[NSRCA-discussion] AAA NimH batterys

[Jerry Budd]

For the 2002 Nats I switched to a AAA 700 mAh NiMH battery pack to 
make weight.  While practicing at the Kokomo field I discovered that 
the pack was good for about 1-1/2 flights (don't ask me how I know 
that!).

Fortunately, I got control back (well - partially) after the 1-1/2 
downline snap and was able to coax the plane back onto the ground. 
Not fun.

At the post-flight debrief I figured out that the AAA cells simply 
had too high of an internal impedance to deliver enough current to 
keep the voltage above the receiver/servo cut-off level when all the 
servos needed to move at once.  I was using JR 7000 Super Servos for 
aileron which went slow/shut off at 4.6V whereas the other JR servos 
kept on working down to 4.2V.

Jerry


>Ed is right.  The smaller the cells the higher the internal resistance.  Run
>them down to 20% remaining capacity and put a heavy load, like 5 Amps on
>them and read the voltage.  You will probably not like what you see.
>
>Jim O
>
>
>----- Original Message -----
>From: "Ed Alt" <ed_alt at hotmail.com>
>To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
>Sent: Thursday, January 26, 2006 3:06 PM
>Subject: Re: [NSRCA-discussion] AAA NimH batterys
>
>
>>  Ed:
>>  You might get disappointing results due to the inherently high internal
>>  resistance of NiMH.  Going with AAA cella and such a low capacity might
>mean
>>  that you don't get as many flights as you expect before a voltage test
>under
>>  load dips below an acceptable value.
>>
>>  Ed
>>  ----- Original Message -----
>>  From: "Ed Miller" <edbon85 at charter.net>
>>  To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
>>  Sent: Thursday, January 26, 2006 9:05 AM
>>  Subject: [NSRCA-discussion] AAA NimH batterys
>>
>>
>>  > Is anyone using AAA NimH batteries for a RX pack ??. I am looking at
>>  > Batteries America ( EHYOST ) and they seem to have AAA NimH's in 720,
>800
>>  > and 900mah ratings. I currently use their 2/3A 5 cell NimH pack at
>1100mah
>>  > and a weight of 3.85 ounces complete with the long lead I have on the
>>  > pack.
>>  > Going to their AAA 5 cell pack looks like I can save about an ounce or
>so.
>>  > Mah isn't an issue, I can get in excess of 7 to 8 flights on the 1100mah
>>  > pack I use now before charging so going to 900mah shouldn't be a big
>hit.
>>  > Don't suggest Lithium anything as lighter, want to continue to use my
>>  > Alpha
>>  > 4 charger and am not convinced those new batteries are safe.
>  > > Ed M.

-- 
___________
Jerry Budd
Budd Engineering
(661) 722-5669 Voice/Fax
(661) 435-0358 Cell Phone
mailto:jerry at buddengineering.com
http://www.buddengineering.com