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'[EE]: powering from NiCads'
2000\09\05@162215 by w. v. ooijen / f. hanneman

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I must power a datalogger (16F84, 24LC256, LM75, IR LEDs, TSOP17 IR
detector) from NiCad or other rechargeable batteries. Current use ~ 3 mA,
must run for 14 days, so 2AH is plenty. But how should I get the right Vcc?
The TSOP seems rather picky about its supply, below 5 V the detection
suffers considerably. 6 V is the (lowest) maximum for all components, so 5
- 6 V will be the operational range. 4 NiCads provide < 5 V for most of the
discharge period, so 5 are needed. 5 * 1.2 = 6.0, but I measured a fully
loaded NiCad at 1.34 V, which would result in way above 6.0. My current
idea is to put a 1N4148 diode in series, drop ~ 0.6, so the usefull range
of the battery is 5.6 - 6.6 V, or 1.12 - 1.32 V per cell. This should
include most of the discharge period, although I might need to assure that
the fully loaded voltage (with external load current!) never exceeds the
6.6 V. Does this sound like a good approach? Could a simple step-up
converter compete with this scheme? Using a low-current regulator seems a
waste of the extra battery voltage that would be needed. Would charging the
NiCads to only 1.2 V sharp (no 1N4148) waste much of the capacity? Would
using NiMh give better results (e.g. 5 fully loaded still <= 6V?). I guess
someone has tackled this problem before?
Wouter

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2000\09\05@165020 by Dale Botkin

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On Tue, 5 Sep 2000, w. v. ooijen / f. hanneman wrote:

> I must power a datalogger (16F84, 24LC256, LM75, IR LEDs, TSOP17 IR
> detector) from NiCad or other rechargeable batteries. Current use ~ 3 mA,
> must run for 14 days, so 2AH is plenty. But how should I get the right Vcc?
> The TSOP seems rather picky about its supply, below 5 V the detection
> suffers considerably. 6 V is the (lowest) maximum for all components, so 5
> - 6 V will be the operational range. 4 NiCads provide < 5 V for most of the
> discharge period, so 5 are needed. 5 * 1.2 = 6.0, but I measured a fully
> loaded NiCad at 1.34 V, which would result in way above 6.0. My current
> idea is to put a 1N4148 diode in series, drop ~ 0.6, so the usefull range
> of the battery is 5.6 - 6.6 V, or 1.12 - 1.32 V per cell. This should
> include most of the discharge period, although I might need to assure that
> the fully loaded voltage (with external load current!) never exceeds the
> 6.6 V. Does this sound like a good approach? Could a simple step-up
> converter compete with this scheme? Using a low-current regulator seems a
> waste of the extra battery voltage that would be needed. Would charging the
> NiCads to only 1.2 V sharp (no 1N4148) waste much of the capacity? Would
> using NiMh give better results (e.g. 5 fully loaded still <= 6V?). I guess
> someone has tackled this problem before?
> Wouter

Wouter, if you're going to use a 2AH battery, I'd suggest a low drop-out
regulator similar to ICL7663 or LT1121 with 5 NiCd or 4-5 alkalines (not
rechargeable, I know). 3mA for 14 days is only half the battery capacity.
The quiescent current of these regualtors is quite low, as is the minimum
Vin-Vout voltage difference.

I've also used 4 alkalines (Duracell Ultra) with no regulator with good
results, but the circuit was in SLEEP mode much of the time, so I don't
know how long that would drive 3mA before the voltage dropped below 1.25
per cell.  Duracell's data sheets...  well, they suck.

Dale
---
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discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
               -- Isaac Asimov

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2000\09\05@172422 by Bob Blick

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> I must power a datalogger (16F84, 24LC256, LM75, IR LEDs, TSOP17 IR
> detector) from NiCad or other rechargeable batteries. Current use ~ 3 mA,
> must run for 14 days, so 2AH is plenty. But how should I get the right Vcc?

If your maximum is 6 volts, you will need something(LDO, zener, transzorb
or ??) to limit it, especially if you charge in circuit. I would suggest 5
cells and a low-dropout regulator. There are many very inexpensive ones
that have quiescent draw under 100 uA and maximum current >100mA.

> using NiMh give better results (e.g. 5 fully loaded still <= 6V?). I guess
> someone has tackled this problem before?

Self discharge will prevent NiMh from operating 14 days. NiCad is better,
but 14 days is a long time to them too, so using 2AH is a good choice, not
oversized as one would think just multiplying .003 * 336

Cheers,

Bob

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2000\09\05@174533 by Barry King

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Wouter,

The "usual" answer for 5 V systems is to use a 5 or 6 cell battery,
and a low-dropout regulator (LDO).

5 cells gives optimal efficiency for linear regulation (minimum
"wasted" headroom), but 6 cell pre-fabbed packs are common.  (The Ni-
Cd "9V transistor battery" size are usually 6-cell "7.2V" batteries).

