One-Chip solution for charging NiMh batteries

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Hi all,

For an upcoming project, I wish to charge some NiMh batteries in circuit. I
understand that there should be a temperature sensor and charge finishes at
a predetermined delta temp.

I wish to make the circuit as compact and simple as possible. I can see
there are many battery charging chips out there, but is there one that
anyone can recommend based on experience?

I guess the best "one chip" solution for me would be a chip that has an in
built temperature sensor, that could be integrated within the battery pack.

I'd prefer a Dip package, but SMD would be OK I guess. Thanks for your help.
It's going to be a 9.6V battery pack by the way.





Re: One-Chip solution for charging NiMh batteries



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That's probably the most reliable way of detecting end of charge with
NiMh cells, particularly with fast charging.

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Most of the chips I've seen are more charge controllers than full
chargers, and they usually need quite a few external components.  Maxim,
TI (who bought out Unitrode and Benchmarq), and National all have these
kinds of controllers.  Other IC manufacturers probably have similar
devices, but I'm not aware of a "one chip" solution.

A lot of people design their own charge controllers nowdays, using a PIC
or Atmel microcontroller (or in fact just about any microcontroller).
Again, though, you'd still need a few external components.

I'm not aware of any chip that has its own internal battery pack
temperature sensor - all use external temperature sensors, in some cases
two or three.  I believe some chips do have some kind of internal sensor
to measure ambient temperature, but because it needs to measure ambient,
you couldn't attach the chip to the battery back.

It's unclear exactly what you're trying to do - perhaps more detail
would help with suggestions.  For example, what is the capacity of your
battery pack?  What is the current draw of what it's powering?  How fast
do you want to charge the battery pack?

Also, are you intending to leave the charger connected to the battery
pack all the time?  If so, I'm not aware of any nimh battery charging
chip or circuit that will restart the charging sequence without having
to be manually reset or having the battery pack disconnected first.

Something else to keep in mind - depending on how fast you're intending
to charge the battery pack, and the condition of the cells in it, you
may need to find some way to measure the temperature of more than one cell.

Is this for a single charger, or is it something that you need to
manufacture or duplicate?

Googling web sites for this kind of thing often doesn't turn up much
real information, but you could give it a try with something like:

http://www.google.com/search?hl=en&lr=&safe=off&q=nimh+battery+charger+ic&btng=search&sa=N&tab=gw

Searching newsgroups may be better:
 
http://groups.google.com/groups?hl=en&lr=&safe=off&site=groups&q=nimh+battery+charger+ic&btng=search

Regards, Peter

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