Power

//Welcome to POWER group.//



and Brent Higgins.

Overview
The power group for the digital health problem is in charge of creating and choosing the appropriate power supply which will operate all of our equipment.

In order to decide on the appropriate power supply for our equipment, multiple issues need to be addressed. How each component is wired will greatly affect the necessary power supply. Every TEC and Heat Sink will require a specific amount of voltage and current for it to operate at its maximum potential. In addition the amount of run time desired will also affect our decision for the power supply. The power supply must be able to be recharged and be carried around with the person wearing the device. A lightweight portable power supply will be our only option.

The Evolution of Our Power Supply
We originally used a variable power supply until we finished our calculations and got our final estimates. However this is bulky and not portable so it is only a temporary option. Our handy variable power supply was able to achieve our goals in finding the appropriate power to run each component. We determined that the TECs cannot be best run at 14.7V as our battery will power. When running at half of that, 7.35V they cool and heat at an optimum rate. This decrease in power supplied to the TECs will be regulated by a MOSFET and Arduino which will run a duty cycle at 50%. This will cause the power to the TECs to be reduced by half. Therefore they will be operating at the 7.35V with the 14.7V power supply. The battery below is going to be the source for the TECs and heatsink fan's power.
 * Our Original Power Supply for Testing Purposes || Our Final Power Supply for Running the TECs and Heatsinks ||
 * [[image:http://di1-1.shoppingshadow.com/images/pi/90/51/30/69717181-149x149-0-0_B+K+BK+Precision+Power+Supply+1672+Triple+Output+D.jpg width="309" height="248" caption="http://www.bkprecision.com/products/model/1672/triple-output-quad-display-dc-power-supply-2-0-32v-0-3a-15v-3a.html"]] || [[image:http://www.all-battery.com/ProductImages/july2006/Li-18650-14.8V-4400.jpg caption="http://www.all-battery.com/li-ion18650148v4400mahpcbpreotectedrechargeablebatterywithbareleads.aspx"]] ||

About Our Battery
The battery we are using is a Lithium Ion battery. We determined Lithium Ion technology would be the best to use because of their high voltage potential for a battery. These batteries are also rechargeable and retain their charging potential well. Due to Lithium Ion batteries being the closest to an ideal power supply for us, we will be utilizing them. This specific battery will last us enough time to power all of our components significantly long enough. It is rated for 4400mAh (Milli-Amp hours). Below at the battery life calculations is the math showing how long our battery will last.

Using 12V Regulators
Either a 12V or 14.7V power supply will be used to power the fans and thermoelectric coolers. If a 14.7V power supply is employed, then the fans will require a 12V regulator and the TECs might require a 9V regulator- this remains to be tested. If a 12V power supply is employed it is possible to run both the fans and the TECs and leave power regulation to the MOSFETs embedded in the design of the controller. It Therefore we will be connecting two 12V regulators in parallel from the power supply to control the voltage they receive. The 12V regulator can output a maximum of 1Amp. However, when the fans are connected to a 12V source they draw only about 800mA. This is enough to run the fans at an extremely fast pace. This pace will be significant enough to operate our heatsinks. Below is an image of the 12V regulators we are using. They require an input voltage of at least 14.6 volts which is supplied by our 14.7 volt lithium-ion battery.

Using Duty Cycles
show equations for duty cycle which causes 7.35V average voltage
 * e**xplain how duty cycles work here

Using MOSFETs
In order to use the duty cycle for our power supply we are using multiple MOSFETs. The pulse width modulation will determine the amount of time the full 14.7V is being applied to the TECs. The arduino micro-controller will be controlling each of the MOSFETs. When the micro-controller is sending 5V to the MOSFET, it allows our power supply's current to pass through. When the micro-controller is not sending any voltage, the MOSFET does not allow current to pass. Therefore if the MOSFET is switched open about 50% of the time using a pulse width modulation, the average voltage delivered to the TECs will be about 7.35V as shown above. There will be two MOSFETs for each fan as well but these will be regulated the majority of the time so the fans will continue to have about 12V applied to them at all times. The advantage of the MOSFET is you can regulate the average power supplied to the devices through the pulse width modulation. Below is an image and a schematic showing how the MOSFET works. MOSFET Schematic - []
 * [[image:http://dlnmh9ip6v2uc.cloudfront.net/images/products/10256-01_i_ma.jpg caption="http://www.sparkfun.com/products/10256"]] ||
 * MOSFET Power Control Kit ||

Battery Life Calculations
Average Power Consumption Estimation component || 4.0A || 1.4A || Maximum mAh used in one hour = 4.0A + 1.4A = 5.4A Equation to determine how long this battery will last: 5400mAh / 60mins = 4400mAh / battery life Battery Life = 48.88mins.
 * || TECs || Fans ||
 * Voltage Sent || 14.7V || 12V ||
 * Duty Cycle || 50% || 100% ||
 * Average Voltage Consumed || 7.35V || 12V ||
 * Average Current || 2.0A || 0.7A ||
 * Multiplied by 2 for each

Using these calculations we can determine that our battery will last about 48.88 minutes at average operation. This is enough to power the circuit longer than the micro-controller's battery will control the device. Below we show how long the micro-controller will be powered.

