NimH AAA to 5V, suggestions?
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From: krw on 6 Aug 2010 20:38 On Sat, 07 Aug 2010 09:39:34 +1000, Grant <omg(a)grrr.id.au> wrote: >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? No such animal in modern NiCads, at least not as such. >They don't mind going to zero? No, =0 is fine, < 0, not so much. >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. Right. This point should be chosen depending on the number of cells. With more cells this point has to be set higher. >>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.
From: dagmargoodboat on 7 Aug 2010 17:35 On Aug 6, 1:08 pm, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > On a sunny day (Fri, 6 Aug 2010 09:35:10 -0700 (PDT)) it happened > dagmargoodb...(a)yahoo.com wrote in > <48030cf6-4982-4bc9-a33f-5e979bb69...(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> I think they're talking about multiple cells in series--batteries--not cells. The next Wiki paragraph (on "over-discharge") clarifies that the danger is not over-discharging but polarity-reversing the cell. That's possible with batteries, not with single cells. Would the manufacturer's literature carry any weight with you? http://www1.duracell.com/oem/Pdf/others/TECHBULL.pdf See sections 5.3, 5.6, and 5.8. Summary: Cells are not damaged by 0v, and can be stored without damage in the zero-volt condition. Party on! -- Cheers, James Arthur
From: dagmargoodboat on 7 Aug 2010 18:03 On Aug 6, 1:11 pm, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > On a sunny day (Fri, 6 Aug 2010 09:28:00 -0700 (PDT)) it happened > dagmargoodb...(a)yahoo.com wrote in > <cfbeee0b-9301-410a-997d-e61e355b6...(a)f42g2000yqn.googlegroups.com>: > > >I saw the other post--70% efficiency is decent. I get 80% commonly, > >85% with great care in similar circuits. You have to use a low > >Vce(sat) transistor--otherwise 150mV out of 1.2Vcc in a discontinuous- > >mode converter works out to about a 8-10% loss. > > It is just a BC547, 'made in China' nothing special. > You also lose .5V in the Schottky, at 5V that is an other 10%. A synchronous rectifier saves half that, but at unreasonable added complexity and expense. It's not usually worth it.
From: Jan Panteltje on 7 Aug 2010 18:10 On a sunny day (Sat, 7 Aug 2010 14:35:08 -0700 (PDT)) it happened dagmargoodboat(a)yahoo.com wrote in <36d8ae32-6af6-4987-b271-3308982f6eec(a)z10g2000yqb.googlegroups.com>: >I think they're talking about multiple cells in series--batteries--not >cells. The next Wiki paragraph (on "over-discharge") clarifies that >the danger is not over-discharging but polarity-reversing the cell. >That's possible with batteries, not with single cells. > >Would the manufacturer's literature carry any weight with you? > http://www1.duracell.com/oem/Pdf/others/TECHBULL.pdf > >See sections 5.3, 5.6, and 5.8. > >Summary: Cells are not damaged by 0v, and can be stored without damage >in the zero-volt condition. Party on! First I want to thank you for that nice pdf link,. As I use Duracell (among other batteries) it is good info to have. How much I would like to agree with you, because it would make the design simpler, the 1.0 V discharge limit is all over that pdf. And consider this quote from page 19, it sort of confirms what I wrote about my single cell mp3 player that has a cutoff, <quote> Cycle life is also affected by the depth of dis- charge. Depending upon the charge termination method, up to 500 cycles can be obtained with the battery being fully discharged on each cycle (100 percent depth of dis- charge, or "DOD"). Considerably higher cycle life can be obtained if the battery is cycled at shallower charge/ discharges. <end quote> In the end product there is of course also the possibility that somebody puts in a normal not rechargeable, so it would make sense to not discharge that to the leaking point.
From: dagmargoodboat on 7 Aug 2010 21:06
On Aug 7, 6:10 pm, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > On a sunny day (Sat, 7 Aug 2010 14:35:08 -0700 (PDT)) it happened > dagmargoodb...(a)yahoo.com wrote in > <36d8ae32-6af6-4987-b271-3308982f6...(a)z10g2000yqb.googlegroups.com>: > > >Would the manufacturer's literature carry any weight with you? > > http://www1.duracell.com/oem/Pdf/others/TECHBULL.pdf > > >See sections 5.3, 5.6, and 5.8. > > >Summary: Cells are not damaged by 0v, and can be stored without damage > >in the zero-volt condition. Party on! > > First I want to thank you for that nice pdf link,. > As I use Duracell (among other batteries) it is good info to have. > How much I would like to agree with you, because it would make the design simpler, > the 1.0 V discharge limit is all over that pdf. > And consider this quote from page 19, it sort of confirms what I wrote > about my single cell mp3 player that has a cutoff, > <quote> > Cycle life is also affected by the depth of dis- > charge. Depending upon the charge termination method, > up to 500 cycles can be obtained with the battery being > fully discharged on each cycle (100 percent depth of dis- > charge, or "DOD"). Considerably higher cycle life can be > obtained if the battery is cycled at shallower charge/ > discharges. > <end quote> > > In the end product there is of course also the possibility that somebody > puts in a normal not rechargeable, so it would make sense to not discharge that to the leaking point. Yes, you get more cycles if you reduce the depth of discharge, but ISTM the limiting factor in most real-life applications today is getting fried a little every time they're charged. (I haven't seen a charger yet that comes close to table 7.2.1's recommended temperature limits.) So, with available chargers you might get better life using the full charge and recharging a cell fewer times. Any which way, full discharging and 500 cycles is nothing to sneeze at... -- Cheers, James Arthur |