new life for these 2D kryptons?

[Illum]

I'm sure may of us started LED retrofits before we bought our first LED flashlights. So I'm confident that no " :hahaha: " smilies will be used when I say that I have a component tray worth of 2D, 3D, 4D PR kryptons.

The simplest way of driving a LED is by a resistor right? Light bulbs steals alot of volts right? Light bulbs also burn out when too much current is forwarded right?

so....
What are the chances of success that a light bulb (or light bulbs) can be used in pair with LEDs to drive them from a high DC source? say 12V or 24V being both a resistor AND a fuse?:nana:

At this point the only thing I can do with PR lamps is to gut them and stuff it with a white 10mm LED and some 1/8W resistor on one end...obviously not very scientific:shakehead

 

[abvidledUK]

I've installed RGB colour changing leds ( with Ω's )into some of my old PR2's, use them at Christmas.

 

[metlarules]

I would just stick some 5mm leds in them for use during power outage/emergency time.

 

[bluepilgrim]

If I understand you you are thinking about using the old incandescent light bulbs instead of a resistor for an LED current limiter -- which would result in both the LED and bulb shining at the same time.

As long you get the hot resistance of the incandescent bulb right (and that varies a whole lot from the cold resistance) I don't see why it should not work. But getting it right would be tricky. You would need to operate at the correct current so that the voltage drop across the bulb would be OK for LED, and the also the current would be proper for both the LED and the bulb.

I had something similar to keep the food warm for the cat I had in the garage: I had a food warming tray which was normally too hot, so I hooked it with a double bulbed goosenech desk lamp wired in series with the tray. If I turned one bulb on (I think I used 100 watts, but maybe 60) the tray got warm, with two bulbs on it got warmer (for colder weather). But I had to do by trial and error -- trying to figure out the hot resistance of the filaments at various voltages and currents, consulting temperature vs resistance tables for tungston alloys was well beyond my being able to calculate it.

You would have that with an LED and incandescent lamp too: as more current went through the bulb it would get warmer, and the resistance would change, and so would the voltage dividing between the LED and bulb. A resistor (carbon, ordinary wirewound, etc.) would stay about the same regardles of the current across it as long as it was within the wattage rating.

The only way I can think of doing it would be to find the effective resistance and voltage drop of the LED and get an equivalent resistor to hook up with the incandescent bulb so you could run some experiemnts -- and then risk the LED by hooking it up to see if it would work -- you might need an additional resistor in series, parallel, or a network configuration to be able to use the bulb. It would be neat if you could do it, but it's pretty wild and not at all straightforward.

Even hooking up two different incandescent bulbs in series to use a higher voltage source would get hairy -- it's not ike using two of the same bulbs where each of them would drop the same voltage, so that twice the volts would give you the right voltage across each them with the proper current flowing through both. I expect with a semiconductor -- an LED -- that curves for voltage, current, voltage drop, etc. would not be linear. (At one point one could figure the drop across a (silicon?) diode was a constant of about .7V, but that was long ago in a galaxy far away.)

 

[Illum]

If I understand you you are thinking about using the old incandescent light bulbs instead of a resistor for an LED current limiter -- which would result in both the LED and bulb shining at the same time.

As long you get the hot resistance of the incandescent bulb right (and that varies a whole lot from the cold resistance) I don't see why it should not work. But getting it right would be tricky. You would need to operate at the correct current so that the voltage drop across the bulb would be OK for LED, and the also the current would be proper for both the LED and the bulb.

right, the "hot resistance" is going to be way way less than whats measured from a "cold" lamp...two 2.4V 0.24A PR lamps in parallel could see through 0.35A to drive an LED without going out, but thats on paper

certain times when your powering LEDs from wallworts [I get basically free most of the time shopping thrift stores] driverboards may interfere with the wallworts and create heat issues in the process [some wallworts burn out when your pulling too much current]. So in these cases I would go with resistors. Unfortunately wallworts aren't designed to drive LEDs and theres almost always a heck of alot of heat dissipating over resistors and sometimes heatsinking them is a bigger job than heatsinking the LEDs

A light bulb will create heat...but they are designed as such, so whats a little more light, a fuse, and a LED power indicator compared to extra aluminum fins, thermal epoxy, and electrical isolation?

I had something similar to keep the food warm for the cat I had in the garage: I had a food warming tray which was normally too hot, so I hooked it with a double bulbed goosenech desk lamp wired in series with the tray. If I turned one bulb on (I think I used 100 watts, but maybe 60) the tray got warm, with two bulbs on it got warmer (for colder weather). But I had to do by trial and error -- trying to figure out the hot resistance of the filaments at various voltages and currents, consulting temperature vs resistance tables for tungston alloys was well beyond my being able to calculate it.

Interesting, good to know I wasn't the only one this crazy

You would have that with an LED and incandescent lamp too: as more current went through the bulb it would get warmer, and the resistance would change, and so would the voltage dividing between the LED and bulb.

I figured this was certainly going to be the difficult part off the bat...controlling a temperature variable resistor, From the looks of it I might have to try it out similar to the way the linear thermistor circuits are.

The only way I can think of doing it would be to find the effective resistance and voltage drop of the LED and get an equivalent resistor to hook up with the incandescent bulb so you could run some experiemnts -- and then risk the LED by hooking it up to see if it would work -- you might need an additional resistor in series, parallel, or a network configuration to be able to use the bulb. It would be neat if you could do it, but it's pretty wild and not at all straightforward.

Now I think about it....maybe it would be just best to stuff these PR cans with 5mms and 10mms afterall:candle:

 

[bluepilgrim]

"the "hot resistance" is going to be way way less than whats measured from a "cold" lamp" -- actually, that's reversed: hot has more resistance (maybe that's what you meant, but you don't want to get it backwards).

Yah -- you can stuff bulb cases with LEDs, but it wouldn't be as much fun.

The first time I saw a light bulb being used as a load was at a ham 'field day' (really a 'field night', back when. The idea was to run radios out in the woods in preparation for emergencies. They had a generator hooked up to a regulating circuit, with a bulb as load -- the thing kept blinking on and off all night as the power generated ebbed and surged. A bulb can be used, but these guys were experts at electronic kludging (with elegance, even).

(BTW -- don't forget the heat-sinking capability of the wire. At one time, at least, it was said that about half the wattage a resistor dissappated was through the leads. If you hook up a led with large gauge wire (number 10?), maybe with a little pigtail at the connection end, and maybe too with the rest of the wire hammered flat, like a fin, (and annealed to soften it again, to lower the resistance) you might get rid of a lot of heat that way. Copper is a good heat conductor too. I'm assuming that drawing heat out of the LED and driver electrical connections would be useful.)

** Crazy is the mother of invention! **