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'[EE]: NiCd/NiMH Burp/reflex charging (was [EE] Cla'
2005\08\26@155602 by Philip Pemberton

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In message <spam_OUT23075D38FE1C8144847DFAECA3565F2704E54FA6TakeThisOuTspampai-smx-01.europe.bkhm.net>>          "Michael Rigby-Jones" <.....Michael.Rigby-JonesKILLspamspam@spam@bookham.com> wrote:

> Burp/reflex charging has been around for eons though.  It's the method
> often used in the various primary cell rechargers that have cropped up in
> the past.  I suppose it possible that this high school student has refined
> the technique in some way, but I have my doubts.  It's been possible to
> charge NiCd/Mh in 15 minutes for many years now and still get more than "a
> few recharges" from them.

Does anyone have any more info on this type of charger? My NiMH charger has
just gone bang (literally) and I'd like to build a replacement. Reflex
charging looks quite interesting, but how do you detect end-of-charge on a
NiMH? What sort of timing and currents are used (e.g. how long to charge,
what wait time, how long to discharge, charge/discharge current...)?
I'm aiming for a charge time of around four hours for four 1.2V 1600mAh
NiMHs.
I might also see about implementing charge balancing (make sure all the
batteries end up at the same voltage).

Thanks.
--
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
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... If at first you don't succeed, destroy all evidence that you tried.

2005\08\27@090703 by David Van Horn

picon face
> Does anyone have any more info on this type of charger? My NiMH
charger
> has
> just gone bang (literally) and I'd like to build a replacement. Reflex
> charging looks quite interesting, but how do you detect end-of-charge
on a
> NiMH? What sort of timing and currents are used (e.g. how long to
charge,
> what wait time, how long to discharge, charge/discharge current...)?
> I'm aiming for a charge time of around four hours for four 1.2V
1600mAh
> NiMHs.
> I might also see about implementing charge balancing (make sure all
the
> batteries end up at the same voltage).

NIMH cells are quite complicated to charge, if you really do it right.

Discharging before charge is not needed, and just spends cell life.

Typical fast charge is around 1C, with a range of 0.5C to 2C. Outside
this range, the end of charge signals will become less distinct.

Check the cell specs carefully.
If they are cheap Chinese cells, I'd advise against anything faster than
0.5C. And I'd suggest a face shield and gloves.

I've done this, using the AVR.
Implementing the reverse (discharge) burp is pretty easy, you can use a
mosfet and big 0.2-ish ohm resistor, or use a series R/C with discharge
R across the C (safer in development)

End of charge is detected in a number of ways.

1: Final backup, a timer that simply counts to say 120% normal charge
time.
2: A pipo over temperature cutout made into the battery pack.
3: Absolute temperature of > 40C
4: Rate of rise of temperature > 1C/min
5: Absolute voltage > 1.6V/Cell
7: Negative delta V of a few mV/Sec

Take your voltage measurements at the end of the burp, or pause, where
they are more stable.

Feeding the cells with constant current is a big help, it exaggerates
the voltage and temperature curves.

I did a monitoring system using a PMD1208LS USB DAQ to monitor the
battery and charging system during development.  Good batteries give a
sharp thermal spike at end of charge. The cheap ones have a very mushy,
or even more or less linear curve of temperature over time. Those cells
I would store in a metal can, if I were you.

Good resources, though somewhat conflicting:

McGraw-Hill's handbook of batteries
Sanyo and Panasonic data sheets.
Data sheets from your cell manufacturer.
Data sheets on charge ICs from Galaxy power.
Data sheets from the Cadex web site.




2005\08\27@093343 by Philip Pemberton

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In message <.....570CCF7BBB512341BA0EBA19E95084FB61D8KILLspamspam.....server.MicroBrix.local>>          "David Van Horn" <EraseMEdvanhornspam_OUTspamTakeThisOuTmicrobrix.com> wrote:

> Typical fast charge is around 1C, with a range of 0.5C to 2C. Outside
> this range, the end of charge signals will become less distinct.

1C it is then. Guess I need to find a 2A PSU.
Am I right in thinking that trickle charging is actually bad for NiMHs?

> Check the cell specs carefully.
> If they are cheap Chinese cells, I'd advise against anything faster than
> 0.5C. And I'd suggest a face shield and gloves.

Japanese actually. Kodak 1600mAh, "Made in Japan for Eastman Kodak Company".
Very nice cells actually - certainly better than the Chinese-made Uniross
junk I used to use in the digicam.

> 1: Final backup, a timer that simply counts to say 120% normal charge
> time.
> 2: A pipo over temperature cutout made into the battery pack.
> 3: Absolute temperature of > 40C
> 4: Rate of rise of temperature > 1C/min
> 5: Absolute voltage > 1.6V/Cell
> 7: Negative delta V of a few mV/Sec

Is it worth monitoring the current going into the cell, or is that not a
reliable way to detect end of charge?