Seiko and others make LDOs with very low quiescent current, which is
more capacity efficient than just dropping the raw pack by one diode
drop, because the dropout is less than 0.6 V (at low current draw)
when the battery is low.  I use the CMOS Seiko S81250-SG, but there
are others.

Look carefully at the discharge curves for the cells you choose to be
sure that the regulator will supply your load through the whole
discharge range.  Ni-Cds hold terminal voltage fairly constant until
near capacity, so its easier than, say, "alkaline" batteries, which
tail off slowly.

NiMH chemistries have better energy density (Watt-Seconds / Kilogram)
than NiCd, but are fussier to charge- check the spec sheets.
However, Cadmium is has to be disposed of (recycled?) carefully, so
some consumer applications are migrating away from NiCd even when
they don't need higher performance.  If you are planning around
commercially available batteries, you may be able to buy the
batteries and chargers off-the-shelf.

-Barry.
------------
Barry King, KA1NLH
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
Check out the accumulated (PIC) wisdom of the ages at:
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2000\09\05@191717 by Plunkett, Dennis

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{Quote hidden}

       These batteries (Alkaline) are considered flat when the terminal
voltage is under 0.8V with a load of 2% of the ratted capacity. This is a
bit fixed,as a AA has 1700mAh, and a D has 18000mAh (Yep, thats correct!) I
have found that either a diode*2 or a FET (for reverse polatity) is better
than a low drop out regulator (Note that at high temperatures a new cell is
over 1.5V.
       The great thing about alkalines is that at low temperatures (-40c)
they don't deliver full current capacity (Internal resistance increases),
but raise the temperature and the interanal resistance drops and the
capacity comes back (I.E not lost like some other batteries).

       As for when they are under 1.25V, that is not very long, alkalines
are not a long term platu type cell, and it depends on the temperature.
However if you assume a straight line, then an AA will go for about 8.4
days. In this case, you will need C or D cells

       Dennis





> Dale
> ---
> The most exciting phrase to hear in science, the one that heralds new
> discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
>                 -- Isaac Asimov
>
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2000\09\05@193823 by Dale Botkin

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On Wed, 6 Sep 2000, Plunkett, Dennis wrote:

>         These batteries (Alkaline) are considered flat when the terminal
> voltage is under 0.8V with a load of 2% of the ratted capacity. This is a
> bit fixed,as a AA has 1700mAh, and a D has 18000mAh (Yep, thats correct!) I
> have found that either a diode*2 or a FET (for reverse polatity) is better
> than a low drop out regulator (Note that at high temperatures a new cell is
> over 1.5V.

<nit>
The Duracell AA's are rated at something like 2850mAh, I think, according
to the data sheet.  I'm sure that number varies *widely* from brand to
brand.
</nit>

Dale
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discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
               -- Isaac Asimov

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2000\09\05@200805 by xandinho

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><nit>
>The Duracell AA's are rated at something like 2850mAh, I think, according
>to the data sheet.  I'm sure that number varies *widely* from brand to
>brand.
></nit>

       What about maximum discharge rate? Will it gimme 20 amps for 6 minutes?


--------------8<-------Corte aqui-------8<--------------

       All the best!!!
       Alexandre Souza
       xandinhospamKILLspaminterlink.com.br

--------------8<-------Corte aqui-------8<--------------

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2000\09\05@201014 by Dan Michaels

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Wouter wrote:
>I must power a datalogger (16F84, 24LC256, LM75, IR LEDs, TSOP17 IR
>detector) from NiCad or other rechargeable batteries. Current use ~ 3 mA,
>must run for 14 days, so 2AH is plenty. But how should I get the right Vcc?
>The TSOP seems rather picky about its supply, below 5 V the detection
>suffers considerably. 6 V is the (lowest) maximum for all components, so 5
>- 6 V will be the operational range. 4 NiCads provide < 5 V for most of the
..........


Wouter,

Be a little careful about how you choose the "maximum" Vcc value.
It was 6.0v on the older Mchp silicon, but is now 5.5v with "some" of
the newer chips. You need to double-check the datasheets before plugging
in a chip.

16C84   6.0v
16F84   6.0v
16F84a  5.5v

Similar for going from '74 to '74a or '74b.

- danM

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2000\09\05@205634 by Bane Jakovljevic

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> I must power a datalogger (16F84, 24LC256, LM75, IR LEDs, TSOP17 IR
> detector) from NiCad or other rechargeable batteries. Current use ~ 3 mA,
> must run for 14 days, so 2AH is plenty. But how should I get the
> right Vcc?

Consider using a MAX757 boost circuit. You can set it to output 5V. It can
be fairly efficient (this depends on the capacitor and inductor you use - up
to 85% efficiency), and the battery voltage can drop under 1V, so you will
have good usage of the batteries, before needing to recharge them.

