Saturday, Jun 05, 2004 at 00:02
Magnus, a couple of things you said in your reply above worry me.
Firstly, charging a battery for an extended time with a voltage in excess of 15v is detrimental to it. Cut it back to 14 V and you can leave it hooked on as long as you like. Smart chargers do just that, they hit the battery first with a higher voltage to press more current into it, then throttle the voltage back (or pulse it) to top the battery up, finally settling at around 13.8 - 14V to maintain the battery charge.
However, they sense the 'current' that the battery will accept, if it starts tapering back the charger throttles back also. Watching a volt meter during charging will tell you nothing much useful with regard to state of charge.
Secondly, you cannot get a true 'fully charged' voltage reading from a battery until it had been disconnected from the charger for some hours and no load had been connected meanwhile. If it then reads at least 12.6V it is fully charged.
Thirdly, the best way to measure the output of a solar panel is not by measuring volts at all. Connect an Ampmeter ( set to 10 Amp range or so) directly across the solar panel terminals. Yes, that does practically short circuit it but any solar panel can handle a short circuit indefinitely.
MAKE VERY SURE THE BATTERY IS DISCONNECTED FOR THIS
TEST>
Point the panel at the sun and read of the maximum current by varying the angle of the panel. The maximum available charging current is a little less than that since the battery (and wiring) does have some resistance.
I think that a 20W panel is very much underrated to feed an Engel fridge. I did wreck a good deep cycle battery some years ago - it powered a 15l Engel on a boat - and I only had a 20W solar panel.
Now, my boat has a much more efficient eutectic fridge and 76W of solar panel power. This is sufficient IF the sun shines at least every other day - if not, the genny has to be used as
well.
Klaus
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