Saturday, June 28, 2014

Solar Power in the Telescope Garage

I had mentioned a couple of months back that the 5W solar panel that I bought for solar power inventions a few years back seemed to be dead.  I went out to the telescope garage this afternoon, and discovered that it was apparently a problem of having the polarity to the battery minder wrong.  Once it was in direct sunlight after the polarity reversal, the tender showed that it was charging the 12V battery.

Measuring the power output, I found about 1.8W, which reflects what I have long suspected: that Harbor Freight's specifications on products may have a wide range of output.  Or perhaps it was because it was late afternoon.  On the other hand, at 8:20 PM, the battery minder still showed that it was charging the battery.

UPDATE: Never assume that your components work.  It was kinda Rube Goldberg, but attached to the battery terminals I put a alligator clamp to cigarette lighter adapter, then a 12 VDC cigarette lighter plug to 110 VAC converter, then I plugged in a lamp with a CFL bulb.  And nothing.  But after testing each component, I discovered the 12 VDC -> 110 VAC converter (originally purchased for a 2001 East Coast trip to recharge the Hi-8 camcorder) no longer works.  It would not power a cell phone recharger, for example. 

Of course, I don't have a 12 VDC light anywhere to try on a direct connection, but if I get serious about powering lamps, I am going to need something that does the 12 VDC -> 110 VAC conversion in a way that gives more than just one plug.


  1. Harbor freight and other low price outfits are reselling PV panels that have been removed from service at large commercial installations which no longer meet the voltage/amperage standards. a brand new panel should be putting out over 14 volts.

  2. It is putting out over 14 volts. The wattage was only 1.8.

  3. Late afternoon and high latitude? Cosine and atmospheric loss of 65% sounds quite reasonable to me.

    An online calculator has alt/az of sun at 4PM in Boise as 56.1/243.5 degrees (and maximum alt at 69.5 degrees @ 1:40PM), so cos(243.5) * cos(13.4) =~ 0.434. There's most of the losses right there.