Em 27/12/2012 22:39, Brent Brown escreveu:
> On 27 Dec 2012 at 16:04, YES NOPE9 wrote:
>
>> This may be obvious... I am not clear on all the ramifications ....
>> What is the most efficient way to convert battery energy into heat ?
>> ( I would like to get all the energy out of the battery =3D=3D> heat  )
>> The battery will be a LION rechargeable.  I can stop discharging at
>> whatever voltage is the best tradeoff between lifetime for the
>> battery and amount of energy extracted. I am going to heat a small
>> object to about 28C to 32C.  The object is insulated and thermally
>> conductive. Ambient will vary from 0C to 20C. I will have a
>> temperature sensor for the object and I could have one for the
>> ambient. When a battery discharges into a resistor, does most of the
>> energy convert to heat from the resistor ?  I understand that a
>> small amount will be lost to wire resistance and the internal
>> resistance of the battery.=20
> Most efficient current to heat converter is a resistor, 100% is hard to b=
eat. Make that=20
> a BJT or FET operating in the linear region and you have a variable resis=
tor, a devie=20
> in a power package has a tab you can mechanically connect to where you wa=
nt hte=20
> heat. There is the question of maximum power point for best energy transf=
er, will=20
> depend on source resistance. In your case I though, without any figures, =
I'd=20
> speculate and say the battery internal resistance could be very much lowe=
r than=20
> your heater element, and if so the heat generated in the battery will be =
low. And=20
> maybe even heat generated in the battery (and wires) will find it's way t=
o heating the=20
> object itself?


Batteries don't like too low temperatures, and the target temperature
the OP wants (28 C to 32 C) is well withing the operating ranges of most
batteries, so I would suggest putting the battery in contact with the
object that needs heating (inside the thermal insulation) then he will
use every bit of heat produced.

Isaac

--=20
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