**Battery Life Calculation #2**

Max Power Consumption Estimation component || 7.32A || 1.4A || Maximum mAh used in one hour = 7.32A + 1.4A = 8.72A
 * || TECs || Fans ||
 * Voltage Sent || 12V || 12V ||
 * Duty Cycle || 80% || 100% ||
 * Average Voltage Consumed || 9.6V || 12V ||
 * Average Current || 3.66A || 0.7A ||
 * Multiplied by 2 for each

(And the decision is? -Mike J.)

Brent - numbers need to be more consistent in this section. In the calculation above, the battery is listed as 14.7 but below it is 14.8. In addition the product number of the battery you have listed below corresponds to a different battery entirely. it is suggested we add a third battery life calculation at an even lower power, 6.5V. we also have to consider the situation in which we slightly increase the amount of power sent to the fan. my guess is this will allow us to decrease the amount of power we need to send to the TEC. this option should be at least estimated.

(The 14.8 was obviously a typo. The 6.5V battery would eliminate the purpose of the duty cycle. There is nothing wrong with the calculations at this point. Also if you go with a lower voltage and increase the duty cycle you will most likely be reducing the life of the Arduino battery which is ONLY 110mAh when running at 3.7V. It is NOT 1000mAh. Its not worth estimating because it isnt a reasonable option. I think were past the point of creating new designs. Also you can see the product number clearly printed on the image above. -Mike J.)

Arduino Lily-pad Micro-controller Battery
Fortunately the Lily-pad micro-controllers we are using have their own 3.7 volt power supplies that attach to them. This will be raised to 5V by an arduino lily-pad specific regulator. This eliminates the need for the power group to come up with another device to power the micro-controllers as well. However the 3.7V battery has a battery life of only 110 mAh. We estimate that the lilypad battery will only last about 30-40 minutes. This battery will be drained in multiple ways. There will be four pulse width modulation outputs which will drain the power supply. There will also be a power output to the temperature sensors in order to read the temperature data. Lastly, the battery will have to operate the lilypad as well. Since this battery is going to last about 30-40 minutes and our 14.7 volt supply will last at least 49 minutes, we can estimate our whole system to run for at least 30 minutes. At most the system will last probably about an hour.


 * [[image:http://dlnmh9ip6v2uc.cloudfront.net/images/products/00731-03-L_i_ma.jpg caption="http://www.sparkfun.com/products/731"]] ||
 * 3.7V Lithium Ion Lilypad Battery with 1000mAh. ||

Schematic of our Whole Circuit
The diagram below shows up our circuit is all connected as previously explained in each section. The 14.7V power supply connects directly to the two TECs in parallel. In parallel with those as well is two 12V regulators which are each connected to a CPU fan. These fans and TECs are each connected to their own MOSFET which is connected to ground. The Mosfets are connected to the "Pulse Width Modulation" ports on the arduino as well in order to regulate them. There is also the Arduino power supply which is connected only to the Arduino and ground. The last component is the temperature sensors. These are powered by the Arduino. These are also connected to a digital input port on the Arduino lilypad so it can read the digital temperature readings that they output as well. Due to the large number of components, there are a lot of wires which may look confusing on a diagram of the whole circuit setup.



Specs of Each Part
Below is a chart of each part we had to consider when creating the circuit above. Using these values we were able to alter the pulse width modulations and power supply to give the desired power to each component. The mosfets and 12V regulator components are the components which limit the power supplied to each device to get our desired output.
 * Parts || Max Voltage(V) || Max Current (mA) || Resistance (Ohms ) ||
 * Li-Ion 18650 || 14.7 || 4400 || N/A ||
 * TEC1-12705 || 14.2 || 5300 || 2.4 ||
 * Heatsinks (CPU fans) || 12.0 || 850 || N/A ||
 * Arduino Lily Pad || 5.5 || 40 ||  ||

Resources: [] [] [] [] http://www.all-battery.com/Li-Ion18650-148V6000mAhBatteryPackwithPCB.aspx http://www.sparkfun.com/ http://www.hebeiltd.com.cn/peltier.datasheet/TEC1-12705.pdf http://shoptemplate.allshopoutlet.com/index.php?main_page=product_info&cPath=144_145_150&products_id=1837&zenid=s1h2jhlbf0bmebhook3sqpnnh7 http://www.globalspec.com/LearnMore/Electrical_Electronic_Components/Fans_Electronic_Cooling/Heat_Sinks