Best AA cell in cold weather - Page 1
Forum section: electronics / projects

author: Janne
author_rank: Contributor
timestamp: January 30, 2012, 05:32:49 pm
content: Hi,I've been working on a remote controlled logging winch. The system consists of a receiver (on the winch), which actuates the mechanical arm that controls the winch, and a remote controller to start / stop the winch remotely. Wireless link is build with a pair of 900MHz XBee pros. Both the receiver and transmitter utilize ATMEGA8L's for "brains".The system has been working quite niclely, but with the recent -20degC weather the transmitter has been bogging up. The 2x AA alkaline cells powering the transmitter don't seem to be up to the task at those temperatures.Voltage from the cells is first bumped up to 3.1V, with a boost converter. The biggest power draw on the transmitter is the XBee radio, which consumes 70mA when activated, and short bursts of ~250mA when transmitting, so an instant power of about 800mW (not accounting for any conversion losses, add 200some mW for those) is required.What kind of cells would best work for these loads at low temperatures? I'd hate to discard the neat enclosure I built for it, so I'd like to stick to 2xAA form factor if possible. Reworking the power supply is ok if necessary.On the old days, the NiCd was recommended as having superior performance at low temperatures. Is it still the case?

author: ron
author_rank: Regular Contributor
timestamp: January 30, 2012, 05:42:33 pm
content: Get the Lithuim AA. They hold up better in cold.http://www.photonlight.com/product_images/b/532/AA4-Li-2__49586_zoom.jpg

author: IanB
author_rank: Super Contributor
timestamp: January 30, 2012, 06:35:05 pm
content: Yes, I think lithium AA would be the best choice.NiMH works well down to reasonably low temperatures (like 0 C for instance) but -20 C is a bit too low for good performance.

author: Janne
author_rank: Contributor
timestamp: January 30, 2012, 06:49:58 pm
content: Hi,Thanks for the replies. Looking at energizer datasheets, it would seem that the lithium should be quite superior, at least when compared to alkaline cells. I'll give them a try and see if they work any better... -15-25 temperatures are forecasted for the next week or so, so plenty of good time to do more tests next weekend

author: sorin
author_rank: Frequent Contributor
timestamp: January 30, 2012, 07:16:10 pm
content: lithium and NiMh battery dont work under –20°C.BUT NiCd yes!!!!!for more information read:http://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperaturesI hope that this is helpful to you

author: samgab
author_rank: Frequent Contributor
timestamp: January 30, 2012, 09:09:27 pm
content: Eneloops are unique in that they are claimed to perform down to -20°Chttp://www.eneloop.info/home/performance-details/low-temperature.html...and here is some good info and data on Lithium iron disulphide AA cells which, they claim, perform down to -40°C:http://data.energizer.com/PDFs/lithiuml91l92_appman.pdf

author: DaveW
author_rank: Frequent Contributor
timestamp: January 30, 2012, 10:13:55 pm
content: Lithium Manganese Dioxide work below -23 degrees C, I don't tend to test below that as that's my spec, but as that's high current pulses, it should work below that as the input to a boost converter should work below that.Lithium Iron Disulphide work well at low temperatures, but I don't believe the internal resistance stays as low as alternative chemistries.If you really want to do it properly, have a look at Tadiran cells. Almost indestructible, the specs say -55, but I've tested them below this (to around -70) and they still work extremely well. And last a veeery long time...http://uk.farnell.com/tadiran-batteries/sl360pt/battery-lithium-aa-pcb-3-6v/dp/1187263

author: Janne
author_rank: Contributor
timestamp: January 31, 2012, 12:11:08 am
content: Those Tadiran cells sure look interesting. As a standby / low power devices for extreme climates they would be excellent, but their small maxium continous current (20mA) limits their usability. But the pricing... Over 10€ / piece in farnell finland! Luckily, they're cheaper in ebay, I'm tempted to order some just to try them out.I ordered a pair of NiCd's, so I will test them + some lithium disposables that I can easily get my hands on. It'll be interesting to see how they fare out

author: IanB
author_rank: Super Contributor
timestamp: January 31, 2012, 12:49:45 am
content: There are alternative brands to the Tadiran cells, for example SAFT:http://uk.farnell.com/saft/ls14500ex/battery-lithium-aa-2-6ah-3-6v/dp/1865217You might perhaps find them at a better price from different sources, though in this case they seem to be priced about the same.

author: Psi
author_rank: Super Contributor
timestamp: January 31, 2012, 05:39:01 am
content: You might get a bit more lifespan if you add a large capacitor in parallel with the battery, it will boost it's ability to provide pulses of high current.Ideally something like thishttp://www.jaycar.co.nz/productView.asp?ID=RE6702&keywords=super+capacitor&form=KEYWORDBut even a normal capacitor would help with peak currents.

author: nukie
author_rank: Frequent Contributor
timestamp: January 31, 2012, 01:23:49 pm
content: Won't the ESR of the capacitor drain the battery, especially for long term application?

author: Balaur
author_rank: Unknown
timestamp: January 31, 2012, 02:16:15 pm
content: Quote from: nukie on January 31, 2012, 01:23:49 pmNope, the battery will be discharged by the parallel resistance of the capacitor caused by leakage currents in the (non-ideal) dielectric material.

author: ivan747
author_rank: Super Contributor
timestamp: January 31, 2012, 10:33:00 pm
content: Also electrolytic capacitors' ESR increases A LOT when temperature goes down. Just see page 14 on this random capacitor datasheet:http://www.panasonic.com/industrial/components/pdf/pic_vs_series.pdf

author: Psi
author_rank: Super Contributor
timestamp: January 31, 2012, 11:29:15 pm
content: oh, right.Just how long do you need the batteries to last?

author: ivan747
author_rank: Super Contributor
timestamp: February 01, 2012, 01:09:25 am
content: I would want one month of operation at least (I am not the OP).

author: Janne
author_rank: Contributor
timestamp: February 01, 2012, 11:11:16 am
content: A big capacitor might indeed help, but the remote is already stuffed quite full, so fitting a cap in there would be hard.If I get a few days, mayby weeks worth of life out of the batteries I'll be happy. The actual time the XBee is powered on the job is not that much, mayby 10 minutes / day.. most of the time is spent on other things. Even the alkalines gave good service life until this cold weather.