Storing / charging LiFePO4

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Storing / charging LiFePO4

Buddy Mills @ Cox.net
What is a low cost way to keep/store batteries.  I have 18 LiFePO4 cell left
over from my switch from lead setting in a box.  I got extras for backup and
need to store them until I might need them.  I know they should be a stored
at ½ charge but is there anything else I need to do.  I also would like
recommendation on a low cost way to charge them for their respite.  I would
prefer something out of the box  that I can purchase.  I would be willing to
charge them in parallel, individual or groups.   And last but not least can
someone tell me how I know that they are at ½ charge for storage.  The specs
are 40ah with 3.6 volt max, 2.5 volt min and nominal of 3.2.

 

Thanks in advance,

 

Buddy Mills

 <mailto:[hidden email]> [hidden email]

 

Look mom, no gas.  <http://www.evalbum.com/2887> http://www.evalbum.com/2887

 

Disclaimer:  No animals were harmed or killed in the process of writing this
email.  Any stories to the contrary are, for the most part, either fictional
or greatly exaggerated.

 

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Re: Storing / charging LiFePO4

Michael Ross
Four 3.6 cells are equivalent to a "12V" PbSO4 battery.

If you put four cells in series you can use a car charger.  As long as it
doesn't make more than 14V you can omit using a BMS.  It is more trouble to
make it be a 1/2C SOC.

You need an Ah meter for that.  A JLD 404 and a shunt is a nice investment.
 Then you need a discharge load.  I bought a 200W 200Ohm resistor for doing
this, but it won't be a fast discharge. You could get a lower resistance
higher wattage resistor and go faster. You can use the JLD and a relay to
turn off the charger after a certain number of Ah.  Give it a full charge
and then burn off 20Ah from there.

However, I don't see why you need to be exact on the 1/2C SOC for storage.
 What is that about?  Why can't it be charged up to 14V/4 = 3.5V?  You
could probably put a 4 cell pack in parallel with the PbSO4 battery on your
ICE to get a charge.  12 ICE are regulated to just under 14V.


On Fri, Dec 27, 2013 at 5:48 PM, Buddy Mills <[hidden email]> wrote:

> What is a low cost way to keep/store batteries.  I have 18 LiFePO4 cell
> left
> over from my switch from lead setting in a box.  I got extras for backup
> and
> need to store them until I might need them.  I know they should be a stored
> at ½ charge but is there anything else I need to do.  I also would like
> recommendation on a low cost way to charge them for their respite.  I would
> prefer something out of the box  that I can purchase.  I would be willing
> to
> charge them in parallel, individual or groups.   And last but not least can
> someone tell me how I know that they are at ½ charge for storage.  The
> specs
> are 40ah with 3.6 volt max, 2.5 volt min and nominal of 3.2.
>
>
>
> Thanks in advance,
>
>
>
> Buddy Mills
>
>  <mailto:[hidden email]> [hidden email]
>
>
>
> Look mom, no gas.  <http://www.evalbum.com/2887>
> http://www.evalbum.com/2887
>
>
>
> Disclaimer:  No animals were harmed or killed in the process of writing
> this
> email.  Any stories to the contrary are, for the most part, either
> fictional
> or greatly exaggerated.
>
>
>
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>
>


--
Put this question to yourself: should I use everyone else to attain
happiness, or should I help others gain happiness?
*Dalai Lama *

Tell me what it is you plan to do
With your one wild and precious life?
Mary Oliver, "The summer day."

To invent, you need a good imagination and a pile of junk.
Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html>

A public-opinion poll is no substitute for thought.
*Warren Buffet*

Michael E. Ross
(919) 550-2430 Land
(919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone
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(919) 513-0418 Desk

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Re: Storing / charging LiFePO4

Cor van de Water
In reply to this post by Buddy Mills @ Cox.net
Hi Buddy,
Probably the best thing is indeed to store them in a cool place (between room temp and freezing) after charging them to approx 3.45V.
Probably the best is to get a charger (or a current-limited supply)
that can be set to this voltage and will charge the parallel cells for
a week or so, then you disconnect them all and once in a while you can
check if they are still sitting at acceptable voltage - it should take
longer than a year for them to self-discharge if they are manufacturered without defect.

If you can't find a supply let me know and I can send you a 3.45V 3A supply which will take at least 2 weeks to recharge your cells if they are low.
I am currently using one to test cells.

Regards,

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email] Private: http://www.cvandewater.info
Skype: cor_van_de_water Tel: +1 408 383 7626


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Buddy Mills
Sent: Friday, December 27, 2013 2:49 PM
To: 'Electric Vehicle Discussion List'
Subject: [EVDL] Storing / charging LiFePO4

What is a low cost way to keep/store batteries.  I have 18 LiFePO4 cell left
over from my switch from lead setting in a box.  I got extras for backup and
need to store them until I might need them.  I know they should be a stored
at ½ charge but is there anything else I need to do.  I also would like
recommendation on a low cost way to charge them for their respite.  I would
prefer something out of the box  that I can purchase.  I would be willing to
charge them in parallel, individual or groups.   And last but not least can
someone tell me how I know that they are at ½ charge for storage.  The specs
are 40ah with 3.6 volt max, 2.5 volt min and nominal of 3.2.

 

Thanks in advance,

 

Buddy Mills

 <mailto:[hidden email]> [hidden email]

 

Look mom, no gas.  <http://www.evalbum.com/2887> http://www.evalbum.com/2887

 

Disclaimer:  No animals were harmed or killed in the process of writing this
email.  Any stories to the contrary are, for the most part, either fictional
or greatly exaggerated.

 

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Re: Storing / charging LiFePO4

Matt Lacey
In reply to this post by Buddy Mills @ Cox.net
Hi Buddy,

are these cells brand new - never used?

if so, they are already at 50% soc - they come from the factory like that
after the capacity test and sort process

just store them as is - they don't discharge (I have cells that have been in
storage for 3 years that are all still exactly 3.30v)

Matt
----- Original Message -----
From: "Buddy Mills" <[hidden email]>
To: "'Electric Vehicle Discussion List'" <[hidden email]>
Sent: Saturday, December 28, 2013 6:48 AM
Subject: [EVDL] Storing / charging LiFePO4


What is a low cost way to keep/store batteries.  I have 18 LiFePO4 cell left
over from my switch from lead setting in a box.  I got extras for backup and
need to store them until I might need them.  I know they should be a stored
at ½ charge but is there anything else I need to do.  I also would like
recommendation on a low cost way to charge them for their respite.  I would
prefer something out of the box  that I can purchase.  I would be willing to
charge them in parallel, individual or groups.   And last but not least can
someone tell me how I know that they are at ½ charge for storage.  The specs
are 40ah with 3.6 volt max, 2.5 volt min and nominal of 3.2.



Thanks in advance,



Buddy Mills

 <mailto:[hidden email]> [hidden email]



Look mom, no gas.  <http://www.evalbum.com/2887> http://www.evalbum.com/2887



Disclaimer:  No animals were harmed or killed in the process of writing this
email.  Any stories to the contrary are, for the most part, either fictional
or greatly exaggerated.



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Re: Storing / charging LiFePO4

EVDL Administrator
In reply to this post by Buddy Mills @ Cox.net
On 27 Dec 2013 at 17:48, Buddy Mills wrote:

> And last but not least can
> someone tell me how I know that they are at ½ charge for storage.

I can't answer the other questions, but when I store lithium batteries I
normally charge them to full, then discharge them to between 50% and 70% SOC
based on the published capacity.  For example, with a 20ah battery I use 8-
10ah.

Depending on the voltage, you can use an incandescent lamp of some kind as
your dummy load.  For 12v or 24v modules, I usually use inverters and a 250w
incandescent heat lamp.  A couple of auto sealed beam headlights (if you can
still find them) would work too, but would be slower as they use less
energy.

For small batteries or single cells, you could measure AH with a Watt's Up
meter ($55-60).  One caveat is that its specs say the minimum voltage for it
to self power from the measured source is 4v, so it may have trouble with
single lithium cells unless you get the optional cable (about $3 more) and
power it externally.

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: Storing / charging LiFePO4

Willie2
In reply to this post by Matt Lacey
On 12/28/2013 05:43 AM, matt lacey wrote:
> Hi Buddy,
>
> are these cells brand new - never used?
>
> if so, they are already at 50% soc - they come from the factory like
> that after the capacity test and sort process
>
> just store them as is - they don't discharge (I have cells that have
> been in storage for 3 years that are all still exactly 3.30v)

I generally agree.  They come about 50% charged.  There is no practical
way to determine state of charge without cycling them. Which is not very
practical.  I have not had cells go bad from being stored several
years.  I've been tempted to connect them in parallel and put a small
charger and a single bypass module on them.  I'm sure they do self
discharge, it just seems to be not very significant.  Apparently, it is
less than the generally advertised rate of 1% per month.

I think it is safe to store them for 3+ years without replenishing the
charge.

OTHO, I have had cells go bad after being stored in a car for only a few
months with the BMS modules active.
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Re: Storing / charging LiFePO4

Ruckus
1. Put on shelf in garage.

2. Come back several years later.

3. End of story.

Please do not ruin your cells by charging them with a 12v bat charger as
suggested.  They will not be balanced and the higher cells will be damaged.

I have not heard of LifePo4 discharging, even when left for several years.
 Many projects take a year or two to put together.  The batts may be 2-3
years old before they even get on the road.  No worries, that's why you
bought LifePo4!

Cheers,


On Sat, Dec 28, 2013 at 5:01 AM, Willie2 <[hidden email]> wrote:

> On 12/28/2013 05:43 AM, matt lacey wrote:
>
>> Hi Buddy,
>>
>> are these cells brand new - never used?
>>
>> if so, they are already at 50% soc - they come from the factory like that
>> after the capacity test and sort process
>>
>> just store them as is - they don't discharge (I have cells that have been
>> in storage for 3 years that are all still exactly 3.30v)
>>
>
> I generally agree.  They come about 50% charged.  There is no practical
> way to determine state of charge without cycling them. Which is not very
> practical.  I have not had cells go bad from being stored several years.
>  I've been tempted to connect them in parallel and put a small charger and
> a single bypass module on them.  I'm sure they do self discharge, it just
> seems to be not very significant.  Apparently, it is less than the
> generally advertised rate of 1% per month.
>
> I think it is safe to store them for 3+ years without replenishing the
> charge.
>
> OTHO, I have had cells go bad after being stored in a car for only a few
> months with the BMS modules active.
>
> _______________________________________________
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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> group/NEDRA)
>
>


--
Marcus Reddish
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Re: Storing / charging LiFePO4

J Bills
Totally.  I'm not necessarily proud of it, but my 144v pack of lifepo4 must
have sat there for at least a year and a half and was rock solid 3.3v much
across the board the whole time, same as when I brought the crates home.
All within .05v of each other.
Almost freakish!

early days on that project, I went ahead and picked up a single cell
lithium charger off of ebay for like $20 - I want to say it was 6A and I
remember the cutoff wasn't great but not too bad, might have been 3.8v?   I
mean, don't quote me, never needed to use it, but just saying they are out
there and cheap.




On Sat, Dec 28, 2013 at 9:26 PM, Marcus Reddish <[hidden email]>wrote:

> 1. Put on shelf in garage.
>
> 2. Come back several years later.
>
> 3. End of story.
>
> Please do not ruin your cells by charging them with a 12v bat charger as
> suggested.  They will not be balanced and the higher cells will be damaged.
>
> I have not heard of LifePo4 discharging, even when left for several years.
>  Many projects take a year or two to put together.  The batts may be 2-3
> years old before they even get on the road.  No worries, that's why you
> bought LifePo4!
>
> Cheers,
>
>
> On Sat, Dec 28, 2013 at 5:01 AM, Willie2 <[hidden email]> wrote:
>
> > On 12/28/2013 05:43 AM, matt lacey wrote:
> >
> >> Hi Buddy,
> >>
> >> are these cells brand new - never used?
> >>
> >> if so, they are already at 50% soc - they come from the factory like
> that
> >> after the capacity test and sort process
> >>
> >> just store them as is - they don't discharge (I have cells that have
> been
> >> in storage for 3 years that are all still exactly 3.30v)
> >>
> >
> > I generally agree.  They come about 50% charged.  There is no practical
> > way to determine state of charge without cycling them. Which is not very
> > practical.  I have not had cells go bad from being stored several years.
> >  I've been tempted to connect them in parallel and put a small charger
> and
> > a single bypass module on them.  I'm sure they do self discharge, it just
> > seems to be not very significant.  Apparently, it is less than the
> > generally advertised rate of 1% per month.
> >
> > I think it is safe to store them for 3+ years without replenishing the
> > charge.
> >
> > OTHO, I have had cells go bad after being stored in a car for only a few
> > months with the BMS modules active.
> >
> > _______________________________________________
> > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> > http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> > For EV drag racing discussion, please use NEDRA (
> http://groups.yahoo.com/
> > group/NEDRA)
> >
> >
>
>
> --
> Marcus Reddish
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Re: Storing / charging LiFePO4

Michael Ross
Freakish, eh?  How much does the state of charge change with a variation of
0.05V on a LiFePO4 cell?

Estimating say 90% of the SOC lies between 3.2 and 3.4 (0.2V of change).
0.1V = 45%, 0.01 = 4.5% then a variation of 0.05V on a cell could be a SOC
variation of 22.5%.

So a variation of 1mV could be half a percernt.  Some of inaccuracy could
be from the instrument itself as inexpensive DMMs may not be really good at
measuring a single millivolt.

I am just estimating, but I don't think that 0.05V change is necessarily
"rock solid."

Voltage is just a crapulous way to measure SOC on LiFePO4 cells.


On Sun, Dec 29, 2013 at 4:16 AM, J Bills <[hidden email]> wrote:

> Totally.  I'm not necessarily proud of it, but my 144v pack of lifepo4 must
> have sat there for at least a year and a half and was rock solid 3.3v much
> across the board the whole time, same as when I brought the crates home.
> All within .05v of each other.
> Almost freakish!
>
> early days on that project, I went ahead and picked up a single cell
> lithium charger off of ebay for like $20 - I want to say it was 6A and I
> remember the cutoff wasn't great but not too bad, might have been 3.8v?   I
> mean, don't quote me, never needed to use it, but just saying they are out
> there and cheap.
>
>
> --
Put this question to yourself: should I use everyone else to attain
happiness, or should I help others gain happiness?
*Dalai Lama *

Tell me what it is you plan to do
With your one wild and precious life?
Mary Oliver, "The summer day."

To invent, you need a good imagination and a pile of junk.
Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html>

A public-opinion poll is no substitute for thought.
*Warren Buffet*

Michael E. Ross
(919) 550-2430 Land
(919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone
(919) 631-1451 Cell
(919) 513-0418 Desk

[hidden email]
<[hidden email]>
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Re: Storing / charging LiFePO4

gtyler54
In reply to this post by Matt Lacey
Well, as I said recently, I have some headway cells I have stored for 6
months or so, one dropped to 0.8V. the spec says 5% per month self discharge
but generally it does seem to be close to zero self discharge.

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of matt lacey
Sent: Sunday, 29 December 2013 12:44 a.m.
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Storing / charging LiFePO4

Hi Buddy,

are these cells brand new - never used?

if so, they are already at 50% soc - they come from the factory like that
after the capacity test and sort process

just store them as is - they don't discharge (I have cells that have been in
storage for 3 years that are all still exactly 3.30v)

Matt
----- Original Message -----
From: "Buddy Mills" <[hidden email]>
To: "'Electric Vehicle Discussion List'" <[hidden email]>
Sent: Saturday, December 28, 2013 6:48 AM
Subject: [EVDL] Storing / charging LiFePO4


What is a low cost way to keep/store batteries.  I have 18 LiFePO4 cell left
over from my switch from lead setting in a box.  I got extras for backup and
need to store them until I might need them.  I know they should be a stored
at ½ charge but is there anything else I need to do.  I also would like
recommendation on a low cost way to charge them for their respite.  I would
prefer something out of the box  that I can purchase.  I would be willing to
charge them in parallel, individual or groups.   And last but not least can
someone tell me how I know that they are at ½ charge for storage.  The specs
are 40ah with 3.6 volt max, 2.5 volt min and nominal of 3.2.



Thanks in advance,



Buddy Mills

 <mailto:[hidden email]> [hidden email]



Look mom, no gas.  <http://www.evalbum.com/2887> http://www.evalbum.com/2887



Disclaimer:  No animals were harmed or killed in the process of writing this
email.  Any stories to the contrary are, for the most part, either fictional
or greatly exaggerated.



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Re: Storing / charging LiFePO4

J Bills
In reply to this post by Michael Ross
yes, certainly freakish when you're used to lead!

and to be clear - they haven't "dropped" .05 - they were .05v range from
one another.  As far as I know, they didn't budge an inch that whole year
and a half - they were "around" 3.3 when I brought them home and remained
right there.  If they'd have been dropping noticeably, I might have
considered charging.

Just saying my experience was that they were perfectly fine when stored -
YMMV and there are certainly lots of time consuming ways to measure 45
cells to see how they're holding up while being stored, but that wouldn't
necessarily change the fact that they're being stored and will continue to
be stored.  End result is all that matters.


On Sun, Dec 29, 2013 at 6:42 AM, Michael Ross <[hidden email]>wrote:

> Freakish, eh?  How much does the state of charge change with a variation of
> 0.05V on a LiFePO4 cell?
>
> Estimating say 90% of the SOC lies between 3.2 and 3.4 (0.2V of change).
> 0.1V = 45%, 0.01 = 4.5% then a variation of 0.05V on a cell could be a SOC
> variation of 22.5%.
>
> So a variation of 1mV could be half a percernt.  Some of inaccuracy could
> be from the instrument itself as inexpensive DMMs may not be really good at
> measuring a single millivolt.
>
> I am just estimating, but I don't think that 0.05V change is necessarily
> "rock solid."
>
> Voltage is just a crapulous way to measure SOC on LiFePO4 cells.
>
>
> On Sun, Dec 29, 2013 at 4:16 AM, J Bills <[hidden email]> wrote:
>
> > Totally.  I'm not necessarily proud of it, but my 144v pack of lifepo4
> must
> > have sat there for at least a year and a half and was rock solid 3.3v
> much
> > across the board the whole time, same as when I brought the crates home.
> > All within .05v of each other.
> > Almost freakish!
> >
> > early days on that project, I went ahead and picked up a single cell
> > lithium charger off of ebay for like $20 - I want to say it was 6A and I
> > remember the cutoff wasn't great but not too bad, might have been 3.8v?
>   I
> > mean, don't quote me, never needed to use it, but just saying they are
> out
> > there and cheap.
> >
> >
> > --
> Put this question to yourself: should I use everyone else to attain
> happiness, or should I help others gain happiness?
> *Dalai Lama *
>
> Tell me what it is you plan to do
> With your one wild and precious life?
> Mary Oliver, "The summer day."
>
> To invent, you need a good imagination and a pile of junk.
> Thomas A. Edison<
> http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html>
>
> A public-opinion poll is no substitute for thought.
> *Warren Buffet*
>
> Michael E. Ross
> (919) 550-2430 Land
> (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google
> Phone
> (919) 631-1451 Cell
> (919) 513-0418 Desk
>
> [hidden email]
> <[hidden email]>
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Re: Storing / charging LiFePO4

David Nelson-5
In reply to this post by gtyler54
On Sun, Dec 29, 2013 at 11:13 AM, George Tyler <[hidden email]> wrote:
>
> Well, as I said recently, I have some headway cells I have stored for 6
> months or so, one dropped to 0.8V. the spec says 5% per month self discharge
> but generally it does seem to be close to zero self discharge.

