On Mar 9, 10:55 pm, ehsjr <eh...@bellatlantic.net> wrote:> mrdarr...@gmail.com wrote: > > I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's > > toy electric car (the kind that a kid can ride). The previous battery > > didn't hold a charge when I bought the car. > > > One reference from batteryuniversity.com mentioned something about > > 2.50V per cell for SLA batteries. I'm assuming my battery has 3 > > cells. Another website mentions use of an L200 voltage regulating > > chip (http://www.myra-simon.com/bike/charger.html). > > > I've got a 6VDC (nominal) wall wart that puts out just over 9V open- > > circuit. > > > How should I charge it? > > Per the manufacturer's recommendations. > But that's not what you wanted to hear, > so read below. > > > > > Thanks, > > > Michael > > Here is a way you can charge it: > Build a float charger. Set the float voltage to 7 volts. > Use a 9 or 12 volt DC wall wart (not your 6v wall wart) > The schematic is on the first page of the datasheethttp://cache.national.com/ds/LM/LM317.pdf? > > There are better ways to charge your battery, but this > way won't cook it and is simple to build. > > If you can't build, buy a charger recommended for > that battery. > > EdOk, I built it. Didn't have a 5k pot handy, so I strung up two 1k resistors in parallel and a bunch of 100 ohm resistors in series until I got about 7.2V out. Hooked it up to the battery, and I was surprised to see only 50mA going through the battery. Typically, without the LM317 I got 100+ mA going through. LM317 was cool to the touch (with heatsink). I thought my power supply was underpowered, so I tried a 12V wall wart (about 14V with no load) instead. But then, after going through the LM317, voltage going to the battery was just over 7.2V. Not comfortable with that, so I went back to my 6V power supply. Any ideas why the current is so low with the LM317? Only modification I made to the datasheet schematic was I used a 10uF electrolytic instead of a 1uF. Thanks, Michael
So, how DO I charge a 6V SLA battery?
Started by ●March 10, 2008
Reply by ●March 17, 20082008-03-17
Reply by ●March 17, 20082008-03-17
<mrdarrett@gmail.com> wrote in message news:6c8e287b-fd85-4fb8-bff5-23a1c3e0bcfc@h11g2000prf.googlegroups.com...> On Mar 9, 10:55 pm, ehsjr <eh...@bellatlantic.net> wrote: >> mrdarr...@gmail.com wrote: >> > I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's >> > toy electric car (the kind that a kid can ride). The previous battery >> > didn't hold a charge when I bought the car. >> >> > One reference from batteryuniversity.com mentioned something about >> > 2.50V per cell for SLA batteries. I'm assuming my battery has 3 >> > cells. Another website mentions use of an L200 voltage regulating >> > chip (http://www.myra-simon.com/bike/charger.html). >> >> > I've got a 6VDC (nominal) wall wart that puts out just over 9V open- >> > circuit. >> >> > How should I charge it? >> >> Per the manufacturer's recommendations. >> But that's not what you wanted to hear, >> so read below. >> >> >> >> > Thanks, >> >> > Michael >> >> Here is a way you can charge it: >> Build a float charger. Set the float voltage to 7 volts. >> Use a 9 or 12 volt DC wall wart (not your 6v wall wart) >> The schematic is on the first page of the >> datasheethttp://cache.national.com/ds/LM/LM317.pdf? >> >> There are better ways to charge your battery, but this >> way won't cook it and is simple to build. >> >> If you can't build, buy a charger recommended for >> that battery. >> >> Ed > > > > Ok, I built it. Didn't have a 5k pot handy, so I strung up two 1k > resistors in parallel and a bunch of 100 ohm resistors in series until > I got about 7.2V out. > > Hooked it up to the battery, and I was surprised