Travels with Paddles

a sea kayaking journal

Axel Schoevers (Photo: A. de Krook) Name:
Axel Schoevers
Rijswijk, Zuid-Holland, Netherlands

Thursday, March 08, 2007

Solar Power

In the December 2003 issue of Sea Kayaker Magazine a D-I-Y article was published by Robert Walker about an "Expedition-Capacity Waterproof Solar Battery Charger". I quickly assembled one for my 2004 Faeroe trip.
The idea being that during the day, from the back deck of my kayak, I could charge a 10-pack of 1.2V 1800 mAh AA NiMh batteries (making 12V). During the evening and night I would take the battery pack into my tent to re-charge (for instance) my hand-held VHF radio. And I always would have charged AA batteries to power my then new digital camera, head torch, GPS, etc. Unfortunately the system did not work as planned and I did not have the technical knowledge to figure a way out of this at the time. After the first night of recharging my VHF from the battery pack, it appeared that the batteries would not charge again. At home I found out that when the battery pack is drained below 10.7V, the charge controller would not charge the batteries. Worse, the whole system would not give any voltage, despite the solar panel delivering 20V; Bummer! There are charge controllers that have a 'Voltage Load Disconnect' (VLD) circuit, but these charge controllers tend to be much bulkier. To date I have not found a small size charge controller with VLD. Anyway, I could not figure out to make this system bullet-proof on trips where I do not have access to a normal AA battery charger to 'reset' the system to a 12V battery pack. At about the same time Fiona Whitehead enthusiastically talked about charging her mobile phone directly off a solar panel. To my astonishment she used the same solar panel as I did. Thus directly feeding a car battery adapter from the solar panel. But being focussed on charging AA batteries, I did not continue to use the solar battery charger. Today I took my solar charger out of storage and with a small adaptation put it back into service. Instead of only allowing to recharge from the battery pack, I made an extra connection directly from the solar panel leads. The solar panel can give up to 20V and the charge controller converts this to about 12V. Reading the small print on my mobile phone car charger revealed '12-24V'. The only draw-back is that the waterproof box I use now is too small to hold any equipment other than the battery pack. And other boxes might be too big to carry on the back deck. We'll see how this works for a start.
Mentioning 'Solar Power', the term 'Girl Power' comes to mind... Or is my associative memory playing tricks on me? ;-) Lots of ENERGY there !


Simon said...

Hi Axel
Thanks for a really interesting post which raised a couple of questions for me.

Does this mean you can only charge your mobile phone and not AA batteries?

What make of solar pannel is this and did the charge controller come with it?

Axel said...

Hi Simon,

The Solar Panel is "UniSolar FLX-5". This is a fairly common brand. Often seen (various types/sizes) on sailing boats. Pete Bray used this brand on his cross Atlantic kayak.

The charge controller is "SunGuard 4.5 Amp Solar Charge Controller".

Assembly was described in the mentioned Sea Kayaker Magazine article; putting it in a Pelican Pelicase 1020.

All items bought separately.

The charge controller is only useful when charging a battery pack of 10 AA batteries and/or charging other stuff from the battery pack.

Some 12V car adapters (i.e. my mobile phone charger) can charge directly from the solar panel without the charge controller. As soon as I link the battery pack into the system the power across all leads reverts to 12V. So the charge controller is equalizing the voltage. Again, I am not an electronics expert. Without the battery pack attached the voltage is variable between 0 (no sun) to 20V (direct sun).

Today I bought a 12V AA battery charger that can independently charge 1 to 4 AA batteries, hopefully directly from the solar panel, else with the battery pack in the system.

If a bigger Pelicase is still functional on the back deck than I might want to put all my electronics in that one case. And charge only during daylight hours to prevent over-discharge.

What did somebody say about putting all eggs in one basket?


Wenley said...

Hi Axel,

Have you ever heard of these solar, flexible panels? They have a built-in blocking diode to protect against reverse draining of current, and are waterproof. To my knowledge, they were used two years ago, retracing the Lewis & Clark Expedition:

There are at least, other two brands that I know of:


Axel said...

The GP Travel PowerBank AA NiMh battery charger that I bought is somewhat 'intelligent'. A flashing red light warns for 'incorrect power' from a 12V source. I can charge AA cells individually from the 12V pack and it warns for over discharging the by blinking red. Unfortunately I cannot charge with the PowerBank directly from the solar panel, because it then also is blinking red. But ongoing tests show system is now working properly. Ideally I would need a more 'flexible' AA battery charger that can harnass any current between 12 and 24 Volts.