Forum Discussion

HiTech's avatar
HiTech
Explorer
Jun 12, 2013

Create dump load with a schmitt trigger and controller?

I'd love to have a way to harvest the load wasted when a PWM solar controller moves out of bulk mode and starts PWM cycling the connection to the panels, without significantly impacting the primary controller in its mission.

One simple answer might seem to be a second controller wired in parallel to the panels, but with a high voltage threshold such that it is not powered until the voltage is sufficiently high, such as a voltage near Voc.

Alternately possibly a switching circuit that is triggered by the downside state change of the charging pulses out of the first controller might be used to switch on the input of the second controller (including a capacitor wired across the second controller input to smooth the input pulses).

Is there an inexpensive way to harness the unused solar power from the solar panels between PWM charging pulses?

Jim
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jun 13, 2013
    In storage use an interval timer. The thing is if you want to power grow lights or controller for a still it might be profitable. Calculate your potential kWh gain, times whatever best suits your purpose then decide whether or not the new control system is worth it. Some horsee applications ain't worth it, they eat more hay than the worth of their plow power. If you decide on heating water with a hundred watts or so, you'll need to store it in a vacuum flask or at night the BTU loss will have you spinning your wheels. How about a photoelectric 10 watt LED nightlight with appropriate battery? Or burglar alarm with 200 db piezoelectric screamer?
  • christopherglen's avatar
    christopherglen
    Explorer
    Jun 13, 2013
    It might be easier to tap off the battery, and draw power as it approaches the voltage cutoff for bulk - IE have some load that pulls just enough power to maintain a battery voltage of 14.2-14.3 Assuming it bulks at 14.4. The batteries would absorb as much as they can at 14.2-14.3 and the diversion load would get the excess off the panels. When the batteries are truly low, they would get full solar power until they hit the 14.2.
    The idea is the solar maintains full output, the batteries taper down, and the diversion load increases to maintain battery voltage.
    Might as well loose the charge controller, and only have voltage limiting on the battery by the diversion load.
  • Bend's avatar
    Bend
    Explorer
    Jun 13, 2013
    HiTech wrote:
    In storage, I would never have enough batteries to hold the excess power. So for me it is more running the dump load into things like the water heater or a fan to improve the state of the RV when I come visit it. Or a small beer fridge. :)
    ...
    Jim


    To add to your list... Charge aux/secondary batts: trolling motor batt, cellphone batt, laptop, walkie talkie, GPS, camera, etc...

    I like the idea.
  • HiTech's avatar
    HiTech
    Explorer
    Jun 12, 2013
    In storage, I would never have enough batteries to hold the excess power. So for me it is more running the dump load into things like the water heater or a fan to improve the state of the RV when I come visit it. Or a small beer fridge. :)

    But only with what is not needed to charge the batteries. Something automatic that uses only excess energy (like a solar controller with dump load capability) is unattended and easier, no matter what battery state the charger starts out with, than having to be there and know when to add the load.

    Load prioritization just make more sense to me than everything drawing the solar output at once.

    Jim
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jun 12, 2013
    First:

    Purchase a Dental Floss Ranch in Montana

    Then decide what you're going to do with the excess energy. If you are going to "harvest" 300 watt hours / 24 hours, I would tend to have 2nd through 3,000th thoughts about the viability issue.

    There is -ahem- always the option of dumping the energy into an appropriate added battery. Sorta resolves more issues than it creates.
  • OnaQuest's avatar
    OnaQuest
    Explorer
    Jun 12, 2013
    It's starting to sound like a solution without a problem:?

    The system wouldn't go out of bulk unless your storage facilities are getting full (batteries charged?), Right? So you only need to decide:
    • Do you add more storage (more battery capacity)
    • Do you find something to absorb the power before it's lost.

    In the mean time, why worry that capacity is going unused?
  • HiTech's avatar
    HiTech
    Explorer
    Jun 12, 2013
    LOL complicated for me, child's play for an EE.

    The idea's not hard though. In many other threads people talk about the fact that once you get out of bulk, you are generally not using all the output of the solar panels any more.

    So it's either buy a controller with a dump load feature (I'm all for that but I don't think there is one in my current budget), or find a way to grab those chunks of time when the panels are disconnected, and put some of that unused power to use.

    Jim
  • OnaQuest's avatar
    OnaQuest
    Explorer
    Jun 12, 2013
    It certainly sounds worthwhile doing, but I think you may need a non-vented battery box to store your plutonium required to fuel the flux capacitor. Let us know what you come up with.

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