drop
however since its a type of diode which doesn't coope well with reversed voltage of 250V, a good configuration would be:
a LED with a resistor in series of 248V/20mA =12kOhm
and 20mA x 248V= 0.5watt
parallel over the LED you connect a diode (anode LED to kathode diode and vice versa), this way the reversed voltage will not exceed 0.7V
0.7V x 250/12Kohm gives the power rating of the diode
RE: Replaceing a 250v bulb with a 120v bulb
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Replaceing a 250v bulb with a 120v bulb