walid Posted May 7, 2006 Report Share Posted May 7, 2006 Hi all my friendsWhen somebody build a batt charger that stop charging when batt full, he must use a comparator to compare batt voltage to some referance voltage..when i conect a 3 volt batt to 5v power supply and wat to measure thewoltage across the connection, what would it be?i ask this question to know at what level of charge i must stop the processif i have four 1.2v batts (total = 4.8v), now these batts are not fully charged, its voltage = 4 v or less.i want to recharge them using 6v power supply. if i connect a voltmeter across the connection, what would itsreading at thenbegining and at full chargei hope that u uderstand meyourswalid Quote Link to comment Share on other sites More sharing options...
jtamminen Posted May 7, 2006 Report Share Posted May 7, 2006 Hi.This is not a simple question. Actually we need more information:What kind of battery You are using? NiCad/NiMh etc...For example with NiCad the voltage is not so good indicator, as it stays in 1.2volts but still getting more and more charge. Finally the voltage goes down a little, indicating a fully charge.Other indicator is that when the battery is full, the battery temperature has gone up to about 40-degrees centigrate.Others here have answer with other battery-chemistry I believe. Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 8, 2006 Report Share Posted May 8, 2006 Hi Walid,Read the tutorials about rechargable batteries at www.energizer.com . On the 1st page, click on Technical Info near the top, then on the 2nd page select Ni-Cad or Ni-MH type. Then look at the PDFs of charging and discharging. The voltage changes with chemistry, temperature and the amount of charging current. Tne voltage reaches a peak near full-charge then drops a little. Some battery charger ICs detect the voltage peak or temperature rise to shut-off the charging.Here is a typical voltage curve for a Ni-MH cell: Quote Link to comment Share on other sites More sharing options...
walid Posted May 10, 2006 Author Report Share Posted May 10, 2006 audioguru i go to where you point me but nothingmy question is very simpleforget that it is chargerassume that u connect a fully charged 3v batt to a 5v ps and measure the voltage across this connectionwhat is your reading?thank you Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 10, 2006 Report Share Posted May 10, 2006 my question is very simpleforget that it is chargerassume that u connect a fully charged 3v batt to a 5v ps and measure the voltage across this connectionwhat is your reading?You cannot do that!A Ni-Cad or Ni-MH battery is charged with a current. If you connect a fully charged two-cell battery (about 3.0V) to a 5V power supply then the battery will overcharge with a huge current. The huge current will cause the battery to overheat and vent its chemicals or explode.I showed a curve of battery voltage vs amount of charge. It is more complicated because the voltage changes with the battery's temperature and its temperature is changed by charging. Quote Link to comment Share on other sites More sharing options...
walid Posted May 11, 2006 Author Report Share Posted May 11, 2006 ok ok oki want to tell you that i recharge unrechagable batteries for years and reuse themit is never explodei have not faced any problem with them and after recharge them the last long time specially in remote control and sound toysi want that info to stop the charge process whe it must stopcan you help me? Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 11, 2006 Report Share Posted May 11, 2006 Walid,This was the 1st time that you said you are charging non-rechargable batteries.I will not discuss it because they are not supposed to be charged. Quote Link to comment Share on other sites More sharing options...
Muhammad Abu Bakar Posted May 11, 2006 Report Share Posted May 11, 2006 Hello Walid!I think temperature is the most critical criteria to stop charging. If u have lot of experience charging non-rech bats than u can tell us the avg time to charge common cells like AA, AAA or D. It will be usefull Quote Link to comment Share on other sites More sharing options...
walid Posted May 13, 2006 Author Report Share Posted May 13, 2006 I'm sorry, lets forget what i said before and start again ....the emergency neon lamp has a rechargable 6v rectangular battif i want to charge it using 7.5 to 9 volt power supply and want to stop the charging process when the batt is fully charged using a voltage comparatorat what voltage i must stopthank youHello Walid!I think temperature is the most critical criteria to stop charging. If u have lot of experience charging non-rech bats than u can tell us the avg time to charge common cells like AA, AAA or D. It will be usefullHi Mr Muhammad Abu Bakar, in fact i want to learn about batt charging and how the designer make a decesion in chossing his components and not to measure temperature and ave timeyours walid Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 13, 2006 Report Share Posted May 13, 2006 Hi Walid,Rechargable batteries have different chemicals inside and need completely different charging circuits to match the type of chemicals. For some of the batteries, if it is fast-charged then a temperature sensor is recommended instead of a voltage sensor to stop charging, to avoid an explosion or a fire.Lead-acid?Ni-Cad?Ni-MH?Li-Ion?Li-Po?The battery is probably lead-acid. Old lead-acid batteries in cars had a fully charged voltage of 13.8V, so half is 6.9V.New car batteries have a fully charged voltage of 14.4V, so half is 7.2V.Some lead-acid batteries have a liquid electrolyte and others have a gel.Some have calcium with the lead.Do you know which type is your battery? Quote Link to comment Share on other sites More sharing options...
walid Posted May 16, 2006 Author Report Share Posted May 16, 2006 Do you know which type is your battery?yes, its a 3 cells Lead-acid batt Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 16, 2006 Report Share Posted May 16, 2006 I have never charged a lead-acid battery. My car does it without my attention. Quote Link to comment Share on other sites More sharing options...
indulis Posted May 16, 2006 Report Share Posted May 16, 2006 Look at http://www.national.com/ds/LM/LM138.pdfThe old data books had a much better write-up, but there is a schematic for a 12V charger near the end. I have built a 40A and 5A version of this circuit and both have worked very well for over 20 years!! Quote Link to comment Share on other sites More sharing options...
walid Posted May 18, 2006 Author Report Share Posted May 18, 2006 I have never charged a lead-acid battery. My car does it without my attention.also my car does it without my attention, but i discuss for theory and then for using this theory as a designer, i told you that i live to learnTo indulis thank you very much Quote Link to comment Share on other sites More sharing options...
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