Re: PF train motor

[Eric Albrecht]

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

[Dave Sterling]

In lugnet.trains, Eric Albrecht wrote:

> 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

Eric:

Thanks for the awesome explanation!  I learned new stuff today...does that mean
I can go home now?  :-)  I'm excited to see how the new motor and battery box
pull.  I think the new PF trains could add a lot of functionality to existing 9V
layouts.  I'm planning to incorporate PF into my layout for BW for sure.

Thanks again for the electrical information.  I'm an electrical doofus.  ;-)

Best Regards,
Dave
ToT-LUG

[Eric Albrecht]

In lugnet.trains, Dave Sterling wrote:

> Thanks again for the electrical information.  I'm an electrical doofus.  ;-)

So am I.  However, I'm also into R/C aircraft so I have a long history with
batteries and motors and could talk your ear off about them.  I could also
explain why the battery pack costs so much!

> Thanks for the awesome explanation!  I learned new stuff today...does that
> mean I can go home now?  :-)  

Yes, I give you permission to go home.  You can tell your boss I said so.

> I'm excited to see how the new motor and battery box
>  pull.  I think the new PF trains could add a lot of functionality to existing
> 9V  layouts.  I'm planning to incorporate PF into my layout for BW for sure.

I got to try out the new controller, motor, and battery along with the Emerald
Night train at Brickfest.  I didn't notice any lack of power.  The train was
running on a Power Functions XL motor which oozes with power.  Knowing that the
same motor can also operate on 9-12V, you could always use your own battery pack
if you really wanted more torque.  But I think you will be pleasantly surprised.
Consider that, even at only 7V, a <http://www.philohome.com/motors/motorcomp.htm
PF XL motor has over 14 N-cm of torque>.  Comparatively, the old 9V train motor
had only 1 N-cm of torque at 9V.  The PF motor also runs much slower so needs to
be geared differently to get the same speed, but factoring all this in you end
up with about the same pulling power at the same speed.

Eric Albrecht

<http://www.ericalbrecht.com/technic/ Technicopedia>