j_mchattie

Hi everyone - first post, so please go easy on the abbreviations!

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.

Living in the UK, the panel which is provided with the pump is not powerful enough as it requires direct sunlight.

Can someone direct me to where I can buy/build a converter?

I need to get a frog spitting!

Thanks

James

ericgibbs

hi,
As you are in the UK,look here:

http://uk.farnell.com/jsp/search/bro...convertor&Ntx=

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j_mchattie

Ok thanks - so I can buy it as a module.

That would make it easy.

But my voltage can be between 12 and 22v depending on how strong the sun is.

What can I do about that?

Or should I just buy a 5v 2-3w solar panel?! (Which I couldn't find anywhere)

Thanks

ericgibbs

hi,
You could buy a low cost LM317 voltage regulator ic.
Or even cheaper a 7805 Vreg ic.
+10 to +25Vin, 5V out.[1 Amp max]

Maplins sell them for less than £1.

Where in the UK.?

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PIC tutorials:
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j_mchattie

Oh wow - that's bloomin' brilliant.

So I can just wire that in - no other components - and it will provide 5v even if my panel is providing 22v? For 59p!

I will get one of those - the datasheet also says that I wont even need a heatsink!

Thanks for your help - it has saved me a lot of money.

I live in Coventry, but this is for my Mum in Dartford, Kent.

Thanks again

ericgibbs

hi,
Its a good idea to add a couple of capacitors to the 7805 reg.
Look at the datasheet for the values, if you have a problem post your circuit.

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PIC tutorials:
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j_mchattie

Can you please explain what is meant by transient response and filter capacitor?

I guess the filter capacitor smooths the supply to the pond pump? Is it just wired inline to the pump?

Thanks

j_mchattie

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.

Thanks

Hero999

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.

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j_mchattie

Thanks for your help

ericgibbs

hi,
Perhaps this circuit will help.

Attached Images

Image1.jpg (12.5 KB, 16 views)

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Eric
"Good enough is Perfect"

PIC tutorials:
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Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

petrv

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%.

Petr

Nigel Goodwin

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.

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speakerguy79

I would use a switch mode buck regulator from Texas Instruments:

http://focus.ti.com/docs/prod/folder...pt78st105.html

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).

petrv

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.