Solar Charging WOW

I was down about 15AH when I woke up this morning at 7:00. We had full sun promised for the next week and I needed to charge my laptop. I was doubtful I’d get anywhere near a full charge today, but figured that with the forecast ahead, there was no need to run the engine this morning to give the solar panels a boost.

With the time change, I didn’t start to get much of a charge until well past 8AM. By 11AM, I was down more than 20AH and still wasn’t seeing a positive charge coming in, not even when I turned off the inverter.

I stopped for lunch at 1:00 and was amazing to see that I was now 16.4AH down! In the 20 minutes I took to eat, I saw myself gain a full AH. But that still left me right where I was in the morning.

When I next checked the monitor at 3:00… I got a FULL message! My batteries were charged to maximum capacity!

So it looks like my theory about how the battery monitor works is correct. The amps coming in are only the amps at that moment and every so often, the monitor adds up those amps and adjusts the AH metre up or down as appropriate rather than adjusting the readings in real time.

So the only reading that is truly relevant at any moment is the AH status, and then I can check the amps screen to see if the AH are going to trend up or downwards.

At any rate, full batteries, YAY! Not that I’ve been lacking for power, not by a long shot, but it’s good for the batteries to get a full charge regularly.

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4 Comments

  • I keep my monitor set on the percentage of charge. I understand it and it makes for much less stress. 🙂

    My new trick is turning off my electric fridge at bedtime and turning it back on about 4-5 am when I get up to answer nature’s call. The fridge stays within comfort range when I’m not opening the door and there’s no sun shining on the rig. As long as the day is not completely overcast my batteries catch up enough to be happy. Been 100% the last couple of days.

    Going to get hot this week so it will be interesting to see if my fans are enough to keep me comfortable or if I have to go plug in. I don’t have a generator to run my A/C.

  • According to the user manual for the LinkPRO, the “full” message works like this:
    ( begin quote )
    A charge cycle will be considered complete when both Auto-sync parameters F1.0, F1.1 and F1.2 (see Function setup menu) are met.
    This typically means : when the battery charger switches to float mode. By meeting these conditions, the battery is considered full, which will be indicated by a flashing FULL message on the display. Besides this, the State-of-charge readout will be set to 100% and the Amp hour readout reset to 0Ah.
    ( end quote)

    I take this to mean that as your batteries charge, the monitor will measure how much power is going back into the battery bank and give you a readout of how much power i9t thinks remains for the bank to have a full charge.

    However, when your charger switches to its final phase of the charging process ( “float” ) as determined by the charge voltage and charge current having the right values for long enough, then the monitor will assume the battery bank is charged regardless of how much it thought needed to be put back into the bank.

    So, even if a moment before it showed that 15 Ah needed to be put back into the battery, if those parameters are met, it drops the 15Ah and just shows “full”.

    I would imagine that since you have several battery chargers ( solar charge controller, AC converter, separate battery charger, alternator on the RV motor ) that all could have different charge algorithms, the point at which the monitor thinks your pack is “full” could be different with each one. Just in case things weren’t complicated enough.

    The good news is that as long as you’re charging and showing “full”, I don’t think it matters much.

    If the manual for your main method of charging is detailed enough to give you values for F1.0 and F1.1, then you might want to make sure they match the settings in the LinkPRO.

    Also, I think the real takeaway is that the Ah reading isn’t that exact, particularly on the charge cycle, despite the fact that it shows it’s calculations to the tenth of an Amp Hour. Just like a gas gauge that reads “empty” might have a couple gallons and you’ll make it to the gas station or you might be on fumes and will end up walking, you need to read the trend, not depend on the precision of the numbers displayed.

    I use the % reading with mine.

  • Airmon, thank you for that!!!

    Solar is my main charger and I only believe the battery monitor as to the true state of my batteries.

    I don’t find the percentage values that helpful. To me, ‘You’re 20AH down’ is more helpful than ‘You’re 91.7% down’ because I can look at the weather and know if I’m going to get that 20AH back that day. If the metre tells me I’m 80% down, that sounds good since I still have 20% usable battery capacity left, but there’s no way I’ll get 48AH back in a day and I know I’ll be using at least 20AH the next day. So it’s time to start the engine.

  • […] down today and came home to a FULL reading. I would be frustrated with my badly working monitor if reader airmon hadn’t posted an explanation for that bizarre phenomenon. Instead, I am doing a happy […]

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