Re: PF train motor

In lugnet.trains, Dave Sterling wrote:
>> Paul
>
> I just noticed the new PF Lithium Polymer Battery Box output is 7.4V.  Am I
> missing something here?  Did they drop it from 9V since most people only run
> their train controllers at the 4th or 5th 'hash mark' equating to about 7.4V
> maximum?  Is this going to pose an issue with longer/heavier trains?
>
> Just thinking...
>

They made it 7.4V because all lithium polymer battery cells are 3.6 - 3.8V.
Since this is a pack with 2 cells in series, you get 7.4V.  A 3 cell pack is
typically 11.2V.  As you can see, keeping the old 9V system was not really an
option if using Lithium power.  LEGO could have used Nickel Metal Hydride
(NiMH), but the batteries would have weighed a lot more and had a lot less
capacity.  1150 mAh is pretty substantial when you consider that a car battery
may only be 20x this.

Regarding the motors, I would assume that the new motors were designed to have
adequate power at 7.4V.  There's no reason they couldn't have the same power at
7.4V as the old motors did at 9V, they would simply draw more current.

Eric Albrecht