[Power] Charge controller ?

[Sameer Verma]

On Sat, Mar 6, 2010 at 12:01 AM, Richard A. Smith <richard at laptop.org> wrote:
> On 03/05/2010 08:37 PM, Mikus Grinbergs wrote:
>
>> Rightly or wrongly - my present thinking is that it takes a "charge
>> controller", placed between the solar panel(s) and the battery, to keep
>> a solar-powered charging system happy.
>
> If you have a plan battery (ie one with no charging smarts) then yes you
> have to have a charge controller.  The controller is whats responsible
> for implementing the algorithm that charges the battery.
>
> If you are connecting directly to an XO then you do not need a charge
> controller.  You do however need to keep the voltage < 18V.  Which most
> likely means you need something between you and the panel but there are
> some panels that have a Voc < 18V.
>

I have a Brunton 26 W foldable panel
(http://www.brunton.com/product.php?id=420), which will typically
output 20 V to 22 V unloaded. This was creating a problem in that the
XO EC wouldn't kick in. In fact, I ended up spending a week with the
Brunton guys troubleshooting. Simply standing in front of the panel
(creating a shadow) or folding a couple of the panels would drop the V
to below 18 and load the panel, after which I can plug in two XOs with
a splitter and charge easily.

Brunton does have a solar charge controller
(http://www.brunton.com/product.php?id=361), but I haven't tried it
yet..maybe next week...evidently the Sun has something to do with all
this and I'll need a bright sunny day in San Francisco :-)

cheers,
Sameer

>> Assuming the intent is to have a 12 V battery supplying power to two XOs
>> at a time, any recommendations on "charge controller" __specifications__
>> for that kind of a setup ?
>
> The answers to such questions always depend on what you want to do with
> the system. Supplying power to 2 XO's can mean you want to fully
> recharge the XO's from empty or it can mean that you just want to run
> the XOs without using much of the XO's battery.  Next question is how
> long do you want to be able to go without recharging from the sun?
>
> Once you establish the load requirements and replenish time then you can
> select a PV panel and battery that will meet those requirements.  Then
> you get charge controller that matches.
>
> 90% of the cheaper controllers on the market are for lead acid batteries
> so thats going to skew your battery selection a bit.  There are there
> are some that have other chemistries but they tend to be higher end.
>
> --
> Richard A. Smith  <richard at laptop.org>
> One Laptop per Child
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