[Power] Charge controller ?

[Richard A. Smith]

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.

> 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