Solar powered battery charger for Nickel batteries
in [Design]
|
Prev: A question about Mosfets....
Next: Archie
From: John Fields on 26 Jun 2010 19:14 On Sat, 26 Jun 2010 08:39:29 -0700 (PDT), Bill Sloman <bill.sloman(a)ieee.org> wrote: >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 --- So it looks like, without expressly acknowledging your earlier boo-boo, you've admitted that your reference was bogus since a PV lead-acid charger won't work for NiMH. Unfortunately, and to your detriment, you still haven't addressed the OP's query, which was, basically, "What do I do if the sun goes behind a cloud while the battery is charging?" Instead, you parrot an expensive "Interchangeable thermistor" scheme to guard against overcharging, which the OP has already laid out, but which has nothing to do with PV shading during charging. The way I'd do it would be to completely disconnect the battery from the charging circuitry when the array was shadowed, and then reconnect it when the sun came out again. Got a better idea?
From: Kevin McMurtrie on 26 Jun 2010 19:37 In article <101c265ga7vldq4bmcs5mkuv8c1qsutd4c(a)4ax.com>, Raveninghorde <raveninghorde(a)invalid> wrote: > 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. Not many options left. I've never seen a process to determine NiMH charge level without the use of a long and continuous high current. If you look at all the graphs from manufacturers, you'll see that there are no absolute values to use as triggers. They're all deltas and they're only valid for a range of currents. - Put a LiFePO4 in the solar charger and transfer that to the NiMH. - Let the battery hit thermal cut-off and derate the life expectancy. - Use proprietary fast-charge NiHM cells that have a gas pressure sensor. -- I won't see Google Groups replies because I must filter them as spam
From: Bill Sloman on 26 Jun 2010 21:02 On Jun 27, 1:14 am, John Fields <jfie...(a)austininstruments.com> wrote: > On Sat, 26 Jun 2010 08:39:29 -0700 (PDT), Bill Sloman > > <bill.slo...(a)ieee.org> wrote: > >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 > > --- > So it looks like, without expressly acknowledging your earlier > boo-boo, you've admitted that your reference was bogus since a PV > lead-acid charger won't work for NiMH. > > Unfortunately, and to your detriment, you still haven't addressed the > OP's query, which was, basically, "What do I do if the sun goes behind > a cloud while the battery is charging?" That was the content of the EDN article I pointed to. http://www.edn.com/file/25378-Solar_panel_powers_two_stage_lead_acid_battery_charger_pdf.pdf Why don't you read it? It didnn't address the specific problem posed by Ravinghorde's customer's choice of battery, but somebody with a little more imagination than Ravinghorde might be able to adapt the ideas presented. > Instead, you parrot an expensive "Interchangeable thermistor" scheme > to guard against overcharging, which the OP has already laid out, but > which has nothing to do with PV shading during charging. For PV shading during charging, you need something like a ringing choke inverter, that uses a low voltage source to build up current through an inductor, then switches "charged" inductor to discharge into the battery bank at a voltage determined by the battery bank. Ringing-choke inverters don't exploit core material particularly efficiently, and there are a variety of more complicated schemes around. Linear Technology makes a fuss about its ics that can be used to build buck-boost SEPIC converters. I've never played with them, so I don't know much about the area. Ravinghordes delta-T charge termination scheme only uses a single thermistor to detect the jump in temperature when the cells go over to hydrogen generation; this is cheaper than using and monitoring two thermistors, but there are situations where the delta-T can be masked or faked by the environment. > The way I'd do it would be to completely disconnect the battery from > the charging circuitry when the array was shadowed, and then reconnect > it when the sun came out again. > > Got a better idea? The ringing choke - or one of the elaborations of that basic idea - can be used to step up the solar cell output voltage more when the cells are shaded so that the batteries continue to be charged, albeit more slowly, when there is less sun around. It's obviously a better idea than yours, but it is scarcely mine - people have been doing it for years. -- Bill Sloman, Nijmegen
From: dagmargoodboat on 27 Jun 2010 01:41 On Jun 26, 7:37 pm, Kevin McMurtrie <mcmurt...(a)pixelmemory.us> wrote: > - Use proprietary fast-charge NiHM cells that have a gas pressure sensor. That's not a bad idea--Ray-O-Vac made some of those. 15-minute charging, I believe, so you load them at about 4.5C. The problem with temperature cut-outs and fast charging is that once a cell's full, it still takes a while to heat up. So, you wind up overcharging a bit every time, which cuts the cell's service life. A little OT, but the NiMH comments here were interesting-- http://translogic.aolautos.com/2010/06/24/charged-up-about-batteries-why-are-they-so-expensive/ * Limited service life. If repeatedly deep-cycled, (i.e., the charge is completely depleted and then recharged, especially at high load currents), battery performance begins to deteriorate after 200 to 300 cycles. * Limited discharge current. Repeated discharges with high load currents reduce the battery's cycle life. * Sensitive to high temperatures. Performance degrades if stored at elevated temperatures. NiMH batteries should be stored in a cool place and at a state-of-charge of about 40 percent. * Maintenance. NiMH batteries require regular full discharge to prevent crystalline formation. They say they can make an NiMH pack last the life of a car. -- Cheers, James Arthur
From: Raveninghorde on 27 Jun 2010 05:25
On Sat, 26 Jun 2010 18:14:46 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Sat, 26 Jun 2010 08:39:29 -0700 (PDT), Bill Sloman ><bill.sloman(a)ieee.org> wrote: > >>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 > >--- >So it looks like, without expressly acknowledging your earlier >boo-boo, you've admitted that your reference was bogus since a PV >lead-acid charger won't work for NiMH. > >Unfortunately, and to your detriment, you still haven't addressed the >OP's query, which was, basically, "What do I do if the sun goes behind >a cloud while the battery is charging?" > >Instead, you parrot an expensive "Interchangeable thermistor" scheme >to guard against overcharging, which the OP has already laid out, but >which has nothing to do with PV shading during charging. > >The way I'd do it would be to completely disconnect the battery from >the charging circuitry when the array was shadowed, and then reconnect >it when the sun came out again. > >Got a better idea? I remember reading a paper, which I can't find, years ago. The rough idea was you could use short discharge pulses between charge pulses and the voltage depression during the discharge pulse was related to the state of charge. Whether the technique actually works in practice is another matter, but if it works then it wouldn't depend on the charge current being constant. |