learning101
Always learning
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- Arizona
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- Electrician
If the supplied voltage to an LED indicator light is 120VAC but the light is rated for 110V, is a resistor needed for the longevity of the LED?
Resistor For 110V
- Thread starter learning101
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We did for industrial projects.
An LED has a current limit, not voltage. Drivers regulate current. So if you just had a naked LED with no driver you most certainly need a resistor but that’s a terrible way to do things because the LED will end up pulsed DC, off for half a cycle, and variable output. And your control is limited…high power LEDs exhibit some negative resistance and tend to go into thermal runaway. That’s what the driver circuit does.
So if you have a light fixture, no. If you have just the LED (no driver) then yes.
FWIW we 110Vac for our control systems for things like indicator lights. We used back to back LEDs.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
A better way to put this is that pilot lights that use LEDs have EITHER what's called a "driver" for them, a little printed circuit board that takes in the AC control circuit power and uses a Switch Mode Power Supply circuit to provide low voltage DC to the LED, or a cheap simple circuit consisting of a diode and a dropping resistor, MAYBE a capacitor to smooth out the pulsing DC through the diode.. MOST of those have a fairly wide voltage input range to where 120V would be acceptable. But "your mileage may vary", meaning we don't know WHAT you have and what its specs are.
- Location
- Bremerton, Washington
I ended up using AB universal pilot lights 120-240 volts, LED lamps. Gone were the days of different lamps, etc
learning101
Always learning
- Location
- Arizona
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- Electrician
Below is a link to the part that I'm going to use in an electrical design---see attachment. If a resistor is required to go from 120v down to 110v, I'd assume the resistor would go in-between the load and the part contact?
EPO Push/Pull Button
EPO Push/Pull Button
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I believe anything rated at 110v is intended to be supplied by 120v without needing a resistor, unless the manufacturer says otherwise, in which case they should also specify a value for it.
110V, 115V, and 120V don't matter. Just hook it up, and they'll be okay.
“Standard conditions” with UL and NEMA is nominal voltage +10/-15%. The supply voltage is 120 V so you are allowed 5% voltage drop so the load rating is 110 V nominal. But this is all nominal. It should handle anything between 94 and 121 V.
learning101
Always learning
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- Arizona
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- Electrician
Thank you so much to everybody that responded! Absolutely helpful and quite informative reading the responses!!
-Jake
-Jake
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
That data sheet says right in front,
“110-120V”
I don’t see the issue here.
“110-120V”
I don’t see the issue here.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Many lighting (not so much indicator) LED bulbs avoid much of the energy waste by stacking multiple junctions in series.
And it is more like 97% for a single junction.
Well, yeah. Anything like a typical LED lamp isn't just going to use a resistor to drop 99% (or 97% whatever it happens to be for that particular LED) of the input voltage.Many lighting (not so much indicator) LED bulbs avoid much of the energy waste by stacking multiple junctions in series.
And it is more like 97% for a single junction.
That would be less than 3% efficient before even thinking about the LED efficiency.
And he did say 'indicator light", so I don't think we are talking about typical ambient light fixtures.
I always spec. transformer driven LED's for pilot lights. They cost a little more, and I'm not worried about efficiency, but it just seems like they last longer.
And to think the voltage is not going up as you go down the line!
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