Solar Panels and LIFEPO4 batteries

[Mongo_at_sea]

My understanding is that when not in regular use, Lifepo4 batteries should be kept in a state of partial discharge. So over winter should either a switch be placed between the charge controller and the battery to turn off charging, or the battery disconnected? Thanks

[TheOffice]

Why not set the controller to a lower max voltage?

[Mongo_at_sea]

if you are using them every day, its one voltage, once a month, another voltage? Just curious how much care and feeding these require.

[markcouz]

When on the boat i charge to 3.6V per cell, when off the boat (bilge, fridge and freezer only) i use 3.4V per cell.

I don't ever disconnect entirely because we don't experience freezing conditions - but if i did i would store at 3.3V.

[Mongo_at_sea]

thanks.. it seems there is a little more hand holding than with lead batteries to insure long life, given typical sailboat use.

[CatNewBee]

They are very robust, don't kill them by disconnecting and deep discharge. LFP are great, and it is not noticeable if you use them for 20 years or 21 years. This is the difference between permanent pampering vs. just let the BMS do his work.

[s/v Jedi]

For storage it is recommended to keep the batteries at 30-70% SOC or thereabouts.

As the voltage differences are small, I decided to make the charging on/off decision with the Victron smart battery monitor (using it’s programmable relay output). I can set it to normally charge to 95% and during storage change that to 50%

[dksail]

Here is what Battle Born Suggests:

The storage temperature range is -10°F to 140°F (-23°C to 60°C). We recommend bringing the Battle Born Batteries to a 100% charge and then disconnecting them completely for storage. After six months in storage your batteries will remain 75 – 80% charged.

[Mongo_at_sea]

Just another item to add to the list as you leave the boat: discharge batteries (somehow) to 50-70% SOC, set charger to 50%. Or is it OK to leave chargedLIFPO4 batteries to discharge slowly, then be maintained at 50-70%?

[s/v Jedi]

Originally Posted by Mongo_at_sea

Just another item to add to the list as you leave the boat: discharge batteries (somehow) to 50-70% SOC, set charger to 50%. Or is it OK to leave chargedLIFPO4 batteries to discharge slowly, then be maintained at 50-70%?

A maintainer as used for LA is not suited. You want it completely off until it has gone too low. If you need to store for up to a year, you don’t need charging at all, just check the graph for self discharge and make sure that at the end of the storage period you have at least 30% SOC left. I think they all do that for 12 months when you start at 70%

[Mongo_at_sea]

The discussion is more related to solar charge controllers. I would say a solar charger set to 50-70% SOC for LIFEPO4 per discussion above is basically a maintainer. My original question was whether it made sense to have a cut off switch between chargers and battery, or if there is another management approach that works. The battery management process could become a pain if you have more than one controller and you need to get into each one to adjust every time you leave the boat for two weeks, or if you are fully charged when you get back to the dock, and before you leave you need to discharge to 70%. Maybe I am just overthinking. I do not have LIFEPO4 yet, but I saw this as a potential management concern. When you are on the boat you want it to be able to fully charge, and when off, not so much, if at all. Obviously not a live aboard issue.

[Colin A]

Originally Posted by Mongo_at_sea

The discussion is more related to solar charge controllers. I would say a solar charger set to 50-70% SOC for LIFEPO4 per discussion above is basically a maintainer. My original question was whether it made sense to have a cut off switch between chargers and battery, or if there is another management approach that works. The battery management process could become a pain if you have more than one controller and you need to get into each one to adjust every time you leave the boat for two weeks, or if you are fully charged when you get back to the dock, and before you leave you need to discharge to 70%. Maybe I am just overthinking. I do not have LIFEPO4 yet, but I saw this as a potential management concern. When you are on the boat you want it to be able to fully charge, and when off, not so much, if at all. Obviously not a live aboard issue.

If there are going to be no loads (land storage for example) I would disconnect the batteries at slightly less then full charge (70% probably better). If your talking about it hanging on a mooring with some loads on like electronics pumps etc, I would say just make sure your sources are set to the lower side of battery manufacturers recommended voltages. A system like Jedi mentions would be more ideal but not for everyone.

[Mongo_at_sea]

I am talking more about typical sailing usage in the Northwest. Boat is at dock, un plugged from shore power, but ability to charge with solar panels, say 400 watts. I am away from the boat 2 weeks at at time in summer, up to 4 weeks at a time in winter. Loads when away would be bilge pump in emergency only.

[s/v Jedi]

Originally Posted by Mongo_at_sea

I am talking more about typical sailing usage in the Northwest. Boat is at dock, un plugged from shore power, but ability to charge with solar panels, say 400 watts. I am away from the boat 2 weeks at at time in summer, up to 4 weeks at a time in winter. Loads when away would be bilge pump in emergency only.

In that case we completely disconnect the house bank and let the starter bank do it all, charged by solar. We use agm batteries for that.

[newhaul]

Originally Posted by Mongo_at_sea

I am talking more about typical sailing usage in the Northwest. Boat is at dock, un plugged from shore power, but ability to charge with solar panels, say 400 watts. I am away from the boat 2 weeks at at time in summer, up to 4 weeks at a time in winter. Loads when away would be bilge pump in emergency only.

Just put in a switch in the lead from the bank to the buss bar and disconnect when you leave the boat and as already mentioned let the start bank run the pump. Reconnect when back on board and the running of the engine to get through the locks will charge the bank up to full for the sail north to the islands .