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Old Mar 15, 2005, 11:15 AM
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2 or 3 cell lipo?? Which one is best

Have a corsair and spit and soon to be getting a Mustang. Should I go with a 2 cell or 3 cell lipo? Right now have a 3 cell with an outrunner brushless and noticed that the 3 cell is pretty fat. Can I get the same power out of a 2 cell with high mah?

Any recommendations out there would be great. Where is a cheap place to get some lipos??

Thanks!!
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Old Mar 15, 2005, 11:49 AM
Cal
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Higher mAh will give you longer flight times. More cells will give you more power...........every thing else being equal.
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Old Mar 15, 2005, 12:14 PM
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Quote:
Originally Posted by mrstingray
Should I go with a 2 cell or 3 cell lipo?
Depends on your motor and prop.

Quote:
Can I get the same power out of a 2 cell with high mah?
No. Well, sorta.. it's not that simple.. First the "No":

Big mAh batteries give you two things:
1> Longer flight times
2> Higher max current output

You will *always* see the longer flight time with a bigger capacity battery than a smaller one with a given power train. Drawback is the extra weight- but that's a simple trade to understand.

The second one is wierder: Theoretically, you will *never* see the increased current output with a bigger capacity battery unless you've made a design mistake. The motor/prop will draw what it needs. No more, no less. As long as you aren't overloading (and killling) your battery in the first place, you won't see a change when you move up. (Real-world factors may let you see a >small< increase, but it's mostly negligable.)

So, no, a bigger capacity (mAh) won't give you more power. Same goes for a bigger "C" battery- all that refers to is the max current output.

You may have seen bigger NiCd or NiMh batteries giving "more power," but that's only because the smaller ones were overloaded. It's not a huge deal because Nickle batteries are fairly tolerant of abuse.

Lithium batteries aren't. Be very careful not to use them where the draw exceeds their rated output or you *will* cook them to death, and *may* have something more serious happen.
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Old Mar 15, 2005, 12:25 PM
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Now the sorta:

I said before that bigger capacity (or bigger C) doesn't make power-- all it does is increase the amount of current the battery can supply, not the amount you actually use.

But by picking a higher Kv motor, shorter gear ratio, or bigger/steeper pitch prop you can increase the motor's demand for current (called "draw"). The higher draw combination then takes advantage of the bigger capacity battery's capability and gets more power to the air.

I say "sorta" because it's not strictly the increased capacity that's helping you, but rather a combination of increased capacity and a powertrain to use it.

The trick is matching the airplane's needs with the powertrain's output at a given voltage and then picking a battery to match the powertrain's draw at that voltage.

By choosing different motors, you can get the same "power" from a high current 2 cell or a low current 3 cell.
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Old Mar 15, 2005, 10:10 PM
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Neither is "better", you have to match the battery to the motor your using and as you don't say what motor you have I don't which is better for your application...

If it's a motor suited to 3s and you use a 2s with it your going to develop less power (watts), if it's a 2s suited motor and you use 3s you could over voltage it and fry it.
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Old Mar 15, 2005, 10:13 PM
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Amps = length of flight time, the higher the amps the longer the flight time.

Volts = RPM, higher volts and you get higher RPM's

To high a voltage and you let the smoke out...
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Old Mar 16, 2005, 04:55 AM
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Thanks guys. Will have to do some research to find which is better for my motor. It is a BP21 with an 18amp esc.
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Old Mar 16, 2005, 12:35 PM
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Quote:
Originally Posted by indybudd
Amps = length of flight time, the higher the amps the longer the flight time.
You meant mAh, not "Amps," right Indy?

Because Amps == current, which times voltage makes power, and more amps means you use the juice faster. That's shorter flight times, not longer.

Bigger mAh (what you meant) means more current stored, which means longer flight time.
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Old Mar 16, 2005, 03:01 PM
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yea yea yea, how many amps the battery can deliver, obviously we are talking about the batteries capacity not how much current it can deliver instantaneously!

Amps vs.Amp Hours, Milliamp Hours etc... as a former electronics tech I know what the difference is.
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Old Mar 16, 2005, 03:02 PM
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the motors not going to draw any more amps then its propped for, regardless of how oversized the battery capacity is...
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Old Mar 16, 2005, 04:53 PM
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Quote:
Originally Posted by indybudd
as a former electronics tech I know what the difference is.
I know *you* do- no fair confusing the new guys!

Quote:
Originally Posted by indybudd
the motors not going to draw any more amps then its propped
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Old Mar 16, 2005, 05:23 PM
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sorry for being so careless, just trying to help...
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Old Apr 26, 2014, 02:09 PM
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Hello mrstingray,

I had an extra 300 with about the same specifications of your plane, I used a 11.1v 1500mah 20C in a 18A Esc and had 2 ESC's burned.

Maybe you can use a 3S battery with low amperage or low discharge rate, not to burn your esc that is only 18A.

I always pick the battery according to the model size, trying to get the most powerfull battery for it, if you have a battery 11.1v 1800mah that fits in it, for example, the next step is pick the right Esc, that accept the specifications of battery.

If you want pick the right battery taking as starting point your Esc, you must pay attention to your Esd Cont. current and max burst current to choose your battery

For your Esc 18A, you could choose a 11.1v 1500 mah (1.5A) 10C -------> 1.5A x 10C = 15A, it is inside the limit that your Esc can accept (18A)

Thanks
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Old Apr 26, 2014, 02:27 PM
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Old post, didn't pay attention for that
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