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Electronics => Electronics => Topic started by: aruna1 on March 23, 2010, 03:13:23 PM

Title: LM338 battery charager help
Post by: aruna1 on March 23, 2010, 03:13:23 PM

hi i made this circuit(taken from http://www.talkingelectronics.com/projects/ChargingNiMH/ChargingNiMH.html (http://www.talkingelectronics.com/projects/ChargingNiMH/ChargingNiMH.html)),but doesnt seems to work.as i know voltage drop in R should be 1.2v, but in my circuit its about 4V, i tried R values from 1 ohm to 100 ohm,but couldnt get the circuit working,when using 1 ohm current drain was about 2.45A.
my input is from 12V-0V-12V transformer(24V dc using rectifier bridge) and target is charging a 12V 1500mAh NiMH battery pack.
any ideas?
thanks
(http://www.talkingelectronics.com/projects/ChargingNiMH/images/CircuitD.gif)

Title: Re: LM338 battery charager help
Post by: waltr on March 23, 2010, 05:28:25 PM

Quote

24V dc using rectifier bridge

Do you have a filter cap after the rectifier?

Title: Re: LM338 battery charager help
Post by: aruna1 on March 23, 2010, 07:03:10 PM

yes,220uf

Title: Re: LM338 battery charager help
Post by: billhowl on March 24, 2010, 12:22:03 AM

You may like to try this circuit taken from the datasheet, which limit both voltages and currents to charge the battery. or you can take a look on other charger circuit in the datasheet.
http://www.national.com/mpf/LM/LM338.html (http://www.national.com/mpf/LM/LM338.html)

Title: Re: LM338 battery charager help
Post by: Pratheek on March 26, 2010, 08:53:43 AM

The LM317 is a linear regulator so it will need an input voltage which is greater than the required output voltage by 2V.

So if you need a 12V output, you will need atleast 14V at the input pin.