Bane Jakovljevic
http://www.celestialhorizons.com

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2000\09\06@003034 by Jinx

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> > NiCad or other rechargeable batteries

Alkaline batteries ARE rechargeable. I've had the same set in my
remote controls for many years. Do a web search for alkaline chargers
and you'll find plenty. I was told at the time I first found out about them
that there was a "conspiracy" to not tell consumers that alkalines are
rechargeable, to make them buy replacements. As far as I can tell it's
still not common knowledge, as NiCd are promoted as being THE
most common rechargeable. I cannot discount the fact that there could
be a "conspiracy", although I'd prefer to look on it as "not telling the
whole truth for the good of the company". Same thing with long-life
car tyres, light bulbs, clothes, etc etc

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2000\09\06@014102 by Bob Blick

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At 04:30 PM 9/6/2000 +1200, you wrote:
>> > NiCad or other rechargeable batteries
>
>Alkaline batteries ARE rechargeable.

Yes, and Duracell LEAKS when recharged.

Cheers,

Bob

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2000\09\06@023547 by Vasile Surducan

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On 5 Sep 00, at 22:16, w. v. ooijen / f. hanneman wrote:

> I must power a datalogger (16F84, 24LC256, LM75, IR LEDs, TSOP17 IR
> detector) from NiCad or other rechargeable batteries. Current use ~ 3 mA,
> must run for 14 days, so 2AH is plenty. But how should I get the right Vcc?

 My experience with standard A3 style (500mAh or more) NiCd
accumulators show this batteries like a great discharge current (
about 100mA  or more) for a long life and good level maintenance.
Even if batteries are complete new after two weeks of standing
without any load the potential will be under 1.1 V ( in a best case )
 In your place I will use a greater than 6V solution ( maybe 7.5 or
better 9 V) and a good stepdown regulator.
 The cheapest one may be done with a CMOS flip-flop and a small
ferite transformer . Up to 90% efficiency may be achieved.
Max or LTC regulators for a good cause also...
Vasile
*********************************************
Surducan Vasile
mail: .....vasileKILLspamspam.....l30.itim-cj.ro
URL: http://www.geocities.com/vsurducan
*********************************************

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2000\09\06@030548 by Vasile Surducan

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On 6 Sep 00, at 16:30, Jinx wrote:

> > > NiCad or other rechargeable batteries
>
> Alkaline batteries ARE rechargeable. I've had the same set in my
> remote controls for many years. Do a web search for alkaline chargers
> and you'll find plenty. I was told at the time I first found out about them
> that there was a "conspiracy" to not tell consumers that alkalines are
> rechargeable, to make them buy replacements. As far as I can tell it's
> still not common knowledge, as NiCd are promoted as being THE
> most common rechargeable. I cannot discount the fact that there could
> be a "conspiracy", although I'd prefer to look on it as "not telling the
> whole truth for the good of the company". Same thing with long-life
> car tyres, light bulbs, clothes, etc etc

  Hi Joe,
  Have you done some measurements about electrical parameters
after recharge ? I'm interested in short circuit current and battery
capacity ( mAh ).
  By, Vasile

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Surducan Vasile
email:EraseMEvasilespam_OUTspamTakeThisOuTl30.itim-cj.ro
URL:http://www.geocities.com/vsurducan
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2000\09\06@042543 by Russell McMahon

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>Alkaline batteries ARE rechargeable. I've had the same set in my
>remote controls for many years. Do a web search for alkaline chargers
>and you'll find plenty. I was told at the time I first found out about them
>that there was a "conspiracy" to not tell consumers that alkalines are
>rechargeable, to make them buy replacements. As far as I can tell it's
>still not common knowledge, as NiCd are promoted as being THE
>most common rechargeable. I cannot discount the fact that there could
>be a "conspiracy", although I'd prefer to look on it as "not telling the
>whole truth for the good of the company". Same thing with long-life
>car tyres, light bulbs, clothes, etc etc


Well, yes and no.
To some extent it's true and it will certainly be worth trying but, for
reasons noted below, I believe the results will vary significantly with
application and battery treatment.

Modern "Rechargeable Alkalines" (RA)  are also sort of rechargeable and they
have taken the known rechargeable capabilities of Standard Alkalines (SA)and
optimised them. Consequently you can expect that an optimised (ie standard
Alkaline) will be worse again than one which is optimised for this purpose.
Lest you think there is nothing to the optimisation, note that the major
patent holders are Canadian and Rayovac build rechargeable alkalines under
licence to them.

Let me tell you a little about RAs, I consider it reasonable to assume that
SAs will be no better and quite possibly somewhat worse in many areas. B,
IMBW :-)

I have looked into RAs as a current client insisted on using them in a
product that I am doing part of the electronics for. They are not nice
devices compared to NiCd or NiMH when it comes to rechargeability. They do
have some advantages though including -

- High relative initial terminal voltage (over 1.5v/cell)

- High relative shelf life -potentially years.
 NiCd is months and
 NiMH is best measured in weeks

RA's will weep nice caustic goo if you charge them heavily.
"Heavily" is not well defined in the extensive Rayovac data sheet /
application note.
"For further study" :-)


RAs do not like to be floated up indefinitely - they will accept extra
voltage if you provide it and die.
They need to be limited to a maximum 1.6 - 1.65v per cell (depending whose
data sheet you read).

RAs are best used at low discharge currents and very importantly at low
depths of discharge before recharging.
Paradoxically, if you MUST deep discharge an RA it is much better done at a
high discharge rate. The gross anp-hours provided at high rates of discharge
will  be much  lower than at low rates of current BUT the battery will
recover better and its lifetime will be much less harmed.

If you trickle an RA down to under 1v per cell you may get as few as 10
discharge cycles. if you crash it down at high current you will get many
more cycles of l;ife.

RAs amp-hour capacity starts off relatively high but dies rapidly. The
slower the discharge rate to any given voltage endpoint the worse the
degradation of capacity.

RAs with an apparently healthy open circuit terminal voltage will drop their
voltage severely under load. eg a battery pack of 6 x AA RAs may have nearly
9 volts open circuit voltage but drop to 7 volts odd on a 500 mA load!!!

I'd say the ideal application would be something like a transmitter that
sends data occasionally and charged by a voltage limited solar trickle
charger.


So -

Where does that leave us with recharging SA's
I would guess, and this is a guess, that applications such as the TV remote
control with a relatively frequent current limited top up to a controlled
terminal voltage would be an excellent way to encourage their long life.

Use them in eg a radio and run them flat every time before recharging and
I'd guess they would fail rapidly.



regards,

               Russell McMahon

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2000\09\06@043825 by mike

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<snip>
>I've also used 4 alkalines (Duracell Ultra) with no regulator with good
>results, but the circuit was in SLEEP mode much of the time, so I don't
>know how long that would drive 3mA before the voltage dropped below 1.25
>per cell.  Be careful - later PIC die revisions have lower max supply voltages.
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2000\09\06@045316 by Michael Rigby-Jones

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> -----Original Message-----
> From: Bob Blick [SMTP:bblickspamspam_OUTSABER.NET]
> Sent: Wednesday, September 06, 2000 6:38 AM
> To:   @spam@PICLISTKILLspamspamMITVMA.MIT.EDU
> Subject:      Re: [EE]: powering from NiCads
>
> At 04:30 PM 9/6/2000 +1200, you wrote:
> >> > NiCad or other rechargeable batteries
> >
> >Alkaline batteries ARE rechargeable.
>
> Yes, and Duracell LEAKS when recharged.
>
> Cheers,
>
> Bob
>
>
Rayovac make rechargeable alkaline batteries, much cheaper than NiCD or NiMH
but not as many charge cycles, and for some reason not recomended for high
drain applications.  Which is a shame as I was going to get a set for my
digital camera.

Mike

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2000\09\06@053257 by Jinx

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> Where does that leave us with recharging SA's
> I would guess, and this is a guess, that applications such as the TV
remote
> control with a relatively frequent current limited top up to a controlled
> terminal voltage would be an excellent way to encourage their long life.
>
> Use them in eg a radio and run them flat every time before recharging and
> I'd guess they would fail rapidly.
>
> Russell McMahon

Yes, I've found that, which is why I use them only for RCs. OK, call me
McScrooge, but a buck's a buck and they're quite happy to take a charge
every 6 months or so. I reckon the VCR ones, which get the most use,
were installed in 1995 and they're plenty healthy

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2000\09\06@053518 by Jinx

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Hi Vasile, Russell McMahon seems to have done a lot more work
on this than I have. I was only being cheap so I didn't have to buy
more batteries !! For the remotes they're great, but as Russell says,
run them down too much and they'll die

Been busy building some very important samples. Nearly finished
and looking forward to some time off this week

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2000\09\06@054545 by Russell McMahon

picon face
>detector) from NiCad or other rechargeable batteries. Current use ~ 3 mA,
>must run for 14 days, so 2AH is plenty. But how should I get the right Vcc?


I use the stupidly expensive but superbly specified LM2936 TO92 package 5 v
regulator. SMD version no doubt available.
The no load quiescent current is under 20 uA.
At 3mA the dropout is probably 0.1 - 0.2 v.
When the battery goes under 5v it behaves gracefully and allows you to keep
using the battery, unlike some regulators which suddenly draw high currents
or do other silly things.

I produce a product which runs from 5 NiCds, idles at about 1mA and draws 30
mA on occasional peaks.
I use an LM2936 to power it. This limits the maximum voltage to 5 volts and
allows flattening until rthe rest IC kicks in. Unlike your circuit mine
tolerates under 5 volts albeit not without some potential affects which are
tolerable in the interests of maximum battery life. (It talks).
With the battery at under 1.1 volt per cell the regulator is still happily
producing 5 volts.

