CR 2032 battery question - Page 1
Forum section: electronics / beginners

author: Kdog44
author_rank: Contributor
timestamp: February 04, 2015, 12:37:39 am
content: question: I want to use two CR 2032 batteries in series for a project. The load the batteries will see is about 580 Ohms. The current draw from the batteries is about 10mA. On this datasheet (http://data.energizer.com/PDFs/cr2032.pdf) It gives a voltage reduction curve over time for a 0.19mA draw, my circuit needs to consume 50 times that. So will the batteries voltage decrease approximately 50 times quicker? I know that it is a non-linear relationship between voltage and time for a set load, but is that a good approximation? Also is there anyway better I could get about 5-6 volts to my circuit that I want on a 5X5 cm PCB? I have most of the bottom layer clear, and I want it to be compact.background: I am designing a miniature version of the "Simon Says" game, for practice in PCB prototyping. The base of the game is the PCB itself, and it will have all four LEDs and buttons mounted onto it. In my eagle file I have the two CR2032 battery holders on the bottom of the pcb. I need at-least 5 volts for the micro I am using.

author: IanB
author_rank: Super Contributor
timestamp: February 04, 2015, 12:53:08 am
content: The internal resistance is listed as between 10 and 40 ohms, so with a 10 mA draw you will see a voltage drop of up to 0.4 V per cell. (If the current has peaks higher than 10 mA the situation will be worse.) Taken with the discharge profile of the cell it won't take much to fall below the 5 V minimum.How about the classic solution of a 9 V battery with a voltage regulator?

author: mazurov
author_rank: Frequent Contributor
timestamp: February 04, 2015, 12:56:16 am
content: Quote from: Kdog44 on February 04, 2015, 12:37:39 amIf your draw more current than specified the capacity of the cell decreases in addition to "run time". The relationship is complex and for 50x overload the only sure way to find out is to test.

author: Kdog44
author_rank: Contributor
timestamp: February 04, 2015, 01:12:40 am
content: Quote from: IanB on February 04, 2015, 12:53:08 amHmm I was hoping to keep the overall profile of the board and the battery(s) slim. But I might have to go in that direction if I can't find a better solution.

author: Psi
author_rank: Super Contributor
timestamp: February 04, 2015, 02:19:54 am
content: You should be able to do a Simons said game for less than 10ma continuous battery draw.Use the right LEDs and you will get plenty of brightness from 0.6mAThe mcu can sleep most of the time. Use a big cap to buffer the peaks.Sound might be an issue depending on how loud you want. But shouldn't be too bad.If money isn't a prob put a small Maxwell supercap on the PCB. They're like $10-20, look like a regular electrolytic cap but have huge capacity to buffer high current peaks lasting even a few seconds

author: Kdog44
author_rank: Contributor
timestamp: February 04, 2015, 02:39:52 am
content: Quote from: Psi on February 04, 2015, 02:19:54 amYou are right, I have a couple of 0805 LEDs that can be operated at 0.1mA, and I could put the MCU into sleep mode and being triggered by the buttons as interrupts, but I think I might play it safe for this first revision.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 04, 2015, 11:53:43 am
content: CR2032 are about 200mAh, so 10mA will give you about 20h or so

author: Kdog44
author_rank: Contributor
timestamp: February 04, 2015, 06:09:12 pm
content: Quote from: Ice-Tea on February 04, 2015, 11:53:43 amI am not concerned about the capacity of the battery, I am concerned about the voltage dip because of the drop across the internal resistance.

author: tszaboo
author_rank: Super Contributor
timestamp: February 06, 2015, 08:46:33 am
content: Quote from: Kdog44 on February 04, 2015, 06:09:12 pmTechnically, this type of application should be possible without any voltage regulator with a single 3V battery, if you use red leds, and the correct microcontroller. It would even increase your battery life.

author: Zero999
author_rank: Super Contributor
timestamp: February 07, 2015, 08:59:32 pm
content: Quote from: NANDBlog on February 06, 2015, 08:46:33 amOr blue LEDs can be used with a simple voltage doubler.

author: Stonent
author_rank: Super Contributor
timestamp: February 07, 2015, 09:15:58 pm
content: Quote from: NANDBlog on February 06, 2015, 08:46:33 amI was thinking about MSP430 or some of the ATTINY V series, run the whole thing from a 32K watch crystal.Quote from: MSP430Quote from: ATTiny2313Then you may be able to get by with running the coin cells in parallel or just use 1.In active mode the Attiny at least on paper seems to use less current. But you do get the addition of the ADCs in the 430 which the 2313 does not have. The whole thing could be interrupt driven with sleeps in between. With the 430 you could use the ADCs to sample the voltage of the battery presumably and alter a PWM signal to the LEDs to keep the brightness current. Maybe even switch off to a voltage doubler if you get to a point where the voltage is too low to keep the LEDs visible.