Can't seem to locate any battery specs for Alkaline "D" cells. Tried the Duracell and Raovac sites, but couldn't find much data for standard cells. Read a few notes indicating the capacity of a standard "D cell" is somewhere between 12 and 16 amp hours.
Anybody know what capacity to expect from a standard Alkaline "D cell" at a continuous 0.5mA discharge rate until the voltage falls to 1.1 volts?
Thanks,
-Bill
This guy Al Kaline was not only a fabulous baseball player (over 3000 career hits), but he apparently makes a hell of a battery, too!
Bob
-- == NOTE: I automatically delete all Google Group posts due to uncontrolled SPAM ==
If you design things to work all the way down to 0.9V/cell then it'll be a better fit for NiMHs, and you'll wring a tad more running time out of your battery.
You may find that at such a low current you're limited by the shelf life of the battery (you certainly will be for NiMHs!). Unfortunately that particular data sheet doesn't give it, but alkaline cells seem to last for years on the shelf, so it may not be that much of a consideration.
-- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
Take a look at the so-called "hybrid" NiMH batteries. They claim MUCH longer shelf life, and as a side benefit of this, they come pre-charged.
There are a few manufacturers of this new technology. Sanyo (Eneloop brand) is one of them:
Bob
-- == NOTE: I automatically delete all Google Group posts due to uncontrolled SPAM ==
To name a few I've read about: Uniross Hybrio Sanyo Eneloop Nexcell EnergyOn Accupower Acculoop
I think they are typically a little less in terms of mAh capacity (2000 to 2100 versus 2600+ elsewhere, for example.) Also, I remember reading this:
Not sure if the poster did their work well, or not. But it is a cautionary word on the topic of taking the manufacturers' specs on their face.
If the OP is close on the 12-16 Ah capacity of an alkaline D cell and that is the range the OP is looking for (or better), then with 500uA draw we are talking about 3-4 year operation. NiMH seems wrong on that point.
Jon
This post was a poor choice to proselytize given the life requirements, I just have a 'thing' for folks who design battery-powered systems assuming 1.2V per cell (or 1.5V per cell) because that's what it says on the package.
0.9V per cell is about right for moderate discharge rates with NiCd and NiMH batteries, and you can't exactly harm a primary cell by sucking a bit more juice out of it.I _do_ suspect that for many dry cells, you'll get killed by shelf life (or rust) before the actual circuit drain causes a problem.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html
AAA = 1 AH AA = 2 C = 5 D = 10
Note that each capacity is max. Max capacity for each size occurs at a different current. Your application may be limited by operating temperature and shelf life.
Off the top of my head it was between 2 and 3 Ah.
You'll get better out of other brands than Duracell though.
Graham
Note that the capacity vs discharge curves don't go down that low for D cells. You could try and extrapolate the curves, but that's only guessing. When you get to figures this low you are talking 40000 hours+, the shelf life of the battery.
If you want to use the full capacity of the battery then you need to have a
0.9V cutoff or slightly lower. 1.1V will be wasting a fair bit of the capacity.What is your application?
Dave.
My experience with NiMH is that 1.2 volts per cell is conservative at C/5 discharge rate and 80% of the way discharged. My experience is that NiMH mostly achieves at least 1.25 volts/cell at that discharge rate.
- Don Klipstein ( snipped-for-privacy@misty.com)
In what time frame? I need 2 to 3 year continuous operating time and not sure that's doable with a NiMH battery due to the high self discharge rate.
-Bill
NiMH ain't gonna do that. Use alkaline. I was only commenting on what voltage NiMH delivers.
- Don Klipstein ( snipped-for-privacy@misty.com)
Use alkalines. And forgive me for the tangent; it seems to be drawing more interest than your original post (other than designing for 0.9V per cell, if you can -- it should gain you a month or two of operating time at the end of the battery life curve).
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html
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