to see only 50mA > going through the battery. Typically, without the LM317 I got 100+ mA > going through. > > LM317 was cool to the touch (with heatsink). > > I thought my power supply was underpowered, so I tried a 12V wall wart > (about 14V with no load) instead. But then, after going through the > LM317, voltage going to the battery was just over 7.2V. Not > comfortable with that, so I went back to my 6V power supply. > > Any ideas why the current is so low with the LM317? Only modification > I made to the datasheet schematic was I used a 10uF electrolytic > instead of a 1uF. > > Thanks, > > MichaelThe LM317 will set the voltage. If the battery is already charged, it won't take much current at 7.2V. So, first discharge the battery, then try it again. I've looked around on the internet, and seems to me that you really want to be charging the thing at the 'float voltage' of 6.75V. If you set the LM317 to output 6.75V, and just leave it on there, it'll float up the right charge level after a day or so. You can also just leave the battery on the charger forever at this voltage, which is a plus. The datasheet gives the formula for deriving voltage output. The thing basically tries to keep 1.25V between its output and adj pins. So, pick a resistor to go between the out and adj pins, and then find another one to go between adj and ground that is nearest to 5.4 times the first resistor value. Regards, Bob Monsen
Reply by ●March 17, 20082008-03-17
On Mar 17, 12:24 pm, "Bob Monsen" <rcmon...@gmail.com> wrote:> <mrdarr...@gmail.com> wrote in message > > news:6c8e287b-fd85-4fb8-bff5-23a1c3e0bcfc@h11g2000prf.googlegroups.com... > > > > > On Mar 9, 10:55 pm, ehsjr <eh...@bellatlantic.net> wrote: > >> mrdarr...@gmail.com wrote: > >> > I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's > >> > toy electric car (the kind that a kid can ride). The previous battery > >> > didn't hold a charge when I bought the car. > > >> > One reference from batteryuniversity.com mentioned something about > >> > 2.50V per cell for SLA batteries. I'm assuming my battery has 3 > >> > cells. Another website mentions use of an L200 voltage regulating > >> > chip (http://www.myra-simon.com/bike/charger.html). > > >> > I've got a 6VDC (nominal) wall wart that puts out just over 9V open- > >> > circuit. > > >> > How should I charge it? > > >> Per the manufacturer's recommendations. > >> But that's not what you wanted to hear, > >> so read below. > > >> > Thanks, > > >> > Michael > > >> Here is a way you can charge it: > >> Build a float charger. Set the float voltage to 7 volts. > >> Use a 9 or 12 volt DC wall wart (not your 6v wall wart) > >> The schematic is on the first page of the > >> datasheethttp://cache.national.com/ds/LM/LM317.pdf? > > >> There are better ways to charge your battery, but this > >> way won't cook it and is simple to build. > > >> If you can't build, buy a charger recommended for > >> that battery. > > >> Ed > > > Ok, I built it. Didn't have a 5k pot handy, so I strung up two 1k > > resistors in parallel and a bunch of 100 ohm resistors in series until > > I got about 7.2V out. > > > Hooked it up to the battery, and I was surprised to see only 50mA > > going through the battery. Typically, without the LM317 I got 100+ mA > > going through. > > > LM317 was cool to the touch (with heatsink). > > > I thought my power supply was underpowered, so I tried a 12V wall wart > > (about 14V with no load) instead. But then, after going through the > > LM317, voltage going to the battery was just over 7.2V. Not > > comfortable with that, so I went back to my 6V power supply. > > > Any ideas why the current is so low with the LM317? Only modification > > I made to the datasheet schematic