... it is overcast and my panel array is showing 3.64V. I decided to see what the 200mA setting would show, and the number was .1mA.
That's prolly a correct reading - less than 0.5mW. Not enough to work and certainly not enough to pump any charge into a lead-acid. Lead-acids compete with NiCds for leakiness. In this day and age, SLAs are dinosaurs, don't spend money on them.
On a sunny day I would expect open circuit voltage to hit 11 volts and short circuit current to exceed the rated amperage, although, not by much. The 9 volt rating is what it sags down to (From 11 volts) when loaded to it's maximum power point. A lower loaded voltage (Than the mppt point) provides very little more current which means less than optimal power provided.
When you do get some sunshine and plug the battery in, the PV voltage will just drop down to match the battery. The battery, assuming it's not buggered, will then slowly rise in volts as it charges. You can be the full-charge regulator and disconnect it when the battery is at it's max voltage.
PS: Except for the various Lithium's you can get away with quite a bit of overcharging on most battery types. They will heat up a bit but very little damage occurs. Just don't leave it cooking all day long.
Ray, I wouldn't be too quick to toss that battery. Most lead acid batteries (including sla's) require 14 hours to charge at a current that is 10% ( .1C ) of the rated capacity to fully charge from a totally discharged state. Try charging the battery overnight with a charger that puts out at least 400mA first.
Lead-acids compete with NiCds for leakiness. In this day and age, SLAs are dinosaurs, don't spend money on them.
Actually, I thought the dinosaurs were NiCDs. I'm not certain what you mean by "leakiness", but isn't the self-discharge rate of lead acid batteries much lower than that of NiCD? Though I'm not sure how important that is in a solar system where the batteries will see frequent charging.
You almost can't find NiCDs for sale these days. Places like Walmart and the local grocery or drugstore don't seem to sell them. It appears that NiCD has been almost totally replaced by NiMH
I'm not certain what you mean by "leakiness", but isn't the self-discharge rate of lead acid batteries much lower than that of NiCD? Though I'm not sure how important that is in a solar system where the batteries will see frequent charging.
And the old generation NiMH weren't a whole lot better either. The new (LSD) NiMH are a world away.
It's important when you've only got 100uA charging current!
Yesterday was partly cloudy with more sunshine coming through between noon and four PM. It was about four PM when I pulled the battery and it was reading 2.66V, at that point I decided to put the battery on a charger where it was plugged in for about thirteen hours, the reading for the battery, at the end of the charging session was 2.92V. Now the question is, how much more time do I want to spend on trying to rejuvenate an old battery, if at all possible.
I also had a chance to plug in my BoeBot Li-ion battery pack, when the array was putting out about 8.7V, and the blue LED did start to come on, but not at a consistent rate. I did not have a steady 9.0V output on the array, so I am not sure how much more would have to be added to my array to get that battery pack to get a steady charge.
Since some of my devices that I would like to operate from a battery, like a RPi, need a 5.0V, maybe I should start thinking about using the array for charging a battery or batteries in the 3.0V range. It seems that with my array and the amount workable light that I am getting maybe a smaller voltage battery would be the way to go. The problem would be, what kind of battery would be best suited for this kind of situation? I would like to avoid any kind of really complicated circuitry, or have batteries catching fire or exploding on my windowsill.
Charging a 3V battery pack from a 9V panel would be a very inefficient use of the panel. Better to charge 4 or 5 NiMH cells in series to get 4.8 or 6V. A 5 battery pack with an LDO regulator makes a pretty good 5V supply for low power circuits.
Below is what the base My Solar Array prototype setup looks like. So far I made attachments for a volt meter, next I will setup the Activity Board to data log the solar array. The data logging will be a PropGCC program since I have a software RTC program developed. I also have a mediocre ADC program for measuring the voltage, which I will adapt for this, that also is in PropGCC. Once I decide what battery type I will be pursuing, then I will add the appropriate wiring.
For non-mobile use, I still think a 6 volt SLA battery is a good match for this set up. Very robust with simple charging requirements and 6 volts is a nice fit between the 9 volt solar cell and the 5 and/or 3.3 volts needed for the end use. Most low drop out 5 volt regulators will work fine from a 6 volt battery.