The LM2936 sells for about $US2 in small quantities which is stupid but very
tolerable given what it does.
I have never found another regulator with as good a dropout performance AND
such a low quiescent current.
If anyone knows of one which is as good in both respects, please tell me
about it.



regards


       Russell McMahon

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2000\09\06@054754 by Mark Willis

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I've been mumbling about lead-acid 2.5AH 6V cells, solar trickle
charging, LDO Regulators, and so on here;  Just ignore me, I guess <G>

 Mark

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2000\09\06@075943 by stouchton

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I use them regularly in both a Casio and HP camera and love them.  You might
want to give them a try.

{Original Message removed}

2000\09\06@081435 by stouchton

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I had the standard alkaline recharging argument a while back with a friend
who is a chemist.  I tried it, and got about 1/100 the capacity back into
the cell.  He went through the chemical analysis to prove the process could
not work backwards (cells could not recharge by throwing electrons back in).
Out conclusions were twofold:  #1 Recharging the cell heated it, thus making
it look temporarily "better".  #2  Apparently a small amount of charge was
stored and could be retained for some time.  However, the cell impedance was
quite high, and significant current could not be delivered. Our assessment
at the time was that the electrons were stored due to a capacitive effect.

{Original Message removed}

2000\09\06@091049 by M. Adam Davis

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All cells have an internal resistance, which must be accounted for in high drain
applications.  This resistance varies from brand to brand, varies by
temperature, etc.

Say your cell has a .5 ohm resistance, you cannot draw more than 3A from the
cell at a given time, shorting the cell means there is still a .5 ohm resistance
in it.  Of course, this turns the battery into a 4.5W heating element, which
lowers its resistance, draws more current, etc.

There is a point where you are drawing too much current, in which the chemical
reaction inside the battery is greater than the cell's capacity to contain.  At
that point the cell will start to leak, unless it wants to explode instead
(hydrogen gas, I believe).  Now you have a much more dangerous condition, noted
on the back of battery packs (some warning about an explosion.  I never pay
attention either. ;-)

If you need a high drain, you need to get a battery designed for it.  NiCads and
some other rechargables not only have a low internal resistance, but they also
vent gases when you draw too much current, instead of acting like a pressure
cooker.

Another method is to place many cells in parallel, thus lowering the combined
internal resistance of your battery.

So, in short, no you cannot draw 20amps for six minutes from these cells.

-Adam

"Alexandre Domingos F. Souza" wrote:
{Quote hidden}

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2000\09\06@091058 by M. Adam Davis

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Did you measure the cell under load?  I have a sneaking suspicion that if you
made the battery pack (5 batteries), and put them under a 30mA load (160 ohm
resister) then you'll find it almost exactly 6 volts.

NiCads are nice in that they have a very flat discharge curve, so if the voltage
is still too much you can put in a diode, LED, or low dropout regulator and
expect it to stay above 5v until the end.

-Adam

"w. v. ooijen / f. hanneman" wrote:
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2000\09\06@104308 by Gabriel Gonzalez

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face
>
> Another method is to place many cells in parallel, thus lowering the
combined
> internal resistance of your battery.

What? In parallel?
Can this be really done????

Calvin



>
> So, in short, no you cannot draw 20amps for six minutes from these cells.
>
> -Adam
>
> "Alexandre Domingos F. Souza" wrote:
> >
> > ><nit>
> > >The Duracell AA's are rated at something like 2850mAh, I think,
according
> > >to the data sheet.  I'm sure that number varies *widely* from brand to
> > >brand.
> > ></nit>
> >
> >         What about maximum discharge rate? Will it gimme 20 amps for 6
minutes?
{Quote hidden}

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2000\09\06@110621 by NDuckworth

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Stouchton wrote:
> I had the standard alkaline recharging argument a while back with a friend
> who is a chemist.  I tried it, and got about 1/100 the capacity back into
> the cell.  He went through the chemical analysis to prove the process could
> not work backwards (cells could not recharge by throwing electrons back in).
> Out conclusions were twofold:  #1 Recharging the cell heated it, thus making
> it look temporarily "better".  #2  Apparently a small amount of charge was
> stored and could be retained for some time.  However, the cell impedance was
> quite high, and significant current could not be delivered. Our assessment
> at the time was that the electrons were stored due to a capacitive effect.

Sorry if this has already been covered but I have an Alkaline recharger
purchased from Farnell in the UK and manufactured by Saitek.

It cost around 25 UK Pounds and has more than paid for itself recharging
batteries for my kids toys (er, I mean test equipment if the Tax Man is reading
this).

The only requirement is that the Alkaline cell is not fully discharged, I've
recharged AA cells from a shaver several times without problems.

