How screwed am I? Issue with charger

[Lawrence_craig]

Hi all.

Hope my post title got you interested.

I have a 280aH lithium (DIY) battery connected to a JK BMS on my boat which is currently cycling unattended (i.e. I am away from the boat).

The shore power charging the boat typically charges the batteries during the day (along with the solar PVs) and then they turn the power off at night so the battery discharges.

All has been working fine (monitoring remotely) till recently whereby the shore power doesn't seem to be charging the batteries. So I suspect the battery is cycling and the BMS is cutting the supply off at the low voltage disconnect, then recovering slