# [EVDL] Li-ion pack charging current rates



## EVDL List (Jul 27, 2007)

I request the help of those that are Li-ion experienced and or
knowledgeable. With over fifteen years of charging PbSO4 conversion EV
wet cell packs at low, medium, fast, and 150A DC very-fast, I have a 
large amount of experience. But charging li-ion, not so much.

I see all the newswires stating recharge times for the EVs and phevs
with li-ion packs, but want to know what is not being stated either
by the manufacturer web site or the media (which is only using copy
handed them from the manufacturer).
http://www.nissanusa.com/leaf-electric-car/theBasicsRange/index#/leaf-electric-car/theBasicsRange/index

I remember a GM exec was quoted saying to give the maximum life of a 
battery pack (infering NiMH or Li-ion chemistries), you have to set 
the amount of discharging and charging to not fully discharge nor
fully charge the pack. GM has always been very big on pack life 
preservation even way-way back to the EV1 days (long pack life =
less pack warranty costs?).
http://www.cleanfleetreport.com/electric-vehicles/batteries/nissan-leaf-battery-warranty/

http://gigaom.com/cleantech/electric-sedan-smackdown-nissan-leaf-vs-tesla-model-s-vs-coda-sedan/
So since industries of all kinds play copy-cat of their competitors,
post-2010 Production EVs likely have an over-sized pack capacity as
to keep the pack life up. If this is true, then the pack capacity does
not directly relate to how many kWh are designed to be used to
recharge that so-called 100 mile range EV.
http://www.mynissanleaf.com/viewtopic.php?f=31&t=3624

If I assume all 24kWh of the Leaf EV's pack capacity 'is' used when
a noob naively completely depletes their li-ion pack until it is flat
(It's Dead Jim) and then calculate the recharge time using their
wimpy on board 3.3kW charger, I would expect to see charging 
current curves begin to taper at various SOC (as per the BMS 
design).


I would like to see those charge current curves. Anyone know of 
any graphs I can view?


Please correct this example's assumptions:
SOC% charge-current rate%
00% 100%
60% 90%
70% 75%
80% 60%
90% 40%
95% 20%
100% 00%


What good are graphs?
Well, when a pack's charging current begins to taper because of the 
SOC, is important to EV Charging nuts (like me). We (the public) do 
not get to be privy to how fast the pack is actually recharging at 
various SOC.

When a charging current begins to taper means the difference in charge
times. Whether you are using a level1 or a level2 on a wimpy 3.3kW
charger, or a level2 on a real 6+kW charge that can utilize all the
AC power provided by an EVSE connected to a 240VAC 40A circuit 
(allows 32A to flow to the on-board EV Charger), each will have a
different charge time.

There is also the different charging times regaining a certain amount
of range depending on the charging current at different SOC. Charging
when the pack is nearly depleted will likely be much faster than when
charging above 80% SOC. This is important for me to know exactly when
it the right time to stop the now slowing charging rate by unplugging
and going to the next charge point. Waiting for a full charge when
it is not necessary is a complete waste of time on a trip. I can do
that when it is time for me to sleep.


The media has made a little competition out of the number of GM pish 
and Leaf EV sales. This rather irrelevant since other phev and EVs are
planned to be released. To me, this is similar to the way movies are 
planned for release. It would be bad for business if they all came out
at the same time.

If we ignore the hoopla between the phev and pish sales numbers, and 
focus on post-2010 Production EVs, the leaf is the only one you can 
get on a waiting list for. But that is about to change. The Ford Focus
Electric will be coming out before the end of 2011 and it will have 
charging advantages over the Leaf and GM pish.

The Focus EV will have a full 6+kW on-board charger, plus it will
have liquid pack cooling for its BMS to control. With proper cooling
a pack can be charged a little faster, than an air-cooled pack.

So, I request help in understanding li-ion pack charging current rates
at various SOC states. I look forward to your corrections and or 
additions to what I have stated. You may post it on the evdl for all
to understand or as a private email if you wish.

