Solar Panel, SuperCapacitors and a Buck/Boost

good morning all I'm playing power stations today it's just a bit of fun really I've got some my super capacitor bank it's six 120 farad super capacitors in series on a board which has protection components on it and that's being charged via this connector here from a solar panel which is outside now this is one of these little soppy battery maintainer panels it's supposed to keep your 12-volt lead acid battery topped up it's notionally 2.4 watts at about 17 volts in fact let's bring it in and take a look at the label on the back yeah so this came from Maplin quite a long time ago I've had this quite a while but they're a bit useless so didn't use it much but yeah 2.4 watts at 17.5 fault well actually that's pretty good for the super capacitor bank because that's two point seven volts per capacitor times six I seem to remember that sixteen point eight volts so when that thing is getting near to fully charged this solar panel should start developing maximum power now that super capacitor module is a long way from being fully charged in fact it's going down in voltage because the solar panel is upside down in the room I need to put it back outside pointing at the sky no Sun today I'm afraid it's overcast so we're not getting a lot of power from the solar panel but we're getting some and with the solar panel back outside looking up at the sky yes this super capacitor bank is now charging again so that's up to three point eight volts like I say that should go up to sixteen point eight actually a bit more because I seem to remember those protection circuits kicking a bit late now also connected to that super capacitor bank I've got one of these it's an LTC 37 eighty I think that's what it's called buck boost converter and it's got its fault LED on because I think it's saying that the input is not sufficient not sufficient voltage for it to start generating an output I just looked on eBay and they reckon that the minimum voltage on the input there is five volts and we've only got three point nine so I'm just wondering whether that thing will burst into life when it gets five volts on its input and this output LED will come on currently on the output of the buck boost converter we've got zero volts now the first thing I wanted to know was is it safe to leave that panel 2.4 Watts permanently connected to this super capacitor bank with only those protection components to prevent the capacitors going over voltage because that solar panel can get up to about 20 volts open circuit and I reckon it is because these resistor pairs these what's a 100 on them they're 10 ohm resistors in parallel so that's 5 ohms and you've got V squared over that so two point seven squared possibly even two point eight squared is in excess of one watt so that total board can dissipate six watts at least more than that probably and the panel is only two and a half was so there's no way that panel is going to kill this super capacitor bank this Bank with its protection circuits can prevent itself from going over circuit over voltage of me right the super capacitor bank is now at four volts I happen to know that this meter at four volts goes to two decimal places so we've lost the decimal place so it appears to be counting up slower but it's not that's it beeping to say that it's going to switch itself off any moment and so yes I'm still waiting for that to get to the five volts that this how supply allegedly needs to turn its output on whether it actually will at five volts is another question now I think these buck boost converters are set to twelve volts when they're shipped from the factory that's one of my DVM has gone off actually they've both gone off so what the reason I'm using this is because the voltage on that super capacitor bank is currently four volts when it gets up to five this thing should be able to provide 12 and then as the voltage on that super capacitor bank varies between five volts and its maximum which is about 17 volts this buck boost converter will hold the output at a constant 12 volts so I can use it for something actually useful that's really the main difference between a super capacitor bank and something like a lead acid battery the super capacitor bank has a voltage directly proportional to its state of charge so the voltage is constantly dropping unlike a battery which tends to drop at the beginning and then sits at sort of let fairly level voltage for most of its discharge and then drops off rapidly again at the end this thing is going to drop linearly continuously therefore we need this boost or buck converter to maintain a constant voltage at the output even though the input voltage is falling continuously right something interesting has happened at four point four volts on the super capacitor bank and that doesn't appear to be climbing maybe it is slowly and the output LED this blue LED has come on it is kind of flickering the fault LED is also still on and the DVM measuring yes that is going up four point four one but the DVM on the right is measuring three point four volts and climbing and I'm not sure where the pots are set on this thing so I'll wait until the input voltage it's up to a more reasonable voltage let's save 5 volts and then we'll see what's happening on the output now I'm trying to remember what these pots do I think this near this one that's nearest to the output actually adjusts the output voltage I put a little light bulb on there now all ok that got some sunshine does that mean that the voltage is shooting up really quickly yeah not bad um yes so I think the meant the one in the middle is current limit and the one at this end adjusts the cutoff voltage where the things shots down and says fault so if I undo that one I should be able to get that light to come on with 5 volts on the input keep on doing it until the fault condition goes away yes there we are now cause when the light comes on that voltage plummets on the super capacitor bank and that light won't stay on long as that voltage falls down that light will go off but it's just occurred to me that that light is a constant wattage