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#1 Crispin

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Posted 03 July 2011 - 08:57 PM

Hi Folks, I am building a small monitoring project for a solar array. For it I need to power the netduino and a couple of devices such as ACS714, a xbee etc. Nothing huge. My issue comes in that I would like this all housed in the PV junction box which has the positive and negative from the panels in it (which I am measuring) - the kicker, these are anywhere from 200-500V (max) DC. Looking at a simple voltage divider does not make sense due to the swing on the input. Any tips? I also think that the current draw would be too high for it to run off batteries. Cheers, Crispin
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#2 SimonM

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Posted 04 July 2011 - 12:21 PM

Hi Crispin,
I'm confused by

current draw would be too high for it to run off batteries

Do you mean non rechargeable?

Myself I'd be tempted to look at a small cheap usb charger and modify it.
As you point out resistor dividers have issues not least being VERY wasteful when it comes to power. eg a 25w 10k resistor would be required to give 5v at 50mA. (a lot of power lost!)
I'd rip apart a switch mode 5v psu, and look at the chip set. They work by rectifying the mains, then using a high frequency oscillator to get the power through a step down transformer, to get the power conversion.
I'm sure I telling you some thing you already know: DC KILLS! That's my HSE and get out clause!
Yours Simon M.

#3 Mario Vernari

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Posted 04 July 2011 - 12:33 PM

I'd rip apart a switch mode 5v psu, and look at the chip set. They work by rectifying the mains, then using a high frequency oscillator to get the power through a step down transformer, to get the power conversion.

Ya, but the input source is 200..500VDC...Crispin should have to install a step-down DC-DC converter able to accept up to 600V in input. I'd prefer to swim in a pool fill of sharks!
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Biggest fault of Netduino? It runs by electricity.

#4 Crispin

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Posted 05 July 2011 - 12:53 PM

Even if I ran it off rechargeables I would have to keep replacing them - anything more frequent than 6 months would be a PIA. After a lot of digging I've decided to change things and rather run a CAT5 to it and run power through there as well as return data. More of a PIA than I would have liked and not as cool but hey... I did find some (single package) DC-DC convertors which would accept upto 600VDC (think 100V was min) and give you back 12 or 5 at 10A or 25A depending. The size and sheer overkill of them made me leave them alone. 't-was a cool idea while it lasted...
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#5 Troll feeder

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Posted 26 July 2011 - 10:01 PM

Why can't you tap off a small group of panels? Use the right taps, and tap off any where from 4 to 12 volts then use a boost/buck regulator and some lifepo or nicad batteries. No fancy charging circuits.




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