Regards

Nigel

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2000\09\06@145659 by Dan Michaels

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Russell McMahon wrote:
>
>I use the stupidly expensive but superbly specified LM2936 TO92 package 5 v
>regulator. SMD version no doubt available.
........
>The LM2936 sells for about $US2 in small quantities which is stupid but very
>tolerable given what it does.
>I have never found another regulator with as good a dropout performance AND
>such a low quiescent current.
>If anyone knows of one which is as good in both respects, please tell me
>about it.


A reasonable compromise for an LDO v-reg might be Nat'l Semi LP2950.
About 75 uA quiescent current and .38v dropout @ 100mA.
$1.44US/ea from Digikey, vs $3.19US for the LM3936.

- Dan Michaels
Oricom Technologies
===================

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2000\09\06@150948 by Oliver Broad

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Looking at the switching route it might be better to step up and have
a few big cells, maybe 2 C or D, rather than multiple AA. I understand the
power density should be better. However I do accept that it is hard to get
the circuit to start, I have seen a magazine 'design idea' putting two boost
converters in parallel, one to start the equipment and the other one would
only work when the output voltage was high enough, but handled higher
current.

Also if space permits it's worth looking at DIY switcher designs, if the
current is low enough discontinuous PFM can be used with close to zero
quiescent current.

Oliver.

{Original Message removed}

2000\09\06@151328 by Peter L. Peres

picon face
I think that you can use a depletion mode small VFET in series with the
power. A bipolar and a resistor divider will pull its gate downwards if
the voltage rises above 6V (or 5.5V etc) thus achieving series regulation
with very low power drain. I have put this scheme to good use using BSS129
and BC547, but I used a Zener to drive the base of the BC from VCC. That
was not a PIC project. There is another version of this that uses a second
(same type, depletion) VFET as sensing element. It has even lower power
drain. The ideal seems to be a depletion VFET with no intrinsic reverse
diode and Vgt = 5.0V ;-) Anyone seen such a part ?

hope this helps,

Peter

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2000\09\06@160424 by w. v. ooijen / f. hanneman

picon face
> Did you measure the cell under load?  I have a sneaking suspicion that if
you
> made the battery pack (5 batteries), and put them under a 30mA load (160
ohm
> resister) then you'll find it almost exactly 6 volts.

I measured a loaded NiCad with 330 ohm resistor. 1.34 Volt.

The responses on my question have been very informative, so far:
- watch out for 4.5 - 5.5 PICs
- don't use NiMh
- include some reserve for self-discharge
- consider a low-dropout regulator
- consider a DC/DC converter

I am now looking into using an LT1301 step-up converter, the cheepest one I
can get (I'm aonly a hobbyist, so I'm limited to what the local shops
offer). The nice thing is that I can now compare batteries just on a
money-per-Watt-hour basis. Suddenly a 4 V lead-gel accu looks good, much
cheaper for the same energy that NiCad.

Thanks for all the tips!

Wouter

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2000\09\06@161657 by xandinho

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face
>> Another method is to place many cells in parallel, thus lowering the
>combined
>> internal resistance of your battery.
>What? In parallel?
>Can this be really done????

       Of course! Even if you have different capacity batteries joined togheter, You won't have enough voltage to "recharge" the drained one. Use it without pain


--------------8<-------Corte aqui-------8<--------------

       All the best!!!
       Alexandre Souza
       spamBeGonexandinhospamBeGonespaminterlink.com.br

--------------8<-------Corte aqui-------8<--------------

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2000\09\06@181039 by Brent Brown

picon face
Russell wrote:
> The LM2936 sells for about $US2 in small quantities which is stupid
> but very tolerable given what it does. I have never found another
> regulator with as good a dropout performance AND such a low quiescent
> current. If anyone knows of one which is as good in both respects,
> please tell me about it.

I have recently been using the Linear Technologies LT1121CZ-5. It's
specs are perhaps a little lower than the LM2936 all round except
price is better and it's a 150mA regulator instead of 50mA. The
specs most relevant are 0.13V typ dropout at 1mA, typ 0.42V at
150mA, min ground current typ 30uA, or 90uA typ at 1mA. Worth a
look at NZ$2.60 (US$1.30?) in small quantities from REC. One
thing to watch out for - reverse pin out to "normal" regulators.

PS - I'm keen to hear of anything better and/or cheaper too!

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile: 025 334 069
eMail:  TakeThisOuTbrent.brownEraseMEspamspam_OUTclear.net.nz

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2000\09\06@213052 by Plunkett, Dennis

flavicon
face
Take a look at the Siemens TLE 4266, This has an enable pin that sets the
reg gound current to 0 to 10uA!. Also the maximum ground current is 400uA
over the entire temp range when I out is 1mA. (-40 to +125C)
With I out put to 100mA the ground current is 10mA
Dropout is 250mV to 500mV at full load
Output voltage is +/- 2%

Dennis



> {Original Message removed}

2000\09\07@060806 by Russell McMahon

picon face
>> Another method is to place many cells in parallel, thus lowering the
>combined
>> internal resistance of your battery.
>
>What? In parallel?
>Can this be really done????


