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'[EE] Battery choices'
2005\12\15@081810 by Russell McMahon

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I have a volume application that requires a battery.
Best choice seems to be "sealed lead acid" (SLA) for reasons listed
below. Suggested alternatives welcome.

NB: Solutions MUST NOT redefine the problem, suggest alternatives
which do not meet all criteria etc :-). Often enough when I ask
similar questions many answers address requirements which I do not
have. There are reasons for most of the requirements . I will
partially explain some of them if it seems useful.

Application:

Exercise equipment operated by 'user'. When operating, power is
provided by user actions via an 'alternator'. When at rest or when
user speed drops too low (startup, programming, pausing etc) power is
supplied by a battery. Battery is recharged by user action when
possible. Current drain is up to 250 mA. Supply internal rail is
typically 5V but may use the dread LM7805 type regulators so input
needs to be say 8v min (dropout, headroom, wiring loss, connector
loss, ...). Higher OK but too much higher may stress 7805 thermally as
manufacturer probably anticipated a 6 cell battery pack (nominal 9v).
Equipment is in two parts. Part A draws up to 250 mA as above and its
design cannot be altered. Part B draws under 20 mA, design is flexible
and includes power conversion and control functions.

Requirement:

Rechargeable battery.
Good shelf life under self discharge.
Lowest practical cost.
OK recharge rate (faster the better).
Reasonable capacity - say 1 to 2 AH OK.
Battery life needs not be optimum but should be reasonable. ie some
violation of best practice float etc voltages and charge currents is
OK as long as battery life of say 3+ years is achievable.  Much of
this equipment gets very little use but some is used extensively. A
mains supply is a possible option in some cases but cannot be relied
on. Mass and volume energy densities are not important.

Alternator output is rectified to a smoothed DC rail and may reach 120
VDC plus in some cases. For reasons not covered here this is to be
converted to battery charging and equipment supply voltage by a linear
regulator so dissipation is up to about 30 Watt worst case for short
periods. This can be handled OK.

____________

Solution so far:

12v SLA. Typically 1.2 or 3 AH.

6v SLA with a converter to lift output to about 8v for "part A" supply
is a possibility but cost an issue.

12V SLA requires a voltage rail from alternator of 15v+ to get enough
headroom to charge SLA.
Dissipation in equipment part A at 250 mA is therefore about
(15-5)*0.25 =
2.5 watt. A series resistor can be added to drop some of this.
SLA charging circuit is crude but acceptable (and cheap).
Self discharge of 10% month - may be less. Varies rather with
construction and chemistry.

NiCd, NimH have excessive self discharge rates (typically 20% & 30%
month)

Lithium Ion. Cost?
Capacity degradation with time regardless of usage.
Goodish self discharge.

Lithium Ion Polymer - better self discharge than Nickel chemistries.
Wide voltage swing charged to discharged.
Price ?

Other?



       Russell McMahon



2005\12\15@082950 by Michael Rigby-Jones

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>-----Original Message-----
>From: spam_OUTpiclist-bouncesTakeThisOuTspamMIT.EDU [.....piclist-bouncesKILLspamspam@spam@MIT.EDU]
>Sent: 15 December 2005 13:18
>To: PIC List
>Subject: [EE] Battery choices
>
>
>
>Lithium Ion. Cost?
>Capacity degradation with time regardless of usage.
>Goodish self discharge.
>
>Lithium Ion Polymer - better self discharge than Nickel chemistries.
>Wide voltage swing charged to discharged.
>Price ?
>

SLA sounds by far the most suitable choice for this application.  I guess weight and volume are of secondary importance.  Li-Ion chemistries seem to be overkill IMO, given the far more strict charge/discharge regime you need to stick to.  The polymer batteries are now getting pretty cheap, but they suffer from much the same disadvantages of regular Li-Ion except they are inherently less safe and more likey to rupture ("vent with flame") if abused.

Regards

Mike

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2005\12\15@084717 by Mike Harrison

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On Fri, 16 Dec 2005 02:17:54 +1300, you wrote:

{Quote hidden}

The big problem with SLA is that if it is allowed to discharge and stay flat for long periods, the
battery is then useless. If the nature of the product is such that it may be left unused for over a
month, I would at the very least put in an undervoltage cutout arrangement to prevent deep
discharge.  

