Battery question

[Alexx]

Why does using the side car and internal battery combines last longer than using the side car alone then the internal alone?

[Richard]

Why does using the side car and internal battery combines last longer than using the side car alone then the internal alone?

Because the "side car" charges the internal?

[Alexx]

like playing ATRAC3+ Hi-SP

RH10

side car alone 13.5

internal 12.5

combined 28.5 (when you expect it to be 26)

Because the "side car" charges the internal?

Thats as maybe:

but it should contain the same amount of power!

ie: if theres 40 units of power in the internal, and 50 in the sidecar: then thats 90 units of power.

but if you combine them then they become 100 units!?

andd why is it that in recording more: the internal lasts about double the time of the sidecar, whereas in playback the internal lasts a little less than the sidecar

[greenmachine]

High capacity batteries can handle high currents for a longer time. Two parallel low capacity batteries = one high capacity battery.

Recording draws higher currents than playback does. The figures for the sidecar are propably measured with alkaline batteries, which have higher capacities than the internal NiMH, but can't handle high current loads -> recording time = shorter; playback time = longer. If you use a NiMH in the sidecar as well, it should last longer for both recording and playback. Alkalines are not ideal for high current drawing devices like (Hi-)MD.

[MDX-400]

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High capacity batteries can handle high currents for a longer time. Two parallel low capacity batteries = one high capacity battery.

Recording draws higher currents than playback does. The figures for the sidecar are propably measured with alkaline batteries, which have higher capacities than the internal NiMH, but can't handle high current loads -> recording time = shorter; playback time = longer. If you use a NiMH in the sidecar as well, it should last longer for both recording and playback. Alkalines are not ideal for high current drawing devices like (Hi-)MD.

I disagree but only a little bit. With Hi-MD you're probably spot on, but for standard MD units I think alkalines will last longer. While recording is a higher-current function, playback (with a modern standard MD device at least) is very low current. Hi-MD may be a different story, of course. Alkalines start to drop off in capacity perhaps at disharge of .5C or greater I'd say. Whereas NiMH can take a discharge of as much as 2C even more and still [demonstrably] retain their capacity at said load. Since NiMH AAs are getting up there (most reputable brand AAs are at 2500mAh on average) I would not be surprised if you were able to get nearly the same amount of playing time on a freshly, fully and properly charged NiMH AA as an alkaline. But it is more likely the alkaline, in playback on non-Hi-MD portables [with the exception of older equipment with relatively poor battery life] will outlast the NiMH cell.

But I'm speaking of just the AA alone and none of that even really explains the original question... Why would the "sidecar" (as it seems it is being affectionately referred) allow for more battery run time than playing with the internal until cut-off and then using the sidecar until cut-off? The answer, I speculate, has to do with the cut-off voltage and the power curve of NiMH and alkaline batteries... The answer that the AA charges the internal battery is correct, IMO, but this is a much longer explanation...

You see an NiMH or NiCd cell typically holds its voltage steady, even with significant load applied, and continues to "hold" it's voltage until the battery has literally "run out" of capacity. At that point the voltage sharply drops and that is the end of your battery life. Now it isn't quite as drastic as I make it seem (because otherwise we'd have no battery indicators, obviously) but when compared to an alkaline, and for general understanding, that is what you have to keep in mind. Now an alkaline has an entirely different discharge curve. It begins at a higher nominal voltage than an NiMH cell, but it doesn't hold that voltage. Instead it smoothly and steadily declines (well under say .3C discharge lets say) as its capacity is used. [it's too bad I can't do a drawing here or I'd give a rough idea with graphs, of what I'm talking about.]

So while the NiMH simply drains and cuts off, an alkaline slowly gets lower and lower in its voltage until it reaches the point where the device cuts off. Now, in lower current applications in particular, there is obviously an area/period of time where there is going to be voltage supplied by the alkaline that is less than what the NiMH would provide by the time it went flat--where the NiMH sharply dropped the alkaline still has voltage, albeit low voltage, remaining. So here, a low current device can continue to run for a short time until the alkaline's discharge curve reaches cut off.

Now you might be wondering where I'm going with this... Well if you think about it, the alkaline in combination with the NiMH will stop the cut-off of the MD unit because of its discharge curve. The batteries are not operating strictly in parallel I do not think, for Sony must use some kind of circuitry that regulates the charge between the batteries otherwise you'd end up with a lot of leaking batteries or worse. What the net affect is anyway, is that the alkaline with the NiMH pretty much stops that abrupt cut-off you'd get with the NiMH alone and then you capitalise on that little bit of voltage that would be beneficial in the alkaline to a better degree.

But if you could combine the two you end up with power going into the NiMH from the alkaline and therefore maximising the total capacity of both batteries in terms of the time voltage can be maintained above the terminal voltage of the MD unit in its current operation mode.

So you are taking advantage of the higher voltage of the alkaline and maximising its potential as well as the characteristic of the lower voltage of the NiMH and it's tendency to take charge from the originally higher voltaged alkaline. In the very shortest terms you are taking two battery chemistries and using the benefits of both at the same time.

[rei-gouki]

In not as short, the alkaline keeps the voltage above cut off, but the current (is that what you meant by "C" or did you mean coloumb(sp?)) tolerance is low. NiMH can handle the power sucking a little better but won't keep it above cutoff

hmm... I better check batteryuniversity about that...

[Alexx]

Rejoice.

I sti9ll dont think i'll EVER get 18 hours out my fully charged car and internal: however it's got to be better than I-poops hasn't it

[MDX-400]

In not as short, the alkaline keeps the voltage above cut off, but the current (is that what you meant by "C" or did you mean coloumb(sp?)) tolerance is low. NiMH can handle the power sucking a little better but won't keep it above cutoff

hmm... I better check batteryuniversity about that...

No C means neither current or coloumb... It has to do with load vs. the capacity. It is a strange thing because it kinda hatches the chicken/egg syndrome if you ask me. "C" is a rate of discharge really.

Say a battery has a capacity of 2500mAh, then 1C would be a load of 2.5A. But what doesn't make sense is with batteries like alkalines, they usually have their capacity rated at like very low current meaning that a typical alkaline AA has a capacity of 2800mAh, if it is drained at like 25mA constant current. But that is only .001C really. If you increase the discharge current the capacity becomes much less, in the case of an alkaline. So what I don't get is which comes first the C rating for a battery or the capacity rating???

An NiMH cell that has say 2100mAh discharged at 420mA would be considered a .2C discharge. And most are rated at such a discharge; but with NiMH you could increase that current to 2.0A and you'd get the battery still showing 2100mAh capacity. So I'm not 100% sure how it works but that's the gist of it.

If you have a battery with a rated capacity of 2500mAh, 1C is 2.5A current draw; .5C would be 1.25A current draw; and so on.

Here is a better explanation, if you need it:

http://www.buchmann.ca/chap5-page1.asp

Edited December 3, 2005 by MDX-400

[Human]

WoooW, --- what an interesting load of infos.

I feel jolted - but I must read couple more times cause my grey matter is drained - it is just to much volts or amperes for me to digest in one shot - but I definitely will benefit form reading over and over till I understand more - (another benefit from joining this Forum - I can get electrocuted by Hi-powered knowledge).

Thank U guys for this "electrifying knowledge" trip

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