Charging a 3V battery pack from a 9V panel would be a very inefficient use of the panel. Better to charge 4 or 5 NiMH cells in series to get 4.8 or 6V. A 5 battery pack with an LDO regulator makes a pretty good 5V supply for low power circuits.
Agreed, but Ray is in constantly cloudy conditions and never gets 9V out of his cells. Trying to make lemonade here. He mentioned 4.75V back in post #31. That could charge a 3.6 NiMH pack or marginally a lithium cell. Or put enough in series to get whatever voltage is required.
Otherwise, get a giant Fresnel lens to concentrate more sunlight on the cells and get them back up to 9V.
4.75 volts from one of these panels is probably just about useless.
Yesterday was an almost cloudless day here, but my balcony gets zero direct sun after around 10 a.m. Early in the afternoon one panel, facing clear open sky to the east (no direct sunlight), was able to barely light a yellow LED. And that was without a current limiting resistor. The output was under 6 mA. However, open circuit voltage was over 8.5 volts and when faced more toward the north, it was almost 9.5 volts but still, without direct sun, these panels put out very little current.
...However, open circuit voltage was over 8.5 volts and when faced more toward the north, it was almost 9.5 volts but still, without direct sun, these panels put out very little current.
Under the conditions you just described, I wonder how many more panels you would have to add to get some workable current? Or the question should be, can you get any workable current without direct sun?
I just added an RPi to the mix with a WiFi attached. The RPi it is also connected to the Activity Board, which I will be installing SimpleIDE, then I will program the Activity Board from my desktop. First I am going to do a program to data log the open circuit, just to see what kind of values I am getting during a 24/7 period. Now I am wondering if, on the Activity Board, I can do some kind of circuit to measure for current?
For the open circuit, on the Activity Board breadboard, I will have two 10K resistors in series connected to the ADC, and then I will measure from there. I wonder if there is a way to create a closed circuit and then measure for current using the ADC?
Early this morning, while the solar array was reading 2.46V, I connected a low power LED, I am guessing maybe a 3V, and the led lit brightly. I then got an LED, rated at 5V?, and that lit up, but not as brightly as the other LED, there was no direct sun. I am trying to devise a way of measuring that "workable current" at different solar array voltage outputs. I am wondering if I took a known value, like a 220Ohm resister, and placed that in the circuit, could I get some kind of useful value as to "workable current"?
Today I will probably put together the voltage divider circuit, and get a program to produce some values. It looks like it will be another overcast day so I will be working with low voltage numbers, so I just might skip the divider part and wire up straight to the ADC and capture some values. No on second thought, I will just do the divider thing, so I will not have to mess around later.
I hooked up the voltage divider circuit, and everything seems to working as expected, but I am getting a different reading from the ADC setup. When voltage meter reading, I double checked with another meter, is 6.44V, the program below is showing 6.97V. That is about a half of volt difference, unless both my meters are wrong. I was hoping that the discrepancy would be much smaller, now I am not sure if I can trust the values I am getting from the ADC setup.
Have you taken a reading with a DVM at the junction of the two 10K resistors that you are using for a voltage divider? Is it exactly half the voltage you are applying to the divider? Unless you are using precision resistors both resistors probably have a different value, which could account for some of the discrepancy. You can add a 5K 20-turn trim pot between the resistors and feed the ADC from the wiper lead. Set up your divider circuit on a separate board for testing purposes. Apply a known voltage to the divider and adjust the the trim pot so that the wiper lead (usually the middle one) shows half the voltage on a meter. When back on the Activity Board your readings should be much closer. You may have to further trim the pot to account for Vref being something other than exactly 5 Volts.
Got foiled by another assumption that I made. I forgot that just because the package says 10K resistor on it, it may not be that exact value. Maybe I should add a circuit that measures the resistor values, then have my program reflect that. I have never used a trim pot in any of my circuits, but I think that might be the easier way of adjusting the values to some known numbers.
Has anybody come across an official voltage current graph for these RadioShack solar panels? Now I have to think about what kind of battery I should test out on this solar array. I have a four AA battery holder that came with the BoeBot, maybe load that up with some rechargeable 1.2V batteries, and try to charge them in series. I am not sure, but I think I got a 5 AA battery holder with the ActivityBot, maybe load that up and go for a 6V recharge.
