View Full Version : CX Battery Frustration

02-15-2007, 07:10 PM
Let me start by saying that the CX is amazing. I love it.

I've flown it in my house for 30 batteries or so. I'm always careful to not over discharge the battery. Well, two days ago I flew it until nearly dead and then plugged it in to charge. My mistake was that I forgot to plug in the charger to the wall. I let it sit overnight and the battery is now so dead that it won't initialize a charge. I get charge error.

Is there any way to revive it? I'm about ready to hook up a little 9V battery diretly to it for a few minutes in hopes it will hold just enough charge to initialize on the real charger.

02-16-2007, 11:12 AM
I'm about ready to hook up a little 9V battery diretly to it

Hmmm... well, that makes me just a hair nervous. I suggest putting a 100 ohm resistor in series with the battery if you do that. This will limit the current to 90 ma max. These things can burn so be where you aren't likely to set fire to the house. I don't know if a stone dead battery is recoverable, but I'm tempted to guess not. Anyway, I guess there's nothing to loose by trying. Please post the results of your experiment.

02-16-2007, 01:17 PM
I had a simular problem with a cpp battery (stock e-flight) The work around for me was to start a charge on a cx battery (there's two plugs in the charger one for the CX/CX2 battery and another for the CPP) I plugged in the 3 cell at the same time disconnected the 2 cell cx2 battery and lo and behold the 3 cell charged fine. I have no idea if I risked damaging the charger or the cx battery or my house for that matter but it worked and I'm not out another $37 for a e-flight battery.

02-17-2007, 10:48 AM
You have definitely damaged the battery, it will never perform like it did, but it should be recoverable to some degree. The 9V battery might do the trick, do not worry about how much amperage it will put out as that isn't going to make any difference as a 9v battery doesn't have much to begin with. Its VOLTAGE you are concerned about and the 9v should do the trick to get you charged enough to let the Stock charger take over.

I see people talk about Amperage all the time, but most have no idea how amperage works. It makes absolutely no difference how much amperage something can provide, the item connected to it will not draw more amperage than it needs period. A 1 billion amp 12V battery could be connected to the smallest .00001 amp battery and still charge just fine. Voltage is the determining factor, not amperage. You see people connecting 1 amp chargers to 750 amp auto batteries and there are no problems, what makes anyone think that connecting a small amperage battery to a large one is going to do anything different??

02-17-2007, 06:46 PM
Actually, the current will be the difference between the source voltage and the load voltage, divided by the total resistance, which includes the battery internal resistance; of both, batteries if one battery is being used to charge another. If you were to dead short a 9v battery there would be a high surge current, but of course a 9v battery doesn't have a large capacity. But for a short time, perhaps milliseconds, there will be a high peak current. A small guage wire would get quite hot.

A 1 billion amp 12V battery could be connected to the smallest .00001 amp battery and still charge just fine.

If the 12v battery would hold 12v regardless of current, and if the small battery had an internal resistance of 100 ohms, there would be a charging current of 120 amps. I'm pretty sure there would be smoke as a result of that.

You see people connecting 1 amp chargers to 750 amp auto batteries and there are no problems

The battery chargers are active devices, they limit the current to a preset value. You're right that the 12v battery could have a billion amp hour capacity and not cause a problem, so long as a proper charger is used to transfer the energy to the battery being charged. The circuitry of the charger is designed to provide a certain current. Generally, battery chargers enter a 'current mode' to start with, meaning that they provide a fixed current even if you were to dead short the output of the charger. As the load battery becomes more charged its voltage rises. The charger senses this and, at some point, the charger considers the process completed. Depending on the battery being charged, the charger might enter the "float mode" where it attempts to hold a fixed voltage.

Here is some info that might be interesting.

02-20-2007, 07:05 PM
If you have a chager for ni-cads place the lipo on ther for about 1 monute on a very low chare.This might bring it back up to 6V enough to use th ewall charger,

One note of caution..........DO it OUTSIDE..the battery may catch on fire...>think of it this way... the battery is no good now.If it works then you have a battery.If not you might have a good video for youtube.

Good Luck :twisted: