Raspberry Pi web based solar data logger

[w0067814]

Hi,

On my virtual travels I stumbled upon this interesting project. It is also worth going back to his website home page as he has lots of other interesting raspberry pi projects.

http://www.briandorey.com/post/Raspberry-Pi-Solar-Data-Logger.aspx

Tim

[clivejo]

I like this!  Trying to do something similar for my own system.  Only problem is my main batteries are 48VDC, but I have a 12VDC battery bank too.  Most DC-DC converters I have seen seem to waste a lot of energy converting 48V ->12V, one know a way?

[derekmt]

switch mode converters have high efficiency

[jonesy]

I like this!  Trying to do something similar for my own system.  Only problem is my main batteries are 48VDC, but I have a 12VDC battery bank too.  Most DC-DC converters I have seen seem to waste a lot of energy converting 48V ->12V, one know a way?

If you can split your array and batteries go to 96V.  Most smps will work off that so you only need an inverter for older transformer based stuff.  Then you don't need a 12v battery...
I found telecom gear a good source of 48v to 5 or 12v.  Pricey to buy new 48v smps though.

[clivejo]

I'm currently using a cigarette lighter plug > USB which is powering my Pi.  But as my main system is 48VDC I need some way of charging the 12VDC bank, in an efficient way!  The Pi uses about 700mA at 5V (3.5W) but by the time you factor in the loses in the DC-DC converters it seems to be double or triple the 3-4W the Pi needs to run 

Ideally Id like to power the Pi from the One wire network I intend to build.  Apparently the Pi can be power from the GPIO header, but I'm unsure if that source is regulated like the Micro USB type B is.  Will probably need some kind of electronics to ensure a smooth 5VDC on the GPIO pin.

I guess I could reconfigure my 12v bank into a 6v bank and use it purely for powering the Pi and One Wire network.  Keep it charged via a mains to 6VDC charger.

[w0067814]

I don't know why you think that DC-DC losses are so high. Even when dropping from such a high voltage as 56v (48v bank maximum charge voltage) at a low current you should be able to achieve > 75% efficiency.

As you are playing with something as technical as the Raspberry Pi, I imagine that you can do basic soldering and knock up a circuit on strip board (vero board) or similar?

If so, then why not roll your own SMPS?

National Semiconductor were recently bought by Texas Instruments, but National made a range of SMPS called Simple Switcher which were designed to be easy to design with and make with minimum of tweaking or external components.

http://www.ti.com/lit/ds/symlink/lm2591hv.pdf

If you go to the front page of the TI website, you shall see something called WEBENCH Designer. This would allow you to input the design parameters such as input voltage ragnge, output voltage and current, and then the software would design the circuit for you and suggest suitable components. RS (rswww.com) or Farnell (uk.farnell.com) supply components and can be bought with a credit card.

The above switcher would be suitable and would achieve over 75% efficiently.

Thus your 3.5w Pi load should equate to about 4.66w at the battery. (3.5 / 0.75)

-Tim

PS: The 5V0 rail on the Pi is not regulated at all no matter how you supply the voltage (USB socket or otherwise). Be sure to apply the correct voltage.

[clivejo]

As you are playing with something as technical as the Raspberry Pi, I imagine that you can do basic soldering and knock up a circuit on strip board (vero board) or similar?

If so, then why not roll your own SMPS?

Its a hobby and my hobbies always take back seat  It takes time and planning to order all the correct equipment and in the past I've ordered something and its been wrong or not as Id expected.  Unfortunately that's the disadvantages of ordering stuff online.  I dont know why the loses are so high, it could be the cigarette lighter DC-DC converter.  It could also be the mathematics to blame as I'm calculating it on the capacity of a new fully charged 12v battery.  In the grand scheme of things 4-5W is not much but I'm the kind of person likes to get that figure down unless its absolutely necessary!  Why leave a TV on consuming 2-3W when you can switch it off and not consume power!?!

To be honest I'm very impressed at what the Pi can do with so little power.  I had a small PC doing the same job and it was consuming about 60-100w.  I wonder if anyone is working on a parallel computing OS for the Pi.

<<EDIT>>

Looks like someone has already done it!! 


Source : http://www.southampton.ac.uk/~sjc/raspberrypi/pi_supercomputer_southampton.htm