Agreed, but Ray is in constantly cloudy conditions and never gets 9V out of his cells. Trying to make lemonade here. He mentioned 4.75V back in post #31. That could charge a 3.6 NiMH pack or marginally a lithium cell. Or put enough in series to get whatever voltage is required.
Otherwise, get a giant Fresnel lens to concentrate more sunlight on the cells and get them back up to 9V.
The low output voltage is most likely due to the panel being connected to the battery when the measurement was taken. The intensity of light falling on the panel has a large effect on the current and a much smaller one on the output voltage.
Measure the output voltage of the panel with no load (other than the voltmeter) on it in bright sunlight and on a cloudy day and you will not see a big difference in the output voltage. Do the same thing while measuring the short circuit current and you will see a large difference in the current.
A solar panel behaves a bit like a current limited power supply where the current limit depends on the amount of light falling on the panel.
Measure the output voltage of the panel with no load (other than the voltmeter) on it in bright sunlight and on a cloudy day and you will not see a big difference in the output voltage. Do the same thing while measuring the short circuit current and you will see a large difference in the current.
Yes, this is what I've been seeing - very little change in voltage from dim and shady to intense sunlight, but you do have to measure with no load (open circuit).
The available current varies from (about) the specified 100 mA down to less than 5 mA, I would assume it's linear vs. intensity of the light.
When the voltage is measured across any kind of load it will change according to Ohm's Law. For example, with the yellow LED that I used the voltage reading was about 1.87 volts, which is basically the voltage drop across the LED. Any reasonable precise resistor should work fine for measuring current with an ADC.
Got foiled by another assumption that I made. I forgot that just because the package says 10K resistor on it, it may not be that exact value. Maybe I should add a circuit that measures the resistor values, then have my program reflect that. I have never used a trim pot in any of my circuits, but I think that might be the easier way of adjusting the values to some known numbers.
Has anybody come across an official voltage current graph for these RadioShack solar panels? Now I have to think about what kind of battery I should test out on this solar array. I have a four AA battery holder that came with the BoeBot, maybe load that up with some rechargeable 1.2V batteries, and try to charge them in series. I am not sure, but I think I got a 5 AA battery holder with the ActivityBot, maybe load that up and go for a 6V recharge.
Ray
A simpler method would be to multiply the reading you get from the adc by a correction factor so it matches the meter readings. Taking readings at 3 points (low, mid, high) over the 0-9V range should be enough to calculate the correction factor.
A simpler method would be to multiply the reading you get from the adc by a correction factor so it matches the meter readings. Taking readings at 3 points (low, mid, high) over the 0-9V range should be enough to calculate the correction factor.
Great idea, Kwinn, now why didn't I think of that instead of adding extra hardware. BTW I had thought about suggesting to Ray to just use a single 20K trimpot but then realized it would be very easy to apply an overvoltage to the ADC without some buffer resistors on either side.
I noticed that the guy on ebay is still selling the 10-pack solar panels, with the same offering. Now I am wondering if I were to add six more panels to my array if I would get any substantial gain from doing that? I have room for six more, but nine more of them would be really tight.
I am now considering making my contraption more mobile, but to do that I would have to switch over to using batteries for the main power source. As I mentioned in the other post, I added a Raspberry Pi to the mix, so basically I provide power, 5V 1Amp minimum, to the RPi, which also powers up the Activity Board. The power source that I also have is a power bank, 10Ah 1 and 2Amp output, with a mini din socket for attaching a cable with a USB plug on the other end. The input requirements for charging is 5V, since you can plug into a computer USB to charge the pack, or a special wall socket adapter, I can't remember what amp rate the PC USB 2 is putting out, but that would be the minimum I would think.
Now if add this power bank to the mix, I wonder how difficult it would be to set it up so the power bank could get topped off from the solar power, and I could still plug it into an outlet when skies around here are overcast for a week at a time, fall -> winter -> spring. I think I still have 5V regulator, from my PEK box laying around somewhere. Maybe pick up some supercaps to stabilize the voltage stream, and try hooking it up to the solar array. As a final solution it would be nice to have some kind of circuit where it can determine when the power bank needs to topped of and switches to a topping off stage. Boy this is starting to expand a fast rate.
All of what you are suggesting is possible to do. The level of difficulty depends on how fancy you want to get and how accessible the power bank circuitry is.
...The level of difficulty depends on how fancy you want to get and how accessible the power bank circuitry is.
