LED Bulb Bulb

Other Hardware LEDs and Multiplexing
1

I have a basic desk lamp, plugs into the wall, simple on/off switch, standard bulb socket.
120VAC @ 60Hz goes to that socket.

I have an A19 standard size LED bulb that says "120V 9W 130mA" in there.
My math tells me 120V and 9W means 75mA, not 130mA.

Is there something going on like AC amperage counting as double the amperage?

I'm trying to figure out what this bulb is actually drawing, to see if it's safe to put through a 2A signal relay instead of a beefy power relay. Also would help me sort out listed amp ratings of various devices and understand the distinction between AC and DC amp figures.

2

Signal relays could be rated for a lower voltage.
I have a bunch of small ones here on my desk that are rated for 60volt (open contacts).

Remote controlled RF wall outlets are cheap and safe.
Let an Arduino control them.
Leo..

3

My venture was directed to latching relays. Dual coil, because the mcus I have don't do negative voltage and I'm not going to go to an h bridge when dual coil is an option. I bought a variety, but I am frankly enamored with this one

It's flippin neat. Put ~10ms of 5V @ 28mA and it switches, then stays put. Put the same on the other end, and it switches back, stays put. No energy drawn to hold position.

I was astonished at how tiny these things are, since all I had are the Songle relay modules everyone has.

Anyway, rated to handle the AC. Weirds me out that it's a dinky pin to pass mains level AC....

4

28mA for 10ms shouldn't be a problem for an Arduino pin.
Connect the coil to two Arduino pins, and make one or the other HIGH for that short duration.
Use four schottky kickback diodes, like you see on an H-bridge.
The total resistance of two ports could be ~50ohm.
Just try if that 's a problem or not.
Datasheet says that the relay will work from 3.75volt.
Leo..

5

Relay isn't the problem, the thing switches even with a 3V coin cell.

This thread is to seek an explanation on what amperage figures are relevant in using devices like LED bulbs that convert AC to DC internally.

I'm guessing the wattage is the value blind to type of power, but if the bulb says 130mA, then that means the LED is running around 6V

6

INTP:
I'm guessing the wattage is the value blind to type of power, but if the bulb days 130mA, then that means the LED is running around 6V

I'm guessing they're rating it as 130mA at the peaks of the AC sine wave. 130ma RMS = 130 / sqrt(2) =~ 92ma.

7

That, or they use a capacitive dropper with a terrible power factor. Then it can draw 130mA but only output 9W effectively :slight_smile:

8

Inside the bulb base is most likely a DC/DC converter that is not a resistive load.
And a DC/DC converter also uses power.
Leo..