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Old Aug 06, 2011, 06:02 AM
GilUriel
Israel
Joined Apr 2008
203 Posts
Question
How low do you go with your lipo ?

Hi,

While flying FPV we all get real-time readings of the battery voltage on the plane.

My question is:
How low do you pull your lipo ?

i.e. While I fly with a 3300mAh battery it gets as low as 10.5 - 10.2 volts while consumption shows I used 1800mAh.

Can I "trust" another 1000mAh ? or would it be too low- voltage-wise that it will not do ?

Thanks,
Gil Uriel
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Old Aug 06, 2011, 06:54 AM
Registered User
Joined Nov 2008
605 Posts
I don't like to go below 3.6v resting
so that is 10.8v
below that the cells start to get unequal and life diminishes.
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Old Aug 06, 2011, 07:00 AM
Chris R
United Kingdom
Joined Dec 2009
713 Posts
I use 2500mah on a 3000mah lipo never had a problem. Taking 4s from 16.8v down to 13v.
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Old Aug 06, 2011, 07:02 AM
Kiwi in Germany
whakahere's Avatar
Germany
Joined Jun 2010
2,289 Posts
I normally fly to 11.1 volts resting. With the draw that I am normally pulling I land when it is around 10.8v which relaxes to 11.1v in rest.

It seems like you either have stuffed batteries or you need to calibrate you sensor.
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Old Aug 06, 2011, 07:56 AM
GilUriel
Israel
Joined Apr 2008
203 Posts
Quote:
Originally Posted by whakahere View Post
I normally fly to 11.1 volts resting. With the draw that I am normally pulling I land when it is around 10.8v which relaxes to 11.1v in rest.

It seems like you either have stuffed batteries or you need to calibrate you sensor.
So ...
With a good 3300mA battery I should be able to pull 2600 mA and still be in about 11.1V ? ( I'm going to 2600 because I rememer reading somewhere - a long time ago that lipos should be used up to 80%. Is it so ? )

Thanks,
Gil
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Old Aug 06, 2011, 07:47 PM
Kiwi in Germany
whakahere's Avatar
Germany
Joined Jun 2010
2,289 Posts
Quote:
Originally Posted by giluriel View Post
So ...
With a good 3300mA battery I should be able to pull 2600 mA and still be in about 11.1V ? ( I'm going to 2600 because I rememer reading somewhere - a long time ago that lipos should be used up to 80%. Is it so ? )

Thanks,
Gil
Truth be told I am no expert on batteries. But with my batteries I end up putting about 2800mah after they run down to 11.1v. When you charge do you get a different number then you are reading on your osd screen?
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Old Aug 07, 2011, 12:11 AM
GilUriel
Israel
Joined Apr 2008
203 Posts
Quote:
Originally Posted by whakahere View Post
...When you charge do you get a different number then you are reading on your osd screen?
To be honest,
I have never payed attention to that but I'll do it this week.
(Any reason why the numbers may be different - beside an electronic malfunction of the current sensor ?)

Gil
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Old Aug 07, 2011, 01:13 AM
BEOWULF
North vancouver, B.C. Canada
Joined Apr 2008
18,832 Posts
I useually fly till the voltage is effecting the video and then lay off the throttle and land

or use a separate video battery and bassically drain till 3 volts per cell inthe air for main battery.

