Re: Using LiPoly??

Dont think my Wingo will lift an 80lb LiPo pack. Seriously tho, the packs you describe cannot be cheap or even affordable for the average RC hobbyist. Dont know about the rest of the crowd, but I can barely afford standard LiPo packs let alone "Smart Cells". Maybe in time...

One reason is that the 'smart stuff' for the cells will cut the cells off when charged too hard OR discharged too fast. Do YOU want your airplane to become a lawn dart because the battery was cut off????

David

Cost, weight, and lowering of performance are the three reasons.

HOWEVER a device now exists that is suitable, and its likely that the more expensive packs will incorporate it. The major problem is that ANYTHING in *series* with the pack that can disconnect it under overload will add unacceptable losses when its cranking out the amps in a fast climb. So in general the technique is to shunt charge current away from each cell if they are in danger of being overcharged, but leave the discharge characateristics 'raw'

Compated with the rest of the gear they are not the worst item - in smaller sizes anyway. I've got 5 models now flying off 3 LIPo packs.

four HS55 servos and a decent lightweight receiver leave me little change out of £100. Add in a speed control and its about £120.

I don't resent toppng that off with a £40 battery pack.

A Castle Creations programmable brushless motor control will automatically reduce the throttle when the (user programmed) low voltage threshold is approached in the "soft cutoff mode". Some modelers are splicing in taps to the individual cells in packs and charging seperately or at least testing cells for balance occasionally. Many of the new chargers have advanced safety features such as the optional thermal probe for the Great Planes Triton. I think if the motor controllers, modelers, and chargers all keep getting "smarter" than we can get by on inexpensive "dumb" cells.

The thermal probe will do you little good with lithium cells. By the time they start to heat (there is no gas recombination in overcharge which is the primary cause of heating in Ni-CD or Ni-Mh) it is too late.

-- Red S. Red's R/C Battery Clinic

Maybe too late to save the pack, but doesn't it still provide a margin of safety?

Jim - AMA 501383 (remove NOSPAM to reply)

Red Scholefield wrote: