Saturday 1 December 2012

Car batteries and solar panels

[We have now consolidated everything on attraction calls on this page]

There are some situations where there is no mains power, in which case, the only alternative is a battery, possibly backed up with a solar panel.

Contributed by Dick

There are commercially available bird call systems to solve this problem, for example based upon the Martley Electronics Bird Scarer and the Spark4 Birdsong Player. There is nothing wrong with these systems, except they are probably overkill for a Swift attraction call player, and cost more than you might wish to pay.

We have been exploring the use of a solar panel to recharge a car battery which then powers a Cheng Sheng player amplifier system. At maximum volume, it consumes half an amp at 12 volts (6 watts). At a more reasonable volume it consumes about 0.3 amps (~4watts).

Thus, a car battery of, say, 45 amp-hours could provide 150 hours of continuous running before the battery becomes flat. It is probably not a good idea to run a battery completely flat. However using half its capacity would provide 75 hours. At 4 hours per day, it would run for nearly 19 days.

Such an approach might be workable, recharging the battery every 19 days, longer if you use a bigger battery. This is barely practical if the battery is in a remote location, such as the top of a church belfry (we've tried it), in which case the addition of a solar panel should be considered.

Schematic showing component connections

As the Cheng Sheng player amp consumes up to 6 watts, we bought a 20 watt xm solar panel (costing £30) and a Morningstar SunGuard 4.5A solar regulator (costing £28) from Midsummer Energy in Cambridge, and we used an old car battery which still had about 25 amp-hours capacity. We used a 12 volt digital timer (see here) to limit the playing to 8 hours a day and it has been running successfully (in winter!) for 40 days without the battery going flat [it finally went flat after 50 days on 23rd December after a week of cloud].

It is worth taking some trouble to mount the solar panel at the optimum direction towards the sun. We reckon that, for the period 21 May to 21 July (the main Swift attracting season, one month each side of mid-summer's day), facing south, with the plane of the panel at 35° to the horizontal is about right (the latitude of Cambridge is about 52°N). See here for a useful sun-angle calculator.

For an alternative 12 volt timer, we have tried DC 12V Digital LCD Power Programmable Timer Time Switch Relay 16A. it requires some wiring up, but is a low price and seems to work well. It is also available on Amazon.

1 comment:

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