Thanks,
Bruce Parmenter
brucedp.150m.com

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## EVDL List (Jul 27, 2007)

Bruce,

You are likely to get a wide range of input on this one. I'll
summarize my experience and my current understanding here but you may
also want to look at my blog post after I had my LiFePO4 pack in
service for a year at:
http://2003gizmo.blogspot.com/2011/01/year-with-lifepo4-batteries-what-have=
-i.html

First and foremost it is important to note what Li chemistry is being
talked about. Some think it doesn't matter but looking at charge and
discharge curves for different Li types shows that they are not the
same and should not be treated the same. What I am talking about here
is specifically the LiFePO4 battery and I understand that the LiFeYPO4
batteries behave the same though I haven't any direct experience with
the latter. What ever you do, if you are moving to a Li battery pack I
recommend you spend some time with a bench PS and a cell or two to
learn the characteristics of the particular battery type you have. It
helped me get a practical understanding of my cells and dispelled some
myths about end of charge voltages.

My battery pack is made up of 40 TS-LFP100AHA cells made in November
2009. I have these in a 2p20s arrangement in my Gizmo. I charge them
with a Zivan NG1 set to an EOC (end of charge) voltage of 3.485vpc.
Through testing I found that there is less than 1% capacity between an
ending voltage of 3.45vpc and 4.00vpc when the EOC current is small,
0.01C or less. This is important because, like lead acid, there is a
charging procedure to follow. You don't just stop charging when a
particular terminal voltage is reached. Unlike lead acid, however, the
charge procedure is much simpler: basically it is charge at max
current until your target voltage is reached, hold that voltage until
the current tapers to the minimum charge current and turn off. What I
found is that the lower the ending current the lower the ending
voltage should be. Those who are charging their LiFePO4 cells to more
than 3.5-3.6vpc with currents in the 0.01C or lower range are over
charging their cells. This can be seen by playing around with the
cells on the bench before putting them in your car. Since my Zivan
tapers the current back to under 150mA (a measly 0.0075C for my pack)
at the end of charge I don't charge to as high of a voltage as I would
if the ending current were 0.01C or the TS recommended 0.015C.




> brucedp5 <[email protected]> wrote:
> 
> > I would like to see those charge current curves. Anyone know of
> > any graphs I can view?
> ...


----------



## EVDL List (Jul 27, 2007)

Thanks David that is what I was looking for.

Let's assume life is beautiful and the temperature of that cell on the bench
was optimal:
SOC% charge-current rate%
00% 100%
90% 100%
95% 100%
99% 100%
99.5% 96%
99.6% 80%
99.8% 60%
99.9% 25%
100% 0%

But what if the pack temperature was below 40 degrees or higher than 90
degrees F. 
The BMS would kick in to reducing the charging current to keep from
overheating 
the li-ion pack, right? 
What effects will pack temperature have on the charging current?

Also, I am interested when charging at a level2 rate where the source is
providing
240VAC 32A and factoring in a 97.5% PFC charger makes for a 7.5kW charging
rate.
A pack of individual cells would have some get hot sooner than others, thus
the BMS
would have senors detecting that and reduce the charging current when
charging at
the higher currents, right?

Am I right in assuming that there will be a difference in charging current
curves
when charging at a level1 rate, the 3.3kW wimpy rate because the Leaf has an 
underpowered charger, and the Level2 rate of a Escort Electric that has a
true 6+kW
on board charger that can used all 7.5kW being supplied to it?


{brucedp.150m.com}

-
On Sat, 14 May 2011 21:36 -0700, "David Nelson" <[email protected]>


> wrote:
> > My observations:
> > SOC% charge-current rate%
> > 00% 100%
> ...


----------



## EVDL List (Jul 27, 2007)

> But what if the pack temperature was below 40 degrees or higher than 90
> degrees F.
> The BMS would kick in to reducing the charging current to keep from
> overheating
> the li-ion pack, right?
> What effects will pack temperature have on the charging current?

I have observed that a colder pack takes a little longer at the end of
charge but this is a function of the battery apparently not rising in
voltage as quickly since my charger does not have a temperature probe
attached. I have not charged my pack at anything below 0=B0C. The few
times it was that cold it was above freezing by the time I drove my 3
mi home from work drawing 2-300A on acceleration and hill climbing.
This was enough to raise the temp of the pack above freezing. I have
heard that charging shouldn't be done below freezing but I have not
been able to find any data on why or what happens if they are charged
at extremely low temperatures.

