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Light Globe as Inrush Current Limiter for Vectrix VX1?
Submitted by Mik on Sun, 04/05/2009 - 13:56
Could a light globe be used as the resistor in the Inrush Current Limiter (ICL)?
The circle with "40W" written in it represents a 240V, 40W incandescent light bulb.
I believe the globe would actually light up whilst the capacitors on the motor controller are being pre-charged.
Here are some calculations regarding this:
40W = 240VAC x 0.16666A (Current flow through filament at 240V grid voltage)
240V / 0.166666A = 1.44kΩ (Resistance of HOT globe filament)
140VDC / 1.44kOhm = 97.2mA
The calculations are only approximate, for starters, maybe a RMS correction (factor 1.414) needs to be thrown in somewhere??? Comments, please!
Another factor is the variable resistance of the filament, depending on it's temperature:
From Wikipedia: http://en.wikipedia.org/wiki/Incandescent_light_bulb
Incandescent lamps are nearly pure resistive loads with a power factor of 1. This means the actual power consumed (in watts) and the apparent power (in volt-amperes) are equal. The actual resistance of the filament is temperature-dependent. The cold resistance of tungsten-filament lamps is about 1/15 the hot-filament resistance when the lamp is operating. For example, a 100-watt, 120-volt lamp has a resistance of 144 ohms when lit, but the cold resistance is much lower (about 9.5 ohms)  . ....
For a 100-watt, 120 volt general-service lamp, the current stabilizes in about 0.10 seconds, and the lamp reaches 90% of its full brightness after about 0.13 seconds. 
The resistance of the cold filament might then be: 1.44kΩ / 15 = 96Ω
The current through that resistance, at 140VDC battery voltage, would be: 140V / 96Ω = 1.458A.
Please check these maths for me and comment if you can!