Hello,
My LiPo charger has a decent quality but allows to discharge LiPos only at 1 Amp. To discharge a fully charged 4S 3000 mAh pack to the storage voltage takes about three hours and I have four of these batteries that I use to fly eParrot.
I charged these four batteries at 1C on Wednesday June 28,2017 afternoon because I wanted to fly Thursday morning and the weather turned bad for the next three days (this is exactly what is happening right now in Toronto, Ontario, Canada.). There are different opinions about how long the fully charged LiPo batteries can wait without degradation in performance in the future.

Everybody using LiPo batteries agrees that it is better to keep them in the storage voltage when they are not in use but there exists just one little problem - to discharge my four 4S 3000 mAh I need 12-14 hours and this is ridiculous.

I started digging on the web and found that people, especially R/C people flying helis, use specially build dischargers to speed up this process.
Please see: https://oscarliang.com/lipo-discharger-light-bulb/ or https://www.helifreak.com/showthread.php?t=277056.

What is your opinion about faster discharging? I think it is ok and it will be even better to discharge LiPos at higher currents. Why not discharge using a very large electric motor that draws, say, 20 Amps. of static current with certain prop. and monitor this discharge using the Power Panel?

Large motor has large thermal mass and the additional cooling can be provided by one of the home or office AC fans.

If this works, the 4S 3000 mAh LiPo can be brought to the storage voltage in a very short time.

I am waiting for your comments, preparing my Cobra 2826/10 with 10x5 APC prop and 60 Amps. Cobra ESC for tests. If this works, for the price of roughly $120 USD I will have the active discharger that will work fast and in the way simulating the "normal" LiPo usage.

Regards,
M

"Learning never stops and when it stops this means you are dead"

 




 

Hi Matt

I think all ESC's have a low-voltage cut-off point that will automatically shut off the system.  However that usually occurs at some automatically set MINIMUM voltage.  Instead it is possible with at least some ESC's to SET the voltage cut-off point - at say 3.7V.  If you can do that please do!

PLAN B:  Set up the motor with a prop about 2" smaller than your flight prop.  Use something like the Hubin FM-0c timer set to its maximum run time of 6 minutes.  One neat thing about this timer in this role is that over the run time it ADDS throttle to compensate for the reduction in battery voltage.  For a discharge  rig tha means it will keep the RPM's up and the battery drain actually increases over the duration.

Plug it all in and let it run.  It will not get down to a "perfect" storage voltage but it will definitely discharge the battery similar to a similar state as a flight would.  The timer helps protect from over-discharging too.  6 Minutes to discharge is better than 12-14 hours!  BTW, I think your 2826 motor with a 10x5 would fit the bill.

After you do a few packs you might decide to use a slightly larger or smaller prop to change how much you discharge.  Besides, I find its a GREAT way to use up my otherwise unusable IC and CCW props..! (flak jacket on)
 

More ideas here on a similar thread

https://stunthanger.com/smf/gettin-all-amp'ed-up!/battery-discharger/

I still use the discharger, and field charge with other lipos.  If you have flown batteries and fully charged, you can do some "balancing" at the field.

Matt,

You didn't say what charger you are using.  If it uses the balance plug to monitor individual cell voltage during discharge you may be able to simply add an external power resistor to dissipate additional power above what your charger can handle.  See attached for the iCharger expanded discharge mode.  Simple, safe & quiet.

Paul

Buy a lab 8 charger/discharger and accompanying charging board  and never look back at inferior charging methods. Capable of charging up to 6 cell batteries 6 at a time and up to 5C. Discharging is not tedious and is reasonably fast and efficient with all batteries discharged to about 49/51%.
Not cheap but it is the last combination you will need to fly electric C/L
 

If this works, the 4S 3000 mAh LiPo can be brought to the storage voltage in a very short time.

Matt, define "in a very short time".  Are you thinking approximately the same as flight time?  If so, it seems to me that in effect, that exposes the batteries to another heating cycle similar to flying and will reduce battery life.  I use the following discharger.  http://www.myrcmart.com/rcx-3in1-battery-balancer-discharger-voltage-indicator-150w-discharging-p-4767.html

This morning I came back from the field with three used batteries and two still fully charged.  In the time it took to bring the three discharged batteries up to storage level the discharger had taken the two fully charged ones down to storage level.  I don't see the need for anything faster than that.

Howard built one with 2 units and added a monitor that will sound.

https://stunthanger.com/smf/gettin-all-amp'ed-up!/battery-discharger/

There is a great thread here

https://www.rcgroups.com/forums/showthread.php?2406395-An-effective-variable-load-automatic-LiPo-discharger#post31524795

The estimate was 4 amp discharge/unit in the RC thread, so Howard's should be about 8 amp discharge.  Also a good rate to condition new batteries.