The power bank, which itself looks like it is in a white case, is completely sealed in a clear acrylic case. So, you would have to break open the acrylic case to get at the unit itself. I really like this power bank, it never gets hot when I leave on the charge function for a long time, but I guess when the batteries inside finally give up, then either I toss it or break the thing open. That I guess limits the outside control of this unit since all you can do is work with the mini din charge cable. I really like the idea that all you need is 5V to charge the power bank, which sounds like a good fit for the solar array. I bought this unit at Adafruit, which looked like a good fit for my RPi.
Doing a new experiment, I found a Tenergy 3.7V Li-ion battery laying around, it reads 3.95V, but I think these can be charged up to 4.0V. Using some big rubber bands to attach some wire to the ends of the battery, it is now connected to the solar array, I will leave it connected until the battery starts to get warm, ballooning, or an hour has passed, which ever comes first. With the battery attached, I checked the ADC reading and it is showing 4.96V. Yes, the sun has come out from behind the clouds, but I am not getting any direct sun on a hundred percent of the array, maybe about a third of the array, on the open circuit it was reading ~7.0V.
This should be interesting, maybe I will have to commandeer the other Tenergy battery and try charging both at the same time.
... In this day and age, SLAs are dinosaurs, don't spend money on them.
I might have to eat my words on that one. I've just been informed of a SLA variant called Lead Crystal that can endure a 1000+ recharges at 50% DOD (Compared with maybe 200 at 30% for your average car battery.) and are typical SLA dirt cheap pricing. Only a patch on high end Lithium Phosphate capabilities (5000 at 80%, amongst other features) but still at that price they are very competitive for grid storage.
Yesterdays experimentation results, using the 3.7V battery, start reading of 3.95V, finish reading 4.01V after about a 45 min charge. I also had a chance to drain the battery down to 3.98V, and then do another charge session, in the late afternoon, where I as not getting any direct sun light on the panels, finish reading 4.02V after about another 40 minute session. Since I was not measuring the battery itself, I do not know how many minutes it would have taken to get to ~4.0V. I have to really think about these results in terms of direct sun and indirect sun on the panels. It seems to me that, in my conditions, with some indirect sun, you would need more panels and still get a very good charging condition. Now, I am almost tempted to add six more panels to the array, just to see what sort of charge conditions I get when there is indirect sun or open circuit readings of 8V.
Yesterday I ordered some battery holders for the 3.7V batteries, I will be wiring two of the batteries in series, ~8V, and powering my Activity Board which in turn will be powering the RPi B+ board. This way I will be able to measure the batteries to see what kind of drain I will be getting in the new configuration of powering the boards. Now the question is, how many of these 3.7V 2.4Ah batteries, and in what configuration would I have to have, to get 12Ah rating?
Early this morning, while the solar array was reading 2.46V, I connected a low power LED, I am guessing maybe a 3V, and the led lit brightly. I then got an LED, rated at 5V?, and that lit up, but not as brightly as the other LED, there was no direct sun. I am trying to devise a way of measuring that "workable current" at different solar array voltage outputs. I am wondering if I took a known value, like a 220Ohm resister, and placed that in the circuit, could I get some kind of useful value as to "workable current"?
Today I will probably put together the voltage divider circuit, and get a program to produce some values. It looks like it will be another overcast day so I will be working with low voltage numbers, so I just might skip the divider part and wire up straight to the ADC and capture some values. No on second thought, I will just do the divider thing, so I will not have to mess around later.
A 12Ah rating using 2.4Ah batteries would need 12 / 2.4 = 5 batteries. Amp hours are a poor choice for comparing batteries since it does not take into account the battery voltage. Watt hours provide a much better rating for comparison since it takes into account the total energy the batteries provide.
A 6V 12Ah battery would be 72Wh and a 7.2V 2.4Ah battery pack would be 17.28Wh so you would need 4 packs to get close to 72Wh.
Of course transferring all that energy from the solar panel to the battery and then to the load with minimal loss is another whole can of worms.
@Bean, Thanks for the generous offer, at this time I will have to pass. I am to old too become an independent solar panel tester and evaluator. :-)
Of course transferring all that energy from the solar panel to the battery and then to the load with minimal loss is another whole can of worms.
