NMP 7.4v 2Amp Battery Packs

[rcaerobob at cox.net]

Great explanation, Jim.  Clears up a misconception I had!!! Thanks!

Bob P.
> 
> From: "JOddino" <JOddino at socal.rr.com>
> Date: 2004/08/25 Wed PM 01:16:47 EDT
> To: <discussion at nsrca.org>
> Subject: Re: NMP 7.4v 2Amp Battery Packs
> 
> Digitals do not draw any more peak current at start or at stall.  That current is basically the applied voltage divided by the resistance of the motor winding.  Three Ohms is typical so the current would be 6 volts divided by 3 Ohms or 2 amps.  As soon as the motor starts moving it generates an emf, like a generator that bucks the input voltage and reduces the current.  however if you get a bunch of servos buzzing you can draw a lot of current.
> What makes the digitals draw more average current is the fact that they send more pulses to the motor with very little error signal.  In other words if you press on the elevator to create an error between commanded position and true position, the digital will send more average current than the so called analog trying to get back to the commanded position.
> Jim.
>   ----- Original Message ----- 
>   From: gene.maurice at comcast.net 
>   To: discussion at nsrca.org 
>   Sent: Wednesday, August 25, 2004 6:06 AM
>   Subject: Re: NMP 7.4v 2Amp Battery Packs
> 
> 
>   Adam
>   I think that if you were to put a fairly fast amp meter in the power circuit on an all digital plane, you'll find the peak draws MUCH higher than 1 amp. A local guy has an EagleTree system in an all digital plane (sample response time is only about 1/10 of a second, pretty slow) and it shows AVERAGES of 1.0 - 2.0 amps with peaks up in the 3 - 4 amp range. These peaks are very short in duration but require a battery capable of delivering that sort of amperage none the less.
> 
>   Digital servos draw large amounts of current when asked to move, especially under aerodynamic loads. In addition, their holding power will draw as much current as it takes, or is available, to maintain a position. 
> 
>   Check it out, I think you'll be surprised.  
> 
>   --
>   Gene Maurice 
>   AMA 3408 NSRCA 877 
>   Plano, TX 
>   gene.maurice at comcast.net
> 
> 
>     -------------- Original message -------------- 
> 
>     > Dieter Rozek wrote: 
>     > 
>     > > I just purchase these battery packs and according to the included 
>     > > instructions is mentions to "Only use NMP's Lithium charger to charge 
>     > > these packs." I was wondering if anyone might know why this would be 
>     > > the case. Shouldn't any Li battery charger work? I already have a 
>     > > Kokam Li battery charger which allows me to charge at various rates. 
>     > > Is there a legitimate reason why I should buy their charger or should 
>     > > any Li charger work? Also, I was surprised at the diminutive size of 
>     > > the pack. Does this pack have enough juice to power 3x JR9411, 1x3412 
>     > > and 1x8411 in a Temptation? At 2A I would assume that this would be 
>     > > more than plenty? I would be interested in hearing anyo! ne's 
>     > > experience with these packs. 
>     > > 
>     > > Thanks 
>     > > 
>     > > DIeter 
>     > > 
>     > > ===================================== 
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>     > > 
>     > I'm estimating our peak draw with a fully digital plane is around 1amp, 
>     > so any lithium battery over 250mah shouldn't have a problem staying 
>     > above 6.0v during those draws. 
>     > ===================================== 
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>     >
> 

Bob Pastorello, El Reno, OK, USA
rcaerobob at cox.net
www.rcaerobats.net

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