D celll alkaline battery capacity

I'm trying to determine the lifetime of a alkaline 'D' battery with a very low discharge rate of 3.5 milliamps. I see a lot of data that suggests the capacity ranges from 12,000 to 18,000 maH or about 200 days. But I suspect the battery will last 1 or 2 years at 3.5 milliamps. Anybody have a chart s howing battery life at very low discharge rates?

Reply to
billbowden12
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The alkaline batteries in my Archimedes (arc310) computer is the third set since I bought it in 1988, the third pack inserted 2 month ago. So in my case almost 15 years for each set.....

Oh, and that old lady is still working, when I tried it a few weeks ago.

Reply to
Sjouke Burry

Bill - some readings on a AA battery with 150 ohms across it showed 1 volt after 12 days. 2 batteries were tested, duracell & energiser, and first readings were 1.6 volts. You might adjust the results by weight.

Hul

snipped-for-privacy@gmail.com wrote:

Reply to
Hul Tytus

Something to be aware of (and perhaps concerned about): the chances of an alkaline cell starting to leak, seem to go up sharply once you've taken it "off the shelf" and started discharging it. You might find the service life in your application to be as much limited by reliability (odds of a leak developing) as by capacity.

Reply to
Dave Platt

The thing you have to watch out for is that if there is more than one cell the weakest one will eventually be made to leak by the others as they reach their lowest ebb. Worth detecting low battery and changing them before that happens. The claimed makers battery life in Ah always seems to me to have been extrapolated to the zero current limit.

Otherwise battery leaks from alkalines tend to do a surprising amount of damage and there isn't much margin between the point where the low current device stops working and the batteries flood the compartment with caustic. It may even still be working with leaking batteries.

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Regards, 
Martin Brown
Reply to
Martin Brown

y low discharge rate of 3.5 milliamps. I see a lot of data that suggests th e capacity ranges from 12,000 to 18,000 maH or about 200 days. But I suspec t the battery will last 1 or 2 years at 3.5 milliamps. Anybody have a chart showing battery life at very low discharge rates?

The battery holds chemical constituents that are consumed at a rate determi ned by the current. 12000 mAh (that's the right capitalization for milliamp hours) i s on the high side, but might be achievable. At 3.5 mA, that'd be a dead battery in about 34

00 hours, or 142 days.

Oh, the battery will still be there after that, but probably not delivering useful current at rated voltage. I've used manufacturer's data to get circa 2-5% accurac y on useful life.

There's no magic in 'low discharge', it's only wasteful at high discharge r ates, linear and predictable otherwise.

Reply to
whit3rd

ery low discharge rate of 3.5 milliamps. I see a lot of data that suggests the capacity ranges from 12,000 to 18,000 maH or about 200 days. But I susp ect the battery will last 1 or 2 years at 3.5 milliamps. Anybody have a cha rt showing battery life at very low discharge rates?

mined by the

is on the high side,

3400 hours, or

ng useful current

acy on useful life.

rates, linear and predictable otherwise.

Do you have any data to indicate it is clearly linear at lower discharge ra tes? The chemical processes involve diffusion which is an energy loss elem ent non-linear with current. I suppose the degree of energy loss at low cu rrent approaches linear in the approximation, but the question would be wha t current would be considered "low" in that context.

Rick C.

Reply to
gnuarm.deletethisbit

According to wikipedia, that's at the low end of the Ah range. Wikipedia claims a range of 12 to 18Ah for an alkaline D cell versus 8Ah for a Zinc- Carbon cell.

Interestingly, the table shows a capacity ranging from a low of 2.2Ah to a high of 12Ah for a NiMH cell (I suspect the low is the result of using a sleeved AA cell - sadly an all too common deceit widely practised at the behest of the retail trade, typically Pound and Dollar shop emporia).

A quote taken from that page:-

"Energizer brand rates its alkaline D cell at approximately 20,000mAh at

25mA draw, but estimates performance closer to about 10,000mAh at 500mA draw."

A current draw of just 3.5mA might extract another Ah's worth again so assuming an effective 21Ah capacity, that should give a total discharge time in the ball park of 6000 hours or 250 days depending on the chosen endpoint voltage (1.0 or 0.8 volt per cell). That's still notably shy of the OP's 1 to 2 years estimate though.

If the OP is planning on using a set of four cells to create a 6v battery, a longer life battery option would be to use a 6v alkaline lantern battery such as the energizer 529 - presumably the exemplar for the 26AH alkaline rating in the chart on the following page:

Looking at a pdf on the Energizer 529 data sheet, it looks like the 26Ah rating is for a 25mA load down to 0.8v per cell. Presumably, drawing a

3.5mA current might add a couple of Ah's worth which could give a ball park figure of 8,000 hours or 333 days and 8 hours.

If space is no object, there's always the "R40" Zinc-Carbon cell. That's rated for a 35 to 40 Ah capacity so should last a minimum of 10,000 hours or about 1 year and 2 months, give or take. :-)

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Johnny B Good
Reply to
Johnny B Good

[snip]

I expect it will still deliver approximately 3.5mA for much longer than that provided that you can tolerate the lower voltage (until it leaks).

Even at high discharge rates to first order the losses are primarily resistive resulting in lower terminal voltage and internal heating waste heat. Once the heating becomes non-trivial all bets are off.

C/100 seems to give close enough results to test manufacturers claims without having to wait too long to find out. If you are paranoid then test at C/50 and C/200 as well and extrapolate to C/infinity.

Battery manufacturers always specify the most favourable looking number if it isn't qualified by a discharge rate.

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Regards, 
Martin Brown
Reply to
Martin Brown

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