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PICList Thread
'Battery Charger'
1996\11\15@064125 by ang (Chee Foon Tiang)

   Any PIC-ers have every done a
   Multi-battery (NiMH,NiCD & Li-ion) or
   Smart Battery charger?
   Would like to share notes.
Peter Tiang

1996\11\15@085835 by Brian Hackett

picon face
>    Any PIC-ers have every done a
>    Multi-battery (NiMH,NiCD & Li-ion) or
>    Smart Battery charger?
>    Would like to share notes.

Dear Peter,

I you do hear about anything, please let me know.  I am trying to use 4 NiMH
batteries in a pack and need a battery charger.  Thanks.  Brian.

1996\11\15@093243 by Larry G. Nelson Sr.

I just finished a smart charger with a benchmarq BQ2003 chip. Not fancy and
not as good as can be done with the Microchip part but the design was quick
and works well. No gas gauge or anything like that but charge before
discharge is supported as well as a large variety of charge termination

At 09:09 AM 11/15/96 -0500, Brian Hackett wrote:
{Quote hidden}

Larry G. Nelson Sr.

1996\11\15@100135 by Ray Gardiner

EDN ran a few articles last year on battery charging methods,I seem to recall
that the key was to look at the first derivitive of the battery volts and
look for inflections, you could try and do a search
of their back issues archives. If you already have a pic doing other stuff
then you will want it to look after the battery management. It is a complex
task and when the battery management fails the system as a whole fails!

If cost is not an issue then a solution like the microchip/zilog/benchmarq
parts may be a better solution.

{Quote hidden}


Ray Gardiner, Shepparton, Victoria 3630,  Australia,

1996\11\15@192706 by Jeff Otterson/N1KDO

picon face
Look at Maxim's MAX712 (NiMH) and MAX713 (NiCd) chips.  No PIC involved,
sorry.  I hava a schematic for a NiCd charger based on the MAX713 at my

Jeff Otterson
Maker and user of tools
PGP key available at

1996\11\15@202544 by ang (Chee Foon Tiang)

>I'm just inside this topic for my proper use. I fly some electric glider and
>now i'm studying a Hi-Tech charger with trickle mode, peak detection, charge
>with pulse and controlled current. But this project is waiting in my mind now.
>I'm thinking using a 8031 instead a PIC, because 8031 need only an EPROM and I
>can just program 16C84, 71 , 54..57, and EPROM that's all.
>As these chip seems to have not enought I/O and RAM, (means no RAM extension
>except trought I2C), my design will certainly use a 8031. In addition, most of
>A/D and D/A converter need a data bus sequence and 8031 have already a built
>in one.
>But nothing is fixed yet.
>The charger must do:
>        - delta-V charge,

   The charge termination method that is usually employed in the
   industry are:
   i.   minus delta V  - This is applicable to NiCD and NiMH batteries
                         although the NiMH has a smaller drop in
                         its terminal voltage upon full charge
                         Resolution required : -8mV/cell (for normal 6V
                         cellular batteries would be around -20~-40 mV)
                         This method is not applicable to the Li-Ion
   ii.  dT/dt          - This method monitors the rate of change in
                         temperature and is very suitable for NiMH
                         batteries with termination at 0.8C/min.
   iii. const V, min I - This method is used for the Li-Ion batteries
                         which requires a constant V charge (you can
                         start as const I but must end with const V) as
                         oppose to constant I charge for the NiMH/NiCD.
                         Method is to charge at the rated voltage and
                         monitors the drop in I until a minimum cutoff.
   iv.  max V, max T & timer cutoff
                       - these are provided as a backup in the event of
                         i, ii & iii termination failure.

>        - pulse charge/measurement

   Pulse charge are suggested to prevent large crystals formation
   in batteries with continuous charge.

>        - cycling a batterie,

   Cycling basically discharges a battery follow by full charge.
   Discharging eliminates "memory effect" which are basically battery
   hysteresis. This is really important only for NiCD batteries.
   Newer batteries like NiMH and Li-Ion does not require discharge before

>        - discharge with controlled current/voltage

   This is a bit tricky, pulsed discharge (unless you have other method of
   controlling I/V) is not recommend as I heard somewhere that it
   damages the cell materials.

>        - trickle mode
>        - allows to charge more than 16 elements with a car batterie

   Car batteries are made of Lead acids elements, don't have much experience.

>        - allow to charge a minimum of 2 pack simultaneously with different
>        parameter,
>        - record the curve of charge/discharge, (EEPROM or RAM)
>        - be able to comunicate with a PC

   I would recommend that you build a big-banged RS-232-C interface to the
   PC and any data collected on the charge/discharge curve be store on it.

>        - have a LCD panel, some buttons
   LCD based on the Hitachi 44780 are quite good, especially if you
   use the 4-bit data interface (which saves you 4 I/Os, only 7 required)

>As you see, I just begin to think it. Seems to need a minimum:
>        - 16K RAM/or EEPROM

   If a PC is used you don't really need that much RAM or EEPROM.