@kwinn, Yes it looks like that is the direction I am heading. Since this will be a mobile array for evaluating charging conditions at different locations around the house and maybe even outside, it will have to be self powered. As soon as I get some figures as to how long a pack of two 3.7V= ~7.4V - 8.0V will last powering an Activity Board -> RPi Board, I will try to determine how many cell packs I will need to have the panel contraption work 24/7(maybe). Hopefully, have it configured in such a way that when there is charging power it will charge the most needed pack. This almost sounds like I need some kind software/hardware activated pack switching doodad, whatever that may be.
Now I have to find some more 10K resistors so I can set up another battery check circuit, which will be the BoeBot Li-ion power pack which will be plugged into the Activity board that also powers the RPi.
Yesterdays experiment results were very interesting, I rewired the power distribution for the Activity Board (AB) and the Raspberry Pi (RPi), so everything would be powered from the BoeBot Li-ion battery pack (BLBP). The aim was to find out how long the BLBP would last.
I first checked the BLBP, at the barrel plug, which showed 7.98V. The RPi basically acts as a headless WiFi so I can, from my desktop using mstsc, program the AB using SimpleIDE and view the voltage readings. The AB now has two ADC circuits, one for the solar array open circuit, and the second one now checks the BLBP for its voltage, and of course you have the two green power LEDs on the AB. The electrical current demands for the boards are at the minimal requirements, for my experiments, to get a better feel for what a minimum would require.
After I updated the existing program to add another volt reading and started the program, the first reading for the BLBP was 6.79V. Then I proceeded to do manual data logging at a fifteen minute mark, to see what the V readings would be, tedious but affective.
I was kind of surprised that the BLBP kept the RPi alive until it reached a 4.96V reading, which took four hours to get there. The other thing that surprised me was that the two power LEDs on the AB were still on, I thought everything would have shut down at a 6.0V reading, after all, at the barrel socket it shows 6 - 9V, I assumed those were the operating conditions. I also checked the individual battery readings at RPi shutdown, 3.07V and 3.46V, which could imply that with the RPi out of the loop, the BLBP was still putting out 6.53V, which was still within the AB recommended operating range? So the BLBP provided a four session, maybe working with a two BLBP setup would not be unreasonable?
Comments
That's prolly a correct reading - less than 0.5mW. Not enough to work and certainly not enough to pump any charge into a lead-acid. Lead-acids compete with NiCds for leakiness. In this day and age, SLAs are dinosaurs, don't spend money on them.
On a sunny day I would expect open circuit voltage to hit 11 volts and short circuit current to exceed the rated amperage, although, not by much. The 9 volt rating is what it sags down to (From 11 volts) when loaded to it's maximum power point. A lower loaded voltage (Than the mppt point) provides very little more current which means less than optimal power provided.
When you do get some sunshine and plug the battery in, the PV voltage will just drop down to match the battery. The battery, assuming it's not buggered, will then slowly rise in volts as it charges. You can be the full-charge regulator and disconnect it when the battery is at it's max voltage.
PS: Except for the various Lithium's you can get away with quite a bit of overcharging on most battery types. They will heat up a bit but very little damage occurs. Just don't leave it cooking all day long.
Actually, I thought the dinosaurs were NiCDs. I'm not certain what you mean by "leakiness", but isn't the self-discharge rate of lead acid batteries much lower than that of NiCD? Though I'm not sure how important that is in a solar system where the batteries will see frequent charging.
You almost can't find NiCDs for sale these days. Places like Walmart and the local grocery or drugstore don't seem to sell them. It appears that NiCD has been almost totally replaced by NiMH
And the old generation NiMH weren't a whole lot better either. The new (LSD) NiMH are a world away.
It's important when you've only got 100uA charging current!
I also had a chance to plug in my BoeBot Li-ion battery pack, when the array was putting out about 8.7V, and the blue LED did start to come on, but not at a consistent rate. I did not have a steady 9.0V output on the array, so I am not sure how much more would have to be added to my array to get that battery pack to get a steady charge.
Since some of my devices that I would like to operate from a battery, like a RPi, need a 5.0V, maybe I should start thinking about using the array for charging a battery or batteries in the 3.0V range. It seems that with my array and the amount workable light that I am getting maybe a smaller voltage battery would be the way to go. The problem would be, what kind of battery would be best suited for this kind of situation? I would like to avoid any kind of really complicated circuitry, or have batteries catching fire or exploding on my windowsill.
