Alkaline capacity
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Power Me Up
Enlightened
I recall seeing a data sheet which showed a capacity of 2850 mAh for alkaline AA cells. Not sure about AAA, but probably in the vicinity of 1000 mAh...
You'll only get reasonable run times if you use Low Self Discharge cells such as Eneloops - normal NiMh cells will go flat from self discharge faster than something such as a wall clock will use them.
For most wall clocks, there isn't a direct cost advantage in using rechargeables since they use so little power - rechargeables would takes years to break even. There is however the advantage with rechargeables that they're far less likely to leak and damage the device they're in...
half-watt
Flashlight Enthusiast
last i checked (it may have improved over the last year or so)...
2850mAh AA for a good quality alk. AA
[Note: some Li Primaries are 2950mAh, but also have a much flatter characteristic discharge curve giving much better performance, even in warm weather temps, than the 100mAh difference would lead one to believe]
nominally 1150Ah for AAA alk. cells and even over 1200mAh at some discharge rates at room temp (~21C according to an Energizer datasheet i came across a while ago).
2850mAh AA for a good quality alk. AA
[Note: some Li Primaries are 2950mAh, but also have a much flatter characteristic discharge curve giving much better performance, even in warm weather temps, than the 100mAh difference would lead one to believe]
nominally 1150Ah for AAA alk. cells and even over 1200mAh at some discharge rates at room temp (~21C according to an Energizer datasheet i came across a while ago).
VidPro
Flashlight Enthusiast
a wall clock is not a good place for a rechargable really, mabey an LSD would change that, but if the clock would normally run for a YEAR or 2, then the alkaline will still work good for that.
stuff like clocks, themostats, remote controls, backup batteries and definatly smoke alarms are not good choices for rechargable unless your going to change them more often.
stuff like toys and portables and phones, and lights you use, and boom boxes, and portable chargers and transmitters and radios, wireless mices, and anything that sucks up primaries and cost you a lot to operate because of the batteries is a good choice. not only a good choice but most of the high consuming devices will have better performance.
which just leaves , the leaking aspect, it might be advantageous to use rechargables on VERY low consumption items anyways, and just change them out more , because its less likly to damage the device from leaking.
BUT still not smoke alarms, they ALWAYS say dont use rechargables in them.
stuff like clocks, themostats, remote controls, backup batteries and definatly smoke alarms are not good choices for rechargable unless your going to change them more often.
stuff like toys and portables and phones, and lights you use, and boom boxes, and portable chargers and transmitters and radios, wireless mices, and anything that sucks up primaries and cost you a lot to operate because of the batteries is a good choice. not only a good choice but most of the high consuming devices will have better performance.
which just leaves , the leaking aspect, it might be advantageous to use rechargables on VERY low consumption items anyways, and just change them out more , because its less likly to damage the device from leaking.
BUT still not smoke alarms, they ALWAYS say dont use rechargables in them.
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SilverFox
Flashaholic
Hello George,
There is some early test results that suggest that in order to get the benefit of the low self discharge cells, they have to sit idle. If there is a small current drawn from them (i.e. like for use in a clock) the low self discharge mechanism does not seem to fully kick in. Cameras may also fall into this category.
It seems that these cells do last longer than normal NiMh cells in these applications, but the charge does not last as long as it does when the cell is completely removed from the circuit.
If you had to charge the batteries in your clock twice a year, would that be terribly inconvenient?
Tom
There is some early test results that suggest that in order to get the benefit of the low self discharge cells, they have to sit idle. If there is a small current drawn from them (i.e. like for use in a clock) the low self discharge mechanism does not seem to fully kick in. Cameras may also fall into this category.
It seems that these cells do last longer than normal NiMh cells in these applications, but the charge does not last as long as it does when the cell is completely removed from the circuit.
If you had to charge the batteries in your clock twice a year, would that be terribly inconvenient?
Tom
Yes but that is at a low discharge rate of like 20mA. If you open up the datasheet you will see capacity drops to:
~ 1400mAh at a discharge of 500mAh
A fenix L2D on Max is pulling ~ 1300mAh with NiMh
Power Me Up
Enlightened
Probably due to the self discharge problem.
Since most smoke alarms use 9V batteries and they haven't yet come out with LSD 9V batteries, that advice would still be valid...
Power Me Up
Enlightened
Interesting!
Is this testing that you've done yourself or something you've read somewhere?
Any numerical results yet, or is it too soon?
SilverFox
Flashaholic
Hello Power Me Up,
This information is from informal observations. I would guess that it takes a while for the passivation layer to form, and if you are constantly drawing a little from the cell, it interferes with its formation.
I have been thinking how to set up a test for this... any ideas?
Tom
This information is from informal observations. I would guess that it takes a while for the passivation layer to form, and if you are constantly drawing a little from the cell, it interferes with its formation.
I have been thinking how to set up a test for this... any ideas?
Tom
Power Me Up
Enlightened
OK, doing some quick calculations, to completely drain a 2000 mAh cell evenly over a 1 year period would require a current of about 0.23 mA.
Taking into account the low self discharge rate of Eneloops, the external load would need to be about 0.2 mA.
A 6.8kOhm resistor would be close to enough to give a target of 0.2 mA
I'd say then to get several Eneloop cells, one as a control which wouldn't be connected to a load, one connected to a load of 6.8kOhms, perhaps another couple connected to 3.3k and 12k resistors for a spread of loads. You could also make it 2 or 3 cells in each group to account for individual cell differences and other variances.
Charge all the cells up and let them sit together in the above configurations for 30 days, then do a discharge test on a C9000 and see what capacities are left for each group. Depending on the results, the experiment could be repeated again, but for 60 days.
How does that sound? I'm not sure if you'd want to potentially tie up up to 12 Eneloops for 30 days to do such a test.
SilverFox
Flashaholic
Hello Power Me Up,
That sounds good. Let me see what I can rig up.
I was also wondering about using these cells in something like a remote control for the TV. This would involve a period of use, followed by a rest period. This may be a little more involved...
Tom
That sounds good. Let me see what I can rig up.
I was also wondering about using these cells in something like a remote control for the TV. This would involve a period of use, followed by a rest period. This may be a little more involved...
Tom
Power Me Up
Enlightened
Good point. The suggestion that I made was probably closer to that used by wall clocks, although wall clocks would generally use even less power...
I use Eneloops in my Logitech Harmony 520 remote control, but it's hardly your typical remote control: It uses 4 AAA cells and sucks a relatively large amount of power for a remote control. The Eneloops last about 3 months with the usage we put it through here - about the same amount of time as a set of alkalines.
My parents and my grandparents also have Harmony 520 remotes that I bought for them - they don't watch as much TV as we do - when I swapped over the Eneloops in their remotes at about the same time, they averaged about 235 mAh remaining...
Like I said though, these aren't typical of most remotes - all I can really say from the above is that I'd expect Eneloops to last significantly more than 3 months in typical remotes...
Power Me Up
Enlightened
I forgot to also mention that one problem with putting Eneloops in a typical remote as test would be that you wouldn't know how much power the remote has drawn from the cells and how much has been lost due to accelerated self discharge...
uk_caver
Flashlight Enthusiast
In one sense, that's certainly true, but if determining whether Eneloops would be good in remotes, a test in a remote could still be useful, as could comparison between in-remote cells and cells unused for the same period.
Some rough baseline power draw data could be estimated from the expected runtime - if you still have the original cheap bundled alkalines in the remote, and you bought the appliance N years ago and use it regularly, that gives you some idea of the maximum average power consumption.
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