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Old Feb 28, 2007, 11:31 AM
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Oakridge, Oregon
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Question
max voltage per lipo cell

I wanted to know what is the max and min voltage per cell for lipos?
Am I right to assume 3 to 3.2 v per cell is the minimum?

-ryan
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Old Feb 28, 2007, 11:39 AM
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Mooresville, NC
Joined Dec 2004
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Li-Po voltage.....

The maximum is 4.2 V/cell, and this should be checked at times to make sure the charger remains in calibration. When the voltage reaches this point the charge switches from constant current to constant voltage mode, tapering down the current to a cutoff point (usually around 50 mA).

The minimum voltage of 3.0 V/cell is questionable. Usually you don't want to go even that low if you want your Li-Po's to last. They suggest to only discharge them to around 80% of capacity. The no load per cell voltage would be much higher then 3.0V. I would say around 3.5 to 3.75V no load after a 80% discharge.

Michael
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Old Feb 28, 2007, 11:40 AM
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Florence, Al
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Voltage in lipo cells can be broken down like this:

4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%

Jeff
www.CommonSenseRC.com
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Old Feb 28, 2007, 11:40 AM
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Haralson County GA. USA
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Max is 4.2 per cell. Minimum depends on if resting / no load or uinder load and if under load how greater of a load at which stage of the discharge / remaining capacity, temp.. etc.

http://www.rcgroups.com/forums/showp...68&postcount=1



Charles
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Old Feb 28, 2007, 02:28 PM
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Oakridge, Oregon
Joined Jul 2004
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Thanks for the replies. I had always seen different takes on when the minimum was from all the reading I had done. Now, I understand that I need to keep the lipo well above 3.2v and below 4.2v per cell for the longevity of the pack. Lipos for me sometimes seem a bit mysterious at times even after the countless hours of reading about them, but I think I am starting to get it.

Thanks for the help,
Ryan
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Old Nov 05, 2008, 05:37 PM
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Santa Clarita, CA
Joined Sep 2008
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Hi, Ryan;

I just read your question and thought you'd be interested to know that our new Proton 4 Digital Balancing Charger has a feature that figures this out for you. While charging, the Proton 4 scrolls through three different data screens, and the first gives you a "fuel" rating that calculates the pack's state of charge as a percentage (like Tram did above).

The Proton gives a lot of other useful info too, like voltages of individual cells and the mAh supplied to the pack during the charging cycle thus far. Check it out and let me know if you have any questions.

Scott Smith
Common Sense RC
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Old Mar 30, 2009, 08:51 AM
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Sweden, Skåne, Malmö Municipality
Joined May 2007
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Quote:
Originally Posted by Tram
Voltage in lipo cells can be broken down like this:

4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%

Jeff
www.CommonSenseRC.com
I've made an Excel document that should help calculate this percentage.
(Requires Office 2007)

If you don't have Office 2007, you can try it (without the nice graphic) in your browser here: http://sheet.zoho.com/view.do?url=ht...Calculator.xls
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Old Mar 30, 2009, 10:22 AM
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Or download the free OpenOffice program which opens all the MS stuff.
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Old Apr 12, 2009, 09:30 PM
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So, if I have a plane that uses a 5 cell NiMH (5 x 1.5 volts = 7.5 volts), can I replace the NiMH pack with a dual cell LiPo @ 2 x 4.2 = 8.4 volts w/o frying anything?

What about a 6 cell NiMH at 6 x 1.5 volts = 9 volts?

Interested in converting a NiMH plane to Lipo, but have never done this before, and am looking for a good starting point...

Thanks!
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Old Apr 12, 2009, 10:57 PM
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Florence, Al
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You should be able to get away with 2S and 3S packs respectively..

Jeff
www.CommonSenseRC.com
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Old Jun 11, 2009, 10:06 PM
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Joined Oct 2003
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Hey guys,
What would happen if one of the cells charged up to 4.3 v? Is it doom for the cell, as dropping below 3v?

Thanks,
Rob
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Old Jun 12, 2009, 07:13 AM
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Space Coast
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The important question is "Why did it charge up to 4.3V"?
If that was a non-balancing charge it meant that one of the other cells might have been at 4.1V. If that was the case, during discharge, that cell would be well below the others.

Not a doom situation but a charging problem that needs to be fixed.

What were the voltages of the other cells?
Was it a balancing charge?
Did you check all the cell voltages after flying?
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Old Jun 24, 2009, 11:02 PM
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Chilliwack, BC, Canada
Joined Aug 2003
28 Posts
Here's a slightly different battery question. NiMH pack, 5 cell, 1600 mAh in a full house glider (6 non digital servos working all the time, elevator mixed with flap, ailerons mixed with rudder, crow braking etc) draws up to 1,000 mAh on a watt meter on the ground with no aerodynamic loads. (can't put the watt meter in th fuse and fly it, not enough room!) Several flyers maintain that if I were to use a 2 cell LiPo of 1,000 mAh insted of the NiMH pack, it would last longer.
Logic says a miliamp is a milliamp regardless of it's source, so can anybody tell me who is right?
Which lasts longer- and if you can, why?

Cheers!
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Old Jun 25, 2009, 08:43 AM
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Space Coast
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2 cell lipo = 8.4V x 1.0Ah = 8.4WHr
5 cell NiMH = 6V x 1.6Ah = 9.6WHr

For what that's worth as I've never tried it.
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Last edited by hoppy; Jul 27, 2014 at 08:54 PM. Reason: Typo's
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Old Jun 25, 2009, 01:23 PM
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Chilliwack, BC, Canada
Joined Aug 2003
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Thanks Hoppy, I was kinda hoping that would be the answer- anything else smacks of 'magical' properties of one type of battery over another.
Next question: Voltage decay over time at constant load. Does anybody have a graph that shows what happens as the battery pack approaches exhaustion?
Just curious.

Cheers!
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