Ray
Ray
Agreed, but Ray is in constantly cloudy conditions and never gets 9V out of his cells. Trying to make lemonade here. He mentioned 4.75V back in post #31. That could charge a 3.6 NiMH pack or marginally a lithium cell. Or put enough in series to get whatever voltage is required.
Otherwise, get a giant Fresnel lens to concentrate more sunlight on the cells and get them back up to 9V.
Yesterday was an almost cloudless day here, but my balcony gets zero direct sun after around 10 a.m. Early in the afternoon one panel, facing clear open sky to the east (no direct sunlight), was able to barely light a yellow LED. And that was without a current limiting resistor. The output was under 6 mA. However, open circuit voltage was over 8.5 volts and when faced more toward the north, it was almost 9.5 volts but still, without direct sun, these panels put out very little current.
I just added an RPi to the mix with a WiFi attached. The RPi it is also connected to the Activity Board, which I will be installing SimpleIDE, then I will program the Activity Board from my desktop. First I am going to do a program to data log the open circuit, just to see what kind of values I am getting during a 24/7 period. Now I am wondering if, on the Activity Board, I can do some kind of circuit to measure for current?
For the open circuit, on the Activity Board breadboard, I will have two 10K resistors in series connected to the ADC, and then I will measure from there. I wonder if there is a way to create a closed circuit and then measure for current using the ADC?
Ray
Today I will probably put together the voltage divider circuit, and get a program to produce some values. It looks like it will be another overcast day so I will be working with low voltage numbers, so I just might skip the divider part and wire up straight to the ADC and capture some values. No on second thought, I will just do the divider thing, so I will not have to mess around later.
Ray
Ray
/* solarv.c */ #include "simpletools.h" #include "adcDCpropab.h" int main() { // Add startup code here. adc_init(21, 20, 19, 18); float v3; while(1) { // Add main loop code here. v3 = adc_volts(3); v3 = (v3*2); // Multiply by 2 putChar(HOME); print("%f \n",v3); pause(200); } }Has anybody come across an official voltage current graph for these RadioShack solar panels? Now I have to think about what kind of battery I should test out on this solar array. I have a four AA battery holder that came with the BoeBot, maybe load that up with some rechargeable 1.2V batteries, and try to charge them in series. I am not sure, but I think I got a 5 AA battery holder with the ActivityBot, maybe load that up and go for a 6V recharge.
Ray
The low output voltage is most likely due to the panel being connected to the battery when the measurement was taken. The intensity of light falling on the panel has a large effect on the current and a much smaller one on the output voltage.
Measure the output voltage of the panel with no load (other than the voltmeter) on it in bright sunlight and on a cloudy day and you will not see a big difference in the output voltage. Do the same thing while measuring the short circuit current and you will see a large difference in the current.
A solar panel behaves a bit like a current limited power supply where the current limit depends on the amount of light falling on the panel.
Yes, this is what I've been seeing - very little change in voltage from dim and shady to intense sunlight, but you do have to measure with no load (open circuit).
The available current varies from (about) the specified 100 mA down to less than 5 mA, I would assume it's linear vs. intensity of the light.
When the voltage is measured across any kind of load it will change according to Ohm's Law. For example, with the yellow LED that I used the voltage reading was about 1.87 volts, which is basically the voltage drop across the LED. Any reasonable precise resistor should work fine for measuring current with an ADC.
A simpler method would be to multiply the reading you get from the adc by a correction factor so it matches the meter readings. Taking readings at 3 points (low, mid, high) over the 0-9V range should be enough to calculate the correction factor.
Great idea, Kwinn, now why didn't I think of that instead of adding extra hardware. BTW I had thought about suggesting to Ray to just use a single 20K trimpot but then realized it would be very easy to apply an overvoltage to the ADC without some buffer resistors on either side.
I am now considering making my contraption more mobile, but to do that I would have to switch over to using batteries for the main power source. As I mentioned in the other post, I added a Raspberry Pi to the mix, so basically I provide power, 5V 1Amp minimum, to the RPi, which also powers up the Activity Board. The power source that I also have is a power bank, 10Ah 1 and 2Amp output, with a mini din socket for attaching a cable with a USB plug on the other end. The input requirements for charging is 5V, since you can plug into a computer USB to charge the pack, or a special wall socket adapter, I can't remember what amp rate the PC USB 2 is putting out, but that would be the minimum I would think.
