Solar panel help for newbie...

[AndrewG]

I'm a newbie to creating circuits, though I can happily put together pre-designed ones!

I have a need to run two PC fans (12V 0.11A) from a 12V solar panel. There is nothing clever needed - simply put - the sun shines, the fans are on!!

Now - the rating for the panel is as follows

Peak Voltage 17V
Peak Current 0.59A
Peak Power 10W

I need to create a board which will expose two pins for each fan (and maybe a 3rd and 4th for future expansion). My fans already have 2-way 2.54mm kk PCB plugs attached...

I was thinking of somthing like this - but I might be wrong! (This is for Stripboard with the copper strips running vertically)

(From Solar Panel)

+.............-
+--R---L--- + -
+ xxxxxxxx -
+--R---L--- + -
+ xxxxxxxx -
+--R---L--- + -
+ xxxxxxxx -
+--R---L--- + -


R being a resistor, L being an LED, and the + - being the PCB interconnect pins that the fans will plug into. (the xxx's are when I cut the copper strips to keep each row separate)

I hope thats clear enough, though I fear its probably not! I'd like to know if this is enough to go on, and what the value and safe power rating of R would be... I'm not sure I've got the LEDs either, so I can actually do without them, I assume this won't affect the value of R too much?

Hope someone can help, cheers...

 

[(*steve*)]

You may be best off creating a simple "amplified zener" to act as a shunt regulator across your solar panel and then take the 12V directly from this.

See here. Use the circuit for the battery charger and omit the series diode.

You would need to use something like a 2N3055 attached to a heatsink to dissipate the additional power your solar panel is producing. A 1W zener should be fine. something around 11V to 11.5V 1W should be fine. No real need for the additional diodes in the base either.

 

[AndrewG]

Thanks for that - I think I get the idea - though I don't have any Zeners for 12V - 6V is the max in my parts box...

Would a 12V regulator be enough? Something like an L78S12C - 12V up to 2A... With a decent heatsink? Not as exact, but as its for fans, which will cope with less coming from the panel, would it be enough?

 

[(*steve*)]

Look at the solar charger circuit. No resistors necessary.

Try 2 x 6V zeners in series. It will give you about 12.6V which may be fine for the fans.

 

[AndrewG]

Look at the solar charger circuit. No resistors necessary.

Try 2 x 6V zeners in series. It will give you about 12.6V which may be fine for the fans.

Haha - I was afraid you were going to say that... I've only got the one 6V left, and I'm not sure what the power rating of it is anyway!

Sorry for the dumbass-ness, as I said, total newbie!

 

[(*steve*)]

Hahahaha, Isn't it always the way. I've got some, but I would't expect you're nearby

See what else you've got. Any other zener diodes? You'll almost certainly be able to get away with a lower wattage rating -- especially if you've not got the panel in the blazing sun.

 

[AndrewG]

What about this type of thing? http://www.reuk.co.uk/buy-12-VOLT-REGULATOR.htm

I'm just wondering if I have to make a small parts order for the bits I need, plus postage, its probably not going to cost much more to get one pre-made!!

 

[(*steve*)]

That's OK, but a shunt regulator is better as the solar panel voltage gets down to 12V.

Mind you, that one will also probably run cooler though.

 

[AndrewG]

Cheers for the help - I went for the prebuilt regulator, and they are putting 4x output terminals so that I can connect up the fan.

Now - for the fans themselves - will I need to put a resistor on each 'channel' for each of the 4 fans - to limit the current. If so - given that my fans are 110mA - do I just calculate using V=12, I=0.11, so R=~100R, and should I get 3W resistors, given that my panel us putting out 10W peak (I'm measuring only 300mA in full sun, so I'm not sure I'll ever get 10W, never mind run all 4 fans from it!) ?

Also, what should I do with my 'unused' channels, if I only have 2 fans working, and the other 2 channels disconnected, will the panel put out too much juice for the 2x3W resistors to cope with?

 

[AndrewG]

Hmm - just done a quick calc... If I work on a 'parallel' configuration - with 100R resistors and a fan on each 'channel', I work out that each channel will have 12/100=120mA - and the power through each channel is 12x0.12 = 1.44W - so 3W resistors would be OK wouldn't they?

 

[Resqueline]

Each fan draws only 110mA as needed and thus have an equivalent resistance of about 100 ohms. That does not mean you should connect additional 100 ohm resistors.
But if you want to reduce the fan noise level while still conserving available current then just connect 2 and 2 fans in series.
There's no point in loading down the panel or the regulator to the max. The regulator puts out only 12V regardless if there are loads or not. Nothing burns or goes wrong.

 

[AndrewG]

Each fan draws only 110mA as needed and thus have an equivalent resistance of about 100 ohms. That does not mean you should connect additional 100 ohm resistors.
But if you want to reduce the fan noise level while still conserving available current then just connect 2 and 2 fans in series.
There's no point in loading down the panel or the regulator to the max. The regulator puts out only 12V regardless if there are loads or not. Nothing burns or goes wrong.

Awesone - that simplifies it quite a bit - so the fans can go straight on to the panel, I don't need to restrict the current - like I would with an LED.

If I connect 2 fans in series though - aren't I then splitting the voltage - giving only 6V across each fan? This is basic stuff I know - but once I know the answers, the less likely I am to ask the questions again!

 

[Resqueline]

The fans are made for direct connection to approx. 12V so connecting them to the 12V from the regulator will ensure their proper operation.
White & blue LED's have a voltage drop of approx. 3-3.5V but needs a well defined current, and so needs a resistor or some electronics to stabilize their current draw.
Yes, series operation leaves 6V for each fan, just enough to make them start & run.