# [EVDL] Li-Ion balancing, was: conversion reliability



## EVDL List (Jul 27, 2007)

Mike,
This is very important experience data,
thanks for posting this!
Contrary to other claims (granted, for other Li-ion chemistry)
there is a need for balancing, if your experience shows that
one cell may take 20Ah to balance against another cell in
your pack...

55 miles at 250Wh/mi is 13750Wh.
On your 162V nom pack that means at least 85Ah
or at least 85% DoD.
That is indeed uncomfortably low,
especially if you are not sure that
your cells are balanced.

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 Mike Nickerson
Sent: Wednesday, February 16, 2011 11:04 AM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] conversion reliability

I can charge at work, so I'm only using about 50% each way. I wouldn't
be comfortable with what it would do to the batteries round trip.

I drove 55 miles on the pack once. That was about 3-4 miles too many.
I couldn't hear the alarm buzzer from the miniBMS at highway speed so I
noticed the batteries were in distress when I got to my driveway. By
then 2 cells were at 0 volts. I charged them up right away, babied them
during a slow charge and kept close track of the temperature of the
cells. They seemed to recover OK, but I'm still watching them.

I also learned that my cells weren't as balanced as I previously
thought. I had a few other cells that were about 20% lower than the top
cells. That's when I went out and bought the top-up charger in my last
post. That charger does a really nice job of pointing out how low your
cells are. Kind of makes you gulp when it puts in 20Ah just after the
main charging cycle finishes. On a full cell, it measures less than 1Ah
it tried to put in.

I also have found recently that my front disk brakes are dragging.
Fixing that should help range a little. I'm using about 250 Wh/mile
right now.
I'm hoping to get it down to 200-225 Wh/mile when I'm done. With a
well-balanced pack and the car well adjusted, I think I may make 60
mile+ range, but I'm still glad I can charge at work. I also have a
much louder buzzer now, and the alarm circuit is now wired into the oil
pressure idiot light on the dash too.

That energy usage is on a commute that is a combination of highway
(about 55
mph) and a little stop-go traffic as I get into town. However, I've
been driving it for 18 years now, so I know where the speed limit
changes are and when the lights are likely to change. I coast a lot. I
routinely get 35 mpg on an ICE that is EPA rated for 27 mpg. That
definitely makes my range numbers on the high side for variable traffic
and other drivers.

Mike

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of corbin dunn
Sent: Tuesday, February 15, 2011 5:31 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] conversion reliability

Hey Mike,



> Mike Nickerson wrote:
> 
> > I've had my Honda del Sol conversion about 6 months. I drove it very
> > solidly every day for about 3 months before starting some re-wiring
> ...


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## EVDL List (Jul 27, 2007)

That is right. Then I will know that because my BMS boards will give a
warning. But if that point never comes I will not hear from my BMS and
know I could have been fine without it. If I stay above 30% SOC and
below 100% SOC small cell variations won't matter.

In any case I'm not convinced yet that a pack of non-abused cells
needs to be balanced every charge. I believe any balancing can be done
every year or so. Understand my data is for cells in a single battery
box so I don't have data on cells at grossly different temperatures.



> Cor van de Water <[email protected]> wrote:
> > David,
> >
> > If you never balance your cells then
> ...


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## EVDL List (Jul 27, 2007)

I agree that balancing every charge is not necessary,
but this is depending on the way that balancing is done.
As you read from the OP, his setup was not allowing
the BMS to fully balance his cells due to limitation
in the charger (not cutting back when the first BMS
started shunting) so he got only a few minutes of
balanging in each recharge.
This way of gradually nudging the cells closer each
charge will need every opportunity to work and slowly
get the cells closer and closer.
If your charger is smarter or your system designed in
such a way that the BMS can balance all cells
completely in one go (even if *you* are that BMS)
then you need only a balance once in a while,
also depending whether you have any parasitic
loads on each cell, such as monitoring boards,
which can introduce a varying consumption and
thus help Unbalance cells....
=

Regards,

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 Behal=
f Of David Nelson
Sent: Thursday, February 17, 2011 1:09 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Li-Ion balancing, was: conversion reliability

That is right. Then I will know that because my BMS boards will give a warn=
ing. But if that point never comes I will not hear from my BMS and know I c=
ould have been fine without it. If I stay above 30% SOC and below 100% SOC =
small cell variations won't matter.

