CorB 64 Posted March 31, 2015 Share Posted March 31, 2015 Hi, I like the idea of adding a "excess" burner to the code. I was struggling with a small solarpanel with 3xAAA that started to push the charged levels up to 3.9V. Still on the safe edge, my node normally makes the radio (CC110L) go to sleep after sending a small datapack to my RF network. Now above a threshold I dont let the radio sleep anymore and that easily controls the max voltage level. I was nearly going to add an LDO or a Zener to restrict the voltage. Thanks !! Cor Quote Link to post Share on other sites
spirilis 1,265 Posted March 31, 2015 Share Posted March 31, 2015 lol! That is a funny problem, didn't realize at first what @@cubeberg meant by the charge rate "going up", now I see what you mean. Yeah I guess burning power is one solution! I would have used an LDO probably Quote Link to post Share on other sites
cubeberg 540 Posted March 31, 2015 Author Share Posted March 31, 2015 @@spirilis - At first I didn't even consider it. I figured the more likely case was that it wouldn't transmit all the time - apparently I was wrong Certain times of the year - the voltage may regularly be very low - so I'm concerned that an LDO would work great during the summer, but not work well in the winter, or rainy/cloudy days. Looks like TI has some very LDOs with a low dropout (40mV) that might work though. The other issue would be overcharging the NiMh batteries as well. Another solution might be to put in bigger batteries that won't charge as quickly. So far - the rate at which the max charge is going up is slowing - I'm kind of hoping it tops out at some point. For now I've added a warning to node-red in case it hits above a set threshold. FYI - I confirmed yesterday - you can find solar lights at the dollar store right now (at least Dollar General). It's definitely a slightly cheaper implementation - so I need to check and make sure it is operating the same way. They are using AAA batteries instead of AA, although they're both labeled as 200mA. Quote Link to post Share on other sites
CorB 64 Posted March 31, 2015 Share Posted March 31, 2015 In the solar-powered Nodes I use the dark days from october to february/,march do have quite an effect. During the wintermonths the average voltage in 2AA batteries fed from my smallestsolarcell(35mmx35mm) drops from about 2.7V to 2.5V. These node however keeps sending data at least once a minute from its DS18B20 sensors. I am using GP 2100mH cells on this one. The sensor where I am using the burnoff is powered by a special solar-cell from a lamp I had laying around, this cell has a pack with 3AA's attached and seems to easily top them up to nearly 4V. See http://www.voltaicsystems.com/blog/ikea-solar-phone-charger-hack/ Quote Link to post Share on other sites
dubnet 238 Posted March 31, 2015 Share Posted March 31, 2015 Due to this thread I went out and picked up a handful of these at the dollar store. These came with a AAA ni-cad battery. @cubeberg I took a look at the specs for the battery and it looks like they have a fully charged/no load terminal voltage of 1.25 to 1.35 volts so 2 cells should max out at about 2.7V assuming the solar cell isn't able to push them slightly higher. spirilis and cubeberg 2 Quote Link to post Share on other sites
Lgbeno 189 Posted April 5, 2015 Share Posted April 5, 2015 @@cubeberg, would you be able to update the ID for the embedded code about to s4C? Sorry for the inconvenience! Quote Link to post Share on other sites
cubeberg 540 Posted April 5, 2015 Author Share Posted April 5, 2015 @@Lgbeno - all done! @@dubnet - they're well below that then. I'm reading 2.59v right now (it hit my warning value of 220 for a bit today). Quote Link to post Share on other sites
cubeberg 540 Posted April 13, 2015 Author Share Posted April 13, 2015 Had an alert trigger today - voltage went up to 3v. Guess I better figure something out - it's only spring Apparently the core temperature hit 150 F as well. I probably need to look at shading the MCU at a minimum - but I'd guess it's going to get pretty hot in a clear enclosed container. Quote Link to post Share on other sites
dubnet 238 Posted April 13, 2015 Share Posted April 13, 2015 How about a thermostatically controlled exhaust fan? It would kill two, possibly three, birds with one rock. It would keep the temp under control, load the batteries enough to keep the voltage within limits (since the max heating and max charging should be occurring at the same time) and move the air around enough to prevent condensation. Quote Link to post Share on other sites
