solar power & Toolbox

Sat Apr 8 12:06:12 UTC 2006

Here's another variant on solar power setup that worked well for us in PNG:

Two flexible solar panels, 32W each, connected in parallel via a regulator
to a large 12v truck battery. Power to charging devices and laptops via
cigarette lighter adaptors (12V).

The panels: UniSolar brand - we chose 'rollable' rather than 'foldable' ones
because they were much cheaper, yet still, just about, portable. We rolled
them up in our largest suitcase so that the diameter was as large as poss.
(c. 25 - 30 cm) and with plenty of padding inside to avoid creasing.
Apparently the panels are quite vulnerable in this way - unlike the foldable
ones. Anyway we had no problem with them in the field so it seems they
survived our treatment.

The regulator: Steca 6A model - this protects the battery from both over
charge and over discharge if you wire it up the way they suggest i.e. with
the load (the cigarette lighter adaptors) connected to the regulator NOT
directly to the battery. It also provides quite useful diagnostics in the
form of different coloured  LED lights (though I agree that a cheap
multimeter is also really useful, almost essential in fact). Note that this
unit doesn't just warn you if you are taking too much power - it actually
cuts the supply to protect the battery (at least I think it does; we never
actually encountered this situation in practice). This is great for your
battery, and fine if you are just using it to charge other batteries, but it
could be pretty annoying if it caused your computer to crash. For this
reason we generally only used the setup for charging, rather than for
running critical gear directly.

The battery: 120 amp hour, locally purchased (naturally, considering the
weight). I just got the biggest I could find to give us a good buffer. Of
course a proper deep-cycle battery would have been ideal but they tend to be
extremely expensive and a normal, but large battery should suffice. Of
course if you are trying to set up a something permanent, then the
deep-cycle cells would be worth the investment

The cigarette lighter adaptors: available in retail electrical-supply shops
- I bought a cheap two-to-one converter then cut the 'one' bit off so that I
had two sockets with short wire leads attached - this was easier than trying
to wire them myself; meant I didn't need a soldering iron. There are then
two 'things to be known': 1) which wire goes to which part of the socket
(the drum or the centre point) - easily discovered with the multimeter using
resistance or continuity settings, 2) which part is supposed to be
'positive' - an auto electrician told me it is the centre, and he seems to
have been right.

Our system was not designed to be especially portable once in the field, but
it was quick enough to set up - most of the wiring was done in advance, but
in any case only required a knife and a small screwdriver. The panels are
reasonably light and come with eyelets so they were 'simply' tied to the
roof of our hosts' house (with cheap local synthetic cord). I had cut off
the last 30cm or so of the power leads from these panels (more on these
'tails' later) and then brought the truncated leads into the house through
the ridge cap of the iron roof. They weren't nearly long enough to reach the
battery/regulator set up so I extended them with extra cables via a standard
hardware-store connecter block (putting the panels into parallel in the
process). I thought it worthwhile to use a reasonably heavy gauge of cable
so that voltage drop over the extra length didn't become a problem. These
cables had to be trimmed down a bit to fit into the tiny sockets in the
regulator. The two aforementioned tails consist of two wires each of course.
Each has a useful ring attachment and two of them have inline fuses. I
decided to use them to connect from the regulator to the battery terminals
and in my ignorance thought it a good idea to use the fused wires. Well of
course the fuses kept blowing. In the end I figured out that because they
also handled the loads from the battery (as well as supply to it) these
wires were going to draw far more current than the fuses were designed for
(i.e. to protect the panel in the absence of any other protection, such as
the regulator). So I ditched them altogether and used the non-fused wires. I
was a little uneasy about this but there were no problems with hot wires; I
think the regulator would have packed up first as a protection - albeit an
extreme one - against fire.

No, it wasn't the most sophisticated of installations. Although I had tried
to size equipment for the anticipated load, I felt unsure off my
conclusions. Moreover I knew that once in the field we would have almost no
access to spare parts or expertise. It's possible that I would have only
needed one panel and a much smaller battery, but I didn't want to  find that
out with no way to remedy the situation. With this possibility that our
setup was vastly over specified made clear, I can yet report that it behaved
blamelessly (once we got over the fuse drama) with supplying power over a
three month period to the following list of devices:

2 laptops, one of which did a fair amount of work digitizing video in the
field

2 mini DV video cameras, both using heaviest-duty battery packs for maximum
shooting time

1 digital still camera

1 GPS 

1 mp3 recorder

The laptops behaved as their own chargers of course. We did have to purchase
a special power adaptor (Targus brand, 120W) that had the lighter adaptor
plug. We had several spare batteries and tended to recharge overnight. In
theory we could also have used this adaptor to power a laptop while flying
to and from the field, but the cost of the upgrade to business class was
deemed to outweigh the hypothetical productivity gain.

