[NSRCA-discussion] 8- cells?

[Peter Vogel]

I'm not sure why you would want to go to 8s.  Ultimately it takes a certain
amount of power (W) to accomplish a series of maneuvers and that takes a
certain amount of time (W-hours).

Watts = amps * volts
resistance increases with the square of the current (amps)

If you reduce volts by 20% you increase current by 20% to achieve the same
power, that means you increase resistance (and therefore loss of
efficiency) by 40+%,
that resistance loss turns into heat, in general as electronic things heat
up they get less efficient as well.

For any given airframe, etc. if I determine I don't need 20% of the power I
have on board, I'd much rather reduce amp hours available than reduce
voltage, keep the system running cooler and probably save just as much
weight by reducing cell capacity as I would by reducing the # of cells for
a given capacity.  Checking...

Zippy Compact 8S 5000   (25C) 1030g (2x4S), 905g (8S brick) You probably
would want to move to 35C which looks like it would weigh more...
Zippy Compact 10S 4000 (25C) 1013g (2x5S), 908g (10s brick)

So pretty much a wash as far as weight goes -- why not stay with the higher
voltage, higher efficiency setup?

Peter+

On Tue, Mar 27, 2012 at 5:03 PM, Keith Hoard <khoard at gmail.com> wrote:

> I was checking if anyone who's flown 10S has tried 8S.  Heard rumors, but
> want to hear from guys who've flown both before this years battery
> purchase.
>
> Sent from my iPhone
>
> On Mar 27, 2012, at 18:52, J N Hiller <jnhiller at earthlink.net> wrote:
>
>  Kicking it around. I feel confident I can build an 8S E-powered
> option-160 under 10 lb. I'm in the process of detailing the design and
> probably won't commit until I have some basic airframe parts on the bench.
> An 8S-5000 looks to be about 8 oz lighter than a 10S-5000. Don't know if a
> 10S-4000 would be enough. Too many unknowns but probably worth a try in
> masters. FAI may be too demanding. How much more does it take on a windy
> day? 20%? ??
>
> I know nothing, yet.
>
> Jim H
>
>
>
> -----Original Message-----
> *From:* nsrca-discussion-bounces at lists.nsrca.org [mailto:
> nsrca-discussion-bounces at lists.nsrca.org]*On Behalf Of *Keith Hoard
> *Sent:* Tuesday, March 27, 2012 3:53 PM
> *To:* General pattern discussion
> *Subject:* Re: [NSRCA-discussion] 8- cells?
>
>
>
> Nice..  ;-)
>
>
>
> ROFL
>
> Keith Hoard
>
> Collierville, TN
>
>
> On Mar 27, 2012, at 17:35, Derek Koopowitz <derekkoopowitz at gmail.com>
> wrote:
>
> I've been using 8 cells for the past couple of years... however, I keep
> another 2 cells as insurance.
>
> :-)
>
> On Tue, Mar 27, 2012 at 2:06 PM, Keith Hoard <khoard at gmail.com> wrote:
>
> Is anyone trying 8 cells this year in their 2 meter plane?
>
> Keith Hoard
> Collierville, TN
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-- 
Director, Fixed Wing Flight Training
Santa Clara County Model Aircraft Skypark
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