[Soekris] using solar power for a 4801 (Andrew Dunlap)

[Dr Bruce Griffiths]

soekris-tech-request at lists.soekris.com wrote:


> From: "Andrew Dunlap" <aedunlap at gmail.com>
> Subject: [Soekris] using solar power for a 4801
> 
> Hello everyone,
> 
> I am considering using a 4801 in an area that is a 2-3 hour hike away from
> road access.  There is no access to regular (grid) power.  Solar power
> appears to be the most likely option, fuel generators would be a very
> distant second option.  Poul-Henning Kamp's write up about powering the 4xxx
> line ( http://phk.freebsd.dk/soekris/power.html) has been very helpful.
> Thanks Poul-Henning!  Also, previous mailing list submissions have helped me
> get a better idea of what I should be considering (
> http://lists.soekris.com/pipermail/soekris-tech/2004-April/005550.html).
> 
> If you are using solar power on your Soekris hardware could you share the
> size of your solar panel(s), battery backup, equipment enclosure, charging
> mechanism, and how you adjust charging for temperature swings?  Of secondary
> interest is power sizing adjustments made to account for peripherals
> (wireless mini-pci, pci, etc...).
> 
> My apologies if this is OT.
> 
> Best Regards,
> 
> Andrew Dunlap
> aedunlapTAKECAPSOUT at gmail.com

If you want long term reliability, its best to keep the batteries in a 
separate well ventilated enclosure. This avoids corrosive battery fumes 
etching your circuit board tracks. Even sealed cells can leak.
And if they have overpressure venting mechanisms they have built in 
pressure activated leaks.

To adjust the battery charging for temperature you need to sense the 
battery temperature and use a charger designed to suit the 
characteristics of the batteries used.

If you want to build your own charger you need to select a suitable 
battery charge management IC that is designed for the battery chemistry.
The near universal battery chemistry (selected with jumpers or a 
resistive divider connected to a function pin) charger ICs that were 
available 2-3 years ago appear to be obsolete.


The simpler solar cell chargers use a linear shunt regulator to shunt 
unwanted current generated by the solar cell when the batteries are 
charged are somewhat inefficient. Similarly those using linear series 
regulators are also inefficient.

A switchmode charger is better at using whatever energy is available to 
charge the batteries rather than only being able to charge the 
battteries when the solar cell open circuit voltage is greater than the 
battery voltage.

You really need a solar nobreak supply that uses solar power to charge 
the battery and run the load when solar power is available, only running 
entirely from the battery when there is no solar power available. 
Battery protection from overcharge, short circuit, and deep discharge is 
essential to ensure long life.



Bruce Griffiths