Searching \ for '[EE]: NiMH battery chargers' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/power/batterys.htm?key=battery
Search entire site for: 'NiMH battery chargers'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: NiMH battery chargers'
2001\05\15@150617 by Lawrence Lile

flavicon
face
part 1 2021 bytes content-type:text/plain; (decoded 7bit)

I could easily make the argument that the MAX713 might not be flexible
enough to do what I need to do.  I may still end up cooking up a PIC based
controller from scratch, too.  I've got a call in to maxim about some issues
now that may be showstoppers.

Basically, I've got to charge from solar cells, that are always connected.
The MAX713 charge cycle is initiated by connecting the battery or by
connecting power.  I can't figure out how to make it charge more than once,
with a permanently connected solar cell and permanent battery.

And yes, I may change battery chemistries at some future time, as well.

I guess a PIC based unit would need:

Voltage sensing  (by a resistor divider and a little low pass filter, maybe)

Battery temperature sensing vs. ambient (by a simple 2 thermistor divider)

Switch (such as a power transistor)

Current sensing (such as a series resistor)

The PIC would initiate charging at a fixed minimum voltage,
regulate current through the pass transistor
terminate charging with either negative/zero voltage slope, absolute
voltage, or change in temperature
Could also terminate charging via a maximum amp-hour (fixed amp rate at a
certain time) number.

I would dedicate a small PIC12C671 to this task, as my robot brains have
plenty of other things to do.

I've attached some sketches of the idea.

-- Lawrence Lile


Olin Sez:
>
> I haven't looked at the Maxim chips yet because I'm not ready to think
about
> charger design yet.  I will when the time comes, but I was envisioning a
PIC
> controlling multiple packs charging independently at the same time.  I'd
> like the logic to all be in the PIC so I can screw with it and maybe be
able
> to charge other types of batteries with only a firmware change.
>
>
> ********************************************************************
> Olin Lathrop, embedded systems consultant in Littleton Massachusetts
> (978) 742-9014, spam_OUTolinTakeThisOuTspamembedinc.com, http://www.embedinc.com


part 2 22229 bytes content-type:application/octet-stream; (decode)

part 3 136 bytes
--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email .....listservKILLspamspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body


2001\05\15@154218 by Peter Tiang

flavicon
face
> I guess a PIC based unit would need:
>
> Voltage sensing  (by a resistor divider and a little low pass filter,
maybe)
>
> Battery temperature sensing vs. ambient (by a simple 2 thermistor divider)
>
> Switch (such as a power transistor)
>
> Current sensing (such as a series resistor)


   Need LC filter for switch-mode operation ?

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspamKILLspammitvma.mit.edu with SET PICList DIGEST in the body


2001\05\15@170552 by Lawrence Lile

flavicon
face
That would be nice, but I didn't want to fool around designing a switcher.
Linear regulation should be relatively easy to design.    This has to get
done this summer, in my "spare" time"  (what spare time?)

Peter Pontificated:

>     Need LC filter for switch-mode operation ?
>
> --
> http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> email .....listservKILLspamspam.....mitvma.mit.edu with SET PICList DIGEST in the body
>
>



--Lawrence

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email EraseMElistservspam_OUTspamTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body


2001\05\15@171136 by Olin Lathrop

face picon face
> Voltage sensing  (by a resistor divider and a little low pass filter,
maybe)

For the particular NiMH battery packs that have been going around lately,
the 5V PIC A/D range is just about right.  I connected the battery directly
to the PIC A/D input and did the low pass filtering in software.  There are
plenty of cycles in this app since things happen in seconds or minutes, not
milliseconds.  In the final charger I have to worry about what happens when
the PIC power is off but the battery is still connected.  The battery would
try to power up the circuit thru the PIC protection diode.  Obviously the
final charger circuit is going to require some thought.

> Battery temperature sensing vs. ambient (by a simple 2 thermistor divider)

I'm hoping to get away without having to sense temperature, but that may not
be possible.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olinspamspam_OUTembedinc.com, http://www.embedinc.com

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email @spam@listservKILLspamspammitvma.mit.edu with SET PICList DIGEST in the body


More... (looser matching)
- Last day of these posts
- In 2001 , 2002 only
- Today
- New search...