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Forum index » Electronix » design
NiMH charging circuit.
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Mark
electronics forum Guru


Joined: 03 May 2005
Posts: 329

PostPosted: Fri Jul 21, 2006 2:03 pm    Post subject: Re: NiMH charging circuit. Reply with quote

Derek wrote:
Quote:
Hello my name is derek and i have done the same thing with my mp3
player, if i can dig up my old schematic, i'll send it to you
mark.gillespie@gmail.com wrote:
Hi, I have a small electronic device (portable DAB radio), that runs on
2xAA batteries, but for some unknown reason (cost??), the manufacturer
decided not to provide an external power source socket.

The battery life is horrendous.. 6 hours max..

Anyway, figured it would be very handy to "upgrade" it. would like to
put a couple of NiMH AA batteries in there, a small socket on the side,
and make a in-situ charger from a PC USB supply.

Got a couple of questions, not very good at circuit design, and
wondering if a guru here can help.

1/ Is is OK to charge these sort of things in-situ? I mean charging
the batteries, wilst the player is in use, or will I need to devise a
switching mechanism? (the small connector I have is a 3 way, so I can
do this if I need to, but I want to keep it simple as can be).

2/ As I understand it, NiMH batteries use constant current, how can I
achieve a simple circuit to charge this?

Any help, MUCH appreciated..

two things

1) set up the charger so it chargesd at c/10 rate or less...if your
cells are 2000mA hours, then set up the changer for 200mA and it will
take about 14 hours to charge them....do not overcharge them or let
them get hot, a lower current is better (safer re overcharging) but
takes longer...

2) be sure that the voltage out of the charger will not FRY your unit
if the charger is hooked up and the batteries are removed... you may
need a zener diode of something to limit the no load voltage...

Mark
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Derek
electronics forum beginner


Joined: 23 May 2005
Posts: 5

PostPosted: Fri Jul 21, 2006 11:16 am    Post subject: Re: NiMH charging circuit. Reply with quote

Hello my name is derek and i have done the same thing with my mp3
player, if i can dig up my old schematic, i'll send it to you
mark.gillespie@gmail.com wrote:
Quote:
Hi, I have a small electronic device (portable DAB radio), that runs on
2xAA batteries, but for some unknown reason (cost??), the manufacturer
decided not to provide an external power source socket.

The battery life is horrendous.. 6 hours max..

Anyway, figured it would be very handy to "upgrade" it. would like to
put a couple of NiMH AA batteries in there, a small socket on the side,
and make a in-situ charger from a PC USB supply.

Got a couple of questions, not very good at circuit design, and
wondering if a guru here can help.

1/ Is is OK to charge these sort of things in-situ? I mean charging
the batteries, wilst the player is in use, or will I need to devise a
switching mechanism? (the small connector I have is a 3 way, so I can
do this if I need to, but I want to keep it simple as can be).

2/ As I understand it, NiMH batteries use constant current, how can I
achieve a simple circuit to charge this?

Any help, MUCH appreciated..
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mark.gillespie@gmail.com
electronics forum beginner


Joined: 21 Jul 2006
Posts: 1

PostPosted: Fri Jul 21, 2006 9:05 am    Post subject: NiMH charging circuit. Reply with quote

Hi, I have a small electronic device (portable DAB radio), that runs on
2xAA batteries, but for some unknown reason (cost??), the manufacturer
decided not to provide an external power source socket.

The battery life is horrendous.. 6 hours max..

Anyway, figured it would be very handy to "upgrade" it. would like to
put a couple of NiMH AA batteries in there, a small socket on the side,
and make a in-situ charger from a PC USB supply.

Got a couple of questions, not very good at circuit design, and
wondering if a guru here can help.

1/ Is is OK to charge these sort of things in-situ? I mean charging
the batteries, wilst the player is in use, or will I need to devise a
switching mechanism? (the small connector I have is a 3 way, so I can
do this if I need to, but I want to keep it simple as can be).

2/ As I understand it, NiMH batteries use constant current, how can I
achieve a simple circuit to charge this?

Any help, MUCH appreciated..
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