>        - a 12 bit A/D

   For NiMH/NiCD charging, I don't think you require this kind of
   resolution. However, if you plan to charge Li-Ion batteries,
   it is highly recommended, as a difference in 100mV makes a lot of
   difference in the full charge capacity of the Li-Ion.

>        - two 8 bit D/A
   Why would you need a D/A?

>        - a PWM power
   Step down DC-DC convertor under PWM control would be recommended.
   However, check the maximum frequency of the microcontroller PWM
   that you are using as it ultimately dictates the size of your
   filtering components.
>        - an LCD panel
>        - a RS232 interface,
   As above.

>About Ni-Mh and Li-Ion, I don't have any documentation and I don't know what
>are the
>requierment to charge it in the better way.

   For all "normal" purpose, NiMH/NiCD can be charged in the same way.
   This is because NiMH batteries are designed to mimic the characteristic
   of the NiCD. However take note that it has a smaller -delta V termination
   Li-Ion is a totally type of battery. It can take const I charge but
   must be charged at const V finally. Accuracy of the charging V is

   Hope this gives a brief introduction to battery charging technology.


Peter Tiang

1996\11\16@112103 by Brian Hackett

picon face
>Look at Maxim's MAX712 (NiMH) and MAX713 (NiCd) chips.  No PIC involved,
>sorry.  I hava a schematic for a NiCd charger based on the MAX713 at my

Hi Jeff,

Thanks for the info on the MAX713.  I tried to access your site and got a
"URL not found" error.  I can find Mindspring but can't find you on it.  Pse
advise.  Thanks.


1996\11\16@114829 by Chuck Kirk

At 07:40 PM 11/15/96 +0800, Peter Tiang (Chee Foon Tiang)


Check out the Maxim 2003. Look at the data sheets, app notes etc at:

and ask for a sample.


1996\11\16@143258 by Jeff Otterson/N1KDO

picon face
oooops...  I left the all-important tilde off...


there is a *postscript* copy of the schematic for the max713 based nicad
charger there.  If you don't have access to a postscript printer, then I
guess you could try GhostScript, which is freeware...


At 11:20 AM 11/16/96 -0500, you wrote:
{Quote hidden}

Jeff Otterson
Maker and user of tools
PGP key available at

'Battery charger'
1997\11\26@140444 by Tim Kerby
picon face
How about an intelligent battery charger someone.  To be able to charge
NiCad, Lead Acid (sealed gel type), NiMH and others using bulk, float and
trickle charging at various voltages to get the best performance all in one
unit would be great.  PIC control with an LCD and mini keypad anyone?

Tim Kerby

Personal Web Pages:

1997\11\26@233447 by Michael S. Hagberg

check out the maxim site. i recall recently (this year) seeing specs on an
intelligent charging chip. there was also a schematic with the chip.


{Original Message removed}

'Battery charger'
1997\12\01@081505 by Jason Wolfson
I'm slowly working on a universal charger with a 20x4 LCD and small key pad,
uses a 16C63 and a 14000, very small, just haven't had time to finish the
also want to be able to charge single cells, i.e. 1.2V......
anyone have some pointers to the latest state of the art charging

{Original Message removed}

'Battery Charger'
1999\04\10@145908 by A. Keith Fligg
picon face
Does anyone out there have any info/schematics on charging/conditioning
NiCad batteries, preferably utilizing a PIC (of course!).


- Keith

1999\04\10@180130 by llgren

Well... i cant help you with a pic version of this, but i know that there are cheap and reliable all-ready circuits to buy, for example MAX712/713 ( manages NiMh and NiCd up to 16 cells in series ) and then there are the MAX846 that also can manage Li+ cells.
Price is about 5 - 10 dollars a piece i think. very few outside components are needed. These circits allow you to hook up a NTC resistor, so that the cells wont get to hot, the circuits also goes to maintanance loading when done.

( excuse the poor spelling )


----- Original Message -----
From: A. Keith Fligg <KILLspamkfliggKILLspamspamAZSTARNET.COM>
Sent: Saturday, April 10, 1999 8:37 PM
Subject: Battery Charger

> Does anyone out there have any info/schematics on charging/conditioning
> NiCad batteries, preferably utilizing a PIC (of course!).
> Thanks,
>  - Keith

1999\04\10@194831 by Bob Drzyzgula

You might want to take a look at the Microchip Reference
Design #2, which you can find documented at


On Sat, Apr 10, 1999 at 11:37:04AM -0700, A. Keith Fligg wrote:
> Does anyone out there have any info/schematics on charging/conditioning
> NiCad batteries, preferably utilizing a PIC (of course!).
> Thanks,
>  - Keith

Bob Drzyzgula                             It's not a problem                until something bad happens

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