I think it's 1 watt and if I let the super capacitor bank get up to the max power point of the solar panel which is the high end of the voltage that solar panel should develop under full Sun um in excess of 2 watts so should be able to keep that light on permanently without it doing that and going off and this voltage falling down of course that's now going to start creeping back up so really what I want to do is get this super capacitor bank up to a higher voltage and then the solar panel should be able to sustain having that lamp on all the time the point is that solar panel will only produce 2.4 watts at its max power voltage which was 17 and a half volts so let me do that if its voltage is able to be seventeen and a half volts and it's not at the moment because the capacitor voltage is holding it down now that panel won't miraculously generate more current when it generates lesser voltage it doesn't work like a DC to DC converter the current maximum current is limited and so at lower and lower voltages it will develop less and less power so yes I need to get this super capacitor bank up to a higher voltage to let that panel generate its maximum power the problem I've got is that because the sun's gone back in now that panel is developing so little powers taking ages to get the super capacitor voltage to come up now I've turned that left hand pot fully clockwise screwed it right down in other words which should mean that this thing has its fault light on and doesn't enable the output at a much higher voltage so I'm hoping to let the super capacitor bank climb up to a much higher voltage and I mean hopefully in excess of 12 volts I'm not sure what the range of that battery protect pot is I think that's what the left-hand pot does it protects I suppose notionally lead acid batteries from going under voltage right well now the sun's come out now and this is going a bit quicker it's up to 10 volts now and what I'm doing is I'm just periodically adjusting this low-voltage lockout pot this one nearest to the fault light to make the bulb go off so that I can gradually take this nearer and nearer to the super capacitors maximum voltage which is nominally 16.8 but maybe 17 or even possibly 18 so we had a period of sustained Sun and the capacitor voltage got up to about 16 and a half volts but that's actually dropping now and I suspect that's because the panel which is now in shade is not actually holding its voltage up above 16 volts so the small amount of consumption of this power supply the switch mode buck boost converter is actually now Dre meaning the super capacitor and its voltage is falling course that'll change when the Sun comes out and it is due to come out again fairly soon so let's see if we can push this super capacitor voltage up high enough to start turning on these little blue protection LEDs all right this is up to sixteen point three volts and some of the protection blue LEDs on the super capacitor board are starting to come on they've all gone off again now but I imagine they'll be on back on again quite soon right sixteen point seven volts and those blue LEDs are starting to come on I've got three of them on now the voltage of course starts to drop away because those resistors on that board are now consuming the power so those LEDs are going to just be almost randomly coming on and off to protect the super capacitors that are at the higher voltages they're all at slightly different voltages and that's holding the super capacitor pack at about sixteen and a half volts or somewhere around there and now I've got a situation where the lamp is on and I've had to drop the brightness a bit oh that's my meter gone off that's inconvenient isn't it let's drop the brightness of that bulb a bit but there is now enough power coming from the solar panel which is in full Sun to have the voltage on the super capacitor rising even with that load switched on that's assuming of course that the super capacitor doesn't switch its own protection circuits on none of them are on at the moment so yes with maximum power coming from that solar panel or very close to it we can sustain that a little filament lamp and have a rising voltage on the super capacitor this is great fun isn't it a little super capacitor power system power bank right we've got one of the blue LEDs come on now so the super capacitor voltage is falling and a little lamp not much of a lamp admittedly but if I scaled this whole system up with a bigger solar panel and more of these super capacitor banks maybe I'll buy some more of those then I could have more store power and the ability to draw more power out from the buck boost converter and drive a bigger load than that 100 milli amp bulb right I've turned that bulb brighter now and it was remaining illuminated with the super capacitor voltage going up it's not going up anymore it's going down that's only because the Sun went in I come back out again so will it be able to hold the bulbs brightness and take the capacitor voltage up ah he kind of almost but not quite all the sun's gone in again it's partially cloudy stored my life really isn't it this hopeless cloud situation but yeah certainly with a higher super capacitor voltage the solar panel delivers more power and can sustain the load and keep the capacitor voltage up Suns come back out now and the capacitor voltage is going up well this is great fun and not a lead-acid battery in sight so that's great fun I've had a very enjoyable day today with what little sunshine there was well there's been a little bit playing around with this super capacitor bank the buck boost converter to ensure that we get a steady voltage output of should be around 12 volts for that lamp irrespective of the super capacitor voltage which has been today anything from about 5 volts up to 16 point 6 where it is now and this is the sort of thing I want the Mediterranean workshop for so that I've got nice consistent Sun and I can play around with this sort of experiment I really do enjoy mucking around with solar power anyway that's probably it for the moment so cheerio

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