I thought the resistance was dependent on temperature, not voltage.
Sure, a higher voltage means it will heat up quicker and increase in
resistance quicker. But initially, at least, for a given voltage, the
resistance would be low. Thus, resistance would not proportional to
voltage. Did I miss something?
Peri
------ Original Message ------
From: "paul dove via EV" <[email protected]>
To: "Lee Hart" <[email protected]>; "Electric Vehicle Discussion
List" <[email protected]>
Sent: 05-Nov-15 12:53:10 PM
Subject: Re: [EVDL] Suitable Load?
Yes, Ohms law applies in light bulbs.
Instead of a linear graph you get a curve because of the changing
resistance.As the voltage increases the current increase becomes
smaller and smaller.Since it is not linear the change in current slows
down as the voltage increases.Still, at low voltage you have low
current and at high voltage you have high current as I said.
From: Lee Hart <[email protected]>
To: Paul Dove <[email protected]>; Electric Vehicle Discussion List
<[email protected]>
Sent: Thursday, November 5, 2015 11:01 AM
Subject: Re: [EVDL] Suitable Load?
Paul Dove via EV wrote:
Halogen bulbs are made in general for 6V, 12V, 24V... Using too low
a voltage will produce little current and too high a voltage will
produce high current and overheating of the filament
Actually, light bulbs don't behave like resistors. Ohm's law doesn't
apply. :-)
A light bulb's apparent resistance changes drastically with
temperature.
The cold resistance (measured with an ohmmeter) is easily 1:10th that
of
its hot resistance (current divided by voltage at full rated voltage).
Depending on the type of light, an 8-1 change in voltage only causes
about a 2:1 change in current.
This means that light bulbs can be used as crude constant-current
loads.
The current only changes slightly despite large changes in voltage.
This
characteristic is ideal for testing batteries, where you'd like the
current to stay the same despite changes in cell or battery voltage.
--
Any intelligent fool can make things bigger, more complex, and more
violent. It takes a touch of genius, and a lot of courage, to move
in the opposite direction. -- Albert Einstein
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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