I think Li-Ion is the only thing that is going to do the job really well. Look at a standard format
used by digital cameras or camcorders, as these are multi-sourced and pretty cheap, but keep an eye
on product quality as Bad Things can happen when Li-Ions attack..!




2005\12\15@090210 by Halla - LEAP/Rutgers

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Unless low weight is the single highest priority in the design, anything
other than SLA does not meet your requirements.

SLA can always be recovered from a discharge state, but its remaining
efficiency depends on recovery method and age.


{Original Message removed}

2005\12\15@095357 by Mchipguru

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Hawker has some single cell type lead SLA batteried. Gates made some that had great characteristics. This way you can build a staack less than the 12V ie 2V per cell nominal. Worth a look. I seem to remember they were a bit more money than other options. I remember the ad with an X cell and a paper clip glowing bright across the top.
Larry
>
> From: Russell McMahon <apptechspamKILLspamparadise.net.nz>
> Date: 2005/12/15 Thu AM 08:17:54 EST
> To: PIC List <.....PICLISTKILLspamspam.....MIT.EDU>
> Subject: [EE] Battery choices
>
snip

2005\12\15@100932 by David Van Horn

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> -----Original Message-----
> From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu] On
Behalf
> Of @spam@mchipguruKILLspamspamcharter.net
> Sent: Thursday, December 15, 2005 10:16 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Battery choices
>
> Hawker has some single cell type lead SLA batteried. Gates made some
that
> had great characteristics. This way you can build a staack less than
the
> 12V ie 2V per cell nominal. Worth a look. I seem to remember they were
a
> bit more money than other options. I remember the ad with an X cell
and a
> paper clip glowing bright across the top.
> Larry

Must have been a somewhat discharged cell :)

I use a set of X cells to back up some of my radio gear.
Float charged at 13.8V, been using the same set for 10 years now.

They make them down to D cell size, and I've seen small 6V cells about
1.5 X 1.5 x .5


2005\12\15@102854 by Morgan Olsson

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Russell McMahon 14:17 2005-12-15:
>Best choice seems to be "sealed lead acid" (SLA)

-snip-

>Requirement:
>
>Rechargeable battery.
>Good shelf life under self discharge.

? Have you found a SLA with good shelf life ?
If so where?
I thought they self discharge in a half year or so.
(And after that is pretty damaged.)
Also they last only five years -if handled nicely.

I would try using some tithium.  There are several chemistries, but i think Li-ion is best because of cost as it is miost used)

Then you may also place a green sticker on the product saying Laad free, etc.

/Morgan
--
Morgan Olsson, Kivik, Sweden

2005\12\15@104805 by Michael Rigby-Jones

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>-----Original Message-----
>From: KILLspampiclist-bouncesKILLspamspammit.edu [RemoveMEpiclist-bouncesTakeThisOuTspammit.edu]
>Sent: 15 December 2005 13:51
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Battery choices
>
>The big problem with SLA is that if it is allowed to discharge
>and stay flat for long periods, the battery is then useless.
>If the nature of the product is such that it may be left
>unused for over a month, I would at the very least put in an
>undervoltage cutout arrangement to prevent deep discharge.  
>
>I think Li-Ion is the only thing that is going to do the job
>really well. Look at a standard format used by digital cameras
>or camcorders, as these are multi-sourced and pretty cheap,
>but keep an eye on product quality as Bad Things can happen
>when Li-Ions attack..!

Li-Ion has the same kind of problem though, if their voltage falls below a certain amount (~2.5v IIRC) they may not recover, and you have to be ultra carefull charging them from this state anyway.

Regards

Mike

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2005\12\15@105912 by David Van Horn

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> ? Have you found a SLA with good shelf life ?
> If so where?
> I thought they self discharge in a half year or so.
> (And after that is pretty damaged.)

Maybe primary cells would be a better choice?
It is said that engineering is the art of compromise, and batteries will
certainly rub that in your nose.

> Also they last only five years -if handled nicely.

Not true.  Don't overcharge them, and life is very long.
My radio set is now 10 years old, and I got it used.
Six Gates X cells, float charged at 13.8V
Not a lot of cycles, but I run six radios from them with power drain of
max 200W, with only 15W charger input.



2005\12\15@121753 by Morgan Olsson

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Michael Rigby-Jones 16:47 2005-12-15:
>Li-Ion has the same kind of problem though, if their voltage falls below a certain amount (~2.5v IIRC) they may not recover,

The noramlly built-in protection protects them from that, and the very low internal leakage makes it stand a bit time also after that until they are charged.

