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Voltages when charging
#1
Hey guys, I am charging a 16P strip of cells and it has been over 4 hours. Currently it says it's charging at 0.4A at 4.19V 

Upon testing individual cells most of them register at 4.21V but there are a few stragglers registering at 3.99V and some 4.17V 

Is this normal behavior? I don't want to overcharge any of the cells. The imax b6 will turn off when it's done correct?
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#2
(01-16-2017, 01:15 AM)cstanley Wrote: Hey guys, I am charging a 16P strip of cells and it has been over 4 hours. Currently it says it's charging at 0.4A at 4.19V 

Upon testing individual cells most of them register at 4.21V but there are a few stragglers registering at 3.99V and some 4.17V 

Is this normal behavior? I don't want to overcharge any of the cells. The imax b6 will turn off when it's done correct?

The important thing to remember when charging any cell is that its current as well as voltage that needs to be considered.
Fully charged is 4.2 @ 50mAh.  You should really stop when its at about 0.8A 4.2. for the 16 cells combined

Pluck any stranglers and charge them individually and segregate them, you might find they are wasting energy as heat.
It may just be that some were really flat and havnt caught up yet, at 3.9v though they should be accepting plenty of current.

The B6 will turn off when it detects 4.2 @ 50mAh, which with 16p means overcharged.  Keep that in mind.
I charge 12p with my b6 clone and turn it off when it gets to around 0.5A

I also insert my 12 cells and let them sit for a few hours to parallel balance out a bit.
Maybe try doing this for a while and see what the voltage for all 16 slumps down to.


kind regards
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#3
(01-16-2017, 01:34 AM)3nergE Wrote: ...
I also insert my 12 cells and let them sit for a few hours to parallel balance out a bit.
Maybe try doing this for a while and see what the voltage for all 16 slumps down to.

kind regards
Thanks for the information! This is extremely helpful. Looks like I have them at 4.21V at 25mAh which is slightly overcharged. Should I discharge these some before letting them sit a few hours? 

I just isolated 3 stragglers out of 16 one registers now 3.99V another at 4.17V and another at 4.13V. I just started charging the 3.99V and it's currently eating 0.5A at 4.06V

Thanks again 3nergE you have tons of helpful information to share!

Edit:
They have been sitting for a few hours, and some have dropped from 4.21V down to 4.18V - should this concern me? Some have stayed at 4.21V
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#4
if nothing else is connected, leave them another day, if the voltage keeps dropping you have a self discharging cell in the pack somewhere, or some flux conducting where it shouldn't

To find your leak, use a multimeter that can measure down to mV, and measure the voltage across the fuse, it should be 0 unless current is being drawn,

Its not too uncommon for the chemistry to reduce in voltage slightly after cooling down and balancing internally
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#5
Do you have your terminals on the same end of the battery pack? Or do you have it configured such that there is one terminal on each end and the current goes through the whole pack? If they are both on the same end, that could explain cells closer to the terminals as having a slightly higher voltage since it will be the path of least resistance. Of course, after leaving it sit for a while, it should balance itself out though.
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#6
(01-16-2017, 01:54 AM)cstanley Wrote: They have been sitting for a few hours, and some have dropped from 4.21V down to 4.18V - should this concern me? Some have stayed at 4.21V

No concern at all.

A fully charged cell will slowly drift back towards 4v, dont keep charging a cell that got to 4.2 and drifts down.
Similarly a fully discharged cell will drift back toward 3.5-3.6 depending on the discharge C rate.

A cell charged at a high rate (1000mAh for instance) will drift down faster, whereas a cell charged at 200mAh will stay high for longer.

A cell that is self discharging will barely be noticeable, discharge cells and leave them in order to see self discharge.
A cell thats sitting at 3.5-3.6v with only a few percent capacity will plummet very fast and obviously below 3v if its a bad one.

Similarly a cell thats self discharging will get warm during charge, as bad chemistry uses the energy and creates heat at a proportional rate to both charge and self discharge rate.

(01-16-2017, 01:41 PM)mike Wrote: Do you have your terminals on the same end of the battery pack? Or do you have it configured such that there is one terminal on each end and the current goes through the whole pack? If they are both on the same end, that could explain cells closer to the terminals as having a slightly higher voltage since it will be the path of least resistance. Of course, after leaving it sit for a while, it should balance itself out though.

This is a good point, if you have 4 cradles, put the positive at the top left of the top cradle and the negative at the bottom right of the bottom cradle.

I totally missed making this suggestion mike +1
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#7
Is this an entry or just a moved post ?
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#8
(01-18-2017, 10:09 PM)hbpowerwall Wrote: Is this an entry or just a moved post ?

Entry for what?
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#9
(01-16-2017, 01:34 AM)3nergE Wrote: Fully charged is 4.2 @ 50mAh.

I'm confused. Do you really mean 50 milliamps, not milliamp hours?
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