That just means that the one cell was defective if nothing was hooked
up to it. Just like in a video I watched today of Lipo cells being
manufactured. The last step of the process is charging them up and
letting them sit for several days. They said that the longer they sit
the fewer defective cells make it out the door. They test V and IR to
see if any cells are bad.

If you have a LiFePO4 cell which self discharges then it is defective.
As others have said, Buddy, just leave your cells alone in a cool dry
place. If you find one which has discharged then be glad you found out
before putting it in your car. They should have no measurable self
discharge.

--
David D. Nelson
http://evalbum.com/1328
http://www.levforum.com
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Re: Storing / charging LiFePO4

Jukka Järvinen-3
If I build a pack in a project for a customer the cells are at least one
year old (prototype packs excluded). After manufacturing and formation they
have been transported to storage and charged full. Then stored in cool
place for quality control.

The SOC is not so important in storing the cells when using certain
variations of LiFePO4. And of course it depends what you're trying to
achieve with the storing. It's the high potentials (voltage) which eats
through the cells. 100% SOC LFP-cells are not that far from 50% SOC. But
you can more easier measure the differences by charging full with identical
EOC criteria and to determine how far the formation has gone.

Before installing the pack measure the voltages and capacity lost during
the +12 month storage. By then you should see very well if any cell is out
of the row. I have some cells from year 2004 which are still showing
voltage. They were left as-is after formation (testing,testing,testing :).

It takes capital to keep cells in stock (which no one seems to have
nowadays) or technology in the cell manufacturing which allows less phases
and less variation. There are a lot of tricks to fix quality issues in
production. You will get away with less hassle if using high quality cells
(read: expensive)

If you just buy/sell cells all preemptive measures are really important.
No-BMS chant has reached so many end users already. It's horrifying to see
people going out there with no protection what so ever (electronic condom).
And because they were professionally instructed to do so (do anything for
money?). As if mass produced cells would have 0% failure rate and all cell
defects are found with no QC at the factory?

If no BMS in a Li-ion fire => automatic insurance refusal and additional
throughout investigation to reveal what really happened. We need to know so
we may prevent similar accidents. At least if I'm investigating.

Customer: "I didn't use protection... and now it fell out"
Doctor: .... *sigh*.

-Jukka

P.S.- Take a good look at the capacity (100% DOD) vs cycle charts. Have you
ever seen capacity growing for the 1st 100, 200 or 300 cycles? How's that
for completing the formation process?


http://www.google.com/profiles/jarviju#about


2013/12/30 David Nelson <[hidden email]>

> On Sun, Dec 29, 2013 at 11:13 AM, George Tyler <[hidden email]> wrote:
> >
> > Well, as I said recently, I have some headway cells I have stored for 6
> > months or so, one dropped to 0.8V. the spec says 5% per month self
> discharge
> > but generally it does seem to be close to zero self discharge.
>
> That just means that the one cell was defective if nothing was hooked
> up to it. Just like in a video I watched today of Lipo cells being
> manufactured. The last step of the process is charging them up and
> letting them sit for several days. They said that the longer they sit
> the fewer defective cells make it out the door. They test V and IR to
> see if any cells are bad.
>
> If you have a LiFePO4 cell which self discharges then it is defective.
> As others have said, Buddy, just leave your cells alone in a cool dry
> place. If you find one which has discharged then be glad you found out
> before putting it in your car. They should have no measurable self
> discharge.
>
> --
> David D. Nelson
> http://evalbum.com/1328
> http://www.levforum.com
> _______________________________________________
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
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> http://groups.yahoo.com/group/NEDRA)
>
>
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Re: Storing / charging LiFePO4

Michael Ross
In reply to this post by J Bills
I think the range of 0.05V could be a sign of trouble for the low outliers.
 If they all have the same change history then they might be within a range
of 0.02V and probably better.  Since there is no mechanism for charge to go
away with a healthy battery if it does go away then something is amiss.
 When you have a bad cell in a pack you can have problems if they don't get
balanced right all the time.  Presumably, you are up on all that.

But for storage purposes the good cells require no particular effort.

I asked a question earlier  (just because I question everything) but no one
weighed in...  Why is 50% SOC a good thing for storage?  As I understand it
a higher charge state is only a problem if you are pushing up above 3.8V
per cell and then they potential is breaking up the cell materials just
sitting there. And the major  problem is the excess heat when you make that
high charge state. The thermal expansion starts to break up the particles
of LiFePO4.  3.8V per cell is well above the flat voltage part of the
charge curve.

What is bad about a low SOC?  I hear about cells coming back from very near
zero just fine.


On Sun, Dec 29, 2013 at 5:38 PM, J Bills <[hidden email]> wrote:

> yes, certainly freakish when you're used to lead!
>
> and to be clear - they haven't "dropped" .05 - they were .05v range from
> one another.  As far as I know, they didn't budge an inch that whole year
> and a half - they were "around" 3.3 when I brought them home and remained
> right there.  If they'd have been dropping noticeably, I might have
> considered charging.
>
> Just saying my experience was that they were perfectly fine when stored -
> YMMV and there are certainly lots of time consuming ways to measure 45
> cells to see how they're holding up while being stored, but that wouldn't
> necessarily change the fact that they're being stored and will continue to
> be stored.  End result is all that matters.
>
>
> On Sun, Dec 29, 2013 at 6:42 AM, Michael Ross <[hidden email]
> >wrote:
>
> > Freakish, eh?  How much does the state of charge change with a variation
> of
> > 0.05V on a LiFePO4 cell?
> >
> > Estimating say 90% of the SOC lies between 3.2 and 3.4 (0.2V of change).
> > 0.1V = 45%, 0.01 = 4.5% then a variation of 0.05V on a cell could be a
> SOC
> > variation of 22.5%.
> >
> > So a variation of 1mV could be half a percernt.  Some of inaccuracy could
> > be from the instrument itself as inexpensive DMMs may not be really good
> at
> > measuring a single millivolt.
> >
> > I am just estimating, but I don't think that 0.05V change is necessarily
> > "rock solid."
> >
> > Voltage is just a crapulous way to measure SOC on LiFePO4 cells.
> >
> >
> > On Sun, Dec 29, 2013 at 4:16 AM, J Bills <[hidden email]> wrote:
> >
> > > Totally.  I'm not necessarily proud of it, but my 144v pack of lifepo4
> > must
> > > have sat there for at least a year and a half and was rock solid 3.3v
> > much
> > > across the board the whole time, same as when I brought the crates
> home.
> > > All within .05v of each other.
> > > Almost freakish!
> > >
> > > early days on that project, I went ahead and picked up a single cell
> > > lithium charger off of ebay for like $20 - I want to say it was 6A and
> I
> > > remember the cutoff wasn't great but not too bad, might have been 3.8v?
> >   I
> > > mean, don't quote me, never needed to use it, but just saying they are
> > out
> > > there and cheap.
> > >
> > >
> > > --
> > Put this question to yourself: should I use everyone else to attain
> > happiness, or should I help others gain happiness?
> > *Dalai Lama *
> >
> > Tell me what it is you plan to do
> > With your one wild and precious life?
> > Mary Oliver, "The summer day."
> >
> > To invent, you need a good imagination and a pile of junk.
> > Thomas A. Edison<
> > http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html>
> >
> > A public-opinion poll is no substitute for thought.
> > *Warren Buffet*
> >
> > Michael E. Ross
> > (919) 550-2430 Land
> > (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google
> > Phone
> > (919) 631-1451 Cell
> > (919) 513-0418 Desk
> >
> > [hidden email]
> > <[hidden email]>
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> > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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> >
> >
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>


--
Put this question to yourself: should I use everyone else to attain
happiness, or should I help others gain happiness?
*Dalai Lama *

Tell me what it is you plan to do
With your one wild and precious life?
Mary Oliver, "The summer day."

To invent, you need a good imagination and a pile of junk.
Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html>

A public-opinion poll is no substitute for thought.
*Warren Buffet*

Michael E. Ross
(919) 550-2430 Land
(919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone
(919) 631-1451 Cell
(919) 513-0418 Desk

[hidden email]
<[hidden email]>
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Re: Storing / charging LiFePO4

Hoegberg .


> From: [hidden email]
> Date: Mon, 30 Dec 2013 10:03:49 -0500
> To: [hidden email]
> Subject: Re: [EVDL] Storing / charging LiFePO4


> weighed in...  Why is 50% SOC a good thing for storage?  As I understand it
> a higher charge state is only a problem if you are pushing up above 3.8V
> per cell and then they potential is breaking up the cell materials just

- And breaking down, the electrolyte.
(Jukka, correct me if Im wrong about this)  

So if the charger stay long total periods at high voltages, (som kind of constant "float" charge to the top end of the chargecurve,, that would be a bad thing to do, as I understand it _today_..  :-)


> sitting there. And the major  problem is the excess heat when you make that
> high charge state.

- As I understand it today, the heat hurt electrolytes, but I can be wrong about this.




> The thermal expansion starts to break up the particles
> of LiFePO4.  3.8V per cell is well above the flat voltage part of the
> charge curve.
>
> What is bad about a low SOC?  I hear about cells coming back from very near
> zero just fine.

- I dont think it is bad to be at 50-60% DOD,  actually prefered I guess.

Any Lower than 60% DOD, ..I dont know.
But Deep discharges always seems to hurt cyclelife, (in a multi-cycling application) but that might be a true "mechanical" thing(??) If so it _might_ not be a problem if they just sit still  and do nothing  even if we are at low 95% DOD..   "Maybe" But why take the chance?  :-)

Also it might be a grater risk of other handling errors/problems?
For example if they start at a bottom balanced level, and then the customer forget about them.., Maybe some small self discharge over the years and so on..  Or it might be connected to something, or just dirty.  Anyway, it will not be a good thing to do. :-)

// John



>
>
> On Sun, Dec 29, 2013 at 5:38 PM, J Bills <[hidden email]> wrote:
>
> > yes, certainly freakish when you're used to lead!
> >
> > and to be clear - they haven't "dropped" .05 - they were .05v range from
> > one another.  As far as I know, they didn't budge an inch that whole year
> > and a half - they were "around" 3.3 when I brought them home and remained
> > right there.  If they'd have been dropping noticeably, I might have
> > considered charging.
> >
> > Just saying my experience was that they were perfectly fine when stored -
> > YMMV and there are certainly lots of time consuming ways to measure 45
> > cells to see how they're holding up while being stored, but that wouldn't
> > necessarily change the fact that they're being stored and will continue to
> > be stored.  End result is all that matters.
> >
> >
> > On Sun, Dec 29, 2013 at 6:42 AM, Michael Ross <[hidden email]
> > >wrote:
> >
> > > Freakish, eh?  How much does the state of charge change with a variation
> > of
> > > 0.05V on a LiFePO4 cell?
> > >
> > > Estimating say 90% of the SOC lies between 3.2 and 3.4 (0.2V of change).
> > > 0.1V = 45%, 0.01 = 4.5% then a variation of 0.05V on a cell could be a
> > SOC
> > > variation of 22.5%.
> > >
> > > So a variation of 1mV could be half a percernt.  Some of inaccuracy could
> > > be from the instrument itself as inexpensive DMMs may not be really good
> > at
> > > measuring a single millivolt.
> > >
> > > I am just estimating, but I don't think that 0.05V change is necessarily
> > > "rock solid."
> > >
> > > Voltage is just a crapulous way to measure SOC on LiFePO4 cells.
> > >
> > >
> > > On Sun, Dec 29, 2013 at 4:16 AM, J Bills <[hidden email]> wrote:
> > >
> > > > Totally.  I'm not necessarily proud of it, but my 144v pack of lifepo4
> > > must
> > > > have sat there for at least a year and a half and was rock solid 3.3v
> > > much
> > > > across the board the whole time, same as when I brought the crates
> > home.
> > > > All within .05v of each other.
> > > > Almost freakish!
> > > >
> > > > early days on that project, I went ahead and picked up a single cell
> > > > lithium charger off of ebay for like $20 - I want to say it was 6A and
> > I
> > > > remember the cutoff wasn't great but not too bad, might have been 3.8v?
> > >   I
> > > > mean, don't quote me, never needed to use it, but just saying they are
> > > out
> > > > there and cheap.
> > > >
> > > >
> > > > --
> > > Put this question to yourself: should I use everyone else to attain
> > > happiness, or should I help others gain happiness?
> > > *Dalai Lama *
> > >
> > > Tell me what it is you plan to do
> > > With your one wild and precious life?
> > > Mary Oliver, "The summer day."
> > >
> > > To invent, you need a good imagination and a pile of junk.
> > > Thomas A. Edison<
> > > http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html>
> > >
> > > A public-opinion poll is no substitute for thought.
> > > *Warren Buffet*
> > >
> > > Michael E. Ross
> > > (919) 550-2430 Land
> > > (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google
> > > Phone
> > > (919) 631-1451 Cell
> > > (919) 513-0418 Desk
> > >
> > > [hidden email]
> > > <[hidden email]>
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> > > _______________________________________________
> > > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> > > http://lists.evdl.org/listinfo.cgi/ev-evdl.org
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> >
>
>
> --
> Put this question to yourself: should I use everyone else to attain
> happiness, or should I help others gain happiness?
> *Dalai Lama *
>
> Tell me what it is you plan to do
> With your one wild and precious life?
> Mary Oliver, "The summer day."
>
> To invent, you need a good imagination and a pile of junk.
> Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html>
>
> A public-opinion poll is no substitute for thought.
> *Warren Buffet*
>
> Michael E. Ross
> (919) 550-2430 Land
> (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone
> (919) 631-1451 Cell
> (919) 513-0418 Desk
>
> [hidden email]
> <[hidden email]>
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Re: Storing / charging LiFePO4