was I used a 10uF electrolytic > > instead of a 1uF. > > > Thanks, > > > Michael > > The LM317 will set the voltage. If the battery is already charged, it won't > take much current at 7.2V. > > So, first discharge the battery, then try it again. > > I've looked around on the internet, and seems to me that you really want to > be charging the thing at the 'float voltage' of 6.75V. If you set the LM317 > to output 6.75V, and just leave it on there, it'll float up the right charge > level after a day or so. You can also just leave the battery on the charger > forever at this voltage, which is a plus. > > The datasheet gives the formula for deriving voltage output. The thing > basically tries to keep 1.25V between its output and adj pins. So, pick a > resistor to go between the out and adj pins, and then find another one to go > between adj and ground that is nearest to 5.4 times the first resistor > value. > > Regards, > Bob MonsenThank you for the information. Could you provide the links that point to a 6.75V charge? Thanks, Michael
Reply by ●March 17, 20082008-03-17
<mrdarrett@gmail.com> wrote in message news:ae82ec44-fa48-4be4-880b-64cb3666901f@i29g2000prf.googlegroups.com...> On Mar 17, 12:24 pm, "Bob Monsen" <rcmon...@gmail.com> wrote: >> <mrdarr...@gmail.com> wrote in message >> >> news:6c8e287b-fd85-4fb8-bff5-23a1c3e0bcfc@h11g2000prf.googlegroups.com... >> >> >> >> > On Mar 9, 10:55 pm, ehsjr <eh...@bellatlantic.net> wrote: >> >> mrdarr...@gmail.com wrote: >> >> > I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's >> >> > toy electric car (the kind that a kid can ride). The previous >> >> > battery >> >> > didn't hold a charge when I bought the car. >> >> >> > One reference from batteryuniversity.com mentioned something about >> >> > 2.50V per cell for SLA batteries. I'm assuming my battery has 3 >> >> > cells. Another website mentions use of an L200 voltage regulating >> >> > chip (http://www.myra-simon.com/bike/charger.html). >> >> >> > I've got a 6VDC (nominal) wall wart that puts out just over 9V open- >> >> > circuit. >> >> >> > How should I charge it? >> >> >> Per the manufacturer's recommendations. >> >> But that's not what you wanted to hear, >> >> so read below. >> >> >> > Thanks, >> >> >> > Michael >> >> >> Here is a way you can charge it: >> >> Build a float charger. Set the float voltage to 7 volts. >> >> Use a 9 or 12 volt DC wall wart (not your 6v wall wart) >> >> The schematic is on the first page of the >> >> datasheethttp://cache.national.com/ds/LM/LM317.pdf? >> >> >> There are better ways to charge your battery, but this >> >> way won't cook it and is simple to build. >> >> >> If you can't build, buy a charger recommended for >> >> that battery. >> >> >> Ed >> >> > Ok, I built it. Didn't have a 5k pot handy, so I strung up two 1k >> > resistors in parallel and a bunch of 100 ohm resistors in series until >> > I got about 7.2V out. >> >> > Hooked it up to the battery, and I was surprised to see only 50mA >> > going through the battery. Typically, without the LM317 I got 100+ mA >> > going through. >> >> > LM317 was cool to the touch (with heatsink). >> >> > I thought my power supply was underpowered, so I tried a 12V wall wart >> > (about 14V with no load) instead. But then, after going through the >> > LM317, voltage going to the battery was just over 7.2V. Not >> > comfortable with that, so I went back to my 6V power supply. >> >> > Any ideas why the current is so low with the LM317? Only modification >> > I made to the datasheet schematic was I used a 10uF electrolytic >> > instead of a 1uF. >> >> > Thanks, >> >> > Michael >> >> The LM317 will set the voltage. If the battery is already charged, it >> won't >> take much current at 