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Old 11-17-2003, 06:36 PM   #1
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Exclamation Discharger Lights! Watt into Amps!

I bought 4 12V lights and they are suppose to be 50watts each.
How much amps does one bulb pull then?

Please help
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Old 11-17-2003, 06:42 PM   #2
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The automotive bulbs i have are about 2 amps a piece. What type of bulb did you buy?
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Old 11-17-2003, 07:20 PM   #3
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halogen things...
50watt a piece, so 200watt in total.
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Old 11-17-2003, 07:43 PM   #4
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P=VxI
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Old 11-17-2003, 08:07 PM   #5
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what is P?
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Old 11-17-2003, 08:09 PM   #6
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power (watts)
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Old 11-17-2003, 08:17 PM   #7
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so 200 / 7.2 = 27.8 amps

wow.. that's pretty good for guessing and buying 4 bulbs
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Old 11-17-2003, 08:47 PM   #8
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That Ohm fellow was a swell guy
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Old 11-17-2003, 10:40 PM   #9
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Quote:
That Ohm fellow was a swell guy
How about a Cheer for Ohm's law
I
E/R
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Old 11-18-2003, 06:33 AM   #10
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lol...
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Old 11-18-2003, 07:58 AM   #11
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It's true that P=VxI. But you cant just calculate the amps this way 200 / 7.2 = 27.8 amps.

I cant remember the reason but the right way to do it is like this:

The 200 watt is at 12 volt. So 200/12 = 16,7.

Now we now the volt and the amps and thus we can calculate the resistance: U=R*I, that is 12/16,7=0,72 ohm.

So at 7,2 volt, the amps will be: 7,2/0,72=10 amps.

There will however be som inaccuracy: While the bulb gets hotter, the resistance will decrease. So at a lower voltage, the resistance will be a little higher. Besides, when the pack discharge, the voltage will decrease, thus the amps will also decrease.

Anyway, I think there's too muc hype about these discharge rates. The mathcing companies discharge at high rates, simply because higher numbers sell better.

So average Joes like me, do fine with 10 amps discharging. At practising, just drive the car till the pack dumps. At races, discharging between heats at 10 amps, will do fine.
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Old 11-18-2003, 08:11 AM   #12
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Cole I agree with you that the bulbs don't generate 200 watts of energy at 7.2V because they are rated at 12V, but 10 amps doesn't sound right. Unfortunately, I never took any electrical engineering classes so I'm at a loss for explaining why I think it's somewhere inbetween. I'm thinking more like 16.6 amps.

Maybe someone else can assist.
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Old 11-18-2003, 08:30 AM   #13
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You forget that he has 4 different bulbs. So it is not 200/12 but 50/12 --> 4.16 amps per bulb.

Then using Ohm's law, you get R = U/I = 12/4.16 = 2.88 Ohms per bulb.

Then, depending of whether he plugs the bulbs in seria or parallel, we have :

- seria : U = R.I --> I = U/R for each bulb, with U the tension on each bulb (=7.2 / 4) and R the resistance of each bulb.

Thus I = 1.8/2.88 = 0.625 A

- parallel : I = U / R but here we have

-1/R = 1/r1 + 1/r2 + 1/r3 + 1/r4 = 4/r as all r are the same. Thus R = r/4

- U = 7.2 V

thus we have I = 7.2*4/2.88 = 10 A

My conclusion is : better have them linked in parallel...
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Old 11-19-2003, 03:39 PM   #14
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Quote:
Originally posted by Cobra81li200
thus we have I = 7.2*4/2.88 = 10 A

My conclusion is : better have them linked in parallel...
My assumption, was they were in parallel.... however you're right about pointing out, that if they are in parallel, the discharge rate is higher.
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Old 11-20-2003, 12:49 AM   #15
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i went out and bought some automotive headlights, i believe they are around 80W and 100W (theres 2 flint thing..whatever you call them) inside the bulb, and i have them all wired up in parallel..how many amps am i pulling out around???
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