HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jul 05, 2014, 11:42 AM
Registered User
Joined Jun 2014
91 Posts
Question
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?
cantremember is offline Find More Posts by cantremember
Reply With Quote
Sign up now
to remove ads between posts
Old Jul 05, 2014, 11:53 AM
Registered User
flydiver's Avatar
United States, WA, Seattle
Joined Jan 2007
5,189 Posts
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.
flydiver is offline Find More Posts by flydiver
Reply With Quote
Old Jul 05, 2014, 11:53 AM
Registered User
So. Cal.
Joined Oct 2004
7,893 Posts
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.

Mark
mrforsyth is online now Find More Posts by mrforsyth
RCG Plus Member
Reply With Quote
Old Jul 05, 2014, 12:21 PM
Registered User
Joined Jun 2014
91 Posts
Okay thanks for the info!
cantremember is offline Find More Posts by cantremember
Reply With Quote
Old Jul 07, 2014, 04:41 PM
Watching EKRAN
Joined Jul 2013
347 Posts
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.
varis is offline Find More Posts by varis
Reply With Quote
Old Jul 08, 2014, 11:29 AM
Registered User
E-Challenged's Avatar
United States, CA, Garden Grove
Joined Oct 2000
11,752 Posts
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.
E-Challenged is offline Find More Posts by E-Challenged
Last edited by E-Challenged; Jul 08, 2014 at 11:38 AM.
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Feds Say Possession of “Large Amounts” of Weapons May Indicate Terrorist Activity rcjetpilot Life, The Universe, and Politics 75 Oct 20, 2013 12:30 PM
Wanted Small amount of Ultracoat needed!!! Epinephrine Aircraft - General - Miscellaneous (FS/W) 0 Sep 29, 2013 11:12 AM
Discussion motor choice for plane and amount of cells to use scottc39 Power Systems 9 Feb 03, 2013 06:26 AM
Max Allowable cell imbalance amount? tomcor Batteries and Chargers 1 Jan 28, 2004 02:32 AM
more power from same amount of cells.. MarkChinery High Performance 1 Jan 11, 2004 09:50 AM