> Good resources, though somewhat conflicting:
>
> McGraw-Hill's handbook of batteries
> Sanyo and Panasonic data sheets.
> Data sheets from your cell manufacturer.
> Data sheets on charge ICs from Galaxy power.
> Data sheets from the Cadex web site.

Ooo! More light reading for bedtime :)

Thanks.
--
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
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2005\08\27@095153 by Daniel Chia

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Hi,
       Actually trickle charge is bad for NiMh more of because NiMh's
typically do not need as a high a maintenance current as their NiCd
counterparts ( I recall its somewhere around the order of 5% or
something, not sure really). As such, during trickle charging once end
point is reached they tend to get overcharged.

------------------------------------------------------------------------
Daniel Chia

"Genius is one percent inspiration and ninety-nine percent
perspiration."

    - Thomas Edison

E-mail: @spam@danielcjhKILLspamspamyahoo.com.sg
MSN: KILLspamdanstryder01KILLspamspamyahoo.com.sg
ICQ: 37878331
------------------------------------------------------------------------


> {Original Message removed}

2005\08\27@104840 by rosoftwarecontrol
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face
I can see you two have no real experience in field
NiMH. I hope hear your opinion after you do some
experiements. Your comments here are only by your
"feeling and reading", that are often differed from the reality.

By my lesson, what you described here, such 1-7, 05.C
rate, are simly only existed on paper.


{Original Message removed}

2005\08\27@111440 by rosoftwarecontrol

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face
OK, let me talk more about battery.

I worked with my charger for quite long.
I found: ending method
dV and -dV, T rising do exist, but
they exhibit really in the  messy way and seldom
identical, for even same battery, same SW and
same HW. I now believe how the bettery
have been used, discharged, the betteries
are used in RC, digital CAM, flash light,
on/off once or experienced many on/off, all lay a leg
on battery ending behaviors when you recharge them.

Unrealiable and useless are my conclusion
to dV or T rising ending method.

Now I am trying a totally new charging concept
and hope to cope with the complexity. Main method
is pulsing.







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2005\08\28@045007 by Stef Mientki

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microsoftwarecontrol wrote:

{Quote hidden}

What's so new about your method ?

I'm using a puls quick charger (10 minutes) for over 12 years now for NiCd,
with only dV/dT detection
and it works really great (it can even "repair" damaged batteries).

I think all NiMh chargers, sold at this moment are dV/dT chargers.
So that's my second question,
why do you think dV/dT is unreliable (if you do it in the right way ;-)

Stef Mientki

{Quote hidden}

2005\08\28@104920 by David Van Horn

picon face
> I can see you two have no real experience in field
> NiMH.

No real experience, just a couple of years as the primary software guy
on a production charger design, and several years experience with other
chip-based designs prior.

I hope hear your opinion after you do some
> experiements. Your comments here are only by your
> "feeling and reading", that are often differed from the reality.
>
> By my lesson, what you described here, such 1-7, 05.C
> rate, are simly only existed on paper.

It sounds to me, like you have some very poor quality cells.
>From what I have seen, all the charge termination signals are very
distinct in good quality cells, when driven by a constant current.



2005\08\28@161057 by William Chops Westfield

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On Aug 28, 2005, at 1:49 AM, Stef Mientki wrote:

> I think all NiMh chargers, sold at this moment are dV/dT chargers.
> So that's my second question, why do you think dV/dT is unreliable...

I think I can see where he is coming from.  I have a supposedly smart
NiCd/NiMH charger (this one:
  www.aspencer1.com/showitem.asp?ItemID=11387.43
not really high-end, but ought to be relatively intelligent.)
It's only so-so at detecting end-of-charge on the cells I normally
use with it :-(  While dV/dT might be usable in theory, it looks
like in practice the values you're looking for can vary quite a bit,
depending on battery make, age, initial charge state, and so on.

BillW

2005\08\28@165539 by Stef Mientki

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William Chops Westfield wrote:

{Quote hidden}

well I was talking about something havier, full charge in 10 .. 15
minutes !!
About 12 years ago, I build a charger with the ICS1700 or ICS1702.
I then did tests with about 50 NiCd batteries, from all kind of brands.
Most of the batteries (about 40) where totally broke,
capacity was measured before through a normal charger,
and capacity varied from 0% to 80%.
After a few chargers with my charger,
almost all batteries had capacities varying from 110 .. 130% !!!
I also logged the battery voltage (amplified) on a paperwriter (if
that's called so),
and I can assure you that the dV/dT detection is perfect.

But the great trick is when to measure the dV/dT.
The factory that produced the ICS-1700 had patent on that,
check the datasheets !

Now twelve years later, I still use the charger,
and at least half the batteries still are in good condition,
after being used for 12 years !!

