NimH AAA to 5V, suggestions?
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From: Jan Panteltje on 6 Aug 2010 14:59 On a sunny day (Fri, 06 Aug 2010 17:52:51 GMT) it happened Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote in <i3hi5s$abs$1(a)news.albasani.net>: >On a sunny day (Fri, 6 Aug 2010 09:35:10 -0700 (PDT)) it happened >dagmargoodboat(a)yahoo.com wrote in ><48030cf6-4982-4bc9-a33f-5e979bb69cbf(a)f6g2000yqa.googlegroups.com>: > >PS >I just had a cool idea how to do the auto shut off: > -------------> to converter > | + > 1.2V NiMH > _____| - > | d > === g ---------------------------< from Vout (5V nom) > --- s IRLZ34N MOSFET > |C1 | > /// /// > > >The MOSFET is in series with the battery minus connection. >At switch on C1 is discharged, and the circuit will produce 5V output for a few milliseconds before C1 charges. >That is enough to make the MOSFET conduct. >When output voltage drops below Vgs of the MOSFET (say 2.5 V, else use a divider), >the MOSFET Rds increases, output voltage falls further, and zero current will flow. >I mean really ZERO. > >Now that is a minimum component solution of the ultimate kind :-) >The Rds-on of this MOSFET is a few milli-Ohm, so 90 mA current causes millivolts drop, >no losses to speak of,. > >I should patent this :-) > >Still have to try it though :-) >But I *have* this MOSFET. OK tried it, of course the intitial idea was OK, but the polarity wrong. So now it looks like this, and I replaced the cap with a momentary start-button. start button | --- ----0 0---- | | -------------- s d -------> + to converter | g IRLZ32N + | --------< +5 from converter NiMH | | - __| 0-------->[ ] cut off level | stop | 0 | 100k /// buton | /// /// A stop button contact could be made by shorting the gate to ground. Solves the expensive switch problem at the same time, foil swicthes? hehe
From: Jan Panteltje on 6 Aug 2010 15:03 On a sunny day (Fri, 06 Aug 2010 18:59:46 GMT) it happened Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote in <i3hm3d$gpd$1(a)news.albasani.net>: >On a sunny day (Fri, 06 Aug 2010 17:52:51 GMT) it happened Jan Panteltje ><pNaonStpealmtje(a)yahoo.com> wrote in <i3hi5s$abs$1(a)news.albasani.net>: > >>On a sunny day (Fri, 6 Aug 2010 09:35:10 -0700 (PDT)) it happened >>dagmargoodboat(a)yahoo.com wrote in >><48030cf6-4982-4bc9-a33f-5e979bb69cbf(a)f6g2000yqa.googlegroups.com>: >> >>PS >>I just had a cool idea how to do the auto shut off: >> -------------> to converter >> | + >> 1.2V NiMH >> _____| - >> | d >> === g ---------------------------< from Vout (5V nom) >> --- s IRLZ34N MOSFET >> |C1 | >> /// /// >> >> >>The MOSFET is in series with the battery minus connection. >>At switch on C1 is discharged, and the circuit will produce 5V output for a few milliseconds before C1 charges. >>That is enough to make the MOSFET conduct. >>When output voltage drops below Vgs of the MOSFET (say 2.5 V, else use a divider), >>the MOSFET Rds increases, output voltage falls further, and zero current will flow. >>I mean really ZERO. >> >>Now that is a minimum component solution of the ultimate kind :-) >>The Rds-on of this MOSFET is a few milli-Ohm, so 90 mA current causes millivolts drop, >>no losses to speak of,. >> >>I should patent this :-) >> >>Still have to try it though :-) >>But I *have* this MOSFET. > >OK tried it, of course the intitial idea was OK, but the polarity wrong. >So now it looks like this, and I replaced the cap with a momentary start-button. > start button > | > --- > ----0 0---- > | | > -------------- s d -------> + to converter > | g IRLZ32N > + | --------< +5 from converter > NiMH | | > - __| 0-------->[ ] cut off level > | stop | 0 | 100k >/// buton | /// > /// >A stop button contact could be made by shorting the gate to ground. >Solves the expensive switch problem at the same time, foil swicthes? >hehe Typo, reverse drain and source! It works:-)
From: Grant on 6 Aug 2010 18:20 On Fri, 06 Aug 2010 17:08:20 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Fri, 6 Aug 2010 09:35:10 -0700 (PDT)) it happened >dagmargoodboat(a)yahoo.com wrote in ><48030cf6-4982-4bc9-a33f-5e979bb69cbf(a)f6g2000yqa.googlegroups.com>: > >>No need to protect a single NiMH cell--you can't damage it here. Full >>discharge is fine--damage comes from reverse charging the cell. This >>circuit can't do that. > >That iwould be good, that would simplify things. >I was conidering using the analog comparator in the PIC, combined with some I/O and RC time. > >>In practice you won't fully discharge the cell, because the PIC will >>quit before you ever get there anyway. > >Yes it will stop working normally, but all LEDs seem to go on then :-) >A brown out detection and / or watchdog would simply keep restarting it. >and the power conversion circuit will keep running and consuming some power of its own. > >Just looked up NiMH : >Wikipedia seems to disagree with you: > http://en.wikipedia.org/wiki/Nickel_metal_hydride_battery ><Quote> > A fully-charged cell measures 1.4?1.45 V (unloaded), and supplies a nominal > average 1.25 V/cell during discharge, down to about 1.0-1.1 V/cell (further > discharge may cause permanent damage, and the risk is increased with > multi-cell packs). ><end quote> Read further down that page: " A single cell driving a load won't suffer from polarity reversal, because there are no other cells to reverse-charge it when it becomes discharged. Irreversible damage from polarity reversal is a particular danger in systems... " Single cell discharge is not the problem, it's the cell reversal in battery packs that kills the weaker cells that discharged first. Grant.