>and you have to be ultra carefull charging them from this state anyway.

And this is taken care of by tha standard charge IC.
(Or do it in software if you roll your own)
--
Morgan Olsson, Kivik, Sweden

2005\12\15@162521 by M. Adam Davis

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As there are no other requirements (cost?  :-) ) then I would go for
individual SLA cells.  Four will give you 8V.  Pay careful attention
to charge and discharge and you'll likely have a very reliable, long
lasting, and inexpensive solution.

It may be worth looking at Li-Ion batteries and their variants due to
their low discharge.  They aren't that much more dangerous than SLA -
it's just that when SLAs leak or explode they usually aren't leaking
or exploding in someone's pocket.  The problem is the cost, both for
the batteries, and the charge control circuitry.

Lastly, consider a generator/motor with a windup spring to store the
1AH you need, coupled with a lithium coin cell or two for memory.  Use
a catch with a low current solenoid to prevent the spring from
unwinding when you don't need the large current.  It would only be
cost effective if you were planning on making thousands, and it would
require a good mechanical engineer, but it solves a whole bunch of
problems you don't have, and creates a bunch of others you don't want.
Wouldn't that be fun?

-Adam

On 12/15/05, Russell McMahon <spamBeGoneapptechspamBeGonespamparadise.net.nz> wrote:
{Quote hidden}

> -

2005\12\15@163704 by Mark Rages

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On 12/15/05, M. Adam Davis <TakeThisOuTstienmanEraseMEspamspam_OUTgmail.com> wrote:
{Quote hidden}

How about directly solving the problem with a voice alarm?  When the
battery voltage falls, it can call out:

"Hey, lardbutt, shut off the TV and get the treadmill out of the closet!"

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2005\12\15@171532 by olin piclist

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Mark Rages wrote:
> How about directly solving the problem with a voice alarm?  When the
> battery voltage falls, it can call out:
>
> "Hey, lardbutt, shut off the TV and get the treadmill out of the
> closet!"

Yeah, that would go over really well at 3:00am.

******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2005\12\15@202425 by Russell McMahon

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> ... I would go for individual SLA cells.
> Four will give you 8V.

Others also suggested this outside PICList.
Would be better than 12v.
6V/12V SLA has advantage of vast volume and therefore low cost but if
8V, 4V or single cells are available cost effectively then that would
be a good solution.

> it's just that when SLAs leak or explode they usually aren't leaking
> or exploding in someone's pocket.

Although, I've never heard of an SLA actually self-combusting.

> Lastly, consider a generator/motor with a windup spring

That is redefining the problem, which is forbidden  :-)


       RM


2005\12\15@204626 by Jake Anderson

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Just a thaught from exercise equipment I have seen
though it may be "redefining the problem"
Could you put a super/ultra capacitor or some such inplace of the battery,
then before you use it you "run" the machine a little.
The example I am thinking of is a bike at a local gym
you get on it pedal once or twice and the display comes up,
if you stop for a while it will eventually turn off.

You arent supplying power continuously but then at 250mah draw a 3ah
SLA wont last long anyway.
Its also pretty light and small which is typically an advantage.
(Unless the exersice is getting the thing home and out of the box ;->)
It might cost a little more though probbly not when done in quantity.

should be good for 100k uses, and you don't have to worry about some luser
trying to drink the battery acid or dropping it on their cat or some such.


put a low voltage sensor in your code and save your state to eeprom before
switching off, person "pedals" again and it comes back where they left off.

There are some very funky supercaps around the place hundreds of farads in
a C-cell package (though you pay for it ~$10 in qty last I checked) Upside
is you can start a car off a single string of sub-c cells and a bunch of
boostcaps.


> {Original Message removed}

2005\12\16@013239 by William Chops Westfield

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On Dec 15, 2005, at 1:37 PM, Mark Rages wrote:

> How about directly solving the problem with a voice alarm?  When the
> battery voltage falls, it can call out:
>
> "Hey, lardbutt, shut off the TV and get the treadmill out of the
> closet!"
>

Better yet, combine the exercise craze with the tomaguchi/electronic pet
craze.  "Need more energy.  Please exercise to give me energy..."

