I am just wondering how I would include a silicone mat heater rated at 15 watts and 12 volts with a DS18B20 temperature sensor into a circuit with arduino, I understand how the sensor is attached into the arduino and the coding but I am stuck as to what to use for the heating operation, I was thinking about using:
a mosfet for the switching process
4 lipo batteries (14.4v) to power the heater mat
voltage regulator to keep the input voltage of the heater mat at 12v from the batteries.
Does this sound like it would work? would I need any further components and would I need a Solid state relay instead of the mosfet because of the high power intake of the heater mat?
A MOSFET should work fine as long as it's rated for a couple of amps or more. [u]Here is a schematic[/u] for a MOSFET driving a motor. Since the heating mat is non-inductive you can leave out the diode.
15W/12V is 1.25 Amps and the current will be proportionally higher (and more than 15W) at 14.4V. So, take that into account when calculating battery life. Heat takes lots of power so battery-powering a heater is usually a "last resort".
4 lipo batteries (14.4v) to power the heater mat
voltage regulator to keep the input voltage of the heater mat at 12v from the batteries.
14.4V into a 12V heating pad is probably OK... The mat can probably be slightly over-voltaged, especially since you'll have temperature-feedback and you're not going to over heat it. If it was me, I'd leave-out the voltage regulator.
The battery voltage may be slightly higher when fully charged and it will fall below 12V at some point, depending on how far you discharge it. At these current levels, you'd probably want a switching regulator and it's probably not worth the trouble.
On the other hand, an 18V or 24V battery with a switching regulator would give you longer battery life by allowing you go discharge the battery down to about 12V. (You definitely wouldn't want to use a linear regulator to drop that much voltage because the regulator would heat-up, wasting battery power and requiring a big heatsink.)
Thank you for the information it has helped me tremendously, another question though, would I use a switching regulator and a mosfet or solely the switching regulator if I was to use the 18v - 24v battery that you stated? Also I was looking to keep the weight of the battery down, a 18v-24v battery would be quite large and weigh a great deal do you have any suggestions how to overcome this, do you know any batteries that are that voltage range but are relatively small? Thanks again.
The battery size mostly depends on the up-time of the heater. If e.g. heating consumes 1A (average) at the intended temperature, a 1000mAh battery will last for 1 hour. Also check that the battery allows for such a continuous current.