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Beginners / Newbies Interested in getting in the hobby. Not sure where to start. Post your questions here and one of the RCCanada experts will be glad to help you out! |
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05-18-2011, 11:41 AM | #1 |
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Batteries
This may be a dumm question but can somebody tell me what the 3S and 20C stand for on a battery?
Mannywest |
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05-18-2011, 11:45 AM | #2 |
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Re: Batteries
The only dumb question is the one unasked.
'S' is short for 'series' or how the batteries are connected (series increases voltage, 'P' or parallel increases capacity. 'C' is capacity 20 C means you can draw 20 times the cpacity of a pack so a 1000mah 20C pack should be able to deliver 20 amps (20*1000mah) without harming the pack. Hope this helps.
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05-18-2011, 12:17 PM | #4 | |
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Re: Batteries
Quote:
I assumed Lithium as your 20c number is a common rating for regular Lipo cells (which have a nominal voltage of 3.7v) Maybe if you describe what you're trying to accomplish I can help you better...
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05-18-2011, 01:48 PM | #5 |
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Re: Batteries
I was just curious as to what these numbers stood for. I am looking at buying the Floater-jet from Hobby King and was mainly wondering what the C numbers stood for.
Thanks for all your help Mannywest |
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05-18-2011, 05:09 PM | #6 |
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Re: Batteries
The C rating is normally applied to LiPo batteries. JimMcIntyre described it perfectly, but if you are still curious another way to look at it is to compare it to a pail of water.
The amount of water in the pail is the current stored in the battery, rated as the MAh. The C rating would be the size of the hole in the bottom used to discharge and recharge the water in the pail. So, a small pail with a large hole would theoretically be able to supply the same output current as a larger pack with a smaller hole but more "Push". As you would expect the smaller capacity pack would last far less before needing rewinding, so the optimum would be to go with a larger capacity battery if the aircraft can accomodate the size and added weight. This serves two purposes: first is that the larger capacity will obviously give you longer flight times, but the second item is just as important to the life of the pack. If you push the pack too hard by trying to suck the current out at max it's capable of delivering you generally create heat from internal resistance and this damages the chemistry inside the cells. Some other very important points if you are new to electrics are that LiPos are completely intolerant of overdischarging. If you continue to fly till your performance drops, (prop or rotor RPM lags under load) then you have gone too far. Each cell has a critical voltage you do not want to drop below or irreversible internal changes take place inside the cells. This can happen even the first time. The recommendation is to buy a battery monitor, (very inexpensive and likely to plug into the balance lead on the battery) and even then use it as a last resort. The best way is to fly short and conservative flights at first and then if your charger is capable, record the MAh it takes to fully rewind the pack. Basic math with then tell you how much of that type of flying it will take to get you to where you should be planning to land. This helps the pack by slowly building it up to full strength and prevents you running the risk of pushing it too far. The second most important point is that LiPos are also unforgiving of abuse and improper charging. Even with a high quality balance charger you should NEVER leave a LiPo on charge unattended. Their energy for size is incredible and if there is a problem it can all pump out at once. This is a LOT of power! The end result can be fire. In aviation we received a notice that LiPo "Primary Metal Fires" cannot be quenched with any current fire suppression system, meaning if the lithium metal starts to burn nothing will put it out. Don't risk it and monitor the charge. A LiPo Safe bag is also good insurance.
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05-20-2011, 10:52 PM | #8 | |
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Re: Batteries
Quote:
My flying buddy tells me that if I fly till that happens, it's too late, I have already done irreversible damage to my battery pack! True - or - false?
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05-19-2011, 09:16 AM | #10 |
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Re: Batteries
Lots of good info here: http://www.wattflyer.com/forums/showthread.php?t=31071
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