7.2V. >> >> So, first discharge the battery, then try it again. >> >> I've looked around on the internet, and seems to me that you really want >> to >> be charging the thing at the 'float voltage' of 6.75V. If you set the >> LM317 >> to output 6.75V, and just leave it on there, it'll float up the right >> charge >> level after a day or so. You can also just leave the battery on the >> charger >> forever at this voltage, which is a plus. >> >> The datasheet gives the formula for deriving voltage output. The thing >> basically tries to keep 1.25V between its output and adj pins. So, pick a >> resistor to go between the out and adj pins, and then find another one to >> go >> between adj and ground that is nearest to 5.4 times the first resistor >> value. >> >> Regards, >> Bob Monsen > > > Thank you for the information. > > Could you provide the links that point to a 6.75V charge? > > Thanks, > > Michaelhttp://www.jaycar.com.au/images_uploaded/slabatts.pdf Regards, Bob Monsen
Reply by ●March 17, 20082008-03-17
On Mar 17, 12:33 pm, "Bob Monsen" <rcmon...@gmail.com> wrote:> <mrdarr...@gmail.com> wrote in message > > news:ae82ec44-fa48-4be4-880b-64cb3666901f@i29g2000prf.googlegroups.com... > > > > > On Mar 17, 12:24 pm, "Bob Monsen" <rcmon...@gmail.com> wrote: > >> <mrdarr...@gmail.com> wrote in message > > >>news:6c8e287b-fd85-4fb8-bff5-23a1c3e0bcfc@h11g2000prf.googlegroups.com... > > >> > On Mar 9, 10:55 pm, ehsjr <eh...@bellatlantic.net> wrote: > >> >> mrdarr...@gmail.com wrote: > >> >> > I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's > >> >> > toy electric car (the kind that a kid can ride). The previous > >> >> > battery > >> >> > didn't hold a charge when I bought the car. > > >> >> > One reference from batteryuniversity.com mentioned something about > >> >> > 2.50V per cell for SLA batteries. I'm assuming my battery has 3 > >> >> > cells. Another website mentions use of an L200 voltage regulating > >> >> > chip (http://www.myra-simon.com/bike/charger.html). > > >> >> > I've got a 6VDC (nominal) wall wart that puts out just over 9V open- > >> >> > circuit. > > >> >> > How should I charge it? > > >> >> Per the manufacturer's recommendations. > >> >> But that's not what you wanted to hear, > >> >> so read below. > > >> >> > Thanks, > > >> >> > Michael > > >> >> Here is a way you can charge it: > >> >> Build a float charger. Set the float voltage to 7 volts. > >> >> Use a 9 or 12 volt DC wall wart (not your 6v wall wart) > >> >> The schematic is on the first page of the > >> >> datasheethttp://cache.national.com/ds/LM/LM317.pdf? > > >> >> There are better ways to charge your battery, but this > >> >> way won't cook it and is simple to build. > > >> >> If you can't build, buy a charger recommended for > >> >> that battery. > > >> >> Ed > > >> > Ok, I built it. Didn't have a 5k pot handy, so I strung up two 1k > >> > resistors in parallel and a bunch of 100 ohm resistors in series until > >> > I got about 7.2V out. > > >> > Hooked it up to the battery, and I was surprised to see only 50mA > >> > going through the battery. Typically, without the LM317 I got 100+ mA > >> > going through. > > >> > LM317 was cool to the touch (with heatsink). > > >> > I thought my power supply was underpowered, so I tried a 12V wall wart > >> > (about 14V with no load) instead. But then, after going through the > >> > LM317, voltage going to the battery was just over 7.2V. Not > >> > comfortable with that, so I went back to my 6V power supply. > > >> > Any ideas why the current is so low with the LM317? Only modification > >> > I made to the datasheet schematic was I used a 10uF electrolytic > >> > instead of a 1uF. > > >> > Thanks, > > >> > Michael > > >> The LM317 will set the voltage. If