Post by thread:[ee]: solar site charging system

I have a panel that delivers up to 21.5V in full sun with 3.5A short-circuit current. This panel is used to charge a 17Ah 12V sealed lead-acid battery that can be floated at 15V for cyclic usage patterns, with a maximum charge rate of around 1.5A. Using a LM317-T set at 15V with no ballast resistor (using internal battery resistance) this works fine in full sun, but anything short of about 17V at the panel results in zero charging. I would like to utilize the power available when the panel is at any point above the battery voltage so that I am not wasting that energy. A switching regulator with a wide input range, say 12-30V to 15V out would be perfect, but I have yet to find one. Should I drop the 317 and simply shunt the panel output at 15V with a Zener? I don't care about anything over the 15V point, as I don't want to over-charge the battery. This of course assumes I can find a 15V/50W zener to mount on the panel. Are there better alternatives? There is a 16F873 in the project with available A/D and TTL ports, so that may be an option with the right components, but I'm running out of experimentation time, so I'd rather not venture into something that "might" work. I can justify up to about $50 for the components. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

I often use a shunt regulator so as to extract the maximum charge possible from the panel. I run 450 watts of PV panels for Ham radio at home. Use a PNP POWER transistor with a low power zener in the base as your shunt.. BYPASS THE ZENER as it is a great RF source. JB wrote: {Quote hidden}>I have a panel that delivers up to 21.5V in full sun with 3.5A short-circuit >current. This panel is used to charge a 17Ah 12V sealed lead-acid battery that >can be floated at 15V for cyclic usage patterns, with a maximum charge rate of >around 1.5A. Using a LM317-T set at 15V with no ballast resistor (using >internal battery resistance) this works fine in full sun, but anything short of >about 17V at the panel results in zero charging. I would like to utilize the >power available when the panel is at any point above the battery voltage so >that I am not wasting that energy. > >A switching regulator with a wide input range, say 12-30V to 15V out would be >perfect, but I have yet to find one. > >Should I drop the 317 and simply shunt the panel output at 15V with a Zener? I >don't care about anything over the 15V point, as I don't want to over-charge >the battery. This of course assumes I can find a 15V/50W zener to mount on the >panel. > >Are there better alternatives? There is a 16F873 in the project with available >A/D and TTL ports, so that may be an option with the right components, but I'm >running out of experimentation time, so I'd rather not venture into something >that "might" work. > >I can justify up to about $50 for the components. > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics > > > -- * | __O Thomas C. Sefranek spam_OUTtcsTakeThisOuTcmcorp.com |_-\<,_ Amateur Radio Operator: WA1RHP (*)/ (*) Bicycle mobile on 145.41, 448.625 MHz ARRL Instructor, Technical Specialist, VE Contact. hamradio.cmcorp.com/inventory/Inventory.html http://www.harvardrepeater.org -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Try doing a search on "maximum power point" converters. These are pretty common in the solar power industry. I did a PIC based one for a solar powered electric car. There each solar panel had a switching boost converter. The current out of each converter into the battery was monitored. The duty cycle driving the FET in the up converter was varied to maintain the highest output current into the battery. Use of separate converter on each panel allowed for varying illumination of the different panels (since the whole car was covered with them). Harold On Mon, 23 Jan 0102 18:34:33 +0000 JB <.....alphaoneKILLspam@spam@ROF.NET> writes: {Quote hidden}> I have a panel that delivers up to 21.5V in full sun with 3.5A > short-circuit > current. This panel is used to charge a 17Ah 12V sealed lead-acid > battery that > can be floated at 15V for cyclic usage patterns, with a maximum > charge rate of > around 1.5A. Using a LM317-T set at 15V with no ballast resistor > (using > internal battery resistance) this works fine in full sun, but > anything short of > about 17V at the panel results in zero charging. I would like to > utilize the > power available when the panel is at any point above the battery > voltage so > that I am not wasting that energy. > > A switching regulator with a wide input range, say 12-30V to 15V out > would be > perfect, but I have yet to find one. > > Should I drop the 317 and simply shunt the panel output at 15V with > a Zener? I > don't care about anything over the 15V point, as I don't want to > over-charge > the battery. This of course assumes I can find a 15V/50W zener to > mount on the > panel. > > Are there better alternatives? There is a 16F873 in the project with > available > A/D and TTL ports, so that may be an option with the right > components, but I'm > running out of experimentation time, so I'd rather not venture into > something > that "might" work. > > I can justify up to about $50 for the components. > > -- > http://www.piclist.com hint: The list server can filter out > subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

My MOSFET knowledge is pretty limited, not sure how to drive that with a PIC running at 5V. Wouldn't a PNP power transistor do essentially the same thing since the CE drop in saturation is what, maybe .2-.4V? Use a 2n2222 to drive the base on the PNP hard with the PIC output, and use the A/D input as you said to detect hi/low thresholds? Perhaps the MOSFET idea is better, but absent much experience with them, I'm trying to stick with what I know. Also, you could be right on that 14.7V, but the data sheet on this battery claimed that in an application like mine where the battery will be drawn down frequently, it's okay to set the constant voltage charger to 15V. Of course, now that you've challenged that figure, I can't seem to locate that data sheet, but I'm pretty sure that's what it said. JB +AD4- {Original Message removed}

