Battery Operated Resistive Heater Control

[kamongear]

Hi all,

I was considering how best to build a lithium polymer powered heating circuit. The goal is 10-20W of peak output. Known components are 1-2 lipo cells and a resistive heating coil(resistance can be varied to best suit circuit characteristics). My first thought was a PWM controlled transistor acting as a current sink to the coil. Another thought was using a programmable regulator to vary the voltage across the heating element.

Is there one approach that produces a significantly better design than others? Advice on practical considerations a novice might not make would be appreciated.

Thanks.

 

[D.A.(Tony)Stewart]

Of course it depends on you VAh or Wh capacity and how many minutes of heat and what you are trying to heat.

 

[kamongear]

Of course it depends on you VAh or Wh capacity and how many minutes of heat and what you are trying to heat.

The cells that are being used are 2600mAh. Space constraints limit me to 1-2 cells. There also exists the peak 10-20W requirement(the user is assumed to adjust the output to some level under this) and the heater is resistive wire so I assume I can adjust the resistance based on peak current draw needed from the battery.

From there, the problem essentially boils down to choosing the best method to drive the resistive load, no?

My initially reaction was to use a microcontroller(3.3V logic) to drive a power fet that acts as a switch between the resistive heating element and ground. Using one cell at 3.7V, for a 10W peak, the heating element should be designed to be roughly 1.4Ohm. Using two cells in series fro nominal 7.4V, a 2A draw would yield 14.8W and a necessary heat element resistance of 3.7Ohm. In either case, it looks like NTD5867NL should be suitable for this purpose given the safe operating area curve in the datasheet although there may be thermal considerations I am erroneously ignoring.

The design is rather open-ended and I'd be happy to hear other methods of control that might yield better results.