Electronics > Beginners
Incandescence bulbs as dummy load, few questions ...
schmitt trigger:
Well, this thread piqued my curiosity and decided to measure the lamp's resistance vs voltage, using a Variac and a pair of DMMs measuring voltage and current.
The lamp is a Philips 120V, 65W nominal, outside reflector.
An Excel spreadsheet completes the analysis. Horizontal axis is voltage, vertical is resistance.
Of course, the "0" volt resistance was measured with a DMM in ohms mode.
Perhaps you would like to repeat this experiment with a couple of lamps. It only takes a few minutes.
vu2nan:
--- Quote from: IanB on January 13, 2020, 03:22:18 am ---It seems to me that you want to seek out 120 V 25 W bulbs, since their operating current would be 25/120 = 0.21 A. If you put three of these in series you would have a nominal load that would draw 0.21 A at 360 V, and therefore approximately 0.20 A at 350 V.
--- End quote ---
Indeed workable! :-+
Regards,
Nandu.
BravoV:
--- Quote from: schmitt trigger on January 14, 2020, 01:20:11 am ---Well, this thread piqued my curiosity and decided to measure the lamp's resistance vs voltage, using a Variac and a pair of DMMs measuring voltage and current.
The lamp is a Philips 120V, 65W nominal, outside reflector.
An Excel spreadsheet completes the analysis. Horizontal axis is voltage, vertical is resistance.
Of course, the "0" volt resistance was measured with a DMM in ohms mode.
Perhaps you would like to repeat this experiment with a couple of lamps. It only takes a few minutes.
--- End quote ---
Thanks a lot for the chart, really appreciate your effort here. :-+
Yeah, I think I will do some profiling work on various incand. bulbs, now the problem is I forgot where I put my variac, as its rarely used, must be drowned somewhere in the piles of junks. :palm:
Also suddenly pop out in my mind about DC vs AC, does anyone know if there is significant difference when an incandescence bulb is powered AC vs DC ?
Of course, AC is say at 220V or 110V AC RMS@50/60Hz ... vs ... pure DC at 220V or 110V.
IanB:
--- Quote from: BravoV on January 14, 2020, 04:19:43 am ---does anyone know if there is significant difference when an incandescence bulb is powered AC vs DC ?
--- End quote ---
Not in the short term for testing a power supply as planned here.
In real world use for lighting purposes AC lamps should not be used with DC. They can fail sooner and if they do fail the DC supply will sustain an arc much more readily than AC leading to potentially energetic consequences.
Gyro:
--- Quote from: calzap on January 13, 2020, 08:23:04 am ---Why not use high wattage wire-wound resistors? They're not that expensive. And they're more compact and tougher than light bulbs, and their resistance is more stable. You can parallel them if need be to achieve the required wattage. I try not to exceed more than 1/2 the rated wattage, and even then they'll get hot.
Mike in California
--- End quote ---
Incandescent lamp filaments are so hot that they dissipate most of their power as thermal radiation rather than conducted or convected heat (in fact only a small percentage comes out as light). Radiant heat dissipation is way more efficient than conducted or convected. You don't have the same problems with hot casings and heatsinks, the bulb radiates its heat directly to objects within line of site - the walls, ceiling, stuff around them, you. All get warmer, but the large surface area involved means that nothing heats up very much.
The same applies to vacuum tubes, their Anode dissipation is pretty much all by radiation. A power anplifier tube can quite happily dissipate 50W upwards where in the same situation, a transistor would need large heatsinks and possibly fans too.
If you can screen yourself from the annoying light output, a light bulb is an excellent high power load.
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