At 06:38 PM 1/23/02 -0700, jb wrote: >My MOSFET knowledge is pretty limited, not sure how to drive that with a >PIC running at 5V. Wouldn't a PNP power transistor do essentially the same >thing since the CE drop in saturation is what, maybe .2-.4V? Use a 2n2222 >to drive the base on the PNP hard with the PIC output, and use the A/D >input as you said to detect hi/low thresholds? That's why the P-Mos. Ground is on. So you put a 2N3904 or similar on the PIC output to slam the gate to ground, and a pullup resistor on the gate to the drain to turn the FET off, when the '04 is off. Don't forget a base pulldown resistor on the '04 so it's off when the PIC is in reset or crashed! >Perhaps the MOSFET idea is better, but absent much experience with them, >I'm trying to stick with what I know. Learning is good. :) If it makes your head hurt, that's good. Learn till your head explodes, then back off a notch. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 06:38 PM 1/23/02 -0700, you wrote: > >Also, you could be right on that 14.7V, but the data sheet on this battery claimed that in an application like mine where the battery will be drawn down frequently, it's okay to set the constant voltage charger to 15V. Of course, now that you've challenged that figure, I can't seem to locate that data sheet, but I'm pretty sure that's what it said. The number I have stuck in my cranium came out of a Gates Battery Company manual some 20 years ago. It suggested the following for charging lead acid batteries. Charge: 2.467 volts per cell; thus 14.8 volts for a 12 volt battery. Charge until the cell voltage is at least this high to be 100% charged. Float: 2.300 volts per cell; thus 13.8 volts for a 12 volt battery. Float voltage is where you would leave a lead acid battery to keep it charged (after having gone up to 14.8 volts). These numbers have worked for me quite nice. Lead acid cells are not all that picky though; going to 15 won't kill them. Don't leave them there though; above the recommended 14.8 volts, they begin to consume water giving off hydrogen and oxygen. If your car battery gives off a bit, add it back. If your sealed lead acid battery (gel cell) gives off a bit of out gassing, it also gives off a bit of it's life. Tom M. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

You also might look at the charge curves shown in the UC3906 lead acid smart charger chip datasheet... The device itself probably won't get you where you want to be with a solar panel, but it might give you ideas for the pic algorithm... http://www-s.ti.com/sc/ds/uc3906.pdf There's also a switchmode schematic on the TI/Unitrode site using this chip that might work in you're app --it looks to be much more complicated than the pic approach Lawrence suggests however. ----- Original Message ----- From: jb +ADw-alphaone+AEA-ROF.NET+AD4- My MOSFET knowledge is pretty limited, not sure how to drive that with a PIC running at 5V. Wouldn't a PNP power transistor do essentially the same thing since the CE drop in saturation is what, maybe .2-.4V? Use a 2n2222 to drive the base on the PNP hard with the PIC output, and use the A/D input as you said to detect hi/low thresholds? Perhaps the MOSFET idea is better, but absent much experience with them, I'm trying to stick with what I know. Also, you could be right on that 14.7V, but the data sheet on this battery claimed that in an application like mine where the battery will be drawn down frequently, it's okay to set the constant voltage charger to 15V. Of course, now that you've challenged that figure, I can't seem to locate that data sheet, but I'm pretty sure that's what it said. JB +AD4- {Original Message removed}

JB, Find yourself a low dropout regulator. Or make your own with a large PNP or p-channel FET. I am presently working on a project with a Micrel (MIC3902) part with about 375mV drop at 3 amps and even less at 1.5 Amps. It also has a shutdown pin and claims to be well protected from all sorts of screwups like reverse voltage etc. Get it from Arrow for about $5.00. -- Looking forward: Alan Shinn Date: Mon, 23 Jan 0102 18:34:33 +0000 From: JB <alphaoneKILLspamROF.NET> Subject: [ee]: solar site charging system I have a panel that delivers up to 21.5V in full sun with 3.5A short-circuit current. This panel is used to charge a 17Ah 12V sealed lead-acid battery that can be floated at 15V for cyclic usage patterns, with a maximum charge rate of around 1.5A. Using a LM317-T set at 15V with no ballast resistor (using internal battery resistance) this works fine in full sun, but anything short of about 17V at the panel results in zero charging. I would like to utilize the power available when the panel is at any point above the battery voltage so that I am not wasting that energy. A switching regulator with a wide input range, say 12-30V to 15V out would be perfect, but I have yet to find one. Should I drop the 317 and simply shunt the panel output at 15V with a Zener? I don't care about anything over the 15V point, as I don't want to over-charge the battery. This of course assumes I can find a 15V/50W zener to mount on the panel. Are there better alternatives? There is a 16F873 in the project with available A/D and TTL ports, so that may be an option with the right components, but I'm running out of experimentation time, so I'd rather not venture into something that "might" work. I can justify up to about $50 for the components. Experience the beginnings of microscopy. Make your own replica of one of Antony van Leeuwenhoek's microscopes. visit http://www.mindspring.com/~alshinn/ -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Two ways: 1. Use the 317 as before for >17V and a DC/DC boost converter that you get to build for $10 or so below. The dc/dc would cut out when the 317 begins to deliver current (which you sense). 2. Lose the 317 and implement a dc/dc with transformer (to avoid buck-boost) with a standard dc/dc chip or another topology (the one with the series LC) and use the PIC to implement an optimal power transfer operation. This would probably be $30-ish (wild guess). Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.