Solar powered battery sustainer

It seems they're going to keep sending new dongles every 3 years or after a buyout.  Pay per mile insurance might prove unprofitable in the end & we'll just go back to prepaid insurance. 

There is no escape from the day job.

Anchor the pins in some balsa or they'll fall off when soldering.

This one had the same enclosure as the old one.

It proved easier to get the wires out the bottom. 

Left the badge off this one.  It might have held the GPS antenna in.

The trick is to leave the solar panel disconnected until daylight to be sure it isn't going to blow up.

The next idea was a ratchet section paired with the spring section, to dial the spring to just the right tension.  The ratchet mechanism was quite complicated, but seen as cheaper than printing a corkscrew.  

Trying to make a timelapse of the printout was problematic, so sections got printed once in timelapse mode, thrown away, & again without timelapse mode.

Timelapse mode created blobs on 1 side.  The blobs impacted the nozzle & broke the parts off the bed.

The thinnest cylinder was plagued by voids & eventually got more material added to compensate for the voids.

It solved the problem, achieved just the right pressure for any height, but definitely was lacking.  That ratchet mechanism was complicated.  The ratchet desperately needs a stopper to keep from falling out & bumper to make it extend in a straight line.  

The adhesives bond rubber, but not PETG.   PETG facing rubber needs holes to take up adhesive.

A corkscrew would definitely be simpler than the ratchet & probably use the same amount of material, but it would be harder to use & harder to look at.  1 section could have a corkscrew.  Another section could have a tab stick into the corkscrew.  

So the pool noodle compressed instantly & the solar panel fell back down.  The next attempt was a giant toilet roller.  

Made from the cheapest spring currently made.  The lion kingdom wondered who bought plastic toilet rollers for any use other than recycling the spring or who mail ordered a plastic roller from 3 miles away & waited 10 days.

The PETG pieces were surprisingly strong.

Some rubber from sandals was epoxied on.

A previous attempt had joints, but these proved to be 2 extra pieces requiring alignment rather than any improvement.

Unfortunately, the spring had the right tension at only 1 point.  There was much shimming of the spring length to make it stand up at 1 point, but  the spring never reached an ideal tension.  It was seen as the easiest to install because it would only require 1 paw.  In reality, it takes 2 paws to fight the resistance of the spring while positioning the ends.  Because of the variety of alignments required to stand the solar panel up, a better system would use a ratchet.  

Another idea is to make the solar panel fold like a book.  It probably needs a bigger area to apply force.

The Ecoworthy was moved to the back window since that seemed to get more sunlight in the morning. 

Current logging would find the optimum position, but you've got a shunt resistor, an op-amp, feedback resistors, an ADC.  All the resistors have to be schmick to withstand the temperature changes in a car.  Another idea was making a timelapse movie, but the camera needs to withstand high temperatures.  

The battery was never recharged from manes voltage after going to the Ecoworthy, so the results with the Ecoworthy were never fully known.  It definitely wasn't dead.  The car seemed to start as fast as a fully charged battery, after months between drives.  

After much debate, the optimum way to stand up the panel was viewed as a pool noodle.  The front has the instrument cluster to prop it against.  The back has the seats to prop it against.  The front passenger side would be problematic.  The lion kingdom had some 20 year old pipe insulation which could be bundled.  It's unknown how it withstands high temperatures.

$33 later, there was the mighty Ecoworthy.

https://www.amazon.com/dp/B01IFJ73X4

To save money, it was just connected to an LM1117 to limit the voltage to 14.5.  That has a 1V drop at low current & 1.5mA quiescent current.  

Lacking a dummy load, it was easiest to time the charging of a capacitor.  It took around 20 seconds to charge a 36000uF cap to 14.5V in a shaded area.

According to LT, it might have been making 5-10mA in the shade at 13V.  There's a brief time every day when the windshield has direct sunlight.  That's when most of the charging would happen.

 In sunlight, it made 1.5A at 1.5V & the cap charged instantly.  Its peak efficiency is at 18V, so an ideal charger would charge a cap to 18V & discharge just enough current to keep it at 18V.  

A simple PETG enclosure followed.

Then some TPU bumpers would keep it from scratching the car.  A simple trucker's hitch lashed the bumpers down.

Some worthless socks propped it up.  The bumpers definitely made it look more upmarketed than the standard solar panels we see in parking lots.

Helas, in the shaded windshield, it only made 13V with 1.5mA load.   It might be dirt on the windshield, less indirect light under the roof, the load, the panel being rated for lower voltage.  The battery was stuck at its starting voltage of 12.7, whether the panel was fully sunlit or in the shade.  The smaller panel must have generated under 1mA in the shade.

There is no direct sunlight in the summer.  The sun is too high.  Maybe current logging would give more data, but it's a lot of work for what it is.  The lion kingdom doesn't have any other budget besides a $33 panel & linear regulator.  It's easier just to wait another 2 months.