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I am making an IoT project and planning to power it with alkaline batteries. Their safety and low cost are really appealing. Their low discharge capability is not a problem. The batteries need to be able to supply 500mA to a boost converter, but for only seconds every week. For all the time other than those few seconds, the batteries have to supply around 10uA.

My only problem is the temperature. The device needs to operate at -30 celsius temperatures. I can't find a comprehensive source for the effects of alkaline batteries operating at that temperature. An example of lower temperature performance is in the graph for the Duracell AA Coppertop: enter image description here

The loss in energy doesn't look too bad there. Another source is less optimistic, especially at lower temperatures like my required -30C: enter image description here

In ideal conditions, the batteries will last years based on the current draw of my project. However, when it's the coldest month of the winter and they have to endure an average of -10C with a minimum of -30C, I could accept if they survive only 1 month. Also, they still have to be able to provide up to 500mA. Based on this graph, enter image description here

It seems likely that with internal resistance changing from 0.2 ohms at room temperature to 0.5 ohms at -30C, that is probably possible, but I'm not sure about this either.

TLDR

I would appreciate someone with experience with alkaline batteries giving their opinion on the feasibility of alkaline batteries surviving the -30C minimum, -10C average temperature for at least a month, while being able to source 500mA for a few seconds. Not all batteries are created equal, so maybe some alkalines will be capable of meeting my needs while the average isn't?

Bill Mahoney
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    Either use a battery that specifies its behavior over the needed temperature range or else contact the manufacturer and ask for specifications, if they have them but didn't publish them in their simplified documents. There are times when you intend to use a device beyond its specification range and beyond anything the manufacturer has on it. (I've done that with Burr Brown parts.) In such cases, I talk with one of the lead designers on the part. They can look up the details and give you an informed opinion. That's often good enough. – jonk Oct 20 '19 at 01:52
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    you must be near Winnipeg at -30'C my hometown . You need special $ batteries or derate capacity a lot. We used Silver Oxide [packs in the 70's to -50'C – Tony Stewart EE75 Oct 20 '19 at 01:55
  • In my case, the BB designer simply called up the IC masks he'd developed, looking up aluminized trace widths for me, and found a weak point along the pathway that he hadn't been conscious of prior to my asking about it. He then looked up that weak point's limitations for me (they had tables and such) and let me know his opinion about the maximum current I could use at their input without risking excessive metal migration and eventual destruction of that trace segment. He was also able to tell me how much I could push it and what it would cost me to do so, in terms of lifetime of the part. – jonk Oct 20 '19 at 01:55
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    You might look at NiCd types. They are often specified to operate well at somewhat lower temperatures (about -40 C, I've seen.) They will probably have less than 50% of their rated capacity and can only be discharged at perhaps 0.2C. But at least some have a spec. And they aren't damaged if they do freeze over. Which is nice. – jonk Oct 20 '19 at 02:04
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    A favorite quote that I heard somewhere: a battery is a nonlinear function of *everything*. In other words, all predictions are suspect; the only way to really know is to test it with your exact discharge profile. I'd say 500mA for a few seconds, out of a AA, at those cold temps, is a bit of a long shot, but perhaps your very low duty cycle could save you. My personal experience is that all alkaline batteries from the big guys (Energizer, Duracell, Rayovac) are pretty equal in performance; there are no real stand-outs. – Mr. Snrub Oct 20 '19 at 02:14
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    You need to test these and then choose. using dry ice in abox. been there..done this – Tony Stewart EE75 Oct 20 '19 at 03:03
  • I can share a lot of history in Winnipeg on batteries, but maybe they have improved a bit. I doubt if any better than my graph on average and Panasonic is best – Tony Stewart EE75 Oct 20 '19 at 03:17
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    you might be able to mitigate the rise in ESR by paralleling with a lot of capacitance to handle the pulses of high draw, but check their temperature spec as well if you use electrolytics or supercaps for this. – Neil_UK Oct 20 '19 at 06:02
  • @Neil_UK I considered capacitance. It's actually a fairly good solution, because I could leisurely charge up the capacitor from a weak battery (like a silver oxide) in my week of downtime then supply all the power to the load from the capacitor. The only problem is that a supercapacitor providing 10s x 250mA x 3.3V of energy costs about $4-$5 on digikey. This price is pretty undesirable, I'd prefer to have the battery system cost more like $1. But if I profile and find that my energy is smaller than what I'm assuming (which I think is likely) than I might go with this solution. – Bill Mahoney Oct 20 '19 at 13:54
  • @TonyStewartSunnyskyguyEE75 That's a good point about cold testing. I have an old spray which is supposed to cool electronics down to -50, but it might not be appropriate for cooling something as big as a battery, it's probably just for thin SMT components. – Bill Mahoney Oct 20 '19 at 14:14
  • my method is cheap and excellent. it used to be $1/lb for dry ice in paper from any dairy co. Then a picnic box and tiny muffin fan with thermocouple inside. -40 air with a few bricks and -55 contact. did not need a Tenny Oven for 20 grand – Tony Stewart EE75 Oct 20 '19 at 19:44

