>Hi Everyone,
> I am attempting to build a smart battery charger for
> NiMH batteries (8-AA), with a F877. I am going to
> use PWM to control a LM317, and sample the voltage
> with the ADC to look for the delta V.
> I was planning on: (I got these from Panasonic)
> trickle charge .05C which would be 5% duty cycle
> Soft charge    .20C which would be 20% duty cycle
> fast charge    .75C which would be 75% duty cycle
> I have a couple questions:
> 1.) What frequency should the PWM be ?
> 2.) Anybody know a simple circuit to control the
> LM317 with the PWM PIC pin ?
> 3.) How often should I use the ADC to look for the
> delta V to turn off or switch to trickle charge ?
> Any help would be appreciated.
>
> Thanks,
>         Kevin
> PS. I am a programmer not an EE, if you couldn't
> tell from above :)
>

> Hi Kevin,
>
> Check this site :
>
> http://www.angelfire.com/electronic/hayles/charge1.html
>
> He did something same.
> I am designing a similar circuit and have not even
> asked tehse questions myself so i am interested in
> ideas of others / your results.
>
> grtz
>
> Simon
>
> >Hi Everyone,
> > I am attempting to build a smart battery charger for
> > NiMH batteries (8-AA), with a F877. I am going to
> > use PWM to control a LM317, and sample the voltage
> > with the ADC to look for the delta V.
> > I was planning on: (I got these from Panasonic)
> > trickle charge .05C which would be 5% duty cycle
> > Soft charge    .20C which would be 20% duty cycle
> > fast charge    .75C which would be 75% duty cycle
> > I have a couple questions:
> > 1.) What frequency should the PWM be ?
> > 2.) Anybody know a simple circuit to control the
> > LM317 with the PWM PIC pin ?
> > 3.) How often should I use the ADC to look for the
> > delta V to turn off or switch to trickle charge ?
> > Any help would be appreciated.
> >
> > Thanks,
> >         Kevin
> > PS. I am a programmer not an EE, if you couldn't
> > tell from above :)
> >
>
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> At 09:42 AM 2/7/02 -0800, bblick wrote:
> > > I am attempting to build a smart battery charger for
> > > NiMH batteries (8-AA), with a F877. I am going to
> > > use PWM to control a LM317, and sample the voltage
> > > with the ADC to look for the delta V.
> >
> >No, that will not work. It may work a few times, but with 8 cells you will
> >get a good peak only when the cells match perfectly. They won't do that
> >very often. Also delta-V on NiMH is pretty mild. Works OK on NiCd.
>
> You need to feed the batts a constant current, and look at both dV/dT and
> dT/dT (temperature)
>
> NIMH dosen't necessarily give you a peak or droop, so much as flatten to
> zero delta for a while.
>
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