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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Series resistor.
I think I know this but I'd like to be sure. I need to affix a small
neon indicator on to a 240V line. Would 80K be an appropriate resistor to use? Thanks, Lenny |
#2
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Series resistor.
klem kedidelhopper wrote in message
... I think I know this but I'd like to be sure. I need to affix a small neon indicator on to a 240V line. Would 80K be an appropriate resistor to use? Thanks, Lenny usually a bit more , 150 K perhaps |
#3
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Series resistor.
klem kedidelhopper wrote: I think I know this but I'd like to be sure. I need to affix a small neon indicator on to a 240V line. Would 80K be an appropriate resistor to use? Thanks, Lenny Which neon indicator? |
#4
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Series resistor.
On Thu, 15 Nov 2012 06:43:35 -0800 (PST), klem kedidelhopper
wrote: I think I know this but I'd like to be sure. I need to affix a small neon indicator on to a 240V line. Would 80K be an appropriate resistor to use? Thanks, Lenny 82K is correct if the neon indicator has an internal resistor. If it's a 'bare' NE-2 lamp, use 130K. PlainBill |
#5
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Series resistor.
"klem kedidelhopper" I think I know this but I'd like to be sure. I need to affix a small neon indicator on to a 240V line. Would 80K be an appropriate resistor to use? ** The value of 80k is fine, but needs to be rated at 1 watt to have a long life. The usual values found inside 240V neon bezels and illuminated switches is 150k to 220 k ohms - chosen mainly because the resistor needs to be of small physical size it and this dictates one of 0.5 or 0.25 watt rating. The voltage across the resistor is about 200V so 150k dissipates 0.27 watts. ..... Phil |
#6
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Series resistor.
On Nov 15, 7:43*am, klem kedidelhopper
wrote: I think I know this but I'd like to be sure. I need to affix a small neon indicator on to a 240V line. Would 80K be an appropriate resistor to use? Thanks, Lenny bare bulb? assume neon turns on at 90V and extinguishes around 60V. Sinewave are 'so fast' just assume the neon is like a bidirectional zener of 60V: First what power idssipates if there were NO neon bulb: to find R try 240*240/R=Power therefore, R=240*240/Power rule of thumb for resistors is use half their rating, so change formula to R=2*240*240/Power so a 1/4W means R = 460k, close value 470k 5% and 1/2W means R = 230k, close value 220k 5% Now let's 'clip' the voltage that goes to the neon: as a simplistic estimate, 240-60=190, and try again R=2*190*190/Power 1/4W R = 289k 1/2W R = 144k use 1/2W 220k, looks like won't hurt anything. just as a check, how much power is going into the neon? current is (240-60)/220k = 0.86 mA power into the neon bulb is 60*0.86mA = approx 50 mW, so neon is not likely to burn up. Plus, dopn't those GFI outlets limit AC current to something like less than 1 mA, so even if you get your fingers in there you're not likely to be killed. |
#7
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Series resistor.
"Robert Macy" use 1/2W 220k, looks like won't hurt anything. ** Correct. Plus, don't those GFI outlets limit AC current to something like less than 1 mA, * Trip current is normally 10mA and time to trip is 30mS for units that can be plugged in. This is for a 240V country. ..... Phil |
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