At the higher temperatures the resistance lowers so heating isn't as
much of a problem. Since I can't charge at high rates I can only
speculate based on what I have seen on discharge. When I have done
prolonged discharges in the 130A range (0.65C) the pack temp rises
more when cold than when warm. On one run of nearly 45 miles drawing
~130A the battery temp went from 10.4=B0C to 20.1=B0C and on the return
trip it only rose to 25.4=B0F. On each leg about 45min of it was drawing
130A with the remaining 15 min at lower currents except for the final
mile home where the current was 250A climbing a hill. I would presume
that a monitoring system would reduce current when the pack temp was
getting high. From what I have read, 40=B0C (104=B0F) is a conservative
high temperature for LiFePO4 cells.

> Also, I am interested when charging at a level2 rate where the source is
> providing
> 240VAC 32A and factoring in a 97.5% PFC charger makes for a 7.5kW charging
> rate.
> A pack of individual cells would have some get hot sooner than others, th=
us
> the BMS
> would have senors detecting that and reduce the charging current when
> charging at
> the higher currents, right?

If the cells are closely matched they would all be close to the same
temperature throughout the charge. They really don't generate much
heat because of their high efficiency. Even pumping 32A into a 100Ah
pack is a lower rate than my discharge rate I referred to above. I
seem to recall someone charging a small string of cells at a high rate
and not seeing much temperature rise. Jack Rickard, maybe.

> Am I right in assuming that there will be a difference in charging current
> curves
> when charging at a level1 rate, the 3.3kW wimpy rate because the Leaf has=
an
> underpowered charger, and the Level2 rate of a Escort Electric that has a
> true 6+kW
> on board charger that can used all 7.5kW being supplied to it?

Watching my charger and also playing with a bench supply and a single
100Ah cell using different ending currents that would be right. I'm
extrapolating from low currents to the high currents and from
information I've gleaned over the past 3 years. If the ending current
for all charging levels was the same then the programming can be
identical. Charge at max rate until max voltage and hold until current
tapers to 0.015C or what ever. What will be different is that current
will begin to taper back slightly sooner for the higher rate chargers
because the terminal voltage will reach the max set point earlier. If
the charger properly does voltage measurement it can even ignore the
voltage drop between the charger and the battery pack if the ending
current is low since the voltage drop will diminish as the current
drops. The only difference is that current will taper back sooner. The
Zivan is quite consistent in hitting its target voltage. I only wish
it was dual voltage input so I could see how it does with different
input voltages. I've heard that some have had issues with some
chargers having different cutoff voltages depending on input voltage.


-- =

David D. Nelson
http://evalbum.com/1328

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## EVDL List (Jul 27, 2007)

>From what you have stated a Li-ion pack is far superior for slow all
the way up to fast charging.

But there is always that nagging term used in charging. That is a 
manufacturer would say it takes x_hours to fully charge to 80% SOC,
whether talking about level2 (7.5kW) charging, or the much higher 
level3 charging currents. 

Any ideas as to why the time to charge to 80% rating is given?
According to your chart, I should be able to charge to 99%
instead worrying about what happens after 80%. 
What are your thoughts on that.

{brucedp.150m.com}

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## EVDL List (Jul 27, 2007)

> brucedp5 wrote:
> >
> > The Focus EV will have a full 6+kW on-board charger, plus it will
> > have liquid pack cooling for its BMS to control. With proper cooling
> ...


----------



## EVDL List (Jul 27, 2007)

Bruce,

There have been graphs published about Li recharging here,
links to manufacturer data and recommended charging profiles
if I remember correctly, something like constant current C/2
max up to max voltage point, for example 3.7V and keep at that
voltage until current drops to insignificant.
I know of NiMH that is held by the Prius as much as possible
between about 30 and 85% SoC where it has very high efficiency
and the lowest impact on cycle life.
I presume that for Lithium it also is the trick to stay on
the flat portion of the (dis-)charge curve to avoid the
side-effects occurring during full charge and discharge, so
cycling them between 30 and 90% for example will avoid that
a loss of capacity in one cell will cause grave problems and
rapid deterioration, since it needs to lose almost 30% before
you start hitting its bottom, assuming that you can keep the
cells balanced. Staying away from the top will also avoid the
heat-up and other side-effects there.
Yes, you need a bigger pack to do it, but not only the lower
(dis-)charge rates will make the pack live longer,
also by staying away from the extreme areas will be cells
be more efficient and live longer (more Ah out of the cell)
regardless of the number of cycles.
That is the theory anyway, unfortunately I can't find any
references right now...