the battery is already charged, it > >> won't > >> take much current at 7.2V. > > >> So, first discharge the battery, then try it again. > > >> I've looked around on the internet, and seems to me that you really want > >> to > >> be charging the thing at the 'float voltage' of 6.75V. If you set the > >> LM317 > >> to output 6.75V, and just leave it on there, it'll float up the right > >> charge > >> level after a day or so. You can also just leave the battery on the > >> charger > >> forever at this voltage, which is a plus. > > >> The datasheet gives the formula for deriving voltage output. The thing > >> basically tries to keep 1.25V between its output and adj pins. So, pick a > >> resistor to go between the out and adj pins, and then find another one to > >> go > >> between adj and ground that is nearest to 5.4 times the first resistor > >> value. > > >> Regards, > >> Bob Monsen > > > Thank you for the information. > > > Could you provide the links that point to a 6.75V charge? > > > Thanks, > > > Michael > > http://www.jaycar.com.au/images_uploaded/slabatts.pdf > > Regards, > Bob MonsenThanks for that. I'm starting to get dizzy with all the different voltage recommendations. 6.75V http://www.jaycar.com.au/images_uploaded/slabatts.pdf less than 7.2V (<2.4V/cell) float http://hss.energy.gov/NuclearSafety/techstds/standard/hdbk1084/hdbk1084.pdf up to 7.5V (2.5V) for sealed lead acid batteries http://www.batteryuniversity.com/partone-13.htm Michael
Reply by ●March 17, 20082008-03-17
On Mar 17, 12:42=A0pm, mrdarr...@gmail.com wrote:> On Mar 17, 12:33 pm, "Bob Monsen" <rcmon...@gmail.com> wrote: > > > > > > > <mrdarr...@gmail.com> wrote in message > > >news:ae82ec44-fa48-4be4-880b-64cb3666901f@i29g2000prf.googlegroups.com...=> > > > On Mar 17, 12:24 pm, "Bob Monsen" <rcmon...@gmail.com> wrote: > > >> <mrdarr...@gmail.com> wrote in message > > > >>news:6c8e287b-fd85-4fb8-bff5-23a1c3e0bcfc@h11g2000prf.googlegroups.com=...> > > >> > On Mar 9, 10:55 pm, ehsjr <eh...@bellatlantic.net> wrote: > > >> >> mrdarr...@gmail.com wrote: > > >> >> > I bought a 6V, 6Ah battery from Home Depot to power my 3-year-ol=d's> > >> >> > toy electric car (the kind that a kid can ride). =A0The previous=> > >> >> > battery > > >> >> > didn't hold a charge when I bought the car. > > > >> >> > One reference from batteryuniversity.com mentioned something abo=ut> > >> >> > 2.50V per cell for SLA batteries. =A0I'm assuming my battery has=3> > >> >> > cells. =A0Another website mentions use of an L200 voltage regula=ting> > >> >> > chip (http://www.myra-simon.com/bike/charger.html). > > > >> >> > I've got a 6VDC (nominal) wall wart that puts out just over 9V o=pen-> > >> >> > circuit. > > > >> >> > How should I charge it? > > > >> >> Per the manufacturer's recommendations. > > >> >> But that's not what you wanted to hear, > > >> >> so read below. > > > >> >> > Thanks, > > > >> >> > Michael > > > >> >> Here is a way you can charge it: > > >> >> Build a float charger. Set the float voltage to 7 volts. > > >> >> Use a 9 or 12 volt DC wall wart (not your 6v wall wart) > > >> >> The schematic is on the first page of the > > >> >> datasheethttp://cache.national.com/ds/LM/LM317.pdf? > > > >> >> There are better ways to charge your battery, but this > > >> >> way won't cook it and is simple to build. > > > >> >> If you can't build, buy a charger recommended for > > >> >> that battery. > > > >> >> Ed > > > >> > Ok, I built it. =A0Didn't have a 5k pot handy, so I strung up two 1=k> > >> > resistors in parallel and a bunch of 100 ohm resistors in series un=til> > >> > I got about 7.2V out. > > > >> > Hooked it up to the battery, and I was surprised to see only 50mA > > >> > going through the