question

mward avatar image
mward asked

DC Input Low Restart vs Solar Input

I have an odd use case, I am hoping the assembled smart people can help me. On my boat I have a Multiplus II 3000, a MPPT 50/100 with 300w of solar panels, 600ah of lifepo4. I am storing the boat on land in a humid location for hurricane season in a place without 120v shore power. I have a dehumidifier I want to run on board and I have come up with the following case.


Set the low input cutoff to 13v (30% Soc on lifepo4), set the restart at 13.3v (90%). The dehumidifier can run until it gets to 13v and shuts off, then the solar can refill the batteries until it’s at 13.3v at which time it will re-engage the inverter allowing the dehumidifier to run.


One question is - while the solar panels are receiving sunlight will the ‘line voltage’ from the solar input rise above the 13.3v restart level causing the inverter to come back on and use the current from the solar instead of charging the batteries?


If this is the case, I could use a lamp timer to make sure the dehumidifier can only run at night.


If anyone has a more elegant solution than this, I am happy to hear it. Thank you all.

Multiplus-IIsolar
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

4 Answers
kevgermany avatar image
kevgermany answered ·

Not sure what you mean by line voltage. Hope this helps.

Multiplus looks at battery voltage to decide whether to invert or not. Battery voltage and solar output voltage are effectively identical.

Solar will provide power once sufficient illumination on panels. If battery voltage rises above 13.3V, multiplus will start inverting, allowing the dehumidifier to work. This continues until bettery voltage drops to 13V. Depending on output of solar Vs dehumidifier power needs battery may or may not get much charge. I suspect the dehumidifier will run mostly during the day/early evening.

Not sure how long the boat is being stored, but LiFePO4 batteries need to reach 100% charge to balance the cells. Plan for this as you're going to run them at the low end of the charge range pretty much continuously, internal imbalance will happen and may be enough to cause them to cut out and they might not be rechargeable by solar.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

mward avatar image
mward answered ·

So what I think I hear you saying is this is a bad idea if I can't get it to 100% SOC after letting it drop to 30%.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

JohnC avatar image
JohnC answered ·

Hi @Mward

More elegance preferred..

Hows about wiring your dehumidifier to ACOut2 and switching it with Assistants, using SOC (and/or V). That way you could run between two high SOC points and essentially just use excess solar for the load. Batts always well charged, and you could even add in a time delay to allow for batt balancing.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

mward avatar image
mward answered ·

I don't have ACout2 hooked up right now and I have 4 days to get the boat ready. I live about 2000 miles from where it's going to be stored so I can't easily be on hand if there are problems. This is a good idea though. I will probably just take all the soft stuff to climate controlled storage for hurricane season and figure it out next time around. Thank you for taking the time to help me understand this.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Related Resources