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MPPT Solar Caution ...

Funny thing happened ...

I've been using a Blue Sky MPPT charger for a solar system, but because of all of the snow the panels were covered up and not charging and the loads drained the battery bank, just one of those rare things that happens sometimes. Well, the funny part is this - if the battery bank gets too low, the MPPT charger stops working, completely, because it is powered by the battery bank and not by the solar panels, so even if the snow melts and the solar panels are powered up, the charger and battery bank remain dead. Ask me how I know.

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post #2 of 9 Old 02-21-2010
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Your batteries have to be pretty dead for this to happen though. And it doesn't happen with all the MPPT charge controllers...but it is an issue on the Bluesky SB2000E among others.

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Funny thing happened ...

I've been using a Blue Sky MPPT charger for a solar system, but because of all of the snow the panels were covered up and not charging and the loads drained the battery bank, just one of those rare things that happens sometimes. Well, the funny part is this - if the battery bank gets too low, the MPPT charger stops working, completely, because it is powered by the battery bank and not by the solar panels, so even if the snow melts and the solar panels are powered up, the charger and battery bank remain dead. Ask me how I know.

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Your batteries have to be pretty dead for this to happen though.
Like maybe 9.6 volts.

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Considering a 12 vdc battery is considered 100% discharged at 11.6 VDC....9.6 VDC is pretty bad...Might consider getting a batteryminder just in case.
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Like maybe 9.6 volts.

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Considering a 12 vdc battery is considered 100% discharged at 11.6 VDC....9.6 VDC is pretty bad...Might consider getting a batteryminder just in case.
Yeah I think I'm going to use a relay to wire up a low voltage disconnect and run all my loads through that, if i have a zener with a voltage somewhere around 11 volts ..

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Yeah I think I'm going to use a relay to wire up a low voltage disconnect and run all my loads through that, if i have a zener with a voltage somewhere around 11 volts ..
On second thought, that circuit might just sit there and flicker on and off at the cutoff voltage, maybe I should just get the battery minder.

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Nah, go with your home-made contraption and report back at what it does...


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On second thought, that circuit might just sit there and flicker on and off at the cutoff voltage, maybe I should just get the battery minder.

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post #8 of 9 Old 02-21-2010
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Did you have a load running on the boat to drain the bank when there was no solar input? Otherwise, I'm confused, 'cuz the solar panels should have diodes to prevent "leakage" when the sun don't shine and at night.

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Did you have a load running on the boat to drain the bank when there was no solar input? Otherwise, I'm confused, 'cuz the solar panels should have diodes to prevent "leakage" when the sun don't shine and at night.
Yes, there was a load. Usually it isn't a problem, the load is light compared to the input from the solar panels even averaged through cloudy days, etc, I just wasn't counting on the solar panels being covered in snow for weeks.

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