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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
first, are you using the bulb/resistor on the low voltage (primary side) or on the HV side?
Steve Hobley wrote ...
Is it just as simple as Power/Voltager = amps?
So a 25W light bulb will only pass 25/120 amps? Or is this what it transforms into heat/light?
no! no!
25watts / 120 volts = 0.208 Amps !
second, ..... voltage / ohms = amps through resistor third, ......... Voltage across bulb X amps through bulb = watts of heat of bulb itself. therefore .... watts / volts = amps
i think your stuck in your mind on the two factors which kirchoff's princibles describe. review KCL, KVL, and there influence on elements within series circuits. review ohms law too, maybe you should learn the circle diagram.
post again if need help...
my PhD, (EE) thesis is on the DeSeversky design. I am working on a 6 inch x 6 inch 4 inch tall screen which can lift 2.2lbs at 70% electrical effciency, thats why im on this forum...and at chico
Registered Member #1731
Joined: Thu Oct 02 2008, 02:22PM
Location: Indiana
Posts: 52
OK I let me apologise for the slightly confusing wording on my initial post. As I read your response I think we are both talking about the same thing - you maybe a little more eloquently than myself.
When I stated Power/Volts = amps I meant exactly what you posted - Power measured in Watts / Voltage in Volts = Current in Amps.
(Or as I like to remember it Power is Very Important .)
So when I said 25/120 amps I didn't mean divide by "120 amps" I literally meant 25/120 = 0.208 amps
So I *think* (only think) we might be on the same page.
But thanks for the "no! no!" - that always helps
So let me ask this...
If I put a 25W light bulb in series with "Mystery Device X" on 120 V AC supply - is there a maximum current that can pass into "Device X" before the bulb will burn out?
Or, if "Device X" turns out to be just a short - then the whole thing reduces to a simple AC light socket - drawing 0.208 amps of current?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Clearly, the current cannot exceed that passing through the lightbulb even if your mystery device has a notional resistance of zero ohms, as the current through a series string is everywhere equal.
However, the resistance of an ordinary incandescent bulb filament is not constant. It will draw more current in the instant of switching on, and less as the filament temperature - and therefore the resistance - rises to the equilibrium temperature of the ON state.
You should therefore measure the resistance of the filament in its cold state, from which you can calculate the surge current that will flow in the instant after closing the switch.
This surge current is the reason why incandescent light bulbs often fail in the moment they are switched on.
Therefore your contraption must be able to handle this surge current without failing.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
"Lifters" usually shall have current limitation at the HV supply, otherwise sparking between the corona wire and the lifter body may occur. I use a 5 Mohms resistor, made with 5 1 M large resistors (large due to the voltage and the power).
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Formula for light bulb as current limiter