battery. =A0Typically, without the LM317 I got 10=0+ mA> > >> > going through. > > > >> > LM317 was cool to the touch (with heatsink). > > > >> > I thought my power supply was underpowered, so I tried a 12V wall w=art> > >> > (about 14V with no load) instead. =A0But then, after going through =the> > >> > LM317, voltage going to the battery was just over 7.2V. =A0Not > > >> > comfortable with that, so I went back to my 6V power supply. > > > >> > Any ideas why the current is so low with the LM317? =A0Only modific=ation> > >> > I made to the datasheet schematic was I used a 10uF electrolytic > > >> > instead of a 1uF. > > > >> > Thanks, > > > >> > Michael > > > >> The LM317 will set the voltage. If the battery is already charged, it=> > >> won't > > >> take much current at 7.2V. > > > >> So, first discharge the battery, then try it again. > > > >> I've looked around on the internet, and seems to me that you really w=ant> > >> to > > >> be charging the thing at the 'float voltage' of 6.75V. If you set the=> > >> LM317 > > >> to output 6.75V, and just leave it on there, it'll float up the right=> > >> charge > > >> level after a day or so. You can also just leave the battery on the > > >> charger > > >> forever at this voltage, which is a plus. > > > >> The datasheet gives the formula for deriving voltage output. The thin=g> > >> basically tries to keep 1.25V between its output and adj pins. So, pi=ck a> > >> resistor to go between the out and adj pins, and then find another on=e to> > >> go > > >> between adj and ground that is nearest to 5.4 times the first resisto=r> > >> value. > > > >> Regards, > > >> =A0Bob Monsen > > > > Thank you for the information. > > > > Could you provide the links that point to a 6.75V charge? > > > > Thanks, > > > > Michael > > >http://www.jaycar.com.au/images_uploaded/slabatts.pdf > > > Regards, > > =A0Bob Monsen > > Thanks for that. =A0I'm starting to get dizzy with all the different > voltage recommendations. > > 6.75Vhttp://www.jaycar.com.au/images_uploaded/slabatts.pdf > > less than 7.2V (<2.4V/cell) floathttp://hss.energy.gov/NuclearSafety/techs=tds/standard/hdbk1084/hdbk10...> > up to 7.5V (2.5V) for sealed lead acid batterieshttp://www.batteryuniversi=ty.com/partone-13.htm> > Michael- Hide quoted text - > > - Show quoted text -Get your head around the difference between "charging" and "floating" so you don't suffer any more confusion. The ideal charging protocol doesn't take place at a constant voltage, but rather the voltage changes according to the battery's state of charge (as evidenced by current draw). You, however, do not have a sophisticated "smart charger" to tailor the charging curve. You'll operate at a fixed voltage. So you should pick a voltage according to how much time you want to take to charge the battery. If you want the battery to charge reasonably fast, use about 7.3 or 7.4 volts. If you have all the time in the world use about 6.7 or 6.8.
Reply by ●March 17, 20082008-03-17
mrdarrett@gmail.com wrote:> On Mar 17, 12:33 pm, "Bob Monsen" <rcmon...@gmail.com> wrote: > >><mrdarr...@gmail.com> wrote in message >> >>news:ae82ec44-fa48-4be4-880b-64cb3666901f@i29g2000prf.googlegroups.com... >> >> >> >> >>>On Mar 17, 12:24 pm, "Bob Monsen" <rcmon...@gmail.com> wrote: >>> >>>><mrdarr...@gmail.com> wrote in message >> >>>>news:6c8e287b-fd85-4fb8-bff5-23a1c3e0bcfc@h11g2000prf.googlegroups.com... >> >>>>>On Mar 9, 10:55 pm, ehsjr <eh...@bellatlantic.net> wrote: >>>>> >>>>>>mrdarr...