NiMH Battery problem (Full Version)

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Eplane65 -> NiMH Battery problem (12/6/2003 1:45 AM)

I have the following in my Vermont Belle 1300 (48 oz ready to fly):

Motor-Aveox 27/26/1.5 geared
ESC-Castle Creations Phoenix 45
Prop: 13X8 (now a 13X6.5)
Battery: 1700MAH Kan 10 cell Pack

Seems that I'm not getting vertical performance from this battery that NE Sailplanes says I should. I first had a 13X8 prop on it, but the ESC would frequently shut down after 5 seconds indicating lack of battery power or overload. 13X6.5 works ok. For the first couple of minutes, the performance of the plane is pretty good, but not stellar as I had expected. The rest of the flight is pretty mild and the plane just flies around without anything extra in it to do maneouvers.

Is this battery too small for the system? Should I have broken the battery pack in somehow? I've only flown it 4 times and my charger (Triton) has only put 1000 MAH back into the pack at most even though I've flown it until the BEC kicked in. I have the BEC set at 6 volts.

I hate to think of investing in LiPo at this point, but I sure would like to see this thing hover and do some more spectacular stuff. This is my first real venture into high performance electrics.



LesUyeda -> RE: NiMH Battery problem (12/6/2003 6:29 PM)

NiMh batteries are limited in their ability to deliver high currents, and so send your BEC into shut down, even though the capacity remains.

Les



loading -> RE: NiMH Battery problem (12/7/2003 10:34 PM)

With only 4 flights, your pack may not be balanced yet. If you have a the Triton you should be able to cycle the pack on the charger 3 or 4 times. Then give it a try. The Triton will also let you know how many mah it takes out and puts in for each cycle. If you don't get around 1700 on the last few cycles you may have gotten a bad pack. For the discharge I would put it at 3 amps which I believe is as high as the Triton goes, for charging I would go about 1C or 1.7 amps.



Rodney -> RE: NiMH Battery problem (12/7/2003 11:35 PM)

Your first 3 or 4 charges shold also be at c/10, no higher, to break in the batteries.



Matt Kirsch -> RE: NiMH Battery problem (12/8/2003 4:31 PM)

You don't mention the gear ratio. I've run the numbers on various gearboxes using 10 beefy CP2400SCR cells, and the currents I get are much too high for any 1700mAh KAN cells:

4.4:1 ratio = ~45 Amps
5:1 ratio = ~35 Amps

These kinds of currents might be okay on Sanyo CP1700 cells in short bursts, but the KAN cells I'm thinking of can't do more than 25 Amps. Not all 1700mAh cells are created equal. Did NESail tell you to use those specific cells?

Overloading cells causes their voltage to drop drastically without draining much capacity (as long as you don't overload them for long periods of time).

Swap that pack out for a pack of Sanyo HR4/5FAUP 1950mAh NiMH cells. These cells are the same size/weight as the KANs, but have a lot more punch.



Eplane65 -> RE: NiMH Battery problem (12/10/2003 12:19 AM)

Thanks, Matt. I think you are right. My G/B is 4.4:1 and I think I was overproped originally. The 13X6.5 seemed to work better and I'm going to try a 12X8 next. I should be careful only on takeoff and not use full throttle. If this doesn't work, then I'm going to get a 3s3P LiPo pack made from 1500 mAH cells.



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