Hope this helps,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of brucedp5
Sent: Saturday, May 14, 2011 7:57 PM
To: [email protected]
Subject: [EVDL] Li-ion pack charging current rates


I request the help of those that are Li-ion experienced and or
knowledgeable. With over fifteen years of charging PbSO4 conversion EV
wet cell packs at low, medium, fast, and 150A DC very-fast, I have a
large amount of experience. But charging li-ion, not so much.

I see all the newswires stating recharge times for the EVs and phevs
with li-ion packs, but want to know what is not being stated either by
the manufacturer web site or the media (which is only using copy handed
them from the manufacturer).
http://www.nissanusa.com/leaf-electric-car/theBasicsRange/index#/leaf-el
ectric-car/theBasicsRange/index

I remember a GM exec was quoted saying to give the maximum life of a
battery pack (infering NiMH or Li-ion chemistries), you have to set the
amount of discharging and charging to not fully discharge nor fully
charge the pack. GM has always been very big on pack life preservation
even way-way back to the EV1 days (long pack life = less pack warranty
costs?).
http://www.cleanfleetreport.com/electric-vehicles/batteries/nissan-leaf-
battery-warranty/

http://gigaom.com/cleantech/electric-sedan-smackdown-nissan-leaf-vs-tesl
a-model-s-vs-coda-sedan/
So since industries of all kinds play copy-cat of their competitors,
post-2010 Production EVs likely have an over-sized pack capacity as to
keep the pack life up. If this is true, then the pack capacity does not
directly relate to how many kWh are designed to be used to recharge that
so-called 100 mile range EV.
http://www.mynissanleaf.com/viewtopic.php?f=31&t=3624

If I assume all 24kWh of the Leaf EV's pack capacity 'is' used when a
noob naively completely depletes their li-ion pack until it is flat
(It's Dead Jim) and then calculate the recharge time using their wimpy
on board 3.3kW charger, I would expect to see charging current curves
begin to taper at various SOC (as per the BMS design).


I would like to see those charge current curves. Anyone know of any
graphs I can view?


Please correct this example's assumptions:
SOC% charge-current rate%
00% 100%
60% 90%
70% 75%
80% 60%
90% 40%
95% 20%
100% 00%


What good are graphs?
Well, when a pack's charging current begins to taper because of the 
SOC, is important to EV Charging nuts (like me). We (the public) do 
not get to be privy to how fast the pack is actually recharging at 
various SOC.

When a charging current begins to taper means the difference in charge
times. Whether you are using a level1 or a level2 on a wimpy 3.3kW
charger, or a level2 on a real 6+kW charge that can utilize all the
AC power provided by an EVSE connected to a 240VAC 40A circuit 
(allows 32A to flow to the on-board EV Charger), each will have a
different charge time.

There is also the different charging times regaining a certain amount
of range depending on the charging current at different SOC. Charging
when the pack is nearly depleted will likely be much faster than when
charging above 80% SOC. This is important for me to know exactly when
it the right time to stop the now slowing charging rate by unplugging
and going to the next charge point. Waiting for a full charge when
it is not necessary is a complete waste of time on a trip. I can do
that when it is time for me to sleep.


The media has made a little competition out of the number of GM pish 
and Leaf EV sales. This rather irrelevant since other phev and EVs are
planned to be released. To me, this is similar to the way movies are 
planned for release. It would be bad for business if they all came out
at the same time.

If we ignore the hoopla between the phev and pish sales numbers, and 
focus on post-2010 Production EVs, the leaf is the only one you can 
get on a waiting list for. But that is about to change. The Ford Focus
Electric will be coming out before the end of 2011 and it will have 
charging advantages over the Leaf and GM pish.