cubeberg 540 Posted April 14, 2015 Author Share Posted April 14, 2015 @@dubnet That's an interesting thought - I'll have to take a look at that. I'll see how much power the LEDs burn off - that'll help me determine if the fan would use too much power. I believe I figured out what happened yesterday. The device stopped working the day prior at 5 when my daughter moved the sensor. Looks like she knocked a battery out. When the sun was strong enough - the charger started kicking out enough voltage to get the system running again - only without the battery being charged - it was a lot more than expected. Once I put the battery back in - it dropped to a safe voltage (210 vs 255). I'm also kind of wondering if the extra voltage was generated by the lack of battery somehow as well? Quote Link to post Share on other sites
spirilis 1,265 Posted April 14, 2015 Share Posted April 14, 2015 @@dubnet That's an interesting thought - I'll have to take a look at that. I'll see how much power the LEDs burn off - that'll help me determine if the fan would use too much power. I believe I figured out what happened yesterday. The device stopped working the day prior at 5 when my daughter moved the sensor. Looks like she knocked a battery out. When the sun was strong enough - the charger started kicking out enough voltage to get the system running again - only without the battery being charged - it was a lot more than expected. Once I put the battery back in - it dropped to a safe voltage (210 vs 255). I'm also kind of wondering if the extra voltage was generated by the lack of battery somehow as well? Probably - my understanding is that solar cells "build up" a voltage charge, sort of like static, when they don't have any load on them (photons keep smacking the silicon knocking off electrons but those electrons don't have anywhere to go), so the voltage seen at the ADC would be higher than usual... whereas having the battery in the circuit will put a constant load on the solar cell. cubeberg 1 Quote Link to post Share on other sites
enl 227 Posted April 14, 2015 Share Posted April 14, 2015 Solar cells have a pretty high output impedance, compared to a battery. The open circuit voltage can be a good bit higher than the design (loaded) voltage. In your application, the battery is acting to stabilize and regulate. With the battery, you get an equilibrium that is set by the battery charging rate/charge state/terminal potential/temperature relationship. This provides regulation in a manner similar to how the battery in a car or motorcycle stabilize and regulates (exactly how depends on whether the system is a generator or alternator, the regulator type-mechanical or electronic- and other things as well). Brighter sun, where the open terminal voltage of the PV cell would be higher, the battery draws a greater charging current, keeping the voltage down, with the current determined by the difference between the open circuit voltage, the battery voltage, and the effective internal resistance of the battery and the PV cell at the operating conditions. When the battery is near full charge, the current drops, and the terminal potential goes up, leading to your need to load the PV cell to keep it down. More to it, but this is about the limit of my knowledge these days. When I was fresh out of school and in the semiconductor lab (I hate the suits) this was one of the things being played with there, but that was several generations ago. I remember something about source resistance being a function of carrier mobility, incident light flux, current density, and...... This is why both battery charging systems and solar conversion systems are a specialty that should be left to the specialists for critical tasks. spirilis and dubnet 2 Quote Link to post Share on other sites
enl 227 Posted April 15, 2015 Share Posted April 15, 2015 Link to Nat'n'l Inst. pae with good models for PV cells and nice graphs of characteristics: http://www.ni.com/white-paper/7230/en/ Not a ton of theory, but real good for a user. Yup, the need to check myself caught up with me. Nice to see that I dodn't make any major mstakes.... I mean didn't make any major mistakes. Quote Link to post Share on other sites
cubeberg 540 Posted April 20, 2015 Author Share Posted April 20, 2015 Thanks a ton @@enl - I did a bit of reading but I'll have to take more time to go through. Must have happened again this weekend - got a voltage alert today and realized it had been offline since saturday. Going to need to find a more secure battery solution Quote Link to post Share on other sites
Lgbeno 189 Posted April 20, 2015 Share Posted April 20, 2015 @@cubeberg what is the battery configuration of your lights? I thought that it was maybe 1xAAA, that is what most of them that I see are. There is this very under appreciated part from TI called TPS61020. It is normally a boost converter (for stepping up 1.5V to 3.3V) but then if the input voltage exceeds 3.3V, it also has a step down mode where it acts like an LDO, pretty useful in these situations. Quote Link to post Share on other sites
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