Its "very naughty" but it will give you increased current capability.
However, the cells will almost invariably NOT be matched in voltage and one
will charge the other until they are. With rechargeable batteries this MAY
be tolerable BUT the charging current is ill defined and could possibly be
VERY large.

If you connected two or more batteries together with a suitable resistor
until the voltages had equalised you could then hard join them together.
A major problem is that one battery will almost certainly be depleted before
the other - if you ever run this system flat one pack will reverse charge
the other and plate nice whiskers across most of the cells ;-)
These can be "difficult" to remove.

Best not done unless you are desperate.



RM

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2000\09\07@062459 by xandinho

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>However, the cells will almost invariably NOT be matched in voltage and one
>will charge the other until they are. With rechargeable batteries this MAY

       It WILL NOT charge one another. There is just not enough voltage. Even if the discharge rate of one is higher than another. Experiment yourself with a controlled load and an miliamperimeter/timer.

>A major problem is that one battery will almost certainly be depleted before
>the other - if you ever run this system flat one pack will reverse charge
>the other and plate nice whiskers across most of the cells ;-)
>These can be "difficult" to remove.

       It can **never** happen - try it for yourself. I tried it at my lab.


--------------8<-------Corte aqui-------8<--------------

       All the best!!!
       Alexandre Souza
       xandinhoEraseMEspam.....interlink.com.br

--------------8<-------Corte aqui-------8<--------------

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2000\09\07@125503 by acampbell

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...when recharged too fast.  they are fine if filled
veeeeeeeery slooooooooooooooly.

alice

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2000\09\07@163008 by Lance Allen

picon face
On 6 Sep 2000, at 21:02, w. v. ooijen / f. hanneman wrote:


The nice thing is that I can now compare batteries just on a
> money-per-Watt-hour basis. Suddenly a 4 V lead-gel accu looks good, much
> cheaper for the same energy that NiCad.
>
> Thanks for all the tips!
>
> Wouter
>
> --
Just a comment..
If possible , I go out of my way to use SLA batteries.
Because....
They are Cheap
Work in a very wide temp range (including -30degC)
Can stay on full charge for a very long time (NiCd killer)
Simple charging scheme

The down side is the minimum terminal voltage, weight and lack of
full range fast charge. A PIC like 12C672 (With suitable power
mosfet) can make a nice SLA battery minder and load control.

90% all all my other portable gear I built (those not using SLA's) use
primary cells like alkaline or lithium ( lithium iron disulphide!...not
lithium manganese dioxide which are only good for low current
applications ).
I have had a very annoying history with NiCds and they are now on
the use at last resort list.
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

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2000\09\07@171727 by w. v. ooijen / f. hanneman

picon face
> If possible , I go out of my way to use SLA batteries.
> Because....
> They are Cheap

What is an SLA battery?
Wouter

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2000\09\07@172137 by David Kott

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> > If possible , I go out of my way to use SLA batteries.
> > Because....
> > They are Cheap
>
> What is an SLA battery?
> Wouter
>

Sealed Lead Acid.

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2000\09\07@173059 by Lance Allen

picon face
On 7 Sep 2000, at 23:11, w. v. ooijen / f. hanneman wrote:


>
> What is an SLA battery?
> Wouter
>
Sorry, I didnt mean to be a geek.

SLA= Sealed Lead Acid battery, sometimes called Gel Cells as the
electrolyte is in a jelly form.
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

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2000\09\08@024412 by Gabriel Gonzalez

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> >> Another method is to place many cells in parallel, thus lowering the
> >combined
> >> internal resistance of your battery.
> >
> >What? In parallel?
> >Can this be really done????
>
>
> Its "very naughty" but it will give you increased current capability.
> However, the cells will almost invariably NOT be matched in voltage and
one
> will charge the other until they are. With rechargeable batteries this MAY
> be tolerable BUT the charging current is ill defined and could possibly be
> VERY large.
>
> If you connected two or more batteries together with a suitable resistor
> until the voltages had equalised you could then hard join them together.
> A major problem is that one battery will almost certainly be depleted
before
> the other - if you ever run this system flat one pack will reverse charge
> the other and plate nice whiskers across most of the cells ;-)
> These can be "difficult" to remove.

This is why I was wondering if it was possible. Even small differences in
voltage between cells will create a current between them, and even if they
are not used but connected together they will be loosing charge over time,
and for sure, not at the same rate, so there will always be a small current
between them, until they both are discharged, and yes, there is the
possibility of dendrites forming rendering them useless in a short time.