In any case I'm not convinced yet that a pack of non-abused cells needs to =
be balanced every charge. I believe any balancing can be done every year or=
so. Understand my data is for cells in a single battery box so I don't hav=
e data on cells at grossly different temperatures.



> Cor van de Water <[email protected]> wrote:
> > David,
> >
> > If you never balance your cells then
> ...


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## EVDL List (Jul 27, 2007)

>
>
>You don't need to balance every charge. You only need to balance when
>the small differences have gotten large over many charge/discharge cycles.

Depends on the brand of cells and the specific chemistry.

Some cells have a soft voltage curve that tapers gently. The 
impedance also might taper nicely with SOC. Balance is not such a big 
deal with these sort of "sloppy" cells.

Other cells "drop off a cliff" and have very very flat voltage curves 
and invarying impedace over nearly the entire range of SOC. If you 
don't balance these cells every single charge cycle, you are going to 
make problems for yourself.

Bill D. 

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## EVDL List (Jul 27, 2007)

> Bill Dube <[email protected]> wrote:
> >
> >>
> >>
> ...


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## EVDL List (Jul 27, 2007)

> David wrote:
> >For example, I charge my pack to 3.485vpc and have stayed well above
> 30%SOC on all but about 3 occasions. The most I pulled out of the 200Ah
> pack was 179.6Ah and with a 6A load on the pack the lowest cell was at
> ...


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## EVDL List (Jul 27, 2007)

... and certainly, this is one very useful facet of a full-on BMMS - 
the jury is still out, though, on just how long it will take for the 
imbalance to become as significant as 10% and, if it takes 10 years of 
'normal' driving, do we really care? Then, it's going to vary from 
one make of cell to another, and possibly from one batch of cells to 
another. This is why I would rather have the knowledge that a full 
BMMS imparts. I can easily see, however, that most people would not 
want to bother - with the added cost and complexity (and potential 
failures) or the information.

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk



> Lee Hart wrote:
> 
> > On 2/17/2011 1:39 AM, David Nelson wrote:
> >> I'm not convinced yet that a pack of non-abused cells
> ...


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## EVDL List (Jul 27, 2007)

"You will never find out what their cycle life is, for their calendar life
will get them first..." 
What data are you basing this statement on?
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## EVDL List (Jul 27, 2007)

Likely this:

The batteries should be able to last about 10 years for their calendar life.
27.5 full charges in 5 months is 5.5 full charges a month. 10 years * 12
months * 5.5 charges a month is 660 full charges. Lithium cells tend to be
rated for something like 3000 full charges. So the calendar life will expire
well before the # of charges gets anywhere close.



> tomw <[email protected]> wrote:
> 
> >
> > "You will never find out what their cycle life is, for their calendar life
> ...


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## EVDL List (Jul 27, 2007)

Bottom line... they have not been around for 10 years, so they may 
only last 5 or maybe 30. Time will tell.



> Collin Kidder wrote:
> 
> > Likely this:
> >
> ...


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## EVDL List (Jul 27, 2007)

"Likely this:The batteries should be able to last about 10 years for their
calendar life."

That's not data. It's a statement. What is it based on? 
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## EVDL List (Jul 27, 2007)

> tomw wrote:
> >
> > "Likely this:The batteries should be able to last about 10 years for their
> > calendar life."
> ...


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## EVDL List (Jul 27, 2007)

Tom,

What does the datasheet of your batteries say? 


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 tomw
Sent: Saturday, February 19, 2011 7:23 AM
To: [email protected]
Subject: Re: [EVDL] Li-Ion balancing, was: conversion reliability


"Likely this:The batteries should be able to last about 10 years for
their calendar life."

That's not data. It's a statement. What is it based on? 
--
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reliability-tp3305129p3313818.html
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Nabble.com.

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## EVDL List (Jul 27, 2007)

"Tom,

What does the datasheet of your batteries say?"

It only had resistance of each cell. No capacity numbers, no statement on
shelf life - or anything else. Purchased from evcomponents. I think CALB
(at least calib, CALB's U.S. office) provides much more info now. One
person said he received a 20-some page "manual" with his cells as well as
data on resistance and capacity. They also provided cells matched to < 1%
range in capacity.
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