From: firstname.lastname@example.org (Ben Bradley)
Subject: Re: 9VDC Heater?
Date: 21 Nov 2002 22:00:43 -0800
NNTP-Posting-Date: 22 Nov 2002 06:00:43 GMT
In sci.electronics.design, 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
>>> wire or a metal plate to around 125 degrees Celsius. Warmup time
>>> a concern; I just need the plate to be at ~125 or more degrees
>>> for about five seconds, powered from a 9V battery. Whether or not
>>> 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.
The plate acts like a heat sink to draw away heat from the source
(the coil of wire/resistor you're using to heat the plate). A larger
plate will take longer to heat up because of its larger thermal mass
(and different materials have different [ISTR it's called] 'specific
heat'), and will also radiate more heat away and conduct more of the
heat to the air around it, making it take more power to heat to the
temperature you want than a smaller plate. So the answer to your
original question is yes, if the plate is small enough. The next
question is, of course, what exactly is small enough?
Try searching on combinations of these keywords: thermodynamics,
heat sinks, thermal resistance, specific heat, convection, conduction.
Or get a physics or engineering book that covers thermodynamics.
You also need to know the current capabilities of a 9-volt battery,
so you know how much power you have to heat the plate with. You'll
have to scale the resistor or wire to pull this much current from the
You're not going to use this info to make a bomb detonator, are
you? (see "Best bomb detonator? (Hi FBI)" thread) ;)
Quick guys, what explodes at 125 degrees Celcius?
>Thanks in advance.