The Focus EV will have a full 6+kW on-board charger, plus it will
have liquid pack cooling for its BMS to control. With proper cooling
a pack can be charged a little faster, than an air-cooled pack.

So, I request help in understanding li-ion pack charging current rates
at various SOC states. I look forward to your corrections and or 
additions to what I have stated. You may post it on the evdl for all
to understand or as a private email if you wish.

Thanks,
Bruce Parmenter
brucedp.150m.com

--
View this message in context:
http://electric-vehicle-discussion-list.413529.n4.nabble.com/Li-ion-pack
-charging-current-rates-tp3523681p3523681.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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## EVDL List (Jul 27, 2007)

Thank you Cor, 

That gives an insight I was also seeking.
I understand and will read up on Li-ion manufacturer's data.


But if off the cuff I use your presumed %'s as what a post-2010 
Production EV is designed to use of a li-ion battery pack's capacity,
then that could mean of the Leaf's stated 24kWh rating, only 
(30%-90%=) 60% of the li-ion pack's capacity is made available for use
(14.4kWhs). Or 24kWhs is the 60% of the usable capacity and the actual 
li-ion pack capacity is 40kWHs.

That might explain any discrepancy of how much electric power is going
into recharging a pack vs the 'stated' 24kWh pack capacity. To me, 
that might be like the manufacturer is saying we have a nice big box,
yet in reality they are only making available 60% of it ... interesting.


So, a new Leaf EV owner could come plug into a public EV Charging spot
and use the extra time to charge to 90% before unplugging and going to
the next planned charge point. This is quite different (and better) 
than my experience with a PbSO4 wet cell pack where stopping the 
charge to go on to the next charging spot at 60-80% SOC when the 
charging current begins to taper is preferable.


There was a long time EAA member who would help set up the charging
at local EAA EVents. He would also measure the AC power being used 
by various EVs as well as what power factor correction rating their 
on-board chargers had. Robert Wheeler not too long ago, also 
past away. Chuck Hursch knew him quite well. While some non-techie EAA
members knew-not what Bob was doing, some like Chuck and I knew where
Bob was going with his measurements, and the other cool things he did.

In that spirit, perhaps with post-2010 Production EVs, there is a way
to measure the AC power being drawn while charging and compare it to 
the data the EV is providing, then build a time-line chart to better 
understand what is going on during the recharge cycle.

I do not know if the Leaf EV or the Escort EV will a similar data port
that some of the pre-2010 Production EVs had (EV1, etc.), but there 
must be a way to gain access as that charging status data is sent out 
on the phone apps that tell the post-2010 Production EV drivers the 
SOC of their EV.

Sounds like another future project to put in the queue.



{brucedp.150m.com}




-
On Sun, 15 May 2011 21:51 -0700, "Cor van de Water"


> <[email protected]> wrote:
> ...
> > I know of NiMH that is held by the Prius as much as possible
> > between about 30 and 85% SoC where it has very high efficiency
> ...


----------



## EVDL List (Jul 27, 2007)

Jukka,

I was hoping you would add your experience to this thread. I have some
questions inserted below. I'm particularly referring to LiFePO4 cells
such as TS and CALB cells.

2011/5/16 Jukka J=E4rvinen <[email protected]>:
> I'd say at this point that there is just about as many ways to charge
> Lithium cells as there are different variations of them. Thousands.
>
> Electrolyte dissolves when high voltages are maintained. Longer you
> stay up there, faster it breaks down.

I used to charge my pack up to 4.00V but found that there was very
little energy between 3.45V and 4.00V so I now only charge to 3.485V
with a very low ending current. What voltage are you finding is best
to stop at when ending charge current is very low?

> Heat increases the already existing death rate of the Lithium cell.
> Liquid cooling is not an answer. Engineers who think so are fooling
> them selves. Correct sizing of the pack is only feasible solution (and
> it's service free too).

Is running the cells below 10=B0C hard on them? In other words, does
working them cold and below freezing shorten their life or does the
cold not hurt them?