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2000\09\08@062128 by Mark Willis

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Russell McMahon wrote:
> >> Another method is to place many cells in parallel, thus lowering the
> >combined
> >> internal resistance of your battery.
> >
> >What? In parallel?
> >Can this be really done????
>
> Its "very naughty" but it will give you increased current capability.
> However, the cells will almost invariably NOT be matched in voltage and one
> will charge the other until they are. With rechargeable batteries this MAY
> be tolerable BUT the charging current is ill defined and could possibly be
> VERY large.

Folks:  "Thimk" <G>

There's an existing, well thought out solution here:

For n battery packs, get n power diodes - I use Schottky's.  (Rated at
the peak discharge rate of any one battery pack.)

Insert each Schottky, anode to + terminal of each battery pack (perhaps
after a polyswitch or fuse for safety that's AT the + terminal, for
safety?), and common the cathodes together.  Connect that common cathode
point to the load.

Now you can do things like swap battery packs in and out at will - the
most charged pack will run the equipment, the least charged will not be
loaded and could be removed then recharged.

For SLA (Sealed Lead-Acid) batteries, you can voltage charge them, so
you can even go one step better - Add another set of n diodes, cathodes
to the + terminals of the battery packs, and common the anodes together
- plug that into the output of your thermally limited battery charger
(probably best to settle for it charging the conglomerate pack at the
fastest rate any one pack will charge at, or so?)  (Can do the same
thing for medium trickle charging NiCad's / NiMH's, provided you think
about current limiting carefully!)  (These diodes can be lower rated so
long as your charge current's easily handled by them <G>)

To "cheat" and run the load off AC-based power when it's available, add
one more power diode, anode to the battery charger's output, cathode to
the load.  Then the batteries aren't loaded during AC operation, which
is nice!  (Have to then make sure the AC power source is current limited
at Iload + Icharge, for one pack's maximum charge rate that is.)

It's a pretty obvious mod to this to use a bunch of rectifier bridges in
a modified connection scheme to do the same thing.  ("-" terminal to
Charge, AC terminals to battery + terminals, "+" terminals to load;
Short one "AC" terminal to "+" on the last bridge if you have an odd
number of batteries, else drop a diode from "-" to "+" and you're set.)
(Now, where did I see Schottky bridges?  <G>)

This tends to make all batteries run at the same voltage if all start
off equally charged;  Not a horrible thing for any battery chemistry.

 Mark

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2000\09\08@104448 by Barry King

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Lance,

Well, now you've started another sub-thread :)

> primary cells like alkaline or lithium ( lithium iron disulphide!...not
> lithium manganese dioxide which are only good for low current
> applications ).

The lithium/manganese dioxide batteries I've used have pretty low
internal resistance- the DL123A (duracell camera battery) is rated
for over one amp. continuous. Is that low current?

OK, you MIGHT need more than one amp to shock those grad students in
the psych studies. :)

Is it true that Lithium/Iron Disulphide batteries are very expensive
per W-hour compared with others?

Thanks,

Barry.
------------
Barry King, KA1NLH
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
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2000\09\10@165454 by Lance Allen

picon face
On 8 Sep 2000, at 10:27, Barry King wrote:

> Lance,
>
> Well, now you've started another sub-thread :)
>
> > primary cells like alkaline or lithium ( lithium iron disulphide!...not
> > lithium manganese dioxide which are only good for low current
> > applications ).
>
> The lithium/manganese dioxide batteries I've used have pretty low
> internal resistance- the DL123A (duracell camera battery) is rated
> for over one amp. continuous. Is that low current?
>

>
> Is it true that Lithium/Iron Disulphide batteries are very expensive
> per W-hour compared with others?
>

I must confess I was working off manufacturers data sheets from a
few years ago (when I was heavily into marine research equipment
development) when Lithium Manganese Dioxide batteries were no
good above 100mA (typ AA). Sounds like things have changed or
my sources were no good.

I agree the Lithium Iron Disulphate are expensive but if they are the
only option then so be it. I know I entered a discussion on cost
effectiveness etc but my experience was that for extreme
temperature range, reliability and power density the Lith Iron was
my first choice. NiCds simply didn't cut it (temp, self discharge,
memory effect) but we sometimes used SLAs in non weight/size
critical projects.

> OK, you MIGHT need more than one amp to shock those grad
>students in the psych studies. :)

Trouble is... they enjoy that sort of thing ;-)

I have just accepted a position in the Engineering School (Uni of
Auckland) as Manager of the Embedded Systems Laboratory so that
should be a return to the real world. I have already been
approached by people there on designing EEG front ends (I shed
blood sweat and tears getting those little horror circuits working).

They dont use PICs (but are starting to use AVRs).




_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

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2000\09\10@194531 by James Newton

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Lance,
Congratulations on your new position! I hope you stay on the list as I'm
about to try to talk everybody into adding [AVR] and [SX] topic tags. No
reason why the PICList can't support more now that the topic tags seem to be
generally working. And anyway,  your a good guy to have around for [EE] and
[OT] and maybe you will still [PIC] at things a bit.

James Newton, PICList Admin #3
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