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'[EE]: ideas on home-made rolls royce type NiMh bat'
2001\12\10@205848 by Bernard Wood

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I am familiar with charger schematics for single cells, but... I cannot
find any information on charging
multiple cells. (ie 4x AA cells 1600mAhr, e.g. shall I have these cells all
independently
charged or is it reasonably safe to series them all up??)

Anyone know where to point me??  I've looked at a few Maxim and other
dedicated IC charging methods
and found nothing suitable...what IC do commercial chargers use just out of
interest??

Planning on doing a PIC -based charger (to control charge time, LED mode
display to user, PWM operation, and other) that pulse charges using PWM
waveform for say 3seconds then shorts all batteries for 100msec, cycling.
Apparently this charging scheme is the one to go for, for long life of your
batteries to reduce those "dendrites"....

Planning on constant current charging the 4 batteries all connected in
series at around 2C rate normally (selectable C rate via user) as want a
fast charger and willing to trade off battery life slightly for fast charge
times.

Anyone got any help/tips/neat circuit ideas?

Thanks,
Bernard Wood
New Zealand

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2001\12\10@211537 by Kathy Quinlan

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> I am familiar with charger schematics for single cells, but... I cannot
> find any information on charging
> multiple cells. (ie 4x AA cells 1600mAhr, e.g. shall I have these cells
all
> independently
> charged or is it reasonably safe to series them all up??)

most commercial ones do and it does not seem to be much of a problem :o)


> Anyone know where to point me??  I've looked at a few Maxim and other
> dedicated IC charging methods
> and found nothing suitable...what IC do commercial chargers use just out
of
> interest??
>

My Atlas CopCo 12V battery hammer drill has a tl494 in it :o) (and a few
other support IC's)

Regards,

Kat.


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2001\12\10@220652 by Jon Baker

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> I am familiar with charger schematics for single cells, but... I cannot
> find any information on charging
> multiple cells. (ie 4x AA cells 1600mAhr, e.g. shall I have these cells
all
> independently
> charged or is it reasonably safe to series them all up??)

The commercial plug straight into the wall charges series the cells to
provide 2 separate charges of 2xAA or 2xAAA.. or 2 separate 9v charges. I
think theres some quite detailed info about charging if you visit the
battery manufacturesers site-- I have found rayovac t be quite informative.
If your charger is a constant current charger then theres no reason why
cells in series wont charge properly.

> Planning on doing a PIC -based charger (to control charge time, LED mode
> display to user, PWM operation, and other) that pulse charges using PWM
> waveform for say 3seconds then shorts all batteries for 100msec, cycling.
> Apparently this charging scheme is the one to go for, for long life of
your
> batteries to reduce those "dendrites"....

Am thinking of doing the same thing for an alkaline battery 'charger' /
reconditioner- relies heavily on PWM- albeit very low frequency PWM. Be
interested to hear if you get any good results.

> Anyone got any help/tips/neat circuit ideas?

Main hint from experience : for NiCDs.. make sure you discharge them fully
before starting to charge them or your batteries will not last very long. I
think the memmory effect is well documented but underestimated by most
peple- but on the other hand-- NiMh batteries are much nice to deal with
then NICd betteries-- ( & more envirmonmentally friendly as well !)

> Thanks,
> Bernard Wood
> New Zealand

Jon Baker
Birmingham
England.

Ex Australlian resisent, Ex, American Resident :)

Jon Baker
jon@spam_OUTjb707017TakeThisOuTspamhotmail.com

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2001\12\10@225447 by Russell McMahon

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> Planning on doing a PIC -based charger (to control charge time, LED mode
> display to user, PWM operation, and other) that pulse charges using PWM
> waveform for say 3seconds then shorts all batteries for 100msec, cycling.
> Apparently this charging scheme is the one to go for, for long life of
your

Presumably you mean 'load" rather than "short". Shirting would reduce the
life of battery and, quite possibly, charger. Dendrites would be unlikely
though :-)



       RM

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2001\12\11@131455 by Simon-Thijs=20de=20Feber?=

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Hello All,

Please check the following site.

http://www.angelfire.com/electronic/hayles/charge1.html

The schematic is on there, SW you have to make your
own, cause he is not distributing it.

BTW : Complete discharge is absolutely not necessary
!!! This is one of the myths about NIMH's.

If your algorithm is somewhat intelligent you can make
a very good charger (if there was any car better than
a Rolls Royce iw ould have used this comparisson)

grtz

Simon


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2001\12\11@152249 by Benjamin Bromilow

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From: "Jon Baker" <jonspamKILLspamHAYSEED.NET>

> Main hint from experience : for NiCDs.. make sure you discharge them fully

... discharging down to 1v per cell is considered "fully" BTW
.... the "burp" charges are the ones to emulate. The surges of power prevent
crystal formation, thereby improving capacity...

Ben

Ben

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2001\12\12@165351 by Kirk Lovewell

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I am working on the same project for my own use, in the planning stages
right now.

The circuit descibed in this link seems pretty straight-forward, although it
doesn't seem like the 8 bit a/d in the 16C711 (this was the first I had
heard of this series)  would have enough resolution to detect the subtle
voltage peak at full charge.  Wouldn't the 16F87X with the 10 bit a/d be a
better choice these days?

Also, this ciruit uses a linear regulator to control the current, is there a
reason why this is done instead of a more efficient PWM type control scheme?
Do the batteries not like the switched current? Couldn't you use PWM and
filter out the current downstream?

Kirk

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2001\12\12@183304 by John Ferrell

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The "Super Turbo Charger" at http://rc-dymond.com/ is available under
several vendors names. It works very well. Take a look at the specs.

I have found buying generic & off brand NiCads and NiMh cells to be a waste
of money and time. The Sanyo's really perform as the data sheets describe.
http://www.sanyo.com/

Whatever batteries you use will require a few "break-in" cycles to get by
false peaks on new cells.

I use them flying Radio Controlled Aerobatic aircraft where it is possible
to lose $3000 in one mishap.  It pays to know your batteries!

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"



{Original Message removed}

2001\12\16@163534 by Kevin A. Benedict

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Hi Everyone,
I was going to build this circuit(below) and give the
programming a go myself.
Can I replace the BC548 transistor with a 2N3904 ?
Also, for a flash chip would the PIC16F870 be the best choice,
cheapest, with similiar features(A/D,PWM) as the PIC16C711 ?

Thanks in advance,
      Kevin

Simon-Thijs de Feber <@spam@stdf23173KILLspamspamYAHOO.CO.UK> said:

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