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U3S on Solar Power project, noob questions
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Hello all,
Awaiting the release of the QRP Labs U3B, I've already ordered some of those small solar panels from China to experiment with. To get some more experience with- and knowledge of those solar panels I'd like to see if I can power my U3S with them. I've got two sizes panels, one is 52x19mm and the other is 39x19mm. The panels are rated average voltage / average current 0,5 V / 0,3 A and 0,5 V / 0,24 A respectively. My U3S with QLG1 GPS together draws about 110 mA during idle and approximately 220 mA when transmitting on 40m and a little less on 20m. Now my plan is to connect about 15 to 20 solar panels (of the 52x19mm size) in series giving approximately 7,5 to 10 V and enabling a current of 300 mA (which should be enough for the 220mA of the U3S). I then want to feed the power to a voltage regulator bringing down the voltage to a stable 5 Volts (I've made one from one of those cheap car mobile phone chargers) which lastly I connect the U3S to. I only want the U3S to be powered by the solar panels during daylight, so at this point I'm not interested in some kind of battery being charged as well. Am I seeing this too simple, am I missing something here? Any tips and hints would be welcome. To be on the safe side with the current it also has crossed my mind to put two rows of 15 to 20 panels in parallel enabling a current of 600mA. Do I maybe also have to put in a diode in the circuit somewhere? The biggest challenge will probably be soldering to the panels. I will follow the tips and tricks given on this group some time ago. Best 73, Michael PA7MDJ |
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Hi,?
just take 9 of them and you will have just short of 5V and just feed them directly to the board without a regulator, or solder 10-11 of them together and get a 5v LDO, I would also recommend you to get a 5,5v supercapacitor of 1F and fit across the terminals to help suppling enough power during transmit. The solarcells gives about 0,55v / cell |
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Hi Michael,
Anticipate about 35 mA/cm^2 Isc from your PV cells under one-sun illumination at 25 C.? From there, scale it up because sunlight is brighter at high altitudes because there is less air to attenuate it.? And scale it down because your PV cells will rarely face the sun and they will be cold.? Then, scale it down because you won't be operating the cells at Isc; ideally they'll run at Pmax.? You can measure the I-V curve of your cells to understand this further.? Illuminate the solar cell with an incandescent lamp and load it with a variable resistor.? Pmax is the point on the I-V curve where the I*V product is highest.? That's where you want to operate.? When you get less sunlight, the current will drop approximately linearly while the voltage won't drop nearly as much. When your solar cells get cold due to high altitude, all other factors unchanged, their voltage will rise approximately 0.3% per degree C and current should fall about 0.06% per degree C. You may wish to measure the efficiency of your phone charger and substitute a lightweight switching regulator.? An efficient switching regulator will give you more current at the output than it draws at the input if the input voltage is substantially higher than the output voltage.? This may enable use of smaller PV cells and a shorter string. If you use 2 short strings (<10V) you probably won't need a diode unless your cells have a lot of shunting.? If you angle each string differently, you may have more chance of a string being illuminated at any particular time.? But your payload is getting heavy... All this is just from my experience with PV; I haven't flown a balloon yet!? Waiting for U3B! Cheers Halden NR7V |
开云体育Thank you, Mikael! ? I’ve ordered a couple of 5.5V 1F supercapacitors and a couple of L4940 5V LDO’s from China. I will experiment with both. ? 73 de Michael PA7MDJ ? Van: [email protected] [mailto:[email protected]] Namens Mikael Dagman ? Hi,? |
开云体育Hi Halden, ? Thanks for answering my questions about solar cells. I’m not planning on using the described setup as a balloon payload. While I’m awaiting the release of the U3B, I just want to experiment with the solar cells and see if I can power my U3S with them down here on earth. Soldering to the solar cells will be quite difficult, and I want to have some experience with that before the U3B is released. I will use another lighter setup with the U3B. I have no details yet as to what exactly will be on the U3B board already (regulator, battery etc.), so I’ll have to wait for that, but most probably fewer solar cells will do and I definitely will not use the heavy phone charger regulator. The information given is very useful though, and I will do some experiments. I’ve already figured out that PV means photovoltaic, but can you please tell me what Isc means. ? Thanks again and best 73 from a fellow U3B awaiter ? ? Michael PA7MDJ ? Van: [email protected] [mailto:[email protected]] Namens HF via Groups.Io ? Hi Michael, |
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Roberto,IZ7VHF has shared his solar cell builds here -
Should give you an idea what you may want to try.But to power the entire U3S kit would require a lot of solar I would think having the LCD and all. Most are using minimal builds to operate from solar power.The GPS modules can be key to how many cells you will need.I found a uBLOX NEO-6M draws much more current than the NEO-7M.This is just an example,but key to reducing current required when using solar power. I have had great luck using only 6 52x19mm connected directly to the 3.3v LDO reg...no battery.It fires up the boards fine even with low sunlight.Solar cells produce more energy at altitudes...so if they work on the ground...you got it made. Once the U3B is available,I am sure your solar requirements will be much easier to accomplish. Jim,N2NXZ |
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One more note.
The use of a 5v boost module with your solar cells and a modest battery will help a great deal for a more power hungry circuit - These have been successfully used with 7-8 solar cells and a small 100ma battery.Be sure to use a blocking diode so the battery does not drain into the cells. I personally prefer to eliminate the boost module/battery as this is weight best to get rid of for balloon flights. It all boils down to the circuit design as to what you will need for power....weight is critical. Jim |
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If using a constant current source (as PV's) you can get away with zeners to regulate/clamp the voltage. make sure to distribute the heat with several small devices or a single large zener attached to something like the groundplane of the board to dissipate the heat. No need to have much higher voltage than it would need to clamp. |
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Hi Michael, Thanks for the explanation of your plans with U3S and U3B.? I think running the U3S on solar power on the ground is a great idea because you'll learn about PV the fun way.? Then you'll be able to design power management systems for your U3B flights, ham shack, house, town, etc.? I've had good luck using electrically-conductive epoxy to contact PV cells that resist soldering.? But it's expensive and fussy about cure temperature to provide good conductivity.? Isc is short-circuit current -- the current provided by the PV when the terminals are shorted.? The PV current is lower out at the maximum power point where it matters.? Enter "solar cell i-v curve" into a search engine for more. I'll decide whether to use a blocking diode by measuring my array's shunt resistance in the dark at the battery voltage and slightly above it.? If the current leakage loss seems substantial, then I'll evaluate whether it's worth the extra mass to add a tiny schottky or Ge diode and another PV cell to make up for the diode's voltage drop. I don't trust ebay seller's PV cell performance claims considering the bogus battery capacity claims that dominate on ebay. ??I'll measure 'em myself.? My initial estimates indicate that the 39x19mm cells will produce more current than I'll need, so one of my near-term challenges is to develop a cell-dicing technique that doesn't generate microcracks or shunt the pn junction at the edge. I bought a tiny scale for $3.5 and have been weighing various components I may use. Cheers Halden NR7V |
开云体育Thanks to all for the tips, hints, information, and guidance on my U3S solar cell project. I apreciate it very much. I’m trying to channel all the information into a usable plan to power my U3S with the same little Chinese solar cells that I also want to use on a future U3B flight. I guess it will come down to trial and error and a lot of experimenting with the different tips given on here. I’ll keep you updated on any succesful set ups. ? Best 73, ? Michael PA7MDJ ? |
Daniel Ekman SA2KNG