I am going through the throws of re-evaluating my RX battery selection and would love some advice. I fly sport nitro planes with the upper end being 120 four stroke sized with seven HS-475 servos. I do have a number of digital servos but, haven't really found a good excuse to use them. I have all but converted everyting to 2.4 (combination of XPS and the new JR stuff) At this time all of my RX flight packs are 1100 mah (AA) 6 volt. I do use dedicated 4.8 volt packs for mechanical retracts and such. I experimented with a Seagull Dual Ace where I used two independently switched 1100 mah 6v packs each connecting to the RX and it worked perfectly without issues and without any additional hassles - good reduncancy with no down side (except cost). I am now putting my second GP RV-4 arf together and moving toward using two independent 6v packs but I am not sure about the capacity. I prefer NiCd's but very much open to other ideas. I don't want to buy the newest, highest capacity cells and then get a short life or have to baby them or whatever. I have considered the slightly larger 1400 mah 6v packs but I know nothing about their anticipated longevity. I also think that the 1100 mah packs have plenty of capacity for my needs - especially when placed in parallel.

This seems like a fun engineering issue and it may be that there is no bad answer. I am completely open to being influenced and would appreciate your sage advice.

Howard

Howard:

I'm not responding as an expert on batteries (I'll leave that to RED) but rather as the user of the A123 battery technology. A fellow RCr electronic techie friend introduced me to A123 RX battery packs and I'll never go back to nicads or nimhs. My application is a 29% Extra 300 plane with a DA-50 gas engine, JR R921 RX (2.4ghz) with two back-up RX's, 5 digital high torque servos (JR 8611a) and 2 digital servos (JR 821). I put a separate 2300 mah A123 battery pack for the DA electronic ignition, and two 2300 mah A123 battery packs for the RX's. I now have 67 flights on this plane and I'm extremely pleased with the batteries.

They are comparable to 6v nicad/nimh packs in weight but configure differently in size because they are only two cells. Some of the positive aspects of these batteries are that they charge-up in 5-10 minutes; they hold a constant voltage; you can get many flights without re-charging, although they are lithium based they do not have the explosive/fire issues of lipo's/lion's; and they are rated for over a 1,000 charges. The only negative is that the voltage drop-off is not determinable but in RX tests, they have held the constant voltage for up to 15 flights without issue. My experience is that I charge my ignition/RX battery packs while driving to the flying field, and after 6 fligts they still have 80-85% capacity remaining (50% capacity is their minimum requirement) and, then, for safety I recharge all three packs in about 10 minutes.

The issue you need to address is can your RX and servos handle 6.6 volts (3.3 v per cell) that A123 batteries are rated at as opposed to the 6v ratings you see on servos. Futaba and JR has told me that their RX's can handle the 6.6v and there has been a lot of discussuion regarding the 6v rated servos on some threads. With respect to my JR servos, I have been told that it is ok so I do not use a voltage regulator in my flight pack. I never got a satisfactory answer with respect to Futaba servos other than a boiler plate recommendation to use a regulator.

If you want to read about these batteries go to www.sincityjets.com I bought my batteries there and also a Cellpro4s charger for the A123 batteries.