[Elecraft] Solar Panels on sale !!

[G3VVT at aol.com]

You have to be pretty careless at damaging a 7Ah gelcell battery with only 5W 
of solar power at your disposal. Even starting with a fully charged battery, 
it is not going to stay that way too long with a load such as a K2 connected 
and normal TX/RX duty ratio usage with a solar panel so low in output.

The big killer of gelcells and other SLAs is heat. We found this out to our 
cost when the 25 year maintenance free batteries that ran our fiber optic comms 
system started failing after 5 years. The batteries are rated at 25C/77F and 
anything above this severely limits their life which in our case was only a 
20% of nominal. We were running with an ambient temperature of 38C/100F, though 
with the correct charging conditions. Heat build up could occur with extreme 
overcharging for a prolonged period and cause a similar effect. Seems there is 
nothing to beat the plain old refillable/vented lead acid batteries for 
withstanding abuse and this is what we had to go back to in the end.

A point that has not been brought up is would be foolish to run the solar 
powered K2 without a battery connected as an unloaded 12V solar panel can give 
outputs as high as 21V. Under extreme circumstances this may cause failure of 
the radio. As a side issue, professional comms systems commonly run at 48VDC, so 
the solar powered systems have banks of four 12V panel in series. Getting 
your body across the terminals of an open circuit bank of panels can give you 
quite a nasty jolt. Some of our systems had up to 15kW available to wake you up 
if needed.

For what it is worth the standard method that we used for testing solar panel 
outputs was to place a S/C through an ammeter across the panel terminals and 
see what current it will pass. Nominal rating is at 25C/77F for most solar 
panels. This current will increase with reduced temperatures i.e. a much greater 
output in Winter and in Summer a much reduced output with higher solar panel 
surface temperatures.

Bob, G3VVT
K2 #4168