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Old Apr 23, 2012, 07:49 PM
The Sweet Aroma of 92 Octane
electricrc68's Avatar
United States, PA, Downingtown
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What are you supposed to time your flights on?

Hey guys. Obviously, I know nothing about flight times with a lipo. Coming from micros where a 1s lipo can be discharged down to LVC (3v) without damage and then transitioning to larger electrics where i will be using 3s lipos, i have no idea what to base my flight times on. So with a 2200mah 11.1v lipo, would i base my flights times on the individual cell voltages or the MAH in the pack? Or maybe i have it completely wrong and the two are interconnected with eachother?
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Old Apr 23, 2012, 07:57 PM
Dude, I do fly all day long!
rcalldaylong's Avatar
San Jose, California
Joined Dec 2007
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Quote:
Originally Posted by electricrc68 View Post
Hey guys. Obviously, I know nothing about flight times with a lipo. Coming from micros where a 1s lipo can be discharged down to LVC (3v) without damage and then transitioning to larger electrics where i will be using 3s lipos, i have no idea what to base my flight times on. So with a 2200mah 11.1v lipo, would i base my flights times on the individual cell voltages or the MAH in the pack? Or maybe i have it completely wrong and the two are interconnected with eachother?
Base it on mah of the pak, then use this nice excel calculator to get estimate flight times. You'd have to get your max amps at WOT with a watt meter.

http://www.rcgroups.com/forums/showp...41&postcount=3

Keep in mind you never want to drop below 80%, or closer to 3.7v/cell-3.8/cell
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Old Apr 23, 2012, 08:01 PM
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Wrend's Avatar
United States, IL
Joined Jul 2009
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But yes, they are related though. The voltage between a certain range reflects how proportionally full the cell or pack is. To be on the safe side, 3.7 to 3.8 is empty to low and 4.2 is full (voltages per cell).
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Old Apr 23, 2012, 08:05 PM
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C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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Once you hit ~3.75V per cell resting voltage (NOT measured immediately after flying), it's time to call it quits. Give the pack a few minutes to recover before you check its voltage so you get a more accurate number.

You can't really just measure how many mAh are left in the pack, either. You need a charger that tells you how many it's put back in during a charge.

Also note that running any lipo cell down lower than 3.7V at rest is going to be very hard on them. The 3.0V LVC is designed to account for voltage sag in flight, and those LVCs are becoming less and less useful now that we have massively strong lipos that hardly sag at all.
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Old Apr 23, 2012, 08:21 PM
The Sweet Aroma of 92 Octane
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Okay cool thanks guys. i still have one question. based on the chart above that i just downloaded, it doesn't say anything about voltages. how will i know if my pack is at a safe voltage? or does the chart above already calculate the safe voltage based on the MAH?
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Old Apr 23, 2012, 08:56 PM
Dude, I do fly all day long!
rcalldaylong's Avatar
San Jose, California
Joined Dec 2007
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Quote:
Originally Posted by electricrc68 View Post
Okay cool thanks guys. i still have one question. based on the chart above that i just downloaded, it doesn't say anything about voltages. how will i know if my pack is at a safe voltage? or does the chart above already calculate the safe voltage based on the MAH?
No. that chart assumes 100%...

so if you enter 1000mah and entered 1 amp, it gives you the value of 60 min

basically this is 100% of the 1000mah.
Unless you are doing WOT 100% of the time, this time would give you a good estimate.


For obvious reasons, after your first few flights, you should measure resting voltage...
if still above 3.7-3.8, you can probably fly a bit more, if under, you should fly less the next time.
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Old Apr 23, 2012, 09:06 PM
The Sweet Aroma of 92 Octane
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okay cool thanks. so lets say for example my motor pulls 30A (im not sure if it really does, but im just using it as an example). Now lets say i have an 11.1v 2200mah lipo. According to the chart, i would have about 4 minutes at WOT 100% of the time. so after those 4 minutes (obviously i wouldn't be flying at WOT 100% of the time), I land and check the voltages of the lipo and then if it is above 3.7-3.8v then i should fly a bit more, and then if it is under i should decrease the flight time to say, 3 minutes and 25 seconds? sorry if i dont make any sense.
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Old Apr 23, 2012, 09:33 PM
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United States, CA, Westminster
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I think you can get a little wrapped up in the measuring and checking here.

It is well known that cell voltage is not that accurate for measuring flight times.

