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tutorials:capacitor_selection [2026/03/25 14:30] – [Capacitor Sizing: Why Bigger is Not (always) Better] ibchadmintutorials:capacitor_selection [2026/03/25 14:46] (current) – [References and Further Reading] ibchadmin
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 Given the above, we can come up with some general guidelines when selecting capacitors for a batteryless device: Given the above, we can come up with some general guidelines when selecting capacitors for a batteryless device:
  
-Assume short bursts of energy in most cases: it is difficult to match the steady power of a comparable battery device short of some supercapacitors or a source of harvested energy capable of providing more power than is actively consumed.  If either option is not available, then selecting purely for high capacitance may provide no benefit or even be counterproductive, and many batteryless devices will need to be designed with an appropriate checkpointing strategy to best make use of these short bursts. +  * **Assume short bursts of energy in most cases**: it is difficult to match the steady power of a comparable battery device short of some supercapacitors or a source of harvested energy capable of providing more power than is actively consumed.  If either option is not available, then selecting purely for high capacitance may provide no benefit or even be counterproductive, and many batteryless devices will need to be designed with an appropriate [[tutorials:checkpointing_overview|checkpointing strategy]] to best make use of these short bursts. 
-Have enough energy to complete the largest discrete task: At minimum, the capacitor should be able to provide enough charge to complete the largest discrete (i.e. must be done in one power cycle) task: for example, if the device has a radio that it uses to transmit data, it should have enough power to complete the transmission without encountering a power failure. +  * **Have enough energy to complete the largest discrete task**: At minimum, the capacitor should be able to provide enough charge to complete the largest discrete (i.e. must be done in one power cycle) task: for example, if the device has a radio that it uses to transmit data, it should have enough power to complete the transmission without encountering a power failure. 
-The smaller the capacitor, the more reactive the device: the less time a device spends charging, the more often it will be active (and capable of detecting/reacting to events, if necessary).  This is often in tension with the previous point, as many devices have a small number of tasks or peripherals with significantly higher energy demands than the others. +  * **The smaller the capacitor, the more reactive the device**: the less time a device spends charging, the more often it will be active (and capable of detecting/reacting to events, if necessary).  This is often in tension with the previous point, as many devices have a small number of tasks or peripherals with significantly higher energy demands than the others. 
-Be aware of non-ideal behaviors: like batteries, a capacitor’s paper performance can be degraded by various factors such as temperature, humidity, and frequent charge/discharge cycles.  What may work on a test bench or simulation may fail in a practical deployment if these factors are not properly accounted for.+  * **Be aware of non-ideal behaviors**: like batteries, a capacitor’s paper performance can be degraded by various factors such as temperature, humidity, and frequent charge/discharge cycles.  What may work on a test bench or simulation may fail in a practical deployment if these factors are not properly accounted for.
 ===== Capacitor Setups ===== ===== Capacitor Setups =====
  
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 With this flexibility comes increased complexity.  A separate energy management circuit is usually required to measure and distribute energy to the individual capacitors, which leads to increased overhead and circuit size.  The device itself must also be able to account for the current energy state of each individual peripheral or task: using the previous example, if a device wishes to transmit data it must be able to recognize whether or not the radio has sufficient power for operation and adjust its behavior accordingly. With this flexibility comes increased complexity.  A separate energy management circuit is usually required to measure and distribute energy to the individual capacitors, which leads to increased overhead and circuit size.  The device itself must also be able to account for the current energy state of each individual peripheral or task: using the previous example, if a device wishes to transmit data it must be able to recognize whether or not the radio has sufficient power for operation and adjust its behavior accordingly.
  
-Examples +**Examples** 
-United Federation of Peripherals (UFOP) http://dx.doi.org/10.1145/2809695.2809707 +  * [[http://dx.doi.org/10.1145/2809695.2809707|United Federation of Peripherals (UFOP)]] 
-Stash https://doi.org/10.1145/3641511 +  * [[https://doi.org/10.1145/3641511|Stash]]
 ==== Reconfigurable Storage ==== ==== Reconfigurable Storage ====
  
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 Like federated energy, there is a price in both circuit size and complexity, requiring multiple capacitors (even when some may be rarely active) and some control circuitry and logic to switch configurations as needed: there is also some energy loss when the configuration changes, due to equalization of charges across the capacitors.  While capable of a wider range of capacitances than single or federated storage methods, the range of capacitances is ultimately limited by the number of possible combinations, so the energy profile of the device should still be well understood to ensure proper capacitor sizing. Like federated energy, there is a price in both circuit size and complexity, requiring multiple capacitors (even when some may be rarely active) and some control circuitry and logic to switch configurations as needed: there is also some energy loss when the configuration changes, due to equalization of charges across the capacitors.  While capable of a wider range of capacitances than single or federated storage methods, the range of capacitances is ultimately limited by the number of possible combinations, so the energy profile of the device should still be well understood to ensure proper capacitor sizing.
  
-Examples +**Examples** 
-Capybara https://doi.org/10.1145/3173162.3173210 +  * [[https://doi.org/10.1145/3173162.3173210|Capybara]]
  
 ===== References and Further Reading ===== ===== References and Further Reading =====
  
  
-https://engineering.mit.edu/ask-an-engineer/how-does-a-battery-work +  * [[https://engineering.mit.edu/ask-an-engineer/how-does-a-battery-work|How Does a Battery Work?]] 
- +  * [[https://courses.lumenlearning.com/suny-physics/chapter/19-5-capacitors-and-dielectrics/|Capacitors and Dielectrics]] 
-https://courses.lumenlearning.com/suny-physics/chapter/19-5-capacitors-and-dielectrics/ +  * [[https://dl.acm.org/doi/abs/10.1145/3686138.3686144|The Future of Unmanned Aerial Vehicles Has No Batteries]] 
- +  * [[https://lirias.kuleuven.be/retrieve/804774|CapBot: Enabling Battery-Free Swarm Robotics]] 
-https://dl.acm.org/doi/abs/10.1145/3686138.3686144 +  * [[https://www.allaboutcircuits.com/tools/capacitor-Charge-and-time-constant-calculator/|Capacitor Charge and Time Constant Calculator]] 
- +  * [[https://www.allaboutcircuits.com/industry-articles/understanding-capacitor-leakage-to-make-smart-things-run-longer|Understanding Capacitor Leakage to Make Smart Things Run Longer]]
-https://lirias.kuleuven.be/retrieve/804774 +
- +
-https://www.allaboutcircuits.com/tools/capacitor-Charge-and-time-constant-calculator/ +
- +
-https://www.allaboutcircuits.com/industry-articles/understanding-capacitor-leakage-to-make-smart-things-run-longer+
  
tutorials/capacitor_selection.1774449023.txt.gz · Last modified: 2026/03/25 14:30 by ibchadmin
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