Prototyping a solar charger for your truck

[Bryan] got his hands on a solar panel and decided to take it on the road rather than throwing it on the roof of the house. On sunny days it will top off the car battery, letting him use his stereo in the middle of nowhere without needing to keep the engine running. Instead of buying a ready-made solution he chose to design and build his own charging circuitry.

The charger uses an Arduino, which draws its own power from the panel via a regulator. It senses the voltage level of the battery and the available juice from the panel, connecting or disconnecting it from the electrical system as necessary. The system includes a set of LED indicators, which he installed in the dashboard near the cigarette lighter. This also gave him an excuse to install a voltmeter which uses a 2.5 digit seven segment display to read out the battery voltage. You can see a brief overview after the break.

Comments

  1. strange bob brown pants says:

    wow 2 amps from that little panel seriously?

    • RobThePyro says:

      and that prob at <15% efficiency! I still find it hard to believe a sq meter of sun has such an amazing amount of energy!!

    • basroil says:

      Lets see, sun is somewhere between 1100W and 1300W/m^2 on a perfect day in summer. 10 series cells at 1.5V each means 15V. From the size of it, it’s probably half sq. meter. So we have 600W/15V=40A at 100% (not possible). From that max, we get about 5% efficiency for that panel, which is about right. Still not enough power to run an incandescent lightbulb, but good enough for cheap speakers (my nice speakers are about 200W RMS, so I would need about eight of those panels, which doesn’t fit in a car and weighs more than taking along three car batteries)

      That’s the other thing I’m wondering about here, is it worth the extra weight and space compared with just taking along a second car battery?

  2. fartface says:

    Wow he did it the hard way.

    One diode is all that is needed. a car battery if you leave it charging at 2 amps 24/7 for 30 days will do no damage at all. In fact most trickle maintenance chargers float at 2 amp charge on the battery.

    • Craig says:

      I agree the Arduino is a bit overkill, but fun to play with I suppose.

      Alternatively you could just use an op amp in a Schmitt trigger configuration on the battery terminal, then drive the solar panel relay with it.

  3. will1384 says:

    I have a 5w 15v solar panel in my car, under
    my rear window, have had one for years now,
    works well, battery lifespan seems improved
    as the battery seems to last longer before
    it needs to be replaced, the car is always
    easy to start, and if you replace the
    incandescent lamps with leds you have even
    more power to use for something else.

    I had used the solar panel along with
    a larger alternator and second battery
    to help power a carpc and large stereo
    amp, but over the years I did away with
    the second battery as it was not needed.

    The good thing about the small 5w 15v solar
    panel is that it can be wired into the cars
    wiring without any controller, however it does
    use a blocking diode, but thats it.

  4. Bryan says:

    I agree, the Arduino is a little bit overkill right now, but I’m planning on expanding it in the future to also handle maximum power point tracking and solar tracking.

    The one other thing I’d like to point out: At 50W and 14V the panel could output as much as 3.6 amps, which is getting out of the realm of trickle chargers. In the video the panel isn’t pointed directly at the sun. Plus, in a situation where current is going into the battery but not out, the voltage will continue to climb (slower and slower, however) until it reaches the open circuit voltage of the panel, which is around 20 volts in this case. This could result in catastrophic failure of the battery and I do not recommend trying it. Good points though!

  5. NSXtech says:

    Or how about a battery isolator and second small battery? It’s bulletproof off-the-shelf technology that just works.
    Why re-invent the wheel?

  6. BadHaddy says:

    I have 4 130W solar panels on the roof of my van. I just used a cheap 30 amp MPPT (Maximum Power Point Tracking) 3-stage solar charge controller, keeps the two 200 aH batteries well charged for the inverter, and brings them up to fully charged, from 50%, in about a day and a half.

  7. conundrum says:

    Better off using a voltage inverter which feeds panel voltage to the battery until OCV rises above say 14.4V then switches over to a MC34063 based regulator tuned to 13.8V
    Best of both worlds, and also allows the same charger to charge SLAs without frying them.

    Another useful hack, get a cheap LCD voltmeter and harvest the polariser from a cracked LCD panel then refit it 90 degrees out so the panel is white on black using gentle heat to activate the adhesive.
    Doubles the visibility IMHO, and is backlight friendly.

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