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Model Forum / Radio Controlled / Air Models / April 2004Using LiPoly??
Interesting film clip.... http://www.helihobby.com/videos/LithiumBattery.wmv They must have really been pouring the amps to the battery in this demo... Cheers, Bill Interesting video. However, I wonder why the modeling community hasn't gone over to the "smart cells" that are used in industrial applications. I am involved with Unmanned Underwater Vehicles with two 8 cell Li Poly cells that weigh 80 lbs each with 32V (nominal) output. They can be charged without supervision because the control electronics are in the batteries. If an unbalanced situation occurs or if one cell or all cells are being overcharged, the system shuts itself off and notifies the operator via a computer message and log file. Just seems that it wouldn't be hard to adapt it to our applications and add a measure of safety. Jim W > Interesting film clip.... > [quoted text clipped - 5 lines] > > Bill 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...  SignatureFubar of The HillPeople AMA605992 KE6ERB "I've heard the screams of the vegetables." > Interesting video. However, I wonder why the modeling community hasn't gone > over to the "smart cells" that are used in industrial applications. I am [quoted text clipped - 16 lines] > > > > Bill > 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". 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. > 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 >Interesting video. However, I wonder why the modeling community hasn't gone >over to the "smart cells" that are used in industrial applications. I am [quoted text clipped - 16 lines] >> >> Bill > Interesting video. However, I wonder why the modeling community hasn't gone > over to the "smart cells" that are used in industrial applications. I am [quoted text clipped - 5 lines] > computer message and log file. Just seems that it wouldn't be hard to adapt > it to our applications and add a measure of safety. 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' > Jim W > [quoted text clipped - 7 lines] >> >>Bill 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 http://www.rcbatteryclinic.com Check us out for "revolting" information. > A Castle Creations programmable brushless motor control will automatically > reduce the throttle when the (user programmed) low voltage threshold is [quoted text clipped - 4 lines] > think if the motor controllers, modelers, and chargers all keep getting > "smarter" than we can get by on inexpensive "dumb" cells. Maybe too late to save the pack, but doesn't it still provide a margin of safety? Jim - AMA 501383 (remove NOSPAM to reply) > 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 [quoted text clipped - 13 lines] >> all keep getting "smarter" than we can get by on inexpensive "dumb" >> cells. |
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