Lee Hart
In reply to this post by Michael Ross
Michael Ross wrote:
> Freakish, eh?  How much does the state of charge change with a variation of
> 0.05V on a LiFePO4 cell?

As many have observed, the no-load voltage of LiFe cells barely changes
at all from 20% to 80% state of charge. Voltage is worthless as a way to
gauge state of charge in this range. You'll measure about 3.31v no
matter what the cell's state of charge or condition. The differences are
as likely to be caused by brand, model, age, batch number, temperature,
etc. as they are by state of charge.

> Voltage is just a crapulous way to measure SOC on LiFePO4 cells.

That's a great word for it! :-)

Here's my advice on storing LiFe cells: When they arrive, you really
don't know if they are good or weak or bad, and you don't know their
state of charge. Voltage alone is worthless. *Nobody* has ever tested
them, including the factory (they ship *everything* to someone, good or
bad). Like they say in poker, if you don't know who the patsy is, then
*you* are the patsy.

If you're lucky, the vendor may have shipped 100% good cells, all at the
same state of charge, and all with the same self-discharge rate. Since
good cells have a low self-discharge rate, such cells can indeed just be
sat in the corner for a year or more.

However, this has never happened to me. I have *always* found large
variations in the initial state of charge (even though the cell voltages
are the same), and there have always been weak or defective cells in the
batch.

So, it is only prudent to test them. You don't need expensive equipment;
it only requires time. If the cells are going to be stored for a while,
then you have lots of time.

You're only going to spend about 5 minutes per cell. The rest of the
time is just waiting for it to discharge, and then waiting for it to
recharge. You just check and write down the results at the beginning and
end.

Equipment:

  - An adjustable regulated power supply that you can set for 3.6v.
    Anything from 1 to 10 amps will be fine. Get one with meters
    that show volts and amps. There are thousands of these on eBay
    for $50 and less.

    I prefer to get an older used name-brand one than a new junky
    one. It will be more accurate, last longer, and you'll find
    *lots* of uses once you have it.

  - A load "resistor", which can be anything that draws 1-10 amps
    at 3.3 volts. I like light bulbs, because they draw a roughly
    constant current -- a couple 12v car headlights are fine. They
    barely light at 3.3v, but that makes no difference.

    Use your power supply to power your load resistor, and write
    down the current it draws. This will be your "discharge" current.

  - A SPDT relay, with contacts that can switch the load and charger
    current, and a coil that drops out at about 2.5v (the desired
    end-of-discharge voltage).

    A common 12v automotive relay will work. Use your adjustable
    power supply to test its pull-on and drop-out voltages. It will
    probably pull in at 6v-9v, and drop out at 1v-2v. Add cheap
    common diodes (1N4001 etc.) in series with the coil to raise
    its dropout voltage (0.6v per diode) to get to 2.5v.

  - A timer. The cheapest and easiest is an analog clock (the kind
    with hands) that's powered with a single 1.5v AA cell.

  - A reed switch. It's a little glass tube with a wire on each end.
    They are sold at Radio Shack, and any burglar alarm sales and
    service store. This is the thing you attach to a door or window,
    with a magnet on the moving half. When a magnet (or magnetic field)
    is near, the switch closes. When there is no magnetic field, the
    switch opens.

Wiring:

  - Connect the cell positive to the relay's common contact.
  - Connect the normally-closed relay contact to power supply positive.
  - Connect the normally-open relay contact to the load resistor.
  - Connect the negative of the power supply, load resistor, and cell
        all together.
  - Connect the coil (and however many diodes you need to reach 2.5v)
        across the load resistor.
  - Connect the reed switch in series with the AA cell in the clock.
        For example, remove the AA cell, and tape one wire from
        the reed switch to the AA cell's positive end. Hold the
        other wire from the reed switch against the positive contact
        in the clock's battery holder. Now insert the AA cell.
        The tape on its positive end should hold the wires in place,
        but keep them from shorting to each other. Test to see that
        the clock only runs when a magnet is held on the reed switch.
  - Wrap one of the wires to your load resistor around the reed switch
        a couple times. This creates a magnetic field when current
        is flowing to the load, and so starts the clock.

Operation:

  - Set the power supply for 3.6v (or whatever you want your "fully
    charged" voltage to be). The cell will charge at as much current
    as the power supply can provide. Any value is safe for the cell.
    (It's the power supply that may have trouble providing its maximum
    current for many hours -- a cheap one may burn out!)

  - Let the cell charge until the current falls to less than 1% of the
    cell's amphour capacity (i.e. under 1a for a 100ah cell, or 0.1a
    for a 10ah cell, etc.) This is not critical, and may take a day or
    more. For example, a 2 amp power supply will take 50 hours to fully
    charge a dead 100ah cell! So keep checking back once or twice a day,
    looking for a current under 1%.

  - When the cell is fully charged, manually push the relay contact
    closed with your finger. If you can't see the contact (i.e. the
    relay case has a cover), either remove the cover, or momentarily
    touch a 9v transistor radio battery across its coil to make it
    pull in.