For all other devices we used 'Inca' brand chargers. The beauty of these is
that not only are they configured for both AC and 12v DC use (coming with
standard lighter adaptor plugs), but they can take different 'plates' so
that the same charger can charge different types of manufacturer-specific
batteries. They are neither expensive nor bulky so it's still a good idea to
take several chargers (one broke during use). There is also a version for
AA/AAA batteries which we used for the GPS for example. These are available
at camera shops.

A couple of tips about batteries: 

1) We were advised that both the generic and brand name rechargeable
batteries (i.e. the battery packs for specific cameras etc) are made in the
same factories (there are only a few in the world). One is discouraged from
using the generic type, but of course they are quite a bit cheaper. We used
them exclusively and had no problems

2)  Not all devices that run on say AA or AAA batteries are happy to do so
on the rechargeable varieties. In particular we had problems with Sony radio
microphones which wouldn't run well on our Nickel Metal Hydride (Ni-MH)
rechargeables. We had to purchase quite large stocks of top quality 'photo'
grade disposables to get any useful work out of them (the local ones were as
useless as the rechargeables). This came as a bit of a shock - test your
equipment for this behaviour before taking it to the field.

For what it's worth, major costs in 2004 were: UniSolar 32W flexible panels
A$475 each, Steca 6A solar regulator A$79. These prices are before GS tax.
We got them from www.solaronline.com.au <http://www.solaronline.com.au/>  -
presumably that's not of much interest to Gary in Alaska though.

Andrew Margetts

Saliba - Logea  DOBES team

-----Original Message-----
From: Tom Honeyman [mailto:tom at fatuous.org] 
Sent: Thursday, 6 April 2006 10:20 AM
To: Resource-Network-Linguistic-Diversity at unimelb.edu.au
Subject: Re: solar power & Toolbox

AS for the Solar panels, 

I have been using solar panels in the field successfully for several months
now.  I bought foldable solar panels, Global Solar P3.  I have 55W, which
was US$900, but there are cheaper (less powerful) models that ought to work
out just fine.  They weight about 4lbs.  The only catch is that these
require an external battery.  I bought a motorcycle battery in country,
which is smaller than a car battery and thus more portable.   The solar
panels charge the battery with a set of pos/neg clips (which come with the
optional accessory kit), and I had the female end of a car cigarette lighter
rigged to have pos/neg clips as well (this was not something I found
pre-made, but it is easy enough for someone who knows about electricity to
rig up).  Then, all my equipment has cigarette lighter adaptors (cell phone,
battery charger, computer, etc.). I can plug in anything I want that has a
cigarette lighter adaptor (12V). These are widely available adaptors for
many devices.   I agree that

 taking a multimeter into the field for trouble-shooting is a good idea.
They are cheap (about US$10), lightweight, and widely available.  

Please let me know if my answers need clarification. 

Yes, that's basically what I would have said!

My situation was a little different, weight, cost and humidity were big
issues so I had a small Sealed Lead Acid (7 Amp hour / ~2kg) battery and 10W
panel. This was just enough to charge the batteries for the Nagra ARES BB+,
my flashlights (If you need them, make sure they are designed to work with
rechargeables), digital camera etc. I took two 5 hour batteries for the
Video Camera, and never needed to recharge them (we were mostly after audio
this time). I didn't have a laptop. In other words I had a "bare-minimum"
digital system. Unfortunately, the solar panel broke in the first month, so
I ended up getting power from a variety of fairly bizarre sources in the
remaining 4 months... that's when the multimeter came in handy.

So I guess my first recommendation would be to have a backup system if
something goes wrong.

Depending on your constraints, I'd suggest doing a rough estimate of your
power consumption, and purchasing a kit of the right size like the P3 above.

If weight is not an issue, I suggest purchasing a largish Lead Acid battery
in country.

Consider a charge regulator. This will stop you overcharging the battery and
a good one will also indicate when the battery is low so you don't damage it
from drawing too much power. Although, I suppose if you did damage your
battery, you could always pick up another one. Here's a product that is a
protective housing for the battery and battery status indicator:

http://www.whitworths.com.au/main_itemdetail.asp?cat=123
<http://www.whitworths.com.au/main_itemdetail.asp?cat=123&item=4190&intAbsol
utePage=1> &item=4190&intAbsolutePage=1

(Apologies for not finding a better link) The better model has a cigarette
lighter plug. Having a handle on your power source is good because you can
move it around if you use it as a primary power source instead of as a
charger. Using it as a direct power source is more efficient as you have
some power loss in the transfer of power from one battery to another.

The battery acts like a buffer. Because you'll only be charging during the
day, and you usually have your equipment charging while you sleep, you need
a battery big enough for (at least) a couple of nights of recharging (in
case it rains etc).

That's all I can think of for now, I'll post again when I've finished the
report.

Tom Honeyman

PARADISEC Project Research Assistant

Pacific and Regional Archive for Digital Sources in Endangered Cultures

Sydney Unit, room 238, Transient Building F12

University of Sydney NSW 2006

tel +61 2 9036 9557

fax +61 2 9351 7572

tom.honeyman at paradisec.org.au

http://www.paradisec.org.au

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