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From: John Larkin
Subject: Re: 9VDC Heater?
Date: Thu, 21 Nov 2002 08:51:11 -0800
Organization: Posted via Supernews, http://www.supernews.com
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On Thu, 21 Nov 2002 07:23:17 -0800, J81 wrote:
>On Thu, 21 Nov 2002 15:06:35 GMT, John Popelish
>>> I'm wondering if it's possible to use a 9V battery to heat a coil of
>>> wire or a metal plate to around 125 degrees Celsius. Warmup time isn't
>>> a concern; I just need the plate to be at ~125 or more degrees Celsius
>>> for about five seconds, powered from a 9V battery. Whether or not it
>>> uses all of the charge in the battery is not a concern.
>>> Thanks in advance.
>>It all depends on the size of the plate. A 1 mm square plate can be
>>held at this temperature for quite a while by an alkaline 9 volt
>>battery. If the coil of wire can be approximated with a small metal
>>film resistor (say, 1/4 watt) it is a piece of cake.
>Could you tell me how you came to this conclusion? If there are any
>formulas that I can use to determine how much power is required to
>heat a certain sized metal plate to a certain temperature, I'm
>oblivious to what they are and would be very grateful if you could
>provide them. :) Just knowing some of the proper terminologies and
>what to search for on google would be a great help.
>Thanks in advance.
Very roughly, a square inch of surface will have a thermal resistance
of 130-160 K/watt in still air. So a flat piece of metal 1" square
would have a thermal resistance around 70-ish K/w, so would need
roughly 1.5 watts to heat it to 125C; much less if it were insulated
with some foam or whatever. A 9-volt alkaline should deliver 5-10
watts for a while.
The time to reach temperature depends on the thermal mass.
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