Solar powered battery sustainer

Solar power is a pit of despair for lions without money.

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The car battery loses 16Ah every 2 months it isn't driven.  Letting it drop & recharging it every 2 months isn't a solution.  Borrowing $4 million for a house with a real garage isn't affordable, so something had to be done to top it off without manes voltage.

A $16 pile of solar cells

didn't work so well. They were each rated for 60mA at 5V. Wiring them as 5S2P, they gave 15V 75mA in direct sunlight. They gave 3.5V 3.5mA in the shade.

The car burns 270mAh every day, requiring 3.6 hours in direct sunlight to recharge. Being parked in direct sunlight would destroy the paint. Open circuit voltage goes to 30V, so the solar would need protection diodes to avoid blowing up the car if the battery was disconnected.

The lion kingdom was left with a pile of solar cells after a failed attempt to make a car battery sustainer. Enough solar cells to do the job would end up costing more than a new battery.  There isn't any electrified car port for thousandaires. It's hard to believe there was ever a time when houses were only 5x an average annual income, but lions still remember. It's been 20 years since the multiple became 10x & it's never gone down. The average electrified garage is now 15x the average salary. Lions believe the multiple will keep rising as long as the global workforce continues expanding faster than demand for labor.

Solar power is a pit of despair for lions without money. It's amazing they can light up a small LED in ambient light. It is believed they would be better than nothing at sustaining the car battery, despite only making it a hair less flat.

Up close, the cells are a messy bodge of smaller silicon shards.

After contemplating different fates for the solar cells, the decision was made to finish a minimal battery sustainer by tapping into the ODB2 port.  Don't forget to whack in shottky diodes to prevent the 2 solar cell strings from feeding each other or draining the battery.

This included a teardown of the Metromile.  The Metromile has never been torn down before.  There was no tamper protection, so after a few warnings about the unit being disconnected, it resumed functioning after being reassembled.

The battery was fully charged on 2/22.  Then it was driven twice until 3/5.  The solar panel went in on 3/8.  

The lion kingdom decided to recharge it again on 4/24.

Given that it was only sitting for 1.5 months, it might have gone to 11.5Ah if left for 2 months.  The solar panel was generating power at least at a rate of 5Ah over 2 months.  Another $50 of these cells would bring the rating to 12W & be required to indefinitely sustain it.  Once above $30 though, it's cheaper to get a 25W panel instead of 12W of loose cells.  The loose cells would be written off as a low cost test of viability.  It's a case in point for the cheap option always leading to paying twice.

A $50 total is still cheaper than a new battery & lions are so tired of reinstalling the battery every 2 months, it might be worth it.  Still perplexed on what the solar panels could be used for after commuting resumed.  A car battery only takes 2-3 Amps of charging current.  Driving it only a few minutes isn't enough to charge it.

  • 25W panel

    lion mclionhead05/04/2021 at 19:27 0 comments

    $33 later, there was the mighty Ecoworthy.

    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.

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