Now if add this power bank to the mix, I wonder how difficult it would be to set it up so the power bank could get topped off from the solar power, and I could still plug it into an outlet when skies around here are overcast for a week at a time, fall -> winter -> spring. I think I still have 5V regulator, from my PEK box laying around somewhere. Maybe pick up some supercaps to stabilize the voltage stream, and try hooking it up to the solar array. As a final solution it would be nice to have some kind of circuit where it can determine when the power bank needs to topped of and switches to a topping off stage. Boy this is starting to expand a fast rate.
Ray
Ray
This should be interesting, maybe I will have to commandeer the other Tenergy battery and try charging both at the same time.
Ray
I might have to eat my words on that one. I've just been informed of a SLA variant called Lead Crystal that can endure a 1000+ recharges at 50% DOD (Compared with maybe 200 at 30% for your average car battery.) and are typical SLA dirt cheap pricing. Only a patch on high end Lithium Phosphate capabilities (5000 at 80%, amongst other features) but still at that price they are very competitive for grid storage.
I'd never heard of them before.
Yesterday I ordered some battery holders for the 3.7V batteries, I will be wiring two of the batteries in series, ~8V, and powering my Activity Board which in turn will be powering the RPi B+ board. This way I will be able to measure the batteries to see what kind of drain I will be getting in the new configuration of powering the boards. Now the question is, how many of these 3.7V 2.4Ah batteries, and in what configuration would I have to have, to get 12Ah rating?
Ray
Ray, I have a bunch of these http://www.allelectronics.com/make-a-store/item/spl-61/solar-cell-60mm-x-60mm-x2mm/1.html solar panels.
They are CIS construction which I think give much more current when not in direct sunlight than silicon versions.
I'd be willing to send you some to experiment with (free to keep). Send me a PM if you are interested.
What voltage / current are you looking to generate ?
Bean
A 6V 12Ah battery would be 72Wh and a 7.2V 2.4Ah battery pack would be 17.28Wh so you would need 4 packs to get close to 72Wh.
Of course transferring all that energy from the solar panel to the battery and then to the load with minimal loss is another whole can of worms.
@kwinn, Yes it looks like that is the direction I am heading. Since this will be a mobile array for evaluating charging conditions at different locations around the house and maybe even outside, it will have to be self powered. As soon as I get some figures as to how long a pack of two 3.7V= ~7.4V - 8.0V will last powering an Activity Board -> RPi Board, I will try to determine how many cell packs I will need to have the panel contraption work 24/7(maybe). Hopefully, have it configured in such a way that when there is charging power it will charge the most needed pack. This almost sounds like I need some kind software/hardware activated pack switching doodad, whatever that may be.
Now I have to find some more 10K resistors so I can set up another battery check circuit, which will be the BoeBot Li-ion power pack which will be plugged into the Activity board that also powers the RPi.
Ray
I first checked the BLBP, at the barrel plug, which showed 7.98V. The RPi basically acts as a headless WiFi so I can, from my desktop using mstsc, program the AB using SimpleIDE and view the voltage readings. The AB now has two ADC circuits, one for the solar array open circuit, and the second one now checks the BLBP for its voltage, and of course you have the two green power LEDs on the AB. The electrical current demands for the boards are at the minimal requirements, for my experiments, to get a better feel for what a minimum would require.
After I updated the existing program to add another volt reading and started the program, the first reading for the BLBP was 6.79V. Then I proceeded to do manual data logging at a fifteen minute mark, to see what the V readings would be, tedious but affective.
I was kind of surprised that the BLBP kept the RPi alive until it reached a 4.96V reading, which took four hours to get there. The other thing that surprised me was that the two power LEDs on the AB were still on, I thought everything would have shut down at a 6.0V reading, after all, at the barrel socket it shows 6 - 9V, I assumed those were the operating conditions. I also checked the individual battery readings at RPi shutdown, 3.07V and 3.46V, which could imply that with the RPi out of the loop, the BLBP was still putting out 6.53V, which was still within the AB recommended operating range? So the BLBP provided a four session, maybe working with a two BLBP setup would not be unreasonable?
Ray