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General Category => General Discussion => Topic started by: skadamo on October 19, 2009, 10:56:03 PM

Title: Analysis of Blue Sky LiFePo4 Batteries Charge Curve
Post by: skadamo on October 19, 2009, 10:56:03 PM

Figured Guity and others might be interested in this analysis of Blue Sky LiFePo4 cell voltage levels during charging...

http://jackrickard.blogspot.com/2009/10/sky-energys-blue-sky-cell-data.html (http://jackrickard.blogspot.com/2009/10/sky-energys-blue-sky-cell-data.html)

(http://4.bp.blogspot.com/_i_c2BM_uBw4/Ss1zzsFCJnI/AAAAAAAABLQ/aBxcfYXgdks/s1600/blueskychargecurve.jpg)

Title: Re: Analysis of Blue Sky LiFePo4 Batteries Charge Curve
Post by: guity on October 20, 2009, 01:23:54 AM

Wow that looks kind of strange.  I'm interpreting this as the following: when you apply a 75 amp charge to these Blue Sky batteries for 80 minutes, they will be charged to 3.76 volts per cell.  But if you apply that same charge for 85 minutes, they will be at roughly 3.4 volts per cell.  What happens to bring the voltage down in those extra 5 minutes??

Title: Re: Analysis of Blue Sky LiFePo4 Batteries Charge Curve
Post by: Bogan on October 20, 2009, 03:29:05 AM

that what i see too, and shouldnt it be just a line graph (bit picky there) maybe they took it off the charger at 85min, or a few cells self detsructed

Title: Re: Analysis of Blue Sky LiFePo4 Batteries Charge Curve
Post by: skadamo on October 20, 2009, 04:07:49 AM

That drop is where he turned off the charger.

Title: Re: Analysis of Blue Sky LiFePo4 Batteries Charge Curve
Post by: guity on October 20, 2009, 06:09:28 AM

Ah, OK, so maybe that is the same as the famous settling in I keep reading about with Thundersky batteries, where no matter even if you charge them up to their maximum of 4.2 volts, they still drop back down to a working level of 3.4 volts.  So at the 85 minute mark, has the guy only turned off the charger, or has he put the batteries to work a little bit?

Title: Re: Analysis of Blue Sky LiFePo4 Batteries Charge Curve
Post by: skadamo on October 20, 2009, 06:38:16 PM

Here is his explanation...

Quote

So in this graph, after shutting off the power supply, I simply continued to take voltage readings every five minutes as I had been doing. As you can see, the voltage dropped in the first five minutes to 3.3853 vdc. Over the next five, it kept falling to 3.3724. But by 15 minutes it had pretty much stabilized at 3.3668 vdc. So the "nominal" voltage of a fully charged Blue Sky would seem to be about 3.36 vdc.