[NSRCA-discussion] Battery discharge/storage question

Wed May 8 10:46:05 AKDT 2013

At the end of every flying session, I leave the field with the batteries in
whatever state of charge that they have.

I don't do a storage charge at the field.

I do the storage charge at home.

If I am going to fly the next day or in a few days..less than a week, I do
not discharge the already charged batteries..but I DO top them off at the
field the next time out.

Today's chargers usually go into the balance mode immediately when charging
a previously charged battery so I don't believe there is a problem topping
off a previously charged battery.

Before I leave for the field, I charge all batteries that are discharged or
in storage charge.

If I have several flying sessions in a week or so I will NOT put any
discharged batteries in storage charge..

Then I charge them just before I leave home on the next day I go flying.

If I know I am not going to fly for several days then I DO put discharged
batteries in storage charge..AND discharge charged batteries low enough to
put into storage charge.

If I need to discharge any batteries I do it with a 17 ohm 100w Dale
resistor.

I made a 12" heavy zip cord lead with alligator clips on one end and a
matching connector for the battery on the other end.

I use a Fluke DVM across the resistor to monitor the voltage and I discharge
down to about 35 volts.

Then I immediately do a storage charge.

I might not have to take them down to 35 volts but the battery must be below
the storage charge voltage to get the charger into the storage mode.

If you do the math..the discharge on a fully charged battery is about 2.4A
and the resistor is running within its wattage range.

Dave Harmon

NSRCA 586

K6XYZ[at]sbcglobal[dot]net

Sperry, Ok.

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Scott McHarg
Sent: Wednesday, May 08, 2013 1:06 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] Battery discharge/storage question

I got scolded not too long ago for even suggesting it by a ThunderPower rep.
I wanted to top off because after a week, one of my packs had dropped down
to like 94% (yes it was an older pack and had a little over 180 cycles on
it).  I was told that topping off "could" cause damage to the packs
immediately regardless of age.  It was a fairly stern warning.  Honestly, I
didn't ask more because I was already hanging my head from the scolding.  I
just said "Yes sir, sir".  :)

On Wed, May 8, 2013 at 1:00 PM, Atwood, Mark <atwoodm at paragon-inc.com>
wrote:

Okay, I'll bite. Why don't you want to top off the charge? I know a lot of
people who insist on doing this even if they just flew the day before.

Sent from my average intelligence  phone

On May 8, 2013, at 1:44 PM, "Scott McHarg"
<scmcharg at gmail.com<mailto:scmcharg at gmail.com>> wrote:

I haven't seen any issues with a battery left a full charge for a week but I
wouldn't recommend longer at full charge.  Just make sure that you DO NOT
top off the charge prior to flying.  I have started doing what Keith does as
well which eliminates all concerns.  The worst part is having to wait at the
field while you bring that battery back up to 50%.  Last one out has to lock
the gates.

On Wed, May 8, 2013 at 11:23 AM, Keith Hoard
<klhoard at hotmail.com<mailto:klhoard at hotmail.com>> wrote:
I take my batts to the field at 50% and leave the field at 50% charge. If I
can't do that, then I discharge when I get home. My batts seem to last a
long time.

The (dis)charger is supposed to get hot, that is where the energy from the
battery is going - into the heat sink. That's Ok, my PL 8 gets hot too.

The PL8 can only discharge 100 watts by itself, but can do much higher if it
is using "regenerative" discharge - dumping your LiPo's charge back into a
lead acid battery. I don't know if the 10X has that capability or not.
Otherwise I'd just keep using the low discharge rate, or plan your flying
day to end with a storage charge.

Wow, that was a lot of typing to do on a phone!!

Sent from my iPhone

On May 8, 2013, at 11:15, "Bob Kane"
<getterflash at yahoo.com<mailto:getterflash at yahoo.com>> wrote:

I have had to abort a couple of planned flying sessions so far this spring
due to weather.  I have read that lipos should not be left at full charge
for any significant length of time. So what is a significant length of time?

Hours?  Days? Weeks?

My Turnigy 10XS charger has a discharge/storage mode, but the maximum
discharge current is 1 amp. It takes a couple of hours to bring a 10S pack
down to storage level, and the charger gets pretty warm(!) during the
discharge.  Up to now I have only worried about discharging the pack for
long term storage.

If leaving the cells fully charged for more than a day or so is bad, I am
considering building a dedicated discharger, there are some pretty simple
yet effective designs on RCU.

Bob Kane
getterflash at yahoo.com<mailto:getterflash at yahoo.com>
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--
Scott A. McHarg
Sr. Systems Engineer - Infrastructure
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