[Power] Charging XO-1.0 From 12V DC Battery

[scott at solarnetone.org]

Hi Richard,

pardon the delay in responding... quite busy here.


> One user on this list has also measured his charging energy as
> 24.2 Wh. [1]  So I think the 26Wh number is a good across the board
> number to use.
>
> The maximum power input of the XO at the DC jack is 17 Watts and the
> lowest voltage the XO would draw that from would be 11V so each XO-1
> should never draw more than 1.55A.  That's your worse case.
>
> A typical scenario would be a brief spike of up to 17W and then a roll
> off of down to 10W in around 1 to 10 minutes. Then around 10W for about
> 1.5 hours and then starting to taper off to 1W.  Each battery/XO is
> slightly different so there's room for a few Ws wiggle on each
> measurement (except for the max of 17W)  I've tried to be on the high
> side of things.
>
> So you should probably prepare for a several minute spike of 1.5A/XO and
> then a constant draw of around 1A/XO for 1.5 hours. That should let you
> size your wires accordingly.

I promised you a basic parts list for the SN-1 power system, as well as a 
generic solution for 50 XOs.  I will give you general specifications for 
parts, as opposed to specific part numbers and vendors to allow 
flexibility in field deployment, as certain parts may be tough to source 
in some areas.

First, the SN-1:

Panels:
600-650W @ 12V.  I use 8 x 80W 12V panels.  The panels you choose will 
dictate the wiring necessary.  Some panels use screw down terminal blocks 
for connection.  In this case, I use a pair of #10-12AWG to connect each 
panel to the combiner box, detailed below.  Other panels use waterproof 
MC3 or MC4 connectors.  When using these panels, you really should acquire 
the proper matched cabling for the run to the combiner.  Consideration 
must also be made for panel mounting.  While expensive racks are 
available, I find that some 2x4 beams, L-brackets, screws, bolts, nuts, 
and sealant are all that is required to achieve a secure mount.

The combiner box is essentially an outdoor box that is used to parallel 
all the panels.  Each panel is individually breakered (10-15A, depending 
on panel size)on the positive lead.  Power exits this enclosure via, in 
the case of runs less than 10 feet or so, four #4AWG runs... two for 
positive and two for ground.  For a longer run between combiner and main 
breaker enclosures, I would use a single run of #1/0AWG for positive and 
one for ground.

This brings us to our main breaker enclosure.  Inside this enclosure, we 
have bus bars for panel +, battery +, and system ground, which is both 
earth and battery ground, earth ground being achieved by a discrete run to 
earth.  Additionally, there are 60A breakers for panel + on each side of 
the controller, and for battery +, as well as 15A breakers for each load 
circuit.  Our 60A charge controller sits between the panel + and battery + 
rails, regulating the voltage being applied to the batteries and loads. 
All internal connections are made with #4 AWG cable.

I use 8 400Ah @ c-20 rate 6V batteries, in 4 parallel strings of 2 
batteries in series, to achieve a 12V bank.  All battery interconnections 
and the runs from the batteries to the battery + busbar in the main 
breaker box are #4 AWG.

Some images:
breaker box and batteries at Katsina State University in Katsina, Nigeria:
http://www.gnuveau.net/images/sn14.jpg

leads from breaker box to combiner box:
http://www.gnuveau.net/images/pvpowerwire.jpg

breaker box, and internals:
http://www.gnuveau.net/images/mainbreaker.jpg
http://www.gnuveau.net/images/mainbreakerconnections.jpg

combiner box, partially wired:
http://www.gnuveau.net/images/combiner.jpg

charge controller:
http://www.gnuveau.net/images/chargecontroller.jpg

additionally, I find some physical security to be handy:
http://www.gnuveau.net/images/securitysystem.jpg

I will hopefully get to the adjustments to match the 50 XO load 
requirement next week.

Cheers,
Scott