MPPT Solar Caution ...

wind_magic · #1 02-21-2010

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.

sailingdog · #2 02-21-2010

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.

Quote:

Originally Posted by wind_magic

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.

wind_magic · #3 02-21-2010

Quote:

Originally Posted by sailingdog

Your batteries have to be pretty dead for this to happen though.

Like maybe 9.6 volts.

sailingdog · #4 02-21-2010

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.

Quote:

Originally Posted by wind_magic

Like maybe 9.6 volts.

wind_magic · #5 02-21-2010

Quote:

Originally Posted by sailingdog

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 ..

wind_magic · #6 02-21-2010

Quote:

Originally Posted by wind_magic

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.

sailingdog · #7 02-21-2010

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

Quote:

Originally Posted by wind_magic

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.

Stu Jackson · #8 02-21-2010

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.

wind_magic · #9 02-21-2010

Quote:

Originally Posted by Stu Jackson

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.