200W@24V->P30L->12V batteries

Discussion in 'Installations' started by vermontaircooled, Dec 25, 2020.

  1. Greetings. I’ve been happily running with 2 windy nation 100W panels in parallel through a P30L for about 2-1/2 years. (12V batteries at 12V). Used basically April- the end of October.

    Not unhappy with the ‘actual’ performance of the system, but being in Vermont, November and December produce many cloudy days of zero or essentially zero Ah of input. Not a panel problem LOL. Although I don’t live there in the cold months. I have been spending a little time there every week or so this year.

    I’ve noticed that I get a trickle of charge in some conditions but not enough to really amount to anything. So I decided to try an experiment. I made some assumptions:
    1) the 12v charge just wasn’t enough voltage to do much, but perhaps a 24V input would enable more Ah of usable charge due to the voltage differential?
    2) Since the P30L auto selects battery voltage upon connection -so batteries will still be charged at 12V even with a 24V input (I’ve seen 16-17V from the panels at 12V configuration) - I imagined the pwm charge controller would still safely charge my batteries even in full sun
    3) I’ve read where people have stated a pwm with a 24V input to 12V battery will only deliver “1/2 the power” on the output side. So I assumed that to be true. But I was willing live with that if the higher voltage enabled some semblance of usable charge - which at this time of year would be awesome

    My system at 12V would barely recover this time of year to 12.6-12.8 volts (from 12.1-ish) over a week. After changing to 24V input, I have seemed to be running well. 13.1V, 12.9V etc. I was impressed and I’m trying to absorb this.
    However, I came in yesterday to read on the P30L 14.1 volts at a .8Ah charge rate. Now that may have been in equalization mode (and no problem in that case) but I became concerned with the voltage: I didn’t have a meter with me to disconnect and test BUT was that overcharging? I don’t know.

    Will or does the P30L have the ability to safely charge 12V batteries from a 24V solar input? Like what I’ve attempted?

    If that is an acceptable function then I’m going to use it. At least this time of year. That was an overcast morning (hence the low amphours) and to see 14.1V on the screen amazed me. If using 24V enabled that and I can use that configuration safely that’s a valuable tool in “the dark months.”

    I will be moving to a new location in May 2021 and intend to add another 600W with an mppt and possibly some micro wind. I have two places where microhydro would work but I’m not sure about using it as half the little pool of water I’d create is over the property line.
    Operating with 200W and a 1200W pure sine inverter has been educational and experimenting with little ‘fridges and even a shop vac have been entertaining. I suppose if I watched TV or needed a microwave or air conditioning 200W would be pretty useless but it’s worked for my needs. It’s also been fun to push its limits (like with the mini fridge) and discover obvious useful things like use the vacuum in the mornings so you recover 100% to use evening light or make coffee with an electric coffeemaker the following morning. It wasn’t high risk cuz I could always start the jeep and use some jumper cables but with good batteries it hasn’t been necessary.

    Thank you in advance for thoughts and input.

    Mark V
    Northern Vermont

    Last edited: Dec 27, 2020
  2. TomT

    TomT WindyNation Engineer

    PWM 24 input drops to battery voltage but maintains amps.
    So in low light you would see some power over a 12v setup.
    Mppt is the way to go for the future.
    Then you run 24 volts for 12 volt battery.
    You will get more power to the battery.
    And even my setup. I put all my constant loads on inverters.
    Everything is on a power strip. To cut down on power wasters.
    Everything with a clock wastes power. I cut almost 400 watts from my constant loads that way.
    I checked and modified everything. Even my refrigerator uses 400 watts every few hours on a defrost timer.
    I used a relay and 30 min bathroom timer once every week to do the job.
    So experiment. We all did. See what works for you.
  3. Thanks for the reply. It was nice to hear you concur my results from my little experiment. Christmas day back on 12V config it was nearly painful to see “.1Ah” with no rise in volts. I may use that until less clouds snd longer days return. If I was living there for winter I’d probably just buy more panels.

    RE your mppt comments- what I’m planning is a 48V panel configuration into 12V. Probably two mirrored systems so if one component fails I don’t go down 100%.

    the fridge draw you mention.... I’m going to look into if there’s any made that are not frost free now that I read that. I’m using an old camper propane gas fridge but would like to replace that before it is necessary. Defrosting the freezer doesn’t seem like it was much of a burden when I was a kid...
    TomT likes this.

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