Subject:
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Re: The Future of Trains
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Newsgroups:
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lugnet.lego
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Date:
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Tue, 2 Oct 2007 16:37:52 GMT
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Viewed:
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19091 times
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In lugnet.lego, Brian Davis wrote:
> Agreed that weight is a problem. The NXT Li-ion pack is nice weight and
> power-wise, but Li-ions (like any battery, but perhaps more so) do age.
More accurately, Li-Ion batteries, _unlike_ most other battery types, do age.
NiCads wear out through use, or through improper partial charging, and have a
moderate shelf discharge (depleting the charge while just sitting unused).
NiMHs wear out through use and have a high shelf discharge, but are not prone to
memory effects from partial charging. Newer NiMHs even get around the big shelf
discharge problem and claims are that they can hold up to 80% of a charge for a
full year while waiting to be put to use (this type will actually ship
pre-charged unlike the old ones). Li-Ion batteries, however, begin to corrode
internally from the moment of manufacture, and age, more than use, is the most
common cause of death. It is possible to wear them out through use, but you'd
have to use it a lot more regularly than most train systems would be likely to
be used. And considering that for a show you'd have to have several sets
available to keep up with the recharging process, they'd be even less likely to
wear out through use, but they do offer one of the best power-to-weight ratios
of any rechargable battery. They can also be killed by deep discharge, but
that's a mandatory safety feature because recharging them at that point could
result in the battery exploding.
Now, the only battery type that's clearly even better for use in a system like
this than Li-Ion is Lithium Ion Polymer, which has no need for a metal casing,
thus boosting the power-to-weight ratio. LiPo cells, however, max out at 4.23v,
which means two will run slightly less than 9v and three will run much higher.
Incidentally, this is the type of battery used for the NXT rechargable pack,
which would explain why people find it runs a bit underpowered compared to six
fresh 1.5v alkalines (which generally ship at slightly higher than 1.5v). I
don't know if LiPo batteries corrode in the same manner as Li-Ion, but I do know
that for long runs, a rechargable pack that's almost 9v can actually run better
than alkalines, which will slowly drop in voltage as their charge is depleted.
A few hours into a heavy draw discharge, the alkalines could end up running less
voltage than the LiPo/Li-Ion/NiMH/NiCad rechargables would, which is the reason
battery manufacturers market batteries other than standard alkalines for
high-draw devices like digital cameras.
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Message is in Reply To:
 | | Re: The Future of Trains
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| (...) The Medium PF motors is 4 studs wide by 6 studs long, and has a 6x2 plate portion on the bottom (no studs on top). The other motor is called the "XL PF Motor", which would hopefully imply that somebody within LEGO might have been *thinking* (...) (17 years ago, 2-Oct-07, to lugnet.lego)
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