2 Answers2

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Each manufacturer of a battery chemistry category will try and evaluate the temperature behavior of their commercial technologies, because doing so may give them a new market worth pursuing. (Or let them know which markets NOT to pursue.) Some battery types don't even work until the temperature is over \$60^\circ\text{C}\$. While that might seem bad, it's good too as in some hot areas in the world this means the battery is preserved well until the temperature is driven up a little. (They have nice "shelf lives" in hot climates.)

Probably the best researched and most often recommended battery technology for low temperatures in the \$-30^\circ\text{C}\$ area is NiCd chemistry. These types have been well-characterized down to operation at \$-40^\circ\text{C}\$ and documentation on using them in cold temperatures dates back many decades. So lots of experience using them in cold situations to inform your decision.

Since their electrolyte isn't diluted during discharge, the freezing temperature remains at about \$-83^\circ\text{C}\$ regardless of discharge state. And NiCd batteries can still deliver perhaps a quarter to a third of their rated capacity (I've seen charts showing as much as 40%) when operating at \$-40^\circ\text{C}\$. Remarkably, too, they can also accept a charge at these low temperatures and aren't damaged by over-charging (or under-charging.) (However, over-charging still may generate some gas and water loss.) They aren't damaged, if they do freeze (go below \$-83^\circ\text{C}\$.)

Of course, they are in a different category from alkaline. (Primary vs secondary.) So it still may not be applicable in your case. But since you mention only occasional current pulses (which NiCd can handle well) and mention a reasonable period of operation, I think you may still find that some readily available version of NiCd will satisfy your needs. I'd start there. See where it takes you.

There is a publication called "Cold Regions Technical Digest" where they cover some of these details. There are other sources I have used, as well, to write the above text.

jonk
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  • I think NiCd might be the way to go. I was adverse to it because of the high (20%) self-discharge rate per month. (also against it because it is more toxic than alkaline) But if I'm only constraining the winter batteries to last at least a month, then this doesn't break my constraints. In warmer months, I could switch to alkaline in the same form factor (like AA or AAA), and theoretically last the whole year on 1-3 battery changes. – Bill Mahoney Oct 20 '19 at 14:01
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You need special $ batteries and derate capacity. A lot!

We used Silver Oxide [packs in the 70's to -50'C

Silver Oxide types are your best bet. They actually are made in LOTS of sizes but $$.

enter image description here

This one is cost-effective.

enter image description here

https://data.energizer.com/PDFs/silveroxide_appman.pdf

  If you can insulate and keep near earth in a protected structure and increase some capacity.

  There's no free lunch at -30'C.  Just bring hot choco., with heavy down-filled jacket, hat and feather/down or sheepskin filled mitts.  With no wind, it's really quite pleasant in the sun.

  • But you *will** need more capacity than you planned in your power budget. Consider x32 minimum.

  • Otherwise, your unit may be offline for a few weeks or more in February, when it's -30'C. That is, unless you use a super high-gain antenna (6~10dB) and reduce Tx power.

That would be my suggestion. Trust me on this. I have 40 yrs of weak battery experience -30'C to -40'C and learned to cope.

Warning:

Below 0'C all these kinds of batteries WILL lose capacity rise and rise in ESR (effective series resistance) for cold start pulses --- just like CCA in lead-acid where they rate the car batteries for CCA by dropping Vbat to 7.5V so ESR = (12.5-7.5)CCA. That's how they do it. Then loaded voltage drops from the load, R ratio.

(R/(ESR+R)*Vbat=Vbat' (load pulse)

enter image description here

Tony Stewart EE75
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  • This battery meets my temperature constraint which is great, but it would be really hard to get 500mA out of them. It seems like a silver oxide battery is not meant for supplying much over 0.2mA from a few sources I looked up. I'd have to use a supercapacitor in parallel for the pulses. But as I said in my response to @Neil_UK above this isn't a bad solution. It's just probably more expensive, and cost is a strong criteria in this project. – Bill Mahoney Oct 20 '19 at 14:08
  • Bill they make AA cell like sizes too not just buttons. Hard to find, more $$ but work. we used hand size boxes of SiO2 batteries in 70’s. But capacity vs $ vs -T are huge tradeoffs, , here overlooked by op – Tony Stewart EE75 Oct 20 '19 at 19:46