Any rule of thumb to estimate battery life comparison.
Duracell 9V battery vs 9V - Duracell 6 cell AA (in a holder).
Application is very low drain, unknown value.
With the 9V battery the device runs continuously for 6 months.
Just need a guestimate.
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Coppertops are here...
Industrial stuff is here....
10x longer?????Cheers
googling suggest something like 5x, ~500 vs. ~2500mAh
-Lasse
** Life in hours is the mAh rating / mA load.
A lot depends on the lowest working voltage you device can handle since the makers end point voltage is only 0.8V.
** A theoretical 2 to 3 years on that basis.But there is very optimistic to assume reliable contact would be maintained by a regular plastic cell holder for that long with no maintenance.
I would solder connecting wires to the cells for such a job.
... Phil
400mAh vs 2.5Ah makes it around 3 years. Others have explained the details. Note that you won't see a lot of variation between brands, as long as they're the same basic chemistry.
NT
I wonder if soldering on the battery wouldn't reduce it's shelf life more than most any other thing you could do???
At 3mAh/day usage a rechargeable battery or supercap and a small solar panel would be an option. It would last until it wore out provided that a charge controller was protecting the battery from overcharging.
These very low current draw applications work OK with prehistoric zinc chloride cells since their initially higher terminal voltage allows them to just keep going. Anything that has batteries lasting in excess of a year or more it makes sense to leakproof the battery compartment.
I tend to keep "used up" at high current secondary cells for powering low current devices but use rechargeables whenever possible.
I find I have quite a few low current devices where LCD displays barely work at all with fresh rechargeable batteries which is annoying :(
-- Regards, Martin Brown
until the cells leak anyway. Thus making ZnCl a rarely good choice.
NT
Some 9V batteries are 6xAAAA, others are made from 6 flat wafers with the cross section of the 9V battery.
all the opened PP3s I've seen personally have had flat cells stacked
NT
One reason why I don't like (some) 9v batteries:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com
huh?
NT
I didn't take those photos. They were made by a friend who managed to somehow short the alkaline 9V battery with explosive results. The batteries were brand new at the time. Unfortunately, he tossed the remains before I could determine if it was a genuine Mallory Duracell Procell battery or some kind of counterfeit that lacked vents on each cell to deal with rapid outgassing. I haven't been sufficiently inspired to repeat the test.
One of my least favorite parts of the design process is estimating legal exposure. I would not want a product with a battery system capable of exploding and resulting in consequent product liability litigation. My guess(tm) for the reason that we don't see more such exploded cells is the thin wire leads normally used by a wired 9v power connector are sufficient to limit the short circuit current to where it might be considered safe. However a board mounted power connector is not similarly protected by thin wires and might produce an explosion.
My other reasons for not liking 9v batteries is the high cost per watt-hr, the rather unreliable connector, the ability to easily reverse polarize the connector, the amazing range of specified voltages, the lack of case insulation, and a tendency to bulge for no obvious reason. One good feature is that the alkaline version is unlikely to leak electrolyte and destroy the PCB because the 6 AAAA cells are wrapped in an outer metal case.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com
AIUI internal resistance & vents normally prevent short circuit explosion. ZnCs are extra safe, I shorted some new AAAs last year and they didn't even get warm.
excessive cost. Why does it seem to cost so much more per Wh?
PP9s were always better value than PP3, but any such apps are better served by 1.5v cells.
they're a lot more positive (mechanically) than 1.5v connectors
what is there other than 9v?
Surely 1.5v alkalines are too.
NT
tabb
** Rechargeable "9V" batteries come in several voltages.The oldest used 6 NiCd cells and were rated at 7.2V, then came 7 cell versions rated at 8.4V and finally 8 cell ones rated at 9.6V. These have been replaced by NiMH versions with the same voltages.
The latest use two Lithium Polymer cells and are rated at 8.4V and 600-700mAh.
Most of the above are capable of exploding if shorted.
.... Phil
We have a nice set of battery tables and graphs in AoE III, chapter 9 (freely-available sample)
See section 9.12, book page 686, file page 110. Table 9.9: 9V Alkaline batteries give 550 mAhr vs AA cells 2800 mAhr (both at 10mA low-current). The power ratio is 5x, the weight ratio is 2.7, and the volume is much bigger as well. Did you want to compare 9V batteries against AAA cells? Fig 9.100 shows a 9V battery's AAAA cells. All cell choices are round, and suffer area losses.
--
Thanks,
- Win
True nuff. End of life for ZnC or alkaline PP3 is below 6v, so all those rechargeables ought to supply a well designed circuit ok. Of course ought doesn't always fly IRL.
NT
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