Re two batteries, was Miracle switch failures

[s.vannostrand at kodak.com]

If a diode is a new point of failure, what's a regulator?





"Tomanek, Wojtek" <tomanekw at saic-abingdon.com>
Sent by: discussion-request at nsrca.org
03/31/2003 08:53 AM
Please respond to discussion

 
        To:     "'discussion at nsrca.org'" <discussion at nsrca.org>
        cc: 
        Subject:        Re two batteries, was Miracle switch failures


Just FYI
 
I did use a similar two-battery system; the problem is that you have to 
find a high capacity diode (I used at least 1.5 Amp or higher, which is 
better).  The voltage drop is 0.7 for silicon diodes, this works well with 
5C batteries.  However, using diodes introduces an additional single point 
of failure but having two independent systems balances this to some 
degree. 
 
Now I use two batteries each with a switch and charging jack and no 
isolation between the two.  The primary battery is a 5C (NiCd or NiMH) or 
Li-Ion with a 5.6 Volt regulator (other will work too 5.2 ? 6.0 volt). The 
backup battery is a small 4C NiCd 250 mAh.  Both switch connections 
plugged straight to the receiver.  If you have to plug it through a Y with 
a secondary type servo (throttle or gear). 
 
What happens in this system is that the primary battery chargers 
(equivalent to trickle charge) the secondary battery and keeps it at ~ 5.3 
(with the 5.6 Volt regulator).  If the primary battery fails the secondary 
will be enough to land, if the secondary fails the primary will do the 
landing duty.  This assumes only an open circuit failures on a switch, 
plug, or even battery etc.  I generally charge both batteries, but if I do 
not, I notice a little larger drain after the first flight on the primary 
battery (equivalent to two flights). 
 
I always check both batteries before and after each flight that way the is 
less chance of a surprise. 
 
This is not any better than other proposed systems, just what I have used 
for some time. 
 
Good luck
Wojtek
 

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