> Time is one factor but how far you go over certain limits add another
> factor to the equation.
>
> This is why I've been pursuing the learning BMS design for past 10
> years. And it seems to work OK. Prototypes have been working as
> expected on daily use and beta-users have been more than happy. I'd
> say this is another type of EV grin I'm getting every time I even
> think about it 
>
> Tracking the cell over it's formation period (2-3 years, 300-400
> cycles for TS-type LiFePO4) will tell you how to balance the cells to
> gain maximum life. Staring the voltages will do no good on long term.

What kind of care gives the longest life during this formation period.
Also, I'm not sure what you mean by "Staring the voltages..."

> At certain point of life (say 3500 cycles, 6 years) you can do things
> to gain more life out of your cells. It of course depends greatly what
> kind of life you had on the cells in overall. You have set certain
> lifetime on the cells while formatting them in early days. There's not
> much you can do to reverse that effect.
>
> At the end of the life of the pack will be the hardest to handle
> unless you can set the death rate on the cells at the similar curve.

Do you mean that they will tend to lose capacity at varying rates and
also that a given SOC will be at different open circuit voltages for
different cells?

> You can alter the death rate by yanking the cells ovar certain
> conditions when necessary. Pulling to 4,35V on a TS cell will alter
> the behavior of the cell. What other conditions are existing at the
> time have an effect too.

What does going to 4.35V do to the cell? I would think that it will
accelerate its death.

> Summa summarum: More we've studied this more we realize we've just
> scratched the surface.
>
> Then we add to the mix the never ending development of the cells and
> chemistries inside... It's like never ending fun on a roller coaster
> 
>
> If my wish would come true every Lithium EV would have accurate
> datalogger on them and we would have one juicy cloud to dump the logs.
> Cloudy dataminers heaven...

I'm sure that my open circuit voltage readings immediately at the end
of charge doesn't provide much information but it is interesting to
note how things change over time. I have a 200Ah pack and used to
recharge each day even if I only used less than 10% capacity. Now I
usually go longer before recharging unless I know I will be pushing
the range limits the following day. I also don't start charging until
I go to bed so that the pack doesn't sit at full capacity for very
long.

For the past 10 months I haven't been "top balancing" and I'm not
seeing much change in the voltages at the end of charge. I do not,
however, have any data on my pack under load. What have you found
about pack balance and how it changes over the life of a pack?

Finally, I seem to recall you doing some "freezer" testing of cells.
Have you cycled a pack of cells with some in the freezer and some not
and tracked how well the pack stayed together with no balancing
equipment attached? What happened?

Thanks,

-- =

David D. Nelson
http://evalbum.com/1328

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## EVDL List (Jul 27, 2007)

> David Nelson wrote:
> 
> >> Heat increases the already existing death rate of the Lithium cell.
> >> Liquid cooling is not an answer. Engineers who think so are fooling
> ...


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## EVDL List (Jul 27, 2007)

I thank everyone who posted online and send me email on this thread.
I believe I have been educated to know what I was after: that a the 
new battery chemistries (i.e. Li-ion and NiMH) can be much more 
fully charged (95% and 90%) without any serious tapering of the 
charging current, as with a PbSO4 pack. This info has greatly 
improved my understanding of the faster level2 charging use by 
knowing when to unplug and get back on the road with a post-2010
Production EV.

Anymore posts on this thread is icing on the cake for me. 
Thanks again.


{brucedp.150m.com}


-- 
http://www.fastmail.fm - Send your email first class

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## EVDL List (Jul 27, 2007)

Bruce,

Here is a graph of the charge curves of LiFePO4 cells being charged at
1C until full: http://1.bp.blogspot.com/_i_c2BM_uBw4/S88NG8AY82I/AAAAAAAABXQ/bj_KhONGd8w/s1600/+0416chargecurve2.jpg

As you can see the voltage rises quite significantly before the 80%SOC
point which shows why it probably wouldn't be a good idea to keep a 1C
charge rate beyond 80%SOC. For my cells I would start tapering back
the charge current at about the 50%SOC rate and not let the voltage
get above 3.5vpc. This is for LiFePO4 cells, not other types. As long
as the ending current is low 3.5vpc will fill the cells to 99-99.5%SOC
based on my bench tests.

-- 
David D. Nelson
http://evalbum.com/1328

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