Oh I see - transient response is the time from start up to 5v - not important to me.
And the filter capacitor goes across the motor. The 7805 maintains 4.8 to 5.2v - which is perfect for my 4.8v motor.
My plan is to get the 7805, put my panel on it, put the motor on the other end and solder a capacitor across the motor terminals. Now I need to know the capacitor rating I would need - any suggestions appreciated.
No transient response what happens when you connect and disconnect a large load - when the load is connected there's a voltage troff and then the load is disconnected there's a voltage spike. Adding a capacitor in parallel with improve the situation as it will provide power during thr troff and absorb the spike.
Yes 7805 (or LM317) will work and it is a cheap and simple solution - if you don't mind that is is very inefficient. Assuming your pump will draw about 0.2A from the solar panel, at 22V it is already 4.4W - 1 W for your pump and the rest is wasted as heat, warming the regulator (7805 or 317). For such a low current it is perhaps not critical but if you do mind you can try a switching regulator (buck controller) - it can have efficiency over 90%.
I would suggest you try feeding the pump directly from the solar panel, and monitor the voltage across the motor - solar panels aren't very efficient, and their specs are over exaggerated, particularly as you live in the UK.
I would use a switch mode buck regulator from Texas Instruments:
**broken link removed**
It works like a 3-terminal voltage regulator but is much more efficient. They are more expensive but it will keep your solar-powered system working over a wider lighting range because of the efficiency, or at least I would think so.
Ex. If you're panel is outputting 12V, you're looking at 80% efficiency @ 200mA. The efficiency drops a little as you increase the input voltage, but with 12Vin and 5Vout with a linear regulator, it doesn't get any better than 5/12*100 = 42% efficiency.
Of course, th PT78ST105 is $14 at Digikey, vs. about 80 cents for a 1% tolerance 5V linear regulator (I recommend TL780-05 from TI - very good voltage regulation. The last one of those I hooked up read 4.980V with my Fluke multimeter).
Nice solution if you don't mind the really high price ... you can buy 0.5A buck controller for $3 at DigiKey (e.g. LM25007MM from National Semiconductor). It does not contain the inductor inside and you'll need a few passives around but I believe it will be still much cheaper. Of course the price is a bit more complex circuit - more components around the chip.
I have a solar panel which provides 12-22v, 2.4W. I also have a 4.8v 0.9W pond pump, and I would like to put the two together. I need to get a frog spitting!
The question here is if the solar panel can source enough current for the pump. What I am not sure if 2.4W corresponds to 12V output (which is 0.2A) or 22V (which is only 0.1A). The pump needs almost 0.2A. So if it is 2.4W at 12V output a linear regulator could be used but in the second case there is not enough current (and power to waste in as heat the linear regulator) and the buck regulator is necessary.
The question here is if the solar panel can source enough current for the pump. What I am not sure if 2.4W corresponds to 12V output (which is 0.2A) or 22V (which is only 0.1A). The pump needs almost 0.2A. So if it is 2.4W at 12V output a linear regulator could be used but in the second case there is not enough current (and power to waste in as heat the linear regulator) and the buck regulator is necessary.
Solar panels are usually rated at 12V, so 2.4W should give 200mA, enough to make the frog spitting into the pond motor work.
I dont think the is too bothered about wasted energy, just the lowest cost.
Hi,
you can try the linear regulator like 7805 - it is cheap and simple and check how it will work. If the performance is not satisfying (check also different light conditions, measure the current flowing to the pump) you can decide to try the buck controller which should give you better results. Either the simple solution for $14 from TI or the cheaper controller from National (but more complicated circuit). The circuit for the TI buck controller was already posted here, the one with the National chip is in the datasheet: