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Discussion Starter · #1 ·
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
> projects that have had it out of commission for the last 3 months.
> Those weren't driven by reliability problems so much as the new
> owner's desire to tinker 8^). I got a little over 2000 miles during 3

> months. My commute is 46 miles round-trip, so I'll put the miles on
> pretty quickly once I'm back on the road again. Should be within the
> next
couple of weeks.

I see you have 45 100ah TS cells. What is your SOC% after the 46 mile
round trip commute?

--corbin

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Discussion Starter · #2 ·
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
> I am afraid that you will find out the answer
> to your assumption on the occasion that you
> have driven too far for the lower cells,
> then you will know how much unbalance there was.
> The curve for LiFePO4 is so flat that you have
> no clue if a cell is sitting at 90% or 60% or 30%
> until it suddenly drops like a brick.
> You can get all cells very well balanced by
> either top balancing (charging until a fixed
> voltage that is at least slightly above the knee
> for example 3.6V (note: you must measure *each*
> cell, do not rely on charging the whole string
> to N * 3.6V as then one cell may be at 4.5V while
> most are still hovering around 3.4V!)
> or by bottom balancing, discharging each to a
> fixed voltage - for example 2.5V
>
> 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 Beh=
alf Of David Nelson
> Sent: Thursday, February 17, 2011 8:49 AM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] Li-Ion balancing, was: conversion reliability
>
> I think a couple of other questions that need to be asked is what voltage=
were they being charged to and how far were they discharged?
> We'll see over time but so far I'm not seeing a need to balance my pack b=
ased on the data I've collected on it for the past 8 months. The difference=
might be that I'm only charging to 3.485Vpc and not to the stratosphere of=
voltages.
>
> Maybe the reality with LiFePO4 cells is more one of if you charge them to=
more than 3.6vpc they must be balanced at end of charge and if you stay be=
low that, say 3.5vpc, then they don't have to be balanced or that they only=
need to be balanced once every 1-5 years as a standard maintenance procedu=
re.
>
> On Tue, Feb 15, 2011 at 11:50 PM, Jack Murray <[email protected]=
> wrote:
>> The question is how balanced were the cells to begin with, when the
>> pack was constructed?
>>
>> --- On Tue, 2/15/11, Cor van de Water <[email protected]> wrote:
>>
>>> From: Cor van de Water <[email protected]>
>>> Subject: [EVDL] Li-Ion balancing, was: conversion reliability
>>> To: "Electric Vehicle Discussion List" <[email protected]>
>>> Date: Tuesday, February 15, 2011, 11:16 PM 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 dragg

-- =

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

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Discussion Starter · #3 ·
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
> I am afraid that you will find out the answer to your assumption on =

> the occasion that you have driven too far for the lower cells, then =

> you will know how much unbalance there was.
> The curve for LiFePO4 is so flat that you have no clue if a cell is =

> sitting at 90% or 60% or 30% until it suddenly drops like a brick.
> You can get all cells very well balanced by either top balancing =

> (charging until a fixed voltage that is at least slightly above the =

> knee for example 3.6V (note: you must measure *each* cell, do not rely =

> on charging the whole string to N * 3.6V as then one cell may be at =

> 4.5V while most are still hovering around 3.4V!) or by bottom =

> balancing, discharging each to a fixed voltage - for example 2.5V
>
> 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 =

> Behalf Of David Nelson
> Sent: Thursday, February 17, 2011 8:49 AM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] Li-Ion balancing, was: conversion reliability
>
> I think a couple of other questions that need to be asked is what voltage=
were they being charged to and how far were they discharged?
> We'll see over time but so far I'm not seeing a need to balance my pack b=
ased on the data I've collected on it for the past 8 months. The difference=
might be that I'm only charging to 3.485Vpc and not to the stratosphere of=
voltages.
>
> Maybe the reality with LiFePO4 cells is more one of if you charge them to=
more than 3.6vpc they must be balanced at end of charge and if you stay be=
low that, say 3.5vpc, then they don't have to be balanced or that they only=
need to be balanced once every 1-5 years as a standard maintenance procedu=
re.
>
> On Tue, Feb 15, 2011 at 11:50 PM, Jack Murray <[email protected]=
> wrote:
>> The question is how balanced were the cells to begin with, when the =

