Long life battery application - Page 1
Forum section: electronics / projects

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 15, 2015, 11:20:19 pm
content: Hi, am working in a small project a BLE sensor, basically at sleep it use 200uA ( more less than that in fact ) anyway with this magnified approximation a 3V 2Ah battery will run for a bit more than 1 year , client asking for 2 years minimum and 4 if it's possible.First i was looking for a small form so i chosen a 3V 2Ah AA battery, but am not sure they will live for 2 years. So for this 2 to 4 years i think am going with a C or D battery 1.5V 8 to 16Ah and a step-up circuit TPS61220. i can't say am satisfied with this solution, but i can't think about any think else.Any suggesion ?

author: tom66
author_rank: Super Contributor
timestamp: January 15, 2015, 11:23:07 pm
content: Can the receiver be operated at a lower voltage, say 1.8V?Can you pulse the receiver on and off, or turn it between different standby modes?Have you considered other types of cells like lithium AA cells, which can have over 3.5Ah capacity at low discharge currents? Or rechargeable cells like 18650 (beware of self discharge, 1%/month typical)What sensor are you using - are there alternatives?

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 15, 2015, 11:44:26 pm
content: yap sorry for not posting enough detail, my badit's a bluegiga module BLE112 , it run on 2V min.it's going to be placed in inaccessible place, so it should be on all the time, the module support a sleep mode where it can still be detected by host, they claim it only use 0.2uA i can't confirm that, i don't have a uAmp that dave designso using an ampmeter and tried to put a small resistor in series and get a current use over time in the oscilloscope, what i get is more that 0.2uA but certainly way less than 200uA...I do use a lithuim battery and it's a bit expensive so am trying to get an alternative for that ( 8€ / cell ) i don't think a rechargeable cell with good capacity will be cheap enough for this.

author: IanB
author_rank: Super Contributor
timestamp: January 15, 2015, 11:47:38 pm
content: The classic battery for that kind of application is this one:http://www.saftbatteries.com/force_download/LS14250.pdf

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 15, 2015, 11:58:34 pm
content: Quote from: IanB on January 15, 2015, 11:47:38 pmi don't think it's better in anyway that the one i already usehttp://www.farnell.com/datasheets/61398.pdf

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 16, 2015, 01:44:17 pm
content: i can't see any brilliant idea around herewell update , i used this TPS61220 and am getting some weird result, have anyone used it before ?Test condition :-input 1.5V-Output voltage 3V-load 250R-Selected inductor 100uH-Selected capacitor 470uFOutput :-Input current 70mA-Output 12mASo efficiency is around 35%changed load to 10K-Input current 2.1mA-Output current 300uASo efficiency is around 28%for anyone who check the DS , it say that an inductor around 4.7uH is good for most applications, didn't work, not without a output voltage drop to 2V, with the configuration above, output was pretty stable around 3V no problem at all , but efficiency is horrible.In the DS too, a graph indicate efficiency in function of input voltage and output current for may case should be around 80% ... it's notanyone have an idea what is possibly wrong

author: Maxlor
author_rank: Frequent Contributor
timestamp: January 16, 2015, 04:07:28 pm
content: That lithium manganese battery you've chosen seems like a good choice, its self discharge rate is negligible and it has a high enough voltage so you don't need to step up the the voltage, which usually incurs noticeable losses in low power applications. If one isn't enough... how about two?You may have considered all this already, but maybe this is of use:With a recent low power project I built (60uA sleep current, ~120mA active current) I learned that one of the most important choices is which power supply to use. The most important number here is quiescent current (IQ), i.e. the current the power supply alone will consume when nothing is connected to it (or if there are only extremely low power components, such as a sleeping uC that consumes 1uA). I found that there are large variations in IQin different power modules that seem to have similar performance figures at first glance. Second most important number is the efficiency under load.For my project, I was stepping down 4.2-3.7V (LiIon) to 2.8V, and ended up using aDiodes Inc PAM2305, which has an IQof 40uA (so, 2/3rds of my sleep current is just the power supply!), handles the 400mA worst case peaks and runs at about 96% efficiency under load. It's the best module I could findandget my hands on

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 16, 2015, 07:00:46 pm
content: Quote from: Maxlor on January 16, 2015, 04:07:28 pmThanks for your replyWell the problem is the price ... 9€ is a lot.Any other lethium large capacity are also too expensive for this design.agree, Iq is an important parameter here , the bt4 module is mostly in sleep mode and all other circuitry is disconnected from power too, but as i see now it's the last of my problem. i was happy to find this TPS61220 in the lab seems to be exactly what i need ... but now am not sure. will check diode Inc web site to choose a part