Then the rated load resistance must be 2x the battery ESR to give a 2/3 cutout point. Intuitively you know if the cutout voltage is 50% or 1.5V the cutoutĮSR is becomes equal to the load resistance. Obviously, your regulation spec determines how close the battery Rs can approach the ESR of your load. You can estimate it from the rated load resistance and EOL voltage.įrom what I understand, pulsed load does not damage the battery's capacity but rather anything which raises the ESR approaching the load's ESR. The battery capacity in mAh is inversely proportional to the battery ESR. It rises almost 1 orders of magnitude over its capacity lifetime. Note below the graph of ESR of the battery rises sharply with loss of capacity after 2/3rd is consumed. Many suppliers use 33 to 50%, you might need 10~20%. will greatly affect the lifetime reduction from rated capacity. Let's start with these values and neglect ESR of battery. The load ESR increases with duty factor (d.f.) ESR = V/I * 1/d.f. 10% cutout ESR and that also degrades from cold temperature by almost 3x from 23'C to 0'C. Keep in mind the initial ESR is much smaller e.g. If not given you calculate the battery's ESR at rated cutout voltage and load. They need to supply the capacity vs load resistance for your operating temperature. It is important to choose the right size cell and supplier for your application and understand the loss of capacity drops a lot when you exceed the rated load. That's because the short discharge can be approximated well as linear, like we saw earlier, and also I rounded the values. Note that the capacitance is the same as with our constant current charging and discharging. The insulation resistance determines the leakage of charge from the capacitor while waiting between pulses.Ĭeramic capacitors have high IR, and Murata gives information in their datasheets which can obtained from. The important characteristic of the capacitor (apart from its capacitance C) is its insulation resistance (IR). The parallel capacitor will be suitable, but only if you choose it carefully.Īs explained by a capacitor parallel to the load is suitable for pulsed loads. Jennic App note: Using Coin Cells in Wireless PANs Nordic Semiconductor App note: High pulse drain impact on CR2032 coin cell battery capacityįreescale App note: Low Power Considerations for ZigBee Applications Operated by Coin Cell Batteries TI App note: Coin cells and peak current draw In addition, the following documents discuss some empirical assessment / qualitative discussions about running somewhat large loads (with peak current draw on the order of tens of milliamps) using a coin cell: Relevant documents: The following datasheets show various pieces of information, including pulse discharge characteristics, operating voltage vs. Note 2: I'm aware that one could use Li-ion/LiPo batteries but they have higher self-discharge (whether due to their chemistry or due to their protection circuitry), so they may not be ideal for, say, a wireless temperature logger that transmits once every hour. And the Cap/Supercap parallel to the load supply. Note 1: In both cases, I'm considering a generic situation with Coin cell -> 3.3V Boost regulator -> LOAD. I'm interested in an analysis of whether a capacitor-based reservoir can be applied to (and thus, whether it is wise to) run either of the pulse-draw cases above off a coin cell.
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