let the esc do the work for you, it will cut off motor when you get to the programmed voltage
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Old Aug 07, 2011, 01:32 AM
Registered User
Romania, Dolj, Craiova
Joined Sep 2007
15,447 Posts
If you care about your packs, you shuld not draw them completely.
A pack drawn under 20% every flight it's a half life pack, i.e. 50 flights instead 100.
20% is about 3.7-3.75V, 50% is 3.85-3.9V, under no load, so can be taken into account for gliders only ! If you fly something that is under permanent load - a copter - then lower the limit with 0.1V per cell per every 10A consumed. For example 18A quad, subtract 0.18V from per cell from above figures. This estimation is for a typical 10miliOhm average cell internal resistance. For an exact value you should measure your pack internal resistance, because it can range from 3mO for top dogs to 30mO for lemons.
The HK packs I measured range from 7 to 15mO, per cell.
Use these milestones to program your OSD when to return and when to land.
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Old Aug 07, 2011, 05:00 PM
GilUriel
Israel
Joined Apr 2008
203 Posts
Quote:
Originally Posted by RENATOA View Post
If you care about your packs, you shuld not draw them completely.
A pack drawn under 20% every flight it's a half life pack, i.e. 50 flights instead 100.
20% is about 3.7-3.75V, 50% is 3.85-3.9V, under no load, so can be taken into account for gliders only ! If you fly something that is under permanent load - a copter - then lower the limit with 0.1V per cell per every 10A consumed. For example 18A quad, subtract 0.18V from per cell from above figures. This estimation is for a typical 10miliOhm average cell internal resistance. For an exact value you should measure your pack internal resistance, because it can range from 3mO for top dogs to 30mO for lemons.
The HK packs I measured range from 7 to 15mO, per cell.
Use these milestones to program your OSD when to return and when to land.
So, If under normal throttle management I'm at about 6 - 8 Amps, I should go down at 3.6V/Cell ? (that is .. 10.8V) that was suppose to be around 70% used ?

If so, I guess my pack is bad !
at 40% usage I'm in this voltage :-(
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Old Aug 09, 2011, 06:17 PM
Registered User
Poland
Joined Feb 2011
36 Posts
there is almost no difference in capacity between 3,5V/cell and 3V/cell (without load).

If you see 3,5V/cell under 3C load that means it's time for landing and 3,8V/cell for going back to base.
3C is usually enough for slow flat flying.
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Old Aug 09, 2011, 06:24 PM
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Joined Jul 2009
805 Posts
Always 11.1v!
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Old Aug 09, 2011, 09:41 PM
Post # 20 million
Kev.au's Avatar
Joined Aug 2009
2,646 Posts
A bit lower than i should .


FPV Funjet part 1 ARC 28-38-2.5 Dragonlink (9 min 38 sec)


Cheers, Kev.
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Old Aug 10, 2011, 01:05 AM
BEOWULF
North vancouver, B.C. Canada
Joined Apr 2008
18,832 Posts
Its more of a question of how long your video will last.

Give her heck and beat the crap out of our planes and bateries hehehe

For the cost of a plane and fpv set up batteries are relatively cheap, so saveing a plane and needing to land at the right time is important, voltage regulation is very very important.

I set my esc for no lvc off.

Its easy to figure out if you are getting low because of power loss and poorer climb.

once that happens basically the throttle stick is all the way up and you then need to slow amps draw way way down and land .

video will tell you when it is also time to land, low voltage shows in video and tells you when to stop useing throttle and land asap

voltage regulation is very very important

cost of batteries are small to the cost of the plane and enjoyment
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Old Aug 10, 2011, 02:17 PM
GilUriel
Israel
Joined Apr 2008
203 Posts
Quote:
Originally Posted by David22 View Post
Its more of a question of how long your video will last.

.....For the cost of a plane and fpv set up batteries are relatively cheap,
Hi David,

I find myself having one set of numbers on paper (say ... 5-6 Amps while flying so a- 3000mA battery should do half an hour - at least (considering throttle management on the good side and take off on the bad side .. )
And then, in the air - I'm not sure how much I can pull it down so after 15 minutes I'm beginning to think if it time to head home.
- Very frustrating :-(

Of coarse saving the plane worth more then a couple of minutes but usually I enjoy flying up high or extending my range of flying and for distance, the knowing when to turn back is the $1,000,000 question.

( As for video, I'm less afraid of loosing it because I'm counting on the RTH feature that does excellent work.
However - I think I may add a gps tracker just in case I'll have no video and the Autopilot will have no battery to run the motor ... any suggestions on that ? )


Gil
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