From: Jan Panteltje on 6 Aug 2010 18:46 On a sunny day (Sat, 07 Aug 2010 08:20:59 +1000) it happened Grant <omg(a)grrr.id.au> wrote in <ug2p565t8l8p77h8cieiaplavg0ei4a502(a)4ax.com>: >On Fri, 06 Aug 2010 17:08:20 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: > >>On a sunny day (Fri, 6 Aug 2010 09:35:10 -0700 (PDT)) it happened >>dagmargoodboat(a)yahoo.com wrote in >><48030cf6-4982-4bc9-a33f-5e979bb69cbf(a)f6g2000yqa.googlegroups.com>: >> >>>No need to protect a single NiMH cell--you can't damage it here. Full >>>discharge is fine--damage comes from reverse charging the cell. This >>>circuit can't do that. >> >>That iwould be good, that would simplify things. >>I was conidering using the analog comparator in the PIC, combined with some I/O and RC time. >> >>>In practice you won't fully discharge the cell, because the PIC will >>>quit before you ever get there anyway. >> >>Yes it will stop working normally, but all LEDs seem to go on then :-) >>A brown out detection and / or watchdog would simply keep restarting it. >>and the power conversion circuit will keep running and consuming some power of its own. >> >>Just looked up NiMH : >>Wikipedia seems to disagree with you: >> http://en.wikipedia.org/wiki/Nickel_metal_hydride_battery >><Quote> >> A fully-charged cell measures 1.4?1.45 V (unloaded), and supplies a nominal >> average 1.25 V/cell during discharge, down to about 1.0-1.1 V/cell (further >> discharge may cause permanent damage, and the risk is increased with >> multi-cell packs). >><end quote> > >Read further down that page: >" > A single cell driving a load won't suffer from polarity > reversal, because there are no other cells to reverse-charge > it when it becomes discharged. > Irreversible damage from polarity reversal is a particular > danger in systems... Yes, polarity reversal is bad. But total discharge is also bad, this does not nullify that. But if you are so sure will you pay for new cells if I damage these ones by leaving them connected to a load till it reads less then .5 V? I though not. If you are so sure why does my singe cell Muvo (Creative Labs) mp3 player has a power down feature if the battery voltage drops below some level? Creative realy know what they are doing. Maybe that is why these AAA it runs on have already had several hundred charge cycles and are still just fine. Anyways, I found a nice solution with a MOSFET that also creates a touch switch on-off system, so perfection is here :-) See my other post for the ASCII diagram. Usenet Patent of course.
From: Grant on 6 Aug 2010 19:39
On Fri, 06 Aug 2010 22:46:09 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Sat, 07 Aug 2010 08:20:59 +1000) it happened Grant ><omg(a)grrr.id.au> wrote in <ug2p565t8l8p77h8cieiaplavg0ei4a502(a)4ax.com>: > >>On Fri, 06 Aug 2010 17:08:20 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >> >>>On a sunny day (Fri, 6 Aug 2010 09:35:10 -0700 (PDT)) it happened >>>dagmargoodboat(a)yahoo.com wrote in >>><48030cf6-4982-4bc9-a33f-5e979bb69cbf(a)f6g2000yqa.googlegroups.com>: >>> >>>>No need to protect a single NiMH cell--you can't damage it here. Full >>>>discharge is fine--damage comes from reverse charging the cell. This >>>>circuit can't do that. >>> >>>That iwould be good, that would simplify things. >>>I was conidering using the analog comparator in the PIC, combined with some I/O and RC time. >>> >>>>In practice you won't fully discharge the cell, because the PIC will >>>>quit before you ever get there anyway. >>> >>>Yes it will stop working normally, but all LEDs seem to go on then :-) >>>A brown out detection and / or watchdog would simply keep restarting it. >>>and the power conversion circuit will keep running and consuming some power of its own. >>> >>>Just looked up NiMH : >>>Wikipedia seems to disagree with you: >>> http://en.wikipedia.org/wiki/Nickel_metal_hydride_battery >>><Quote> >>> A fully-charged cell measures 1.4?1.45 V (unloaded), and supplies a nominal >>> average 1.25 V/cell during discharge, down to about 1.0-1.1 V/cell (further >>> discharge may cause permanent damage, and the risk is increased with >>> multi-cell packs). >>><end quote> >> >>Read further down that page: >>" >> A single cell driving a load won't suffer from polarity >> reversal, because there are no other cells to reverse-charge >> it when it becomes discharged. >> Irreversible damage from polarity reversal is a particular >> danger in systems... > >Yes, polarity reversal is bad. >But total discharge is also bad, this does not nullify that. >But if you are so sure will you pay for new cells if I damage these ones >by leaving them connected to a load till it reads less then .5 V? > I though not. > >If you are so sure why does my singe cell Muvo (Creative Labs) mp3 player has a power down >feature if the battery voltage drops below some level? >Creative realy know what they are doing. >Maybe that is why these AAA it runs on have already had several hundred charge cycles and are still just fine. Probably my memory of the NiCd cells? They don't mind going to zero? I have lost NiCd and NiMH cells due to over-discharging when there's two or more, but I have one device here (old beard trimmer) that uses a single NiCd cell and is decades old, still works ;) Anything with two or more cells seems to go trash sooner rather than later. Except the camera, it runs a pair of AA and has low voltage shutdown at around 1V/cell. > >Anyways, I found a nice solution with a MOSFET that also creates a touch switch on-off system, >so perfection is here :-) >See my other post for the ASCII diagram. >Usenet Patent of course. > Yes, I saw that. I'm likely to try something that you and Tim cooked up together :) Grant. |