Hello Everyone, I'm new to electric power and have a question about Lipo packs. I bought a Cox Christen Eagle ARF and wanted extra batteries which Cox does not sell so I bought 2 common sense rc batteries and need to know if they will work. The stock battery is a 3S, 11.1v 1800mah with no output rating. Tech support at Cox said it was rated at 18amps continuous discharge although the esc is rated at 16amps. The common sense battery is a 8C, 3S, 11.1v, 2000mah rated at 16amp continuous discharge. I,ve made adjustments for the size and weight difference and CG is OK and have only done some taxi testing so far. My question is will there be a problem with the difference in continuous discharge rates? Also, the common sense battery has a burst rate of 24amps for 5 sec every 30 seconds. Any help would be appreciated. Thanks, Marty

PS: I've also noticed that my horizontal stabilizer is not square to the fuse. It has about a 5/16in. offset from square and the same amount off center. Seems like this may cause some yaw when heavy elevator is applied. I've built many nitro planes so I'm not sure how much affect this will have as I always built them square. Plan to contact Cox about this, but I only realized the problem during final set-up so I'm going to give her a try anyway. Anyone have any experience with this?

You should be fine with both the battery and the tail offset. I'm sure that Cox didn't design their plane's ESC to be operated at its maximum rating, so the 16amp battery should be OK. As far as the tail offset, foamies tend to fly somewhat sloppier than their wooden counterparts, so the slight amount of sloppiness due to the offset should get lost in the overall feel of the plane. I have a ParkZone J3Cub that I bought two years ago as a used plane. It has significantly more misalignment than what your plane has, but it flies perfectly well. Of course the J3 isn't capable of the same maneuvers that the Eagle can perform, but I think that your plane will fly just fine as it is.

Thanks for your help Leo and may I ask one more question of you. Tech support at Cox seemed to think the common sense battery may be too weak as it did not have a continuous discharge rate of 18amps. I'm trying to get up to speed on these new Lipo's and esc's etc.,so please bear with me. Is it possible the common sense battery will limit the output of the motor or, will time at full throttle be limited? I apologize for my lack of knowledge but you seem to know this stuff pretty well. Thanks again!

Typically the problem is not that the battery stops providing current it is that the motor draws too much current and damages the battery. This takes a little while to happen (which is why you have a burst rating). Typically when you start exceeding the c rating the battery starts getting host very quickly. When she gets too hot you start to damage the battery. Of course there might be other ways exceeding the current rating damages the battery.

So, even if 18A is the maximum current, but you fly around somwhere between 1/3 and 2/3 throttle most of the time you should be fine. However, if you fly all the time at WOT you may get into trouble.

Like the last chap said, you are probably fine. However, if you are getting into electric models seriously think about buying a watts up meter (or other brands). It's a device you plug inline between the battery and the motor which allows you to read off amps/volts etc. In all honesty, nothing beats actually measuring the setup and then making a decision based on actual measurements rather than speculation.

Cheers,
Oz.

Thanks Oz, I think I'll take it easy on the throttle and buy a watts meter! Have a Happy Holiday, Marty

Hello, I would say go with a 20C constant pack. It doesnt hurt to get a pack that can handle more amps than you need and if you upgrade your motor or want to use the battery in a differnt plane later your battery will handle it. We have great packs at a low price www.efuelhobbies.com