  - When it pulls in, the relay
        a) disconnects the power supply (i.e. stops charging).
        b) powers its own coil, so it *stays* pulled in.
        c) connects the load.
        d) starts the clock.

  - Set the clock's hands to noon. The clock will run as long as
    the relay is pulled in and the load is being powered. Thus, it
    will show the elapsed time.

  - Check on it at least once every 12 hours. If it is off, write
    down the elapsed time. The cell's amphour capacity is the elapsed
    time multiplied by the load current. For example: Your load draws
    3 amps. The clock started at noon and stopped at 10:00 (10 hours).
    Then the cell delivered 3a x 10h = 30 amphours.

    If the clock is still running when you check, write down the
    elapsed time so far, and set the clock back to noon. With a big
    cell and a small load current, it could take more than 12 hours
    to fully discharge it. For example, it takes 3a x 20 hours to
    discharge a 60ah cell. So you might check and reset the clock
    3 times (reset to noon at 11 hours, then found it off with 9
    more hours when you came back in another 10 hours). So the cell
    is 3a x (11h + 9h) = 60ah.

This setup automatically turns off the load before the cell gets too
deeply discharged, so it prevents damage if you forget to check it.

It also automatically recharges the cell after a discharge test, and
won't hurt the cell if you forget and leave it on too long (3.6v won't
hurt a LiFe cell even if left for days).

It's slow, but cheap! And in the end, you'll know what you really have,
instead of having to rely on the claims of battery salesmen.

> A public-opinion poll is no substitute for thought. *Warren Buffet*

I like this quote. :-)

--
Scientists investigate that which already is. Engineers create that
which has never been. -- Albert Einstein
--
Lee Hart -- See my Xmas projects at www.sunrise-ev.com/projects.htm
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Re: Storing / charging LiFePO4

Lee Hart
In reply to this post by Hoegberg .
>> Why is 50% SOC a good thing for storage?

It's not so much that 50% is "ideal". It's just that your goal is to
avoid extremes. You don't want a cell to run dead, or get overcharged,
or too hot, or too cold; because all of these things shorten their life.

It's a bit like a potted plant. It will die if you over-water it, or
under-water it; but there is a large range in the middle that's just fine.

If you *know* your cells are at 50% state of charge, and *know* that
they all have a low self-discharge rated, then you can just store them
in the closet for years until needed.

The problem is that most people don't KNOW the condition of their cells.
They bought them from the cheapest supplier, who also didn't test them
(any more than a cursory voltage check). The manufacturer also didn't
test them, because there's no warranty and they never give refunds.

This is like deciding that a plant is good because it's green. :-/

--
Scientists investigate that which already is. Engineers create that
which has never been. -- Albert Einstein
--
Lee Hart -- See my Xmas projects at www.sunrise-ev.com/projects.htm
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Re: Storing / charging LiFePO4

Cor van de Water
In reply to this post by Lee Hart
I did not have a reed relay when I was doing a similar test, so in order
to measure the time with the analog clock, I powered the clock from the
battery under test using a series connection of around 100 Ohms resistor
and 3 diodes in series to get about 1.8V for the clock. Connect this to
the load resistor to measure discharge time.
I had to put a large enough Electrolytic capacitor across the clock
power to supply the peak current of the mechanism to move the hands of
the clock.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email] Private: http://www.cvandewater.info
Skype: cor_van_de_water Tel: +1 408 383 7626


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Lee Hart
Sent: Monday, December 30, 2013 10:33 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Storing / charging LiFePO4

Michael Ross wrote:
> Freakish, eh?  How much does the state of charge change with a
variation of
> 0.05V on a LiFePO4 cell?

As many have observed, the no-load voltage of LiFe cells barely changes
at all from 20% to 80% state of charge. Voltage is worthless as a way to

gauge state of charge in this range. You'll measure about 3.31v no
matter what the cell's state of charge or condition. The differences are

as likely to be caused by brand, model, age, batch number, temperature,
etc. as they are by state of charge.

> Voltage is just a crapulous way to measure SOC on LiFePO4 cells.

That's a great word for it! :-)

Here's my advice on storing LiFe cells: When they arrive, you really
don't know if they are good or weak or bad, and you don't know their
state of charge. Voltage alone is worthless. *Nobody* has ever tested
them, including the factory (they ship *everything* to someone, good or
bad). Like they say in poker, if you don't know who the patsy is, then
*you* are the patsy.

If you're lucky, the vendor may have shipped 100% good cells, all at the

same state of charge, and all with the same self-discharge rate. Since
good cells have a low self-discharge rate, such cells can indeed just be

sat in the corner for a year or more.

However, this has never happened to me. I have *always* found large
variations in the initial state of charge (even though the cell voltages

are the same), and there have always been weak or defective cells in the

batch.

So, it is only prudent to test them. You don't need expensive equipment;

it only requires time. If the cells are going to be stored for a while,
then you have lots of time.

You're only going to spend about 5 minutes per cell. The rest of the
time is just waiting for it to discharge, and then waiting for it to
recharge. You just check and write down the results at the beginning and

end.

Equipment:

  - An adjustable regulated power supply that you can set for 3.6v.
    Anything from 1 to 10 amps will be fine. Get one with meters
    that show volts and amps. There are thousands of these on eBay
    for $50 and less.

    I prefer to get an older used name-brand one than a new junky
    one. It will be more accurate, last longer, and you'll find
    *lots* of uses once you have it.

  - A load "resistor", which can be anything that draws 1-10 amps
    at 3.3 volts. I like light bulbs, because they draw a roughly
    constant current -- a couple 12v car headlights are fine. They
    barely light at 3.3v, but that makes no difference.

    Use your power supply to power your load resistor, and write
    down the current it draws. This will be your "discharge" current.

  - A SPDT relay, with contacts that can switch the load and charger
    current, and a coil that drops out at about 2.5v (the desired
    end-of-discharge voltage).

    A common 12v automotive relay will work. Use your adjustable
    power supply to test its pull-on and drop-out voltages. It will
    probably pull in at 6v-9v, and drop out at 1v-2v. Add cheap
    common diodes (1N4001 etc.) in series with the coil to raise
    its dropout voltage (0.6v per diode) to get to 2.5v.

  - A timer. The cheapest and easiest is an analog clock (the kind
    with hands) that's powered with a single 1.5v AA cell.

  - A reed switch. It's a little glass tube with a wire on each end.
    They are sold at Radio Shack, and any burglar alarm sales and
    service store. This is the thing you attach to a door or window,
    with a magnet on the moving half. When a magnet (or magnetic field)
    is near, the switch closes. When there is no magnetic field, the
    switch opens.

