Solar powered battery charger for Nickel batteries
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From: John Fields on 26 Jun 2010 07:13 On Fri, 25 Jun 2010 16:48:54 -0700 (PDT), Bill Sloman <bill.sloman(a)ieee.org> wrote: >On Jun 26, 1:11�am, Raveninghorde <raveninghorde(a)invalid> wrote: >> I am used to charging NiCd or NiMH cells however I haven't done it >> from a solar panel before. I'm happy I can hold the solar panel near >> the point of peak efficiency but I am concerned about charge >> termination due to the variable power available from solar panels. >> >> Normally �for NiCd I would use negative delta V for termination with a >> back up timer. For NiMH I would use a thermistor for delta T >> termination. However I can see potential problems with solar as the >> power source. >> >> In principle I could lay out a 60W panel in Arizona and charge the >> batteries without problems - until someone parks a truck and shades >> the panel dropping the charge current. >> >> So what is the best way to terminate charge on nickel based batteries >> with a variable power source? > >http://www.edn.com/file/25378-Solar_panel_powers_two_stage_lead_acid_battery_charger_pdf.pdf --- OP: ... "nickel based batteries"... BS: ... "lead acid battery charger"... http://csmanagement.files.wordpress.com/2009/08/apple-and-orange.jpg
From: Raveninghorde on 26 Jun 2010 09:43 On Sat, 26 Jun 2010 06:13:42 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Fri, 25 Jun 2010 16:48:54 -0700 (PDT), Bill Sloman ><bill.sloman(a)ieee.org> wrote: > >>On Jun 26, 1:11�am, Raveninghorde <raveninghorde(a)invalid> wrote: >>> I am used to charging NiCd or NiMH cells however I haven't done it >>> from a solar panel before. I'm happy I can hold the solar panel near >>> the point of peak efficiency but I am concerned about charge >>> termination due to the variable power available from solar panels. >>> >>> Normally �for NiCd I would use negative delta V for termination with a >>> back up timer. For NiMH I would use a thermistor for delta T >>> termination. However I can see potential problems with solar as the >>> power source. >>> >>> In principle I could lay out a 60W panel in Arizona and charge the >>> batteries without problems - until someone parks a truck and shades >>> the panel dropping the charge current. >>> >>> So what is the best way to terminate charge on nickel based batteries >>> with a variable power source? >> >>http://www.edn.com/file/25378-Solar_panel_powers_two_stage_lead_acid_battery_charger_pdf.pdf > > >--- >OP: ... "nickel based batteries"... > >BS: ... "lead acid battery charger"... > >http://csmanagement.files.wordpress.com/2009/08/apple-and-orange.jpg Yep, diiferent. Lead acid and lithium are fairly easy to terminate the charge on as they use constant voltage charging.
From: Raveninghorde on 26 Jun 2010 09:45 On Fri, 25 Jun 2010 22:03:37 -0700, Kevin McMurtrie <mcmurtrie(a)pixelmemory.us> wrote: >In article <16da261ntm8hp49umugnu0lvmq54rlmgrv(a)4ax.com>, > Raveninghorde <raveninghorde(a)invalid> wrote: > >> I am used to charging NiCd or NiMH cells however I haven't done it >> from a solar panel before. I'm happy I can hold the solar panel near >> the point of peak efficiency but I am concerned about charge >> termination due to the variable power available from solar panels. >> >> Normally for NiCd I would use negative delta V for termination with a >> back up timer. For NiMH I would use a thermistor for delta T >> termination. However I can see potential problems with solar as the >> power source. >> >> In principle I could lay out a 60W panel in Arizona and charge the >> batteries without problems - until someone parks a truck and shades >> the panel dropping the charge current. >> >> So what is the best way to terminate charge on nickel based batteries >> with a variable power source? > >Keep a device on the battery that measures all current in and out. It >can estimate the charge power well enough to prevent wear. > >LiFePO4 and Li-Po are other options. They'll give you the same power >rate, much better density, less self-discharge in AZ heat, and simpler >charging. I don't get to measure current out of the battery, the state of charge will be unknown when the battery is put on the charger. Unfortunately the customer specifies Nickel based batteries.
