kennydee

Just when I thought I just about had this battery thing figured out? I build a little slowflyer of my own design out of Fan-fold. I've also built a few for my flying friends. One of these guys was flying the 10 to 12 ounce (all up) plane, using a GWS 350 with the "D" gear box (about 6 to 1) and a 10/8 prop. They had been using an 8 cell, GWS, flat 730 milliamp pack. The plane flys well with this set up. Recently, a friend of his let him use his new Kokam 1500 2 cell Lipol (the latest HD pack at 8 or 10C draw). They both told me the plane had noticeably more power on the Kokam 2 cell pack. That doesn't make sense to me. Shouldn't the 8 cell nimh pack at 9.6 volts provide more power to this motor than the 2 cell Kokam pack at about 7.4 volts? I know the lipol is a little lighter but I thought the extra voltage of the nimh pack would more than make up for the extra weight. Could it be that the GWS nimh pack doesn't provide enough amperage for this little motor? I don't have a meter but doesn't this motor pull about 6 amps with the set up mentioned above?

Matt Kirsch

My Feedback: (21)

It's kind of a complicated relationship, but in a nutshell, the Kokam is simply holding up better under the load than the GWS NiMH pack. Your current draw is actually closer to 8 Amps, which is more current than the GWS NiMH pack can comfortably provide. The voltage of the NiMH pack drops under the load, which in turn causes the current to drop. Because the Kokam holds up better under the load, its voltage, and the current, remain higher.

Greg Covey

I agree with Matt. The Kokam cells are holding a higher voltage under load than the 730mAh NiMH pack.

More power and more duration by simply changing battery technology...you gotta love e-flight!

kennydee

Thanks Guys, but I lose the bet. They were telling me that the Kokam was giving more static power than the 8 cell nimh pack and I didn't think that was possible. You cost me one Coke. Boy, I wish all battery manufacturers would print ON THE PACK, the continuous amp draw available and the burst amp draw available. I actually ordered and received packs that had nothing on the shrink wrap, not even the manufactuer. I gotta get me one of those juice meters so I know what my amp draw is. Hey, 6 months ago I couldn't even spell AMP DRAWL, now I are one.

Matt Kirsch

My Feedback: (21)

With NiCd and NiMH, the real capabilities of the cells are not "officially" known. Like the cheap can motors, the NiCd and NiMH cells we use were designed for other purposes, and we're pushing them far beyond their design specifications. The cells can take it, but they don't last nearly as long and have a higher failure rate than the manufacturers will accept. It's kept a "secret" so they don't have to replace faulty cells.