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Skim137's List: Hobby Models and RC

    • 10C from 3S4P? Naming conventions explained.
        How fast a battery can discharge is it's maximum current capacity. Current is generally rated in C's for the battery. C is how long it takes to discharge the battery in fractions of an hour. For instance 1 C discharges the battery in 1/1 hours or 1 hour. 2 C discharges the battery in ½ or half an hour. All RC batteries are rated in milli Amp hours. If a battery is rated at 2000 mAh and you discharge it at 2000mA (or 2 amps, 1 amp = 1000mA) it will be completely discharged in one hour. The C rating of the battery is thus based on its capacity. A 2000mAh cell discharged a 2 amps is being discharged at 1C (2000mA x 1), a 2000mAh cell discharged at 6 amps is being discharged at 3C( 2000mA x 3).
       All batteries have limitations on how fast they can discharge. Because of this many LiPoly batteries are put in parallel to increase the current capacity of the battery pack. When 2 batteries are wired positive to positive and negative to negative they become like one battery with double the capacity. If you have 2 2000mAh cells and you wire them in parallel then the result is the same as 1 4000mAh cell. This 4000mAh cell has the same C rating as the original 2000mAh cells did. Thus if the 2000mAh cells could discharge at a maximum of 5C, or 10 amps then the new 4000mAh cell can also discharge at 5C or (4000mA x 5) 20 amps. This method of battery pack building allows us to use LiPoly batteries at higher currents than single cells could produce.
       The naming convention that allows you to decipher how many cells are in parallel and how many are in series is the XSXP method. The number in front of the S represents the number of series cells in the pack so 3S means it's a 3 cell pack. The number in front of P means the number of cells in parallel. So a 3S4P pack of 2100mAh cells has a total of 12 cells inside. It will have the voltage of any other 3S pack since the number of cells in series determines the voltage. It will have the current handling of 4 times the maximum C rating of the 12 individual cells. So say our 3S4P pack had a maximum discharge of 6C. That means that it has a nominal voltage of 10.8 volts (3x3.6) and a maximum discharge rate of 50.4 amps (2100mAh x 6Cx4P ).
      • Conditioning new cells and packs

          This is often overlooked but most cells, particularly NiMH, will perform best if they are conditioned properly  before using them, especially in high discharge-current situations. The initial conditioning of new cells is  typically done at the factory and is called "forming" or the "formation" step. But, these cells can sit for months  before being used and will need to be properly conditioned to bring their capacity and voltage under load back up  to their rated values. This conditioning causes microscopic changes in the electrodes and electrolyte and helps  them to work as efficiently as possible. 
           
        • If the cells were stored charged (not recommended as this encourages voltage depression, higher internal  resistance and loss of capacity), then discharge them first (at a 1C rate or less) to 0.9V/cell using a pack  or tray discharger.
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        • Charge them slowly, at a rate about 1/10 of the capacity of the cell (1/10C.). For example, use a 300mA  charge for 3000mAH cells. Let them cool.
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        • Discharge at about a 1C rate (e.g., about 3A for 3AH cells) and let the pack cool. We recommend the use of  a pack discharger with a known load and known cutoff voltage so you can track the performance of your packs  as they become conditioned.
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        • Repeat this charge/discharge cycle 2-3 times, being sure the cells are cool before continuing any the  steps. But, at this low rate they'll probably only be a bit warm.
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        • If you have an AH-meter like the Astroflight, Inc. Super Whattmeter or Medusa Research, Inc. Power  Analyzer, use it during the discharge to track the ampere-hours (AH) of capacity you're getting out of the  cells. When the value stops increasing for each cycle, the cells are conditioned and can be used as you wish.
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          If the charger "false-peaks" and ends the charge before the cells are full, just write down the AH put into  the pack and keep restarting the charger until the pack is charged. The first charge may reach over 20% past  the rated capacity of the cells since they are discharged more than usual. Just let the charge continue. Our  3AH NiCd packs can reach up to 3.5AH when charged after a month of storage. Let the temperature of the cells  guide you. If they are getting very warm, the cells are charged. After these 2-3 cycles, the packs should  false-peak a lot less (NiMH cells can keep false peaking for a few more cycles). Your pack is now ready for use. 

          CamLight Systems' 2-Stage Pack Dischargers and Auto-Cutoff Modules were designed to make this new-pack conditioning both safe and easy. They feature adjustable loads and adjustable per-cell cutoffs for 4-10, 10-20, and 15-30 cell packs.
    • we don't recommend letting the outside of a cell ever reach the rated temperature, typically  130°F.-150°F. (55°C.- 66°C.). The inside of the cell can be a lot hotter than this and can  start damaging the cell. Performance might not suffer at first, but the damage is cumulative and  the capacity and voltage under load of the cell will be reduced as time goes on. Even worse, the cell might  vent or rupture.

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    • don’t expect to charge a NiMH pack today and   then use it a week or two from now as NiMH cells lose their charge two   or three times faster than NiCd cells do. You also shouldn’t fast charge   a NiMH cell at as high a charge rate as you would a NiCd cell. That’s   because of the higher internal impedance.

       

    • NiCd cells have an extremely low internal   impedance which means you can draw a lot of current without a   corresponding excessive voltage drop. This makes them perfect for high   current draw applications.

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    • There is no "memory" in any cells or application you'll ever come across. However, several things can the internal chemical structure of a cell to form fewer, larger crystals. Since there are fewer crystals, there's less active surface area and higher internal resistance. This higher internal resistance causes a voltage drop inside the cell. This causes the voltage you measure at the cell terminals to be lower (when being used) and makes the cell seem to be discharged before it actually is. This is called "voltage depression" and is commonly attributed to "memory", but actually isn't.
    • Works great on my mini inferno. Very high quality, Excellent product for the price. Awesome power. You will need a pinion gear for an rc18t to make it work on a mini inferno.
    • have got this for my mini-inferno, and works pretty good!
       Here is the link. http://www.hobbypartz.com/hobbywing-...ess-combo.html
       
       But the issue is that the motor shaft diameter is 1.5 mm rather than 2.0 mm, so that the stock pinion gear does not work on it.
       
       Try an E-Flite pinion gear 14 T 0.4 module (the part # is EFLM 1902). This is a little bit smaller, but it has 1.5 mm hole on it. Put a drop of CA on the shaft and push the gear on the shaft. You should slide the gear very quickly to the proper position on the shaft, because CA kicks in 2-3 seconds, otheriwse the gear will be stuck on the end of the shaft.
       
       For the battery, get 2-cell li-po 1,000 mAh or a little bigger capacity with 20C or 30C. I recommend Turnigy li-po batteries from Hobby King. Those are cheap, and work very good with this BL system.
       
       All of these have been working on my mini-inferno pretty good, and my little daughter really enjoys running it!
       
       I hope you enjoy it, too!
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