Just got to put my new Alfa Fw 190 up and had a ball. I am still fairly new to all this so I would like to ask that all employ the KISS theory on responces if at all possible. I have the Kokam 3 cell 11.1 Volt / 1500 mAh packs to power my MP Jet red Outrunner. Flew two of the packs for about 20 minutes each after charging about a week prior to flying. After the flights I put a digital voltmeter to them and they still showed 11 plus volts, Never really heard or felt the power "fall off" like I am used to with my Nimh packs. I just want to be certain that I am not harming these because they are rather pricey. I also tested one pack that I had not used yet and it was 12 volts. If these are 11.1 volt packs how is that possible. I have an Apache 2500 charger and charged them new at 1200 until it cut off. I want to be able to monitor these because I have read so much about how sensitive they are to overcharging and over discharging. (If that is the correct word) I just figured that after 20 minutes or so of flying they would have read around 8 or so volts instead of 11?

Having the Apache 2500 charger is a good start! It will keep you safe from over-charging your Lithium packs and essentially warn you if you are discharging them excessively by displaying a red flashing warning if it thinks your 3-cell pack is to low. You'll then need to try an initial charge on the 2-cell jumper setting to raise the voltage a bit.

Your 3-cell Kokam 1500 pack should measure around 3x4.2v or 12.6 volts when fully charged and unloaded. The lowest voltage you should read after a flight is 9.0v. If it is lower, try to recharge the pack immediately. Typically, I see around 3.5v/cell or 10.5v after a flight on a 3-cell Kokam 1500 pack.

Good luck!

I guess I just expected to feel or hear the battery get lower and could not believe that it still had 11 volts or better in these packs. I am used to flying the GWS setup in my Corsair and it uses the Nimh Sanyo 8.4 V/ 730 mAh. You know when they start to wind down. I flew for an easy 20 minutes with the Kokams and the Outrunner at about 1/2 to 2/3 throttle and never heard or noticed any power loss. I guess I expected less and got more. About time...

Ahhh, yes, I see now.

Lithium cells hold there voltage fairly level until they are depleted. Once depleted, the voltage drops fast. This is far different from our NiCd/NiMH packs which are strongest in the first few minutes of flight.

In this manner, the Lithium cell effect more closely mimics a glow engine power level.

I'll second that. My 2s 1320mah TP li-po runs strong and then nearly goes flat for about the 20 seconds of flight. I fact by the time I notice the pack is dying there is usually not enough charge left to make a power on landing. At best I can get a little bit of juice at touchdown for a flair.

Thanks for all the good info. Both of you. I will have to look out for the dreaded voltage drop you guys were talking about. That is when you land quick. To be quite honest about it I was about worn out when I sit my bird down after the first two flights, probably 20-25min. each in duration. Like I said it was a maiden flight for the "Red 13" Fw 190. Sure is sweet flying though, everything I hoped it would be. I am ecstatic about the performance of the Kokam 3s and Outrunner motor. Now I need the P51 or the P47 with the same setup.

Thanks again,
Rex

I am new into electric. If the power drops so rapidly at the end of the discharge cycle, would it be wise to skip the BEC and take the penalty of a separete receiver/servos-battery (small lipo) to safeguard the power to the controls once the "main" power battery is depleted?

Joje

It may depend on the type of plane you are flying.
If you were flying a powered glider you would not want to rely on the low voltage cutout. Carefull timing of the motor runs or a seperate battery would be required.
I am currently flying a foam 3D plane. The plane will not stay in the air very long once the motor cuts. The low voltage cuttout and the BEC works well with this plane.