From: Bill Sloman on 26 Jun 2010 11:39 On Jun 26, 3:43 pm, Raveninghorde <raveninghorde(a)invalid> wrote: > On Sat, 26 Jun 2010 06:13:42 -0500, John Fields > > > > <jfie...(a)austininstruments.com> wrote: > >On Fri, 25 Jun 2010 16:48:54 -0700 (PDT), Bill Sloman > ><bill.slo...(a)ieee.org> wrote: > > >>On Jun 26, 1:11 am, Raveninghorde <raveninghorde(a)invalid> wrote: > >>> I am used to charging NiCd or NiMH cells however I haven't done it > >>> from a solar panel before. I'm happy I can hold the solar panel near > >>> the point of peak efficiency but I am concerned about charge > >>> termination due to the variable power available from solar panels. > > >>> Normally for NiCd I would use negative delta V for termination with a > >>> back up timer. For NiMH I would use a thermistor for delta T > >>> termination. However I can see potential problems with solar as the > >>> power source. > > >>> In principle I could lay out a 60W panel in Arizona and charge the > >>> batteries without problems - until someone parks a truck and shades > >>> the panel dropping the charge current. > > >>> So what is the best way to terminate charge on nickel based batteries > >>> with a variable power source? > > >>http://www.edn.com/file/25378-Solar_panel_powers_two_stage_lead_acid_.... > > >--- > >OP: ... "nickel based batteries"... > > >BS: ... "lead acid battery charger"... > > >http://csmanagement.files.wordpress.com/2009/08/apple-and-orange.jpg > > Yep, diiferent. Lead acid and lithium are fairly easy to terminate the > charge on as they use constant voltage charging. Nickel-based batteries are fairly easy to keep track off if you can put a temperature sensor on the battery, and a reference temperature sensor fairly close by. Once nickel cadmium bateries are fully charged, any further changing liberates hydrogen gas at the cathode, which diffuses to the anode and recombines with oxygen (from the metal oxide produced by the same current) to produce water and heat - quite a lot more heat than is generated by the same current when it is charging a less than fully charged battery. "Interchangable" thermistors are quite stable enough to let you reliably detect the consequent extra heating of the battery. http://en.wikipedia.org/wiki/Nickel-metal_hydride_battery -- Bill Sloman, Nijmegen
From: dagmargoodboat on 26 Jun 2010 14:24
On Jun 26, 8:45 am, Raveninghorde <raveninghorde(a)invalid> wrote: > On Fri, 25 Jun 2010 22:03:37 -0700, Kevin McMurtrie > > > > <mcmurt...(a)pixelmemory.us> wrote: > >In article <16da261ntm8hp49umugnu0lvmq54rlm...(a)4ax.com>, > > Raveninghorde <raveninghorde(a)invalid> wrote: > > >> I am used to charging NiCd or NiMH cells however I haven't done it > >> from a solar panel before. I'm happy I can hold the solar panel near > >> the point of peak efficiency but I am concerned about charge > >> termination due to the variable power available from solar panels. > > >> Normally for NiCd I would use negative delta V for termination with a > >> back up timer. For NiMH I would use a thermistor for delta T > >> termination. However I can see potential problems with solar as the > >> power source. > > >> In principle I could lay out a 60W panel in Arizona and charge the > >> batteries without problems - until someone parks a truck and shades > >> the panel dropping the charge current. > > >> So what is the best way to terminate charge on nickel based batteries > >> with a variable power source? > > >Keep a device on the battery that measures all current in and out. It > >can estimate the charge power well enough to prevent wear. > > >LiFePO4 and Li-Po are other options. They'll give you the same power > >rate, much better density, less self-discharge in AZ heat, and simpler > >charging. > > I don't get to measure current out of the battery, the state of charge > will be unknown when the battery is put on the charger. > > Unfortunately the customer specifies Nickel based batteries. The customer hasn't left you many good options. You can determine state-of-charge by hammering the battery (>= 1C charge rate) and seeing if it gets hot, but that's pretty hard on the battery if, for example, your circuit wakes anew each morning, or after a cloud. And that gets messed up if insolation dips mid-cycle; then the battery's full, but doesn't heat as expected. You might terminate (or at least stop blasting) at a temperature- compensated voltage. I think that works, the battery just won't be completely full. NiCd could then be safely trickled up @ 0.1C, but NiMH hates that. -- Cheers, James Arthur |