>> pack was constructed?
>>
>> --- On Tue, 2/15/11, Cor van de Water <[email protected]> wrote:
>>
>>> From: Cor van de Water <[email protected]>
>>> Subject: [EVDL] Li-Ion balancing, was: conversion reliability
>>> To: "Electric Vehicle Discussion List" <[email protected]x.edu>
>>> Date: Tuesday, February 15, 2011, 11:16 PM 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 dragg

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

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Discussion Starter · #4 ·
>
>
>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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Discussion Starter · #5 ·
Bill Dube <[email protected]> wrote:
>
>>
>>
>>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.

So would an example of the "sloppy" cells be Li-poly and the other
type be like the TS LiFePO4 cells? Is there any reputable data
available to show the problems of not balancing every charge cycle?

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 3.177V and the highest was at 3.192V with a pack temp of about
10=B0C. It had been 5 months since I last top balanced the pack and
after the pack had delivered well in excess of 5500Ah. Maybe this is
still too far above the knee to tell anything from it. These are Nov
2009 TS-LFP100AHA cells in pairs with 40 cells total in the pack.

-- =

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

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Discussion Starter · #6 ·
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
3.177V and the highest was at 3.192V

As you can see, LiFePO4 has such a flat voltage-SoC curve for the useful
area that you cannot draw any conclusions from this miniscule 15mV
difference between these cells. The first cell *might* be lower in SoC
than the second. It is more likely, but not guaranteed.
You will only find out what the SoC is when you leave the plateau,
either in the bottom knee when they suddenly drop dead, or in the top
knee at the very end of the charge (if your pack is balanced).

> It had been 5 months since I last top balanced the pack and after the
pack had delivered well in excess of 5500Ah.

5500Ah/200Ah = 27.5 full cycles. You will never find out what their
cycle life is, for their calendar life will get them first...

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

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Discussion Starter · #7 ·
... 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
>> 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.
>
> 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.
>
> ...
>
> What I have found is that the cells get worse as they age. The
> differences between them get larger and larger, until the BMS can no
> longer handle it. You might be able to go for 6 months without
> balancing
> when new, but only a week when they get old. Extreme conditions like
> deeper discharges, high currents, temperature extremes, etc. also
> worsen
> the balancing problems.
>
> --
> Lee A. Hart |

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Discussion Starter · #8 ·
"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?
--
View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/conversion-reliability-tp3305129p3312833.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

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Discussion Starter · #9 ·
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
> will get them first..."
> What data are you basing this statement on?
> --
> View this message in context:
> http://electric-vehicle-discussion-list.413529.n4.nabble.com/conversion-reliability-tp3305129p3312833.html
> Sent from the Electric Vehicle Discussion List mailing list archive at
> Nabble.com.
>
> _______________________________________________
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Discussion Starter · #10 ·
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:
>
> 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.
>
> On Fri, Feb 18, 2011 at 10:02 AM, tomw <[email protected]>
> wrote:
>
>>
>> "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?
>> --
>> View this message in context:
>> http://electric-vehicle-discussion-list.413529.n4.nabble.com/conversion-reliability-tp3305129p3312833.html
>> Sent from the Electric Vehicle Discussion List mailing list archive
>> at
>> Nabble.com.
>>
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Roger Heuckeroth
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Discussion Starter · #11 ·
"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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Discussion Starter · #12 ·
tomw wrote:
>
> "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?

I think TS has "always" stated a 10 year to 80% capacity shelf life.
In looking for a specific statement I found only a cryptic chart here:
http://www.thunder-sky.com/pdf/201121914356.pdf
that shows 80% at about 190 time units. The time units are labeled
with some chinese characters plus "days".

--
Willie, ONWARD! Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime 160 days 7 hours 47 minutes

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Discussion Starter · #13 ·
Tom,

What does the datasheet of your batteries say?


Cor van de Water
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-----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?
--
View this message in context:
http://electric-vehicle-discussion-list.413529.n4.nabble.com/conversion-
reliability-tp3305129p3313818.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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Discussion Starter · #14 ·
"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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