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Old Jul 05, 2014, 11:42 AM
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Amount of cells?

Ok, this is going to sound like a very stupid question to most of you but electricity is a subject I haven't eaten cheese from.

I currently fly an electric 'glider' (and I put that in quotes because without motor power it doesn't glide for very long) and mostly 2000-3600mah battery, 3Cells.

Then I've read on forums that more cells is more efficient? Is it true? So I could fly longer with the same weight?
What are the drawbacks & why doesn't everyone fly on 6cell batteries then?
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Old Jul 05, 2014, 11:53 AM
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The motors are current rated. Too much current they burn up.
They also spin faster with more voltage, that's the "KV" rating you'll see talked about.
If you up the voltage without changing the prop, the motor draws too much current trying to spin faster > fries.
You can downsize the prop to keep the current managable, but, larger props are more efficient. You just don't much see gliders running around with 4" props spinning like crazy. That's for jets.
So what you 'might' gain in so-called battery efficiency you'd likely lose (or more) in prop efficiency.

Flying longer is also a matter of capacity. A glider may have a limited battery area. Going to higher voltage in a same size package (with a smaller prop) isn't going to gain you anything.
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Old Jul 05, 2014, 11:53 AM
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For most typical models, the efficiency gains with higher voltage is completely negligible and would create more hassles (new motor with lower kV, more challenging to balance pack, etc.) than benefits. If you get into higher power models (>500 watts), you'll then want to consider higher voltage (more cells in series) to control the effects of resistive losses.

e.g. - Your 3S power system is likely ideal for your particular application.

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Old Jul 05, 2014, 12:21 PM
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Okay thanks for the info!
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Old Jul 07, 2014, 04:41 PM
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I suppose more cells = more complexity in the end, and all our equipment has been built taking into account that premise.

But who is to say that in 5-10 years people who are still flying lipos will not be doing that as 6S?

Being involved with some particular classes of multirotors, there seems to be a sort of a trickle down. We used to fly 3S and still do, but people have started migrating to 4S and even 6S setups.
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Old Jul 08, 2014, 11:29 AM
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With brushless motors of a certain KV rating, there is a "sweet spot" of current draw, thrust, pitch speed and duration/capacity of battery pack that may cause you to opt for 4 cells instead of 3 (etc) depending on what kind of performance you want from a given model. It is wise to check actual current draw at wide open throttle with an amp meter to be sure you are within motor's maximum current specs.

Go to Innov8tive Designs website, and study prop selection charts for various size/KV rated brushless motors. Compare current draw, thrust and pitch speed for various props at various voltages. I am using a Cobra 3525/12 motor on 4S 4500mah lipos to fly my Maxford Gee Bee E
using a 14x8 APC thin E prop. Duration is from 6-8 minutes depending on how much full throttle flying I'm doing, and battery pack gets warm but not hot.
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