fever16 Posted March 12, 2006 Report Share Posted March 12, 2006 hi alliam working on a school LED project.where we need to use a 3.6v 300ma battery(one used in cardless phones).u know cordless phone chargers are dumb type.can u suggest me some good charger for this battery pack.i don't want hi-fi type of charger.just simple one which makes the battery last for long times without destroying it.and if it got some indictor it would be great.thanks in advance Quote Link to comment Share on other sites More sharing options...
ante Posted March 13, 2006 Report Share Posted March 13, 2006 Hi fever,Welcome to our forum,You could use an LM317 setup as a constant current regulator at 15mA and just leave it on 24/7! Quote Link to comment Share on other sites More sharing options...
fever16 Posted March 13, 2006 Author Report Share Posted March 13, 2006 thanks anteis it possible to make some simple moniter type.imean which got atleast indictor(imean lighting up an LED when charging done) using some transistor like.. Quote Link to comment Share on other sites More sharing options...
ante Posted March 13, 2006 Report Share Posted March 13, 2006 Hi fever,You wanted a simple one, just leave it on and the pack will always be full when you need it. If you go for a “ready LED” circuit things starts to get complicated. Quote Link to comment Share on other sites More sharing options...
fever16 Posted March 14, 2006 Author Report Share Posted March 14, 2006 ohh ok theni did a small search on net and i found below 2.which one of this is best.http://agendawiki.com/cgi-bin/aw.pl?ChargingCircuitsthis one from our forum only.and this is from groups-google-what is ur openion abt these Quote Link to comment Share on other sites More sharing options...
ante Posted March 14, 2006 Report Share Posted March 14, 2006 Hi fever,This is from the LM117/317 datasheet; R1 should be 82 Ohm and you put the pack where it says load! You can power it from any DC-wallwart 9 – 25VDC. ;) Quote Link to comment Share on other sites More sharing options...
fever16 Posted March 15, 2006 Author Report Share Posted March 15, 2006 thanks ante.i'll go with lm317 based circuiti dono much abt these abt these rechargbles.but i think ni-cd shld be chrged at 1.5+pack voltage and c/10 of its current rating it.if it is true then i need 5.1v @ 30ma for 14Hr . Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 15, 2006 Report Share Posted March 15, 2006 i dono much abt these abt these rechargbles.but i think ni-cd shld be chrged at 1.5+pack voltage and c/10 of its current rating it.if it is true then i need 5.1v @ 30ma for 14Hr .I don't know where you learned the wrong voltage formula.Each cell will charge to 1.4V to 1.5V. Therefore the 3-cell battery will be 4.2V to 4.5V when fully charged.The LM3117 needs at least 2V across it and the current-sensing resistor has a 1.25V drop, so the minimum input voltage to the circuit is 7.75V. Quote Link to comment Share on other sites More sharing options...
fever16 Posted March 15, 2006 Author Report Share Posted March 15, 2006 thanks for correcting me.is current calculation is right(c/10 for 14Hrs)if yes then the final result will be 7-8v input to LM317 with R1 82Ohms resistor.(as ante said) can charge a 3.6v battery pack safely in 14Hrs Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 15, 2006 Report Share Posted March 15, 2006 is current calculation is right(c/10 for 14Hrs)?Yes, if the battery is rated for 300mA/hrs.if yes then the final result will be 7-8v input to LM317 with R1 82Ohms resistor.(as ante said) can charge a 3.6v battery pack safely in 14HrsNo. 7V is too low. "The minimum input voltage to the circuit is 7.75V." Quote Link to comment Share on other sites More sharing options...
ante Posted March 15, 2006 Report Share Posted March 15, 2006 Hi Guys,Yes 7 volts is too low, that’s why I said “You can power it from any DC-wallwart 9 – 25VDC.”! ;D Quote Link to comment Share on other sites More sharing options...
fever16 Posted March 16, 2006 Author Report Share Posted March 16, 2006 got it.thanks.is there any particular formula for this resistor value.imean in furture if i want to charge packs of 700ma or 800ma etc i need to change resistors too right.and gyus to charge AA or AAA "single cell" what modification shld be done in lm317 design. Quote Link to comment Share on other sites More sharing options...
ante Posted March 16, 2006 Report Share Posted March 16, 2006 The voltage drop across R1 is always 1.2Volts (controlled by the regulator), using (I = U / R )you get the charge current.Example; 1.2 V / 82 Ohm = 0.0146 A that means about 15 mA!If you increase the charge current to 800mA you need a heatsink for the LM317!Got it? ;D Quote Link to comment Share on other sites More sharing options...
fever16 Posted March 17, 2006 Author Report Share Posted March 17, 2006 as per c/10 for 14Hr rule,current for charging a 300ma battery shld be 30ma. right.but in previous post u said 82 Ohms resistor will work.where as it shld be 40 Ohms for 30ma correct me if iam wrongiam bit confused ??? Quote Link to comment Share on other sites More sharing options...
ante Posted March 18, 2006 Report Share Posted March 18, 2006 Hi fever,That’s correct for C/10 but I suggested 15mA so that you could leave the pack unattended for an “unlimited” period of time. If you like you can add another 82 Ohm resistor in parallel to have C/10 – 14 h charge. I made a drawing for you, if you leave the switch open its C/20 if closed it’s C/10.If you don’t need the C/20 setting just omit the switch. The reason for two resistors is that it’s not easy to find a 40 Ohm resistor but two 82 in parallel is 41 Ohm and that is just fine. 8) Quote Link to comment Share on other sites More sharing options...
fever16 Posted March 18, 2006 Author Report Share Posted March 18, 2006 cool.thanks a lot ante.tomorrow i'll get some resistors of different values.so that i can make it variable.imean 15ma-c/20 30ma-c/10 for 14Hr 60ma-c/5 for 7Hrs (ofcourse not preferable)thanks once again.for helping meu ppl are just really amazing . :-* Quote Link to comment Share on other sites More sharing options...
ante Posted March 19, 2006 Report Share Posted March 19, 2006 OK, let us know how it works out! ;D Quote Link to comment Share on other sites More sharing options...
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