@gmail.com wrote: >>>>>> >>>>>>>I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's >>>>>>>toy electric car (the kind that a kid can ride). The previous >>>>>>>battery >>>>>>>didn't hold a charge when I bought the car. >> >>>>>>>One reference from batteryuniversity.com mentioned something about >>>>>>>2.50V per cell for SLA batteries. I'm assuming my battery has 3 >>>>>>>cells. Another website mentions use of an L200 voltage regulating >>>>>>>chip (http://www.myra-simon.com/bike/charger.html). >> >>>>>>>I've got a 6VDC (nominal) wall wart that puts out just over 9V open- >>>>>>>circuit. >> >>>>>>>How should I charge it? >> >>>>>>Per the manufacturer's recommendations. >>>>>>But that's not what you wanted to hear, >>>>>>so read below. >> >>>>>>>Thanks, >> >>>>>>>Michael >> >>>>>>Here is a way you can charge it: >>>>>>Build a float charger. Set the float voltage to 7 volts. >>>>>>Use a 9 or 12 volt DC wall wart (not your 6v wall wart) >>>>>>The schematic is on the first page of the >>>>>>datasheethttp://cache.national.com/ds/LM/LM317.pdf? >> >>>>>>There are better ways to charge your battery, but this >>>>>>way won't cook it and is simple to build. >> >>>>>>If you can't build, buy a charger recommended for >>>>>>that battery. >> >>>>>>Ed >> >>>>>Ok, I built it. Didn't have a 5k pot handy, so I strung up two 1k >>>>>resistors in parallel and a bunch of 100 ohm resistors in series until >>>>>I got about 7.2V out. >> >>>>>Hooked it up to the battery, and I was surprised to see only 50mA >>>>>going through the battery. Typically, without the LM317 I got 100+ mA >>>>>going through. >> >>>>>LM317 was cool to the touch (with heatsink). >> >>>>>I thought my power supply was underpowered, so I tried a 12V wall wart >>>>>(about 14V with no load) instead. But then, after going through the >>>>>LM317, voltage going to the battery was just over 7.2V. Not >>>>>comfortable with that, so I went back to my 6V power supply. >> >>>>>Any ideas why the current is so low with the LM317? Only modification >>>>>I made to the datasheet schematic was I used a 10uF electrolytic >>>>>instead of a 1uF. >> >>>>>Thanks, >> >>>>>Michael >> >>>>The LM317 will set the voltage. If the battery is already charged, it >>>>won't >>>>take much current at 7.2V. >> >>>>So, first discharge the battery, then try it again. >> >>>>I've looked around on the internet, and seems to me that you really want >>>>to >>>>be charging the thing at the 'float voltage' of 6.75V. If you set the >>>>LM317 >>>>to output 6.75V, and just leave it on there, it'll float up the right >>>>charge >>>>level after a day or so. You can also just leave the battery on the >>>>charger >>>>forever at this voltage, which is a plus. >> >>>>The datasheet gives the formula for deriving voltage output. The thing >>>>basically tries to keep 1.25V between its output and adj pins. So, pick a >>>>resistor to go between the out and adj pins, and then find another one to >>>>go >>>>between adj and ground that is nearest to 5.4 times the first resistor >>>>value. >> >>>>Regards, >>>> Bob Monsen >> >>>Thank you for the information. >> >>>Could you provide the links that point to a 6.75V charge? >> >>>Thanks, >> >>>Michael >> >>http://www.jaycar.com.au/images_uploaded/slabatts.pdf >> >>Regards, >> Bob Monsen > > > > Thanks for that. I'm starting to get dizzy with all the different > voltage recommendations.Yup! That's what my "warning" was about. :-( :-) (It deserves both a "frowny" and a "smiley".) When you want to get a little more complicated, the circuit can be modified to include other features. But modifying the circuit won't get rid of the dizziness. :-) You'll need to decide the charge parameters you want. Ed> > 6.75V http://www.jaycar.com.au/images_uploaded/slabatts.pdf > > less than 7.2V (<2.4V/cell) float > http://hss.energy.gov/NuclearSafety/techstds/standard/hdbk1084/hdbk1084.pdf > > up to 7.5V (2.5V) for sealed lead acid batteries > http://www.batteryuniversity.com/partone-13.htm > > Michael
