NimH AAA to 5V, suggestions?
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From: Jan Panteltje on 8 Aug 2010 07:46 On a sunny day (Sat, 7 Aug 2010 18:06:52 -0700 (PDT)) it happened dagmargoodboat(a)yahoo.com wrote in <9292b61f-ac98-4a12-8e6c-c5ce419fe838(a)w30g2000yqw.googlegroups.com>: >> �<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... I have two original Duracell chargers that accept both AA and AAA, So the ball is in their court so to speak. Also, the voltage converter in the circuit will not work correctly below .9 V or so, the output voltage will drop below 3V and the PIC's brownout detector comes in at 2.85V... I am testing using the brownout detector to switch of the battery, that works, but is messy (the relationship with the real battery voltage is 'vague'. Next I will try using the PIC's internal analog comparator and internal reference voltage as low battery voltage detector. The internal reference has some tolerance too, need to do some calculations. Just to get rid of a trimpot... It seems to me, that if you only discharge to the point where the circuit still just works OK, you not only get more battery life (cycles), but also need less charge time :-). And less frustration 'because it does not work right (because of low battery)', better switch it off completely forcing the people to put in a fresh battery.
From: dagmargoodboat on 8 Aug 2010 08:49 On Aug 8, 7:46 am, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > On a sunny day (Sat, 7 Aug 2010 18:06:52 -0700 (PDT)) it happened > dagmargoodb...(a)yahoo.com wrote in > <9292b61f-ac98-4a12-8e6c-c5ce419fe...(a)w30g2000yqw.googlegroups.com>: > > > > >> <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... > > I have two original Duracell chargers that accept both AA and AAA, > So the ball is in their court so to speak. > > Also, the voltage converter in the circuit will not work correctly below ..9 V or so, > the output voltage will drop below 3V and the PIC's brownout detector > comes in at 2.85V... I am testing using the brownout detector to switch of the battery, > that works, but is messy (the relationship with the real battery voltage is 'vague'. > Next I will try using the PIC's internal analog comparator and internal reference voltage as low battery voltage detector. > The internal reference has some tolerance too, need to do some calculations. > Just to get rid of a trimpot... > > It seems to me, that if you only discharge to the point where the circuit still > just works OK, you not only get more battery life (cycles), but also need less > charge time :-). And less frustration 'because it does not work right (because of low battery)', > better switch it off completely forcing the people to put in a fresh battery. The NiMH cell is pretty close to empty when it hits 1.20v, and has only a percent or two of its energy left at 1.10v, so I'd count those both as "full discharge" as far as affect on the longevity of the cell. You just don't have to worry that these levels or lower will outright damage your cell--they won't. You might well want to cut off earlier for other reasons, like to give the user some warning before the thing dies. If these voltages were accurate and temperature stable (which they aren't) I'd warn at 1.20v and cut off around 1.15v on an NiMH cell, and run alkalines down to 1.0v. Wondering what other designers do, I started picking up AA cells people toss on the road. They're usually 1.3v, only 20% used for an alkaline cell.(*) That's a sin. If we're going to condone toss-aways we ought to at least use them fully, don't you agree? Keeps them off the road, out of the waste stream, and the user enjoys the longer run time too. Win-win. (*)(e.g. http://www1.duracell.com/oem/Pdf/new/MN1500_US_CT.pdf) Whether it's better to get 500 full cycles from an NiMH or 1,000+ half- cycles? That's up to you of course. -- Cheers, James Arthur
From: Jan Panteltje on 8 Aug 2010 13:18 On a sunny day (Sun, 8 Aug 2010 05:49:19 -0700 (PDT)) it happened dagmargoodboat(a)yahoo.com wrote in <2a6b772a-b5ce-41d3-9a2f-bef20de67c71(a)t2g2000yqe.googlegroups.com>: >The NiMH cell is pretty close to empty when it hits 1.20v, and has >only a percent or two of its energy left at 1.10v, so I'd count those >both as "full discharge" as far as affect on the longevity of the >cell. You just don't have to worry that these levels or lower will outright damage your cell--they won't. I did some test today, and ended up using the PICs internal Vref of about 1.024V and its internal analog comparator to drive the MOSFET battery switch. You can program that comparator to have some hysteresis. It now needs a little bit above 1.0 V to keep working. Switches of nicely, and the tolerances according to the PIC datasheet of that reference voltage are not bad at all. I put in a fresh charged 2300mAh NiMh and it is running now. Will see how long :-) It is a 2 component solution, MOSFET + 1 resistor. >You might well want to cut off earlier for other reasons, like to give >the user some warning before the thing dies. If these voltages were >accurate and temperature stable (which they aren't) I'd warn at 1.20v >and cut off around 1.15v on an NiMH cell, and run alkalines down to >1.0v. Yes, exactly. >Wondering what other designers do, I started picking up AA cells >people toss on the road. They're usually 1.3v, only 20% used for an >alkaline cell.(*) That's a sin. If we're going to condone toss-aways >we ought to at least use them fully, don't you agree? Keeps them off >the road, out of the waste stream, and the user enjoys the longer run >time too. Win-win. Do not alkaline sort of go back up after you remove the load? Zi effect? May read 1.3 but could well read 1 V in a camera for example with a lot of current charging the flash capacitor. >(*)(e.g. http://www1.duracell.com/oem/Pdf/new/MN1500_US_CT.pdf) > >Whether it's better to get 500 full cycles from an NiMH or 1,000+ half- >cycles? That's up to you of course. If the thing does not work right on an almost empty battery then 1000 is the best choice :-)
From: dagmargoodboat on 8 Aug 2010 17:13 On Aug 8, 1:18 pm, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > dagmargoodb...(a)yahoo.com wrote in > >Wondering what other designers do, I started picking up AA cells > >people toss on the road. They're usually 1.3v, only 20% used for an > >alkaline cell.(*) That's a sin. If we're going to condone toss-aways > >we ought to at least use them fully, don't you agree? Keeps them off > >the road, out of the waste stream, and the user enjoys the longer run > >time too. Win-win. > > Do not alkaline sort of go back up after you remove the load? > Zi effect? > May read 1.3 but could well read 1 V in a camera for example with a lot of current charging the flash > capacitor. Roadside batteries come mostly from joggers and MP3 addicts. Apparently joggers run on AA cells. -- Cheers, James Arthur
From: Grant on 8 Aug 2010 17:15
On Sun, 08 Aug 2010 17:18:46 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Sun, 8 Aug 2010 05:49:19 -0700 (PDT)) it happened >dagmargoodboat(a)yahoo.com wrote in ><2a6b772a-b5ce-41d3-9a2f-bef20de67c71(a)t2g2000yqe.googlegroups.com>: > >>The NiMH cell is pretty close to empty when it hits 1.20v, and has >>only a percent or two of its energy left at 1.10v, so I'd count those >>both as "full discharge" as far as affect on the longevity of the >>cell. You just don't have to worry that these levels or lower will >outright damage your cell--they won't. > > >I did some test today, and ended up using the PICs internal Vref of about 1.024V >and its internal analog comparator to drive the MOSFET battery switch. >You can program that comparator to have some hysteresis. >It now needs a little bit above 1.0 V to keep working. >Switches of nicely, and the tolerances according to the PIC datasheet >of that reference voltage are not bad at all. >I put in a fresh charged 2300mAh NiMh and it is running now. >Will see how long :-) >It is a 2 component solution, MOSFET + 1 resistor. > > >>You might well want to cut off earlier for other reasons, like to give >>the user some warning before the thing dies. If these voltages were >>accurate and temperature stable (which they aren't) I'd warn at 1.20v >>and cut off around 1.15v on an NiMH cell, and run alkalines down to >>1.0v. > >Yes, exactly. > > >>Wondering what other designers do, I started picking up AA cells >>people toss on the road. They're usually 1.3v, only 20% used for an >>alkaline cell.(*) That's a sin. If we're going to condone toss-aways >>we ought to at least use them fully, don't you agree? Keeps them off >>the road, out of the waste stream, and the user enjoys the longer run >>time too. Win-win. > >Do not alkaline sort of go back up after you remove the load? >Zi effect? >May read 1.3 but could well read 1 V in a camera for example with a lot of current charging the flash >capacitor. > >>(*)(e.g. http://www1.duracell.com/oem/Pdf/new/MN1500_US_CT.pdf) >> >>Whether it's better to get 500 full cycles from an NiMH or 1,000+ half- >>cycles? That's up to you of course. > >If the thing does not work right on an almost empty battery then 1000 is the best choice :-) It varies so much, my canon A580 camera reports Alkaline cell low too early, and doesn't like any but the best NiMH cells. So one can go on to take a few dozen shots sans flash (in warm weather) on alkaline before the cam packs it in and tells one to replace the battery. On NiMH it's only a few shots before death, battery is measured on load too. Some stuff on canon A590, now sadly expired, too expensive to fix. http://bugsplatter.id.au/chdk/ http://bugsplatter.id.au/chdk/a590-power.html http://bugsplatter.id.au/chdk/a590-power-2.html Written up just over a year ago, examines power behaviour of A590 2 AA cell camera, probably roughly applies to other Canon models designed for 2 cell operation. Grant. |