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kroto 29th October 2012 03:36 PM

Need Battery Charger Circuit with Autor Power Off
The battery is Ni-Cad 12V 5Ah.
Can anyone give me one simple charger circuit with auto power off?
& Please give me explanation how the auto power off circuit works so that I can understand the principle.

thanks. :o

TANDBERGEREN 31st October 2012 11:14 PM

Make a powersupply with constant current at about 0,5A.
Make a voltage-detektor cirquit wich monitors the Ni-Cad bank,
set to 14,5V, and let this cirquit detach the battery, but still monitor the charging voltage.
(Remember that the input voltage to the charger should be around 20V to secure good charging. )

Charging time: Approx 14Hrs.

The voltage detector can operate a relay, wich is put in series between the current regulator and battery-pack.

Need schematics?
I might make one, but You could easily find somewhere on the web.

AndrewT 1st November 2012 09:39 AM

add a voltage regulator.
This is fed by the CCS and limits the maximum voltage that the battery sees while charging.
Otherwise severe heating will permanently damage your Nicads.

marce 1st November 2012 10:08 AM

Look around, there are numerous battery charger supervisory IC that will do the job and provide the best solution, you can also add telerature sensing, worth the effort for safety and prevent damage to the battery..
MAxims ahve numerous solutions as do others:
Search Results: chargers - Maxim
Most industrial and commercial designs that require some form of battery charging circuit will use this form of solution copy the reference design.

kroto 18th November 2012 11:45 PM

some simulation
1 Attachment(s)
Thank for your reply guys.

I have a bunch of TL071, maybe I can use that.
how about the scematic?
it seem OK to me when simulating.
if V2=14v4 the comparator output still high (+15V).
if V2=14v5 the comparator output go low (+1V).

@TANDBERGEREN : why the input should be around 20V?
@marce: I think that is too complex for me :D


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