Wiring:

  - Connect the cell positive to the relay's common contact.
  - Connect the normally-closed relay contact to power supply positive.
  - Connect the normally-open relay contact to the load resistor.
  - Connect the negative of the power supply, load resistor, and cell
        all together.
  - Connect the coil (and however many diodes you need to reach 2.5v)
        across the load resistor.
  - Connect the reed switch in series with the AA cell in the clock.
        For example, remove the AA cell, and tape one wire from
        the reed switch to the AA cell's positive end. Hold the
        other wire from the reed switch against the positive contact
        in the clock's battery holder. Now insert the AA cell.
        The tape on its positive end should hold the wires in place,
        but keep them from shorting to each other. Test to see that
        the clock only runs when a magnet is held on the reed switch.
  - Wrap one of the wires to your load resistor around the reed switch
        a couple times. This creates a magnetic field when current
        is flowing to the load, and so starts the clock.

Operation:

  - Set the power supply for 3.6v (or whatever you want your "fully
    charged" voltage to be). The cell will charge at as much current
    as the power supply can provide. Any value is safe for the cell.
    (It's the power supply that may have trouble providing its
maximum
    current for many hours -- a cheap one may burn out!)

  - Let the cell charge until the current falls to less than 1% of the
    cell's amphour capacity (i.e. under 1a for a 100ah cell, or 0.1a
    for a 10ah cell, etc.) This is not critical, and may take a day or
    more. For example, a 2 amp power supply will take 50 hours to fully
    charge a dead 100ah cell! So keep checking back once or twice a day,
    looking for a current under 1%.

  - When the cell is fully charged, manually push the relay contact
    closed with your finger. If you can't see the contact (i.e. the
    relay case has a cover), either remove the cover, or momentarily
    touch a 9v transistor radio battery across its coil to make it
    pull in.

  - When it pulls in, the relay
        a) disconnects the power supply (i.e. stops charging).
        b) powers its own coil, so it *stays* pulled in.
        c) connects the load.
        d) starts the clock.

  - Set the clock's hands to noon. The clock will run as long as
    the relay is pulled in and the load is being powered. Thus, it
    will show the elapsed time.

  - Check on it at least once every 12 hours. If it is off, write
    down the elapsed time. The cell's amphour capacity is the elapsed
    time multiplied by the load current. For example: Your load draws
    3 amps. The clock started at noon and stopped at 10:00 (10 hours).
    Then the cell delivered 3a x 10h = 30 amphours.

    If the clock is still running when you check, write down the
    elapsed time so far, and set the clock back to noon. With a big
    cell and a small load current, it could take more than 12 hours
    to fully discharge it. For example, it takes 3a x 20 hours to
    discharge a 60ah cell. So you might check and reset the clock
    3 times (reset to noon at 11 hours, then found it off with 9
    more hours when you came back in another 10 hours). So the cell
    is 3a x (11h + 9h) = 60ah.

This setup automatically turns off the load before the cell gets too
deeply discharged, so it prevents damage if you forget to check it.

It also automatically recharges the cell after a discharge test, and
won't hurt the cell if you forget and leave it on too long (3.6v won't
hurt a LiFe cell even if left for days).

It's slow, but cheap! And in the end, you'll know what you really have,
instead of having to rely on the claims of battery salesmen.

> A public-opinion poll is no substitute for thought. *Warren Buffet*

I like this quote. :-)

--
Scientists investigate that which already is. Engineers create that
which has never been. -- Albert Einstein
--
Lee Hart -- See my Xmas projects at www.sunrise-ev.com/projects.htm
_______________________________________________
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Re: Storing / charging LiFePO4

Michael Ross
In reply to this post by Ruckus
Following up on Marcus' good comment...

I should amend that if you know the cells are close in SOC (my assumption
from the original message) then you could charge four in series with a
charger for 12V PbSO4 batteries (or by alternator in a 12V ICE car).  It is
not ideal because if one of the cells is very low then the other 3 could be
overcharged.  Or if one is damaged and has a limited capacity compared to
the others.   If you could monitor or check the individual cells carefully
to stop charging when the first cell reaches 3.6V then the others are
protected.

It is just a suggestion in case you don't have a more appropriate charger.

Probably should have kept the idea to myself.

You really need a good Ah meter.  The JLD 404 allows you to shut the
charger off on certain conditions.  Very handy.  A good low cost, DIY tool
for charging and discharging batteries.

I gather there are various more sophisticated and costly BMS / charger
combos.


On Sun, Dec 29, 2013 at 12:26 AM, Marcus Reddish
<[hidden email]>wrote:

> SNIP
> Please do not ruin your cells by charging them with a 12v bat charger as
> suggested.  They will not be balanced and the higher cells will be damaged.
> SNIP

--
Put this question to yourself: should I use everyone else to attain
happiness, or should I help others gain happiness?
*Dalai Lama *

Tell me what it is you plan to do
With your one wild and precious life?
Mary Oliver, "The summer day."

To invent, you need a good imagination and a pile of junk.
Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html>

A public-opinion poll is no substitute for thought.
*Warren Buffet*

Michael E. Ross
(919) 550-2430 Land
(919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone
(919) 631-1451 Cell
(919) 513-0418 Desk

[hidden email]
<[hidden email]>
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Re: Storing / charging LiFePO4

Lee Hart
In reply to this post by Cor van de Water
Cor van de Water wrote:
> I did not have a reed relay when I was doing a similar test, so in order
> to measure the time with the analog clock, I powered the clock from the
> battery under test using a series connection of around 100 Ohms resistor
> and 3 diodes in series to get about 1.8V for the clock. Connect this to
> the load resistor to measure discharge time.
> I had to put a large enough Electrolytic capacitor across the clock
> power to supply the peak current of the mechanism to move the hands of
> the clock.

That's a good solution, too. Though, these clocks only average around
200uA, so a much larger resistor should also work fine.

I'll bet you could use a 4.7k resistor, and a red LED to provide the
1.5v drop. A 1000uF capacitor across the LED should be more than enough
to provide the pulse of current needed once a second when the clock
"ticks". The LED would also provide a visual indication that the load
(and clock) are "on".
--
We live in a society exquisitely dependent on science and technology,
in which hardly anyone knows anything about science and technology.
        -- Carl Sagan
--
Lee Hart -- See my Xmas projects at www.sunrise-ev.com/projects.htm
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12