BillW

2005\12\16@072803 by Gerhard Fiedler

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Russell McMahon wrote:

>> Lastly, consider a generator/motor with a windup spring
>
> That is redefining the problem, which is forbidden  :-)

Why is this? You asked for a battery and didn't specify "chemical". A
"mechanical battery" is just that: a battery... less common, but not less
of a battery :)

Gerhard

2005\12\16@074517 by Gerhard Fiedler
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Jake Anderson wrote:

> You arent supplying power continuously but then at 250mah draw a 3ah
> SLA wont last long anyway.

3 Ah is ~11000 As. Depending on the voltage range that you can go up and
down, that's a /lot/ of farads.

> There are some very funky supercaps around the place hundreds of farads in
> a C-cell package (though you pay for it ~$10 in qty last I checked)

Depending on how many hundreds of farads, that may work out...

Gerhard

2005\12\16@085637 by Alan B. Pearce

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>Better yet, combine the exercise craze with the
>tomaguchi/electronic pet craze.  "Need more energy.
>Please exercise to give me energy..."

<VBG> I have enough trouble with my cell phone tamagochi wanting feeding
when the battery goes flat, and starts beeping to be fed ...

2005\12\16@131525 by Peter

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On Fri, 16 Dec 2005, Alan B. Pearce wrote:

>> Better yet, combine the exercise craze with the
>> tomaguchi/electronic pet craze.  "Need more energy.
>> Please exercise to give me energy..."
>
> <VBG> I have enough trouble with my cell phone tamagochi wanting feeding
> when the battery goes flat, and starts beeping to be fed ...

You could build something around a 'squeezable' generator ;-)

Peter

2005\12\17@035901 by Russell McMahon

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An interesting and useful "Battery Charger Solutions" outline app note
from LT.
High and OK res 24 page PDFs on this page

       http://www.linear.com/designtools/BatSol.jsp

All their "solutions" are far too dear for my current application, but
all interesting.


       RM



2005\12\17@154807 by Dwayne Reid

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At 06:17 AM 12/15/2005, Russell McMahon wrote:
>I have a volume application that requires a battery.
>Best choice seems to be "sealed lead acid" (SLA) for reasons listed
>below. Suggested alternatives welcome.

I'd suggest you stay with the SLA family but would seriously consider
increasing the capacity somewhat.

Most residential and commercial burglar and fire alarm systems use
12V SLA batteries of either 4AH or 7AH.  4AH costs from our alarm
equipment supplier around Can $12.00, 7AH around Can $18.  These are
a generic brand, not name brand.

But they work well, for very long periods of time.  I routinely do a
load test to batteries that have been in service for more than 5
years - most are still in great shape.  Some aren't - that's why we
test them <grin>.

However, allowing a SLA to sit around for long periods of time while
almost or completely discharged kills them dead.

You might (maybe) want to consider some form of automatic shutdown
after some period of inactivity.

You mention that the "first" part of the circuit consumes around
250mA.  I assume most of that is for the alternator field
winding?  Is there any way to rely upon residual magnetism in the
rotor and detect when the unit is being turned before actually
sending full current to the field?  Or - pulse the field winding
occasionally (every second) to see if there is useful energy to be
had out of the alternator before wasting necessary field current?

Of course - I could be way off base - they might be using a PM alternator.

I guess what I am suggesting is: power management might alleviate
some of the shortcomings of SLA batteries.

dwayne

--
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Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2005\12\18@153825 by Russell McMahon

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>>Best choice seems to be "sealed lead acid" (SLA) for reasons listed

> I'd suggest you stay with the SLA family but would seriously
> consider increasing the capacity somewhat.

> Most residential and commercial burglar and fire alarm systems use
> 12V SLA batteries of either 4AH or 7AH.  4AH costs from our alarm
> equipment supplier around Can $12.00, 7AH around Can $18.  These are
> a generic brand, not name brand.

Alas those costs are far too high for this project.
I can get smaller SLAs here semi-retail at much lower prices (not
necessarily lower $/AH) and am assuming an out of Asia price in the
$US1-2 range. Someone there is checking this.

> You mention that the "first" part of the circuit consumes around
> 250mA.  I assume most of that is for the alternator field winding?

"Console" with large bright complex LED display.
This is only when "on". I have total power management control from the
2nd part which is my controller.

Power off can be very off. Up to my engineering skills ;-).

> ... might be using a PM alternator.

It is.


       RM

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