In a message dated 5/2/98 12:58:28 AM Eastern Daylight Time, BobMGT@aol.com
wrote:
>> Light bulbs have a constant current characteristic. If you run that 1446
bulb
> at 14v it will still draw only .20a.
To which I replied:
"Interesting. I knew the current didn't increase linearly with an increase in
the voltage, due to the increased resistance with the increased temperature,
but I didn't know it was self regulating."
Bob,
Being a skeptic, I decided this morning to put this to a test. I connected
two # 1156 bulbs in parallel, and connected them in series with a 0-15 amp
ammeter. I have three power sources -- a 2.5 amp and a 10 amp regulated power
supplies and a car battery. I measure the voltage at the bulb terminals
rather than at the power source to make the tests more consistant. The
following are the results of the tests. Column A is the measured voltage,
column B is the measured current, and column C is the calculated current
assuming test # 2 as the reference and a linear relationship between current
and voltage.
Test # A B C
1 9.95V 3.71A 3.54A
2 11.10V 3.95A reference
3 12.40V 4.17A 4.41A
(test 1 was run on the 2.5A PS. The regulator cranked the voltage down as the
current draw exceeded its capacity)
This test shows current changes not to be linear with respect to voltage
changes, but not constant either.
So running a 1446 bulb at 14 volts will increase the current it draws, unless
I'm missing something in my analysis/test precedures.
Comments? Corrections?
Apologies to those on the list that don't give a hoot, but since it was
discussed on the list, I think the discussion should continue to be posted for
those who do have an interest.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74AOLFRS ~ ( 9dM˜¿a
4/12/98 Majordomo@autox
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