Stef




2005\08\28@171350 by Mark Rages

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On 8/28/05, Stef Mientki <RemoveMEs.mientkiTakeThisOuTspammailbox.kun.nl> wrote:
> >
> well I was talking about something havier, full charge in 10 .. 15
> minutes !!
> About 12 years ago, I build a charger with the ICS1700 or ICS1702.
> I then did tests with about 50 NiCd batteries, from all kind of brands.

dV/dt is much easier to detect on NiCD than on NiMH cells.

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

2005\08\28@171701 by Russell McMahon

face
flavicon
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> No real experience, just a couple of years as the primary software
> guy
> on a production charger design, and several years experience with
> other
> chip-based designs prior.

You call THAT experience ? :-)



       RM

2005\08\28@174847 by Philip Pemberton

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In message <spamBeGone752ad56e1f1562d1b771c13325940bf4spamBeGonespammac.com>>          William "Chops" Westfield <TakeThisOuTwestfwEraseMEspamspam_OUTmac.com> wrote:

> It's only so-so at detecting end-of-charge on the cells I normally
> use with it :-(  While dV/dT might be usable in theory, it looks
> like in practice the values you're looking for can vary quite a bit,
> depending on battery make, age, initial charge state, and so on.

That's one of the (relatively few) reasons that's making me look into Li-Ion
technology. Easy to charge - just feed the pack 4.2V/cell at 0.5C current
limited, wait a few hours for the current to drop to about 0.01C then kill
the power. The problems start arising when you foul up the charge procedure
and end up feeding them (say) 4.5V or 0.75C. Can you say "lithium
firecracker"?

I've got a pair of Compaq Evo laptop packs here that I've been gutting for
cells. A quick call to the local TI and DalSemi distributors got me the
safety management chips, and now I've got a pair of 4AH 3.6V packs and a load
of spare cells. Of course, cellphone battery packs are also a good option if
you don't feel like playing with lithium firecrackers :)

It is relatively easy to test the cell monitors though - feed the cell side
from a 5A PSU, then deadshort the output. If the PSU's ammeter reads current,
the cell protector is fried. Do the same the other way to check the cell
voltage and charge overcurrent protection. DalSemi produced a checklist that
goes over all the tests for Li+ cell protectors - it covers most of the
checks that should be done before wiring a protector up to a Li+ cell/pack.

I really do need to look into building a GPIB-enabled
multimeter/voltmeter/data-logger so I can watch what the charger IC gets up
to. I've been using a Solartron 7150plus (need to get a service manual for
that thing) but I can only monitor voltage or current with it, not both.
Which is rather annoying when you need to keep an eye on both of them.

Later.
--
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2005\08\28@175947 by David Van Horn

picon face



I found the PMD 1208LS by measurement computing to be very handy for
monitoring the charge system.   LM-350 based constant current sinks for
discharge.



2005\08\29@044758 by Vasile Surducan

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On 8/29/05, Russell McMahon <apptechEraseMEspam.....paradise.net.nz> wrote:
> > No real experience, just a couple of years as the primary software
> > guy
> > on a production charger design, and several years experience with
> > other
> > chip-based designs prior.
>
> You call THAT experience ? :-)

 Often we say here something like that: the experience is not what
the man is doing with his life but what the life is doing with the
poor man... :)
(maybe there is a better english equivalent)

Going back to the NiMh. I've noticed most of the GSM customers are
comming back to the store with dead phone batteries after a long
trickle charge usage (many GSM phones are using this charging
algorithm). After a complete regeneration cycle, the battery looks
like new. Just "looks". Going back to the trickle charge cycles, are
dying after 5-10 cycles. I'm talking only about NiMH nothing else, and
nothing else than 600mAh to 1800mAh.

Vasile
it doesn't work more than 10 cycles.

2005\08\29@084629 by David Van Horn

picon face
> Going back to the NiMh. I've noticed most of the GSM customers are
> comming back to the store with dead phone batteries after a long
> trickle charge usage (many GSM phones are using this charging
> algorithm). After a complete regeneration cycle, the battery looks
> like new. Just "looks". Going back to the trickle charge cycles, are
> dying after 5-10 cycles. I'm talking only about NiMH nothing else, and
> nothing else than 600mAh to 1800mAh.

Generally speaking, NIMH cells HATE trickle charge.



2005\08\31@011348 by Ling SM

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> Now twelve years later, I still use the charger,
> and at least half the batteries still are in good condition,
> after being used for 12 years !!

I salute you.

Over here, relative to your rate, I am burning out my chargers and
losing my batteries at the speed of light.

With all the "searching" hours, I wonder is it cheaper and to go
non-rechargeable.

Now I have leave to look for few of my 1 week old NiMH "AAA"s as the
rubbish truck will be arriving soon.

Ling SM

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