The best way is to measure mAh put back in.
To do this -
Fully charge your battery.
Fly your regular routine for 4 minutes.
Land and charge the pack.
Note what you put back into the pack in mAh.
Divide that by the 4min, this equals your usage in mAh/1 min.
Take 80% of your packs capacity divided by your mAh/1 min and that is your flight time.
This will vary a little for each pack and will change with the age of the pack.
Most guys fly about the same routine each time they fly so this method has been very accurate.

I only use voltage as a guide and not an absolute.
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Old Apr 23, 2012, 09:34 PM
Dude, I do fly all day long!
rcalldaylong's Avatar
San Jose, California
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Quote:
Originally Posted by electricrc68 View Post
okay cool thanks. so lets say for example my motor pulls 30A (im not sure if it really does, but im just using it as an example). Now lets say i have an 11.1v 2200mah lipo. According to the chart, i would have about 4 minutes at WOT 100% of the time. so after those 4 minutes (obviously i wouldn't be flying at WOT 100% of the time), I land and check the voltages of the lipo and then if it is above 3.7-3.8v then i should fly a bit more, and then if it is under i should decrease the flight time to say, 3 minutes and 25 seconds? sorry if i dont make any sense.
Yep! that sounds about right.
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Old Apr 23, 2012, 09:39 PM
The Sweet Aroma of 92 Octane
electricrc68's Avatar
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Thewoodcrafter- okay cool thanks i will also try that.

rcalldaylong- sweet thanks!
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Old Apr 23, 2012, 10:38 PM
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Wrend's Avatar
United States, IL
Joined Jul 2009
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I use the capacity ratings and the "C" ratings of packs for reference, and the tested capacity ratings, discharge voltage curves, and voltages as the limiting factors. I trust myself more than someone who is trying to sell me something.

Listed capacities and to a larger extent "C" ratings tend to be rather optimistic estimates.

For the prolonged health of your packs, the general consensus is to not discharge them below 3.7 volts per cell and 80% depth of discharge.

I personally aim for around 3.75 per cell resting voltage.
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Old Apr 23, 2012, 11:24 PM
Dude, I do fly all day long!
rcalldaylong's Avatar
San Jose, California
Joined Dec 2007
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Quote:
Originally Posted by Wrend View Post
I use the capacity ratings and the "C" ratings of packs for reference, and the tested capacity ratings, discharge voltage curves, and voltages as the limiting factors. I trust myself more than someone who is trying to sell me something.

Listed capacities and to a larger extent "C" ratings tend to be rather optimistic estimates.

For the prolonged health of your packs, the general consensus is to not discharge them below 3.7 volts per cell and 80% depth of discharge.

I personally aim for around 3.75 per cell resting voltage.
Yep! voltage is the golden standard. Using mah off of manufacture posted sticker on the Lipo itself is as good as CS at HK , well probably a bit better.

Really, use the voltage. it's a good measure of when to stop flying.
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Old Apr 23, 2012, 11:30 PM
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To the OP -

Read this page and pay particular attention to the "Note on fuel gauges" paragraph.

http://sites.google.com/site/tjinguy...ow-tos/80-rule

And then you can use the voltage reads if you want.
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Old Apr 23, 2012, 11:34 PM
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rampman's Avatar
USA, AZ, Gilbert
Joined Jan 2006
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All, keep in mind LVC is a percentage of starting voltage, not percentage of a full pack. If you fly, have to land to fix something and unplug during the fix, plug in and fly again your LVC may easily be WAY under 3 volts per cell.

For timers I advise a simple timer from a dollar store,,,for a dollar.

Rick
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Old Apr 23, 2012, 11:53 PM
Dude, I do fly all day long!
rcalldaylong's Avatar
San Jose, California
Joined Dec 2007
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Quote:
Originally Posted by TheWoodCrafter View Post
To the OP -

Read this page and pay particular attention to the "Note on fuel gauges" paragraph.

http://sites.google.com/site/tjinguy...ow-tos/80-rule

And then you can use the voltage reads if you want.
Agreed to some point. I only commented and questioned because to me, the 4 min thing is a bit misleading. For some setups, 4 mins will have depleted a pack to zero (0). Take my stryker....WOT is 55 amps and I run a 2200mah 3S. Max I fly is 3 mins and I'm at 11.3-11.4.... At 4 mins, I would be clear past LVC.

That's kinda why I like taking the max amps with a estimate calculated time...fly then check resting voltage.
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