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Author Topic: Acceptable full charge cell voltage?  (Read 715 times)

Offline John Rist

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Acceptable full charge cell voltage?
« on: May 07, 2013, 07:03:39 AM »
What is considered to be an acceptable range of voltages for a fully charged LiPo cell?  I have 4 - 4 cell battries.

The voltages measured as follows:
Bat #1:  4.14, 4.16, 4.16, 4.15
Bat #2:  4.14, 4.15, 4.16, 4.16
Bat #3:  4.16, 4.17, 4.17, 4.17
Bat #4:  4.16, 4.16, 4.17, 4.17

Voltages were measured with a 4 digit VM set at the 20V range.  Is the above an acceptable range for fully charged balanced batteries?
 ???
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Offline John Cralley

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Re: Acceptable full charge cell voltage?
« Reply #1 on: May 07, 2013, 11:05:19 AM »
John,

Tell us more about your charging process. What charger are you using and do you use a separate balancer? How long has it been since these were charged? LiPos do do some self discharge all be it not all that fast.

I don't see this as a problem. Nominally you can charge a LiPo cell to 4.20 volts but I just charged a couple of batteries on my CellPro charger and they came out 4.19, 4.19, 4.19 & 4.18 (4 cell) for one and the other was 4.20 across the board. Your cells were all within .01 -.02 volt of each other and I believe that is probably good enough. The instructions with one of my chargers said that since the final balancing takes a long time you can stop the charger short of that if the cells show balanced but not fully charged.

Others more knowledgeable will correct me if I have it wrong.  ;D
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Offline Tim Wescott

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Re: Acceptable full charge cell voltage?
« Reply #2 on: May 07, 2013, 11:13:18 AM »
John, that comes pretty close to what I know.

Some LiPo cell (cells, not model airplane packs) data sheets say that you can charge to 4.3V, but I haven't seen one that goes below 4.2.

And just about anything to do with batteries is a bit imprecise, unless you're talking about electrochemical reference cells.
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Offline William DeMauro

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Re: Acceptable full charge cell voltage?
« Reply #3 on: May 07, 2013, 11:34:21 AM »
Mine usually come out 4.18-4.20 but that can vary depending on the charger and depending on the pack. your cells are all in an acceptable range. What charger do you have and what brand and size pack do you have.
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Offline Dean Pappas

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Re: Acceptable full charge cell voltage?
« Reply #4 on: May 09, 2013, 12:18:12 PM »
Looks just fine to me, John.
You aren't losing any capacity at 4.17 or 4.18V per cell, and a 20 mV difference within a pack is all you would really expect.
More precision would cost more money, and buy you nothing in terms of performance.
Oh yes, that 20 mV or so precision is most likely the reason the circuit designer has the charger targetting maybe 4.18V, and there is some slight droop shortly after coming off the charger.
The charger manufacturers do not want to exceed 4.200V. Destruction happens slightly above that coltage, and that destruction threshhold is temperature dependant!
A little margin keeps you safe.

Regards,
 Dean
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Offline Howard Rush

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Re: Acceptable full charge cell voltage?
« Reply #5 on: May 09, 2013, 02:01:21 PM »
My current Thunder Power charger firmware has a constant-voltage stage where it holds 4.2V/cell for a long time.  Then it complains that battery voltage is too high.  I think I'd better update the firmware. 
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Offline William DeMauro

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Re: Acceptable full charge cell voltage?
« Reply #6 on: May 09, 2013, 02:45:59 PM »
Howard,
I'm not sure which TP charger you have but there are some lengthy threads over on RC Groups on some thunder power chargers having issues and you are right firmware upgrades usually take care of them.
William
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Offline Howard Rush

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Re: Acceptable full charge cell voltage?
« Reply #7 on: May 11, 2013, 02:16:21 AM »
I have an 820CD.  Fortunately, I waited until the end of the 2012 season to update the firmware to V4.3, which caused the "Battery voltage too high" messages.  After I saw your note, I found V4.34 on Thunder Power's Web site and loaded it onto my charger.  The charger has behaved well for the two days since then. Thanks for the tip.
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