[NSRCA-discussion] Scary night of flying

Mon Aug 23 10:14:53 AKDT 2010

I think if we talk about balancing NiXX batteries instead of "forming" we will understand what is going on and then we won't call it false peaking.  The reason you want to do the 24 hour C/10 charge periodically is to make sure all the cells are fully charged.  If the cells are fully charged and fairly well matched you can then fast charge and all cells will peak at the same time and the charger will turn off when it should.  But let's say the pack has been sitting for a long time and one or two cells self discharge much more than the others.  The other three cells peak when they are charged and the charger turns off before our two low cells are fully charged.  We fly and all is well until the two that started low fall off the plateau and the system gets soft.  If we are lucky we land safely.  And remember measuring the voltage is not a good way to know the state of charge of a NiXX pack.  It only works if you know you have matched cells and you started with a fully charged pack.  You know neither unless you do some cycling after a long period of storage.  And by the way the more cells in the pack the worse it gets.  We had a NiCd pack with 50 cells in series in a missile system.  Extended C/10 charging was the only way to know you had a charge.

All of this discussion should make it obvious that Lithium is the way to go.  We balance them every time we charge and there is no false peaking, there is little self discharge and voltage does give you a good idea of the state of charge.  

Jim

On Aug 23, 2010, at 7:04 AM, Bob Richards wrote:

> Paul,
>  
> For Nicads and NiMh, nothing beats an overnight c/10 charge. A fast charge once in a while is ok, but it is possible (as others have said) to get a false peak when doing a fast charge.
>  
> If I do want to fast charge my nicads or NiMh, I prefer my Accucycle Elite. When it finishes the fast charge, it will switch to a slow charge. You can select the fast charge rate, as well as the slow charge rate. For my transmitter batteries (about the only thing I still use Nicads in) I will fast charge at 350 to 500 ma, and set the slow charge to 50 or 100. It will indicate how many mah capacity it put back into the batteries during the fast charge. The slow charge will then equalize the cells. And I do this outside the transmitter since the internal transmitter wiring and diode will affect the operation.
>  
> The Accucyle Elite also can cycle Nicads as well.
>  
> Some of the fast chargers, or charge-anything chargers, will not switch to the slow rate, they just shut off. That is why I like the Accucycle Elite.
>  
> Bob R.
> 
> --- On Sun, 8/22/10, Paul LaChance <plachance at cox.net> wrote:
> 
> From: Paul LaChance <plachance at cox.net>
> Subject: Re: [NSRCA-discussion] Scary night of flying
> To: "General pattern discussion" <nsrca-discussion at lists.nsrca.org>
> Date: Sunday, August 22, 2010, 11:37 AM
> 
> Hi all,
> 
> Thanks for all the advice.  I have to admit I did not cycle the batteries before flying this time.  They were cycled when purchased and were new for the 2008 NATS.  I already bought a new battery but wanted to know if NiCad can be quick charged on a first charging or do they have to be slow charged like NiMh?  Thanks in advance.
> 
> Paul
> 
> 
> ----- Original Message ----- From: "Lightfoot" <lightfoot at sc.rr.com>
> To: "'General pattern discussion'" <nsrca-discussion at lists.nsrca.org>
> Sent: Sunday, August 22, 2010 11:13 AM
> Subject: Re: [NSRCA-discussion] Scary night of flying
> 
> 
> > Might well have been a case of NiCad "memory". I wouldn't have thrown them
> > away unless after cycling them twice they showed to be weak. Periodic
> > cycling is a must!
> > 
> > Jay Marshall
> > -----Original Message-----
> > From: nsrca-discussion-bounces at lists.nsrca.org
> > [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Paul LaChance
> > Sent: Saturday, August 21, 2010 10:57 PM
> > To: General pattern discussion
> > Subject: [NSRCA-discussion] Scary night of flying
> > 
> > Hi all,
> > 
> > I finally flew my Prestige tonight after not flying it since the NATS 2008.
> > I have not flown it or ANY planes for 2 full years.  I charged everything up
> > 
> > and all seemed well.  Flew my first flight and landed without incident.  I
> > checked the plane over and checked all my batteries and all looked well.
> > 
> > Flew flight 2,  all was going well.  Flew the Advanced pattern twice and
> > landed.  Checked my batteries again and they still read over 6 volts.
> > Engine was running great and all was well.
> > 
> > Flew flight 3 and that is where things got scary.  I flew the sequence once
> > and everything was going well.  When I started my second sequence the plane
> > got sluggish and was not feeling right.  I landed ASAP and as soon as the
> > wheels tounched down, I went to add rudder to stear towards the pits and had
> > 
> > no rudder, no elevator, and only one aileron was working but it barely moved
> > 
> > and was very sluggish.  I shut the plane off and checked the batteries and
> > they were barely reading 4.5 volts.  This was a 5 cell nicad pack.  I guess
> > I had a cell short and kill the pack.  I was just amazed and am very lucky
> > to have been able to get the plane back on the ground before the battery
> > completely failed.
> > 
> > Has anyone had this happen before?  What would cause this?  I am going to
> > get a new pack in the morning and try to fly again tomorrow evening.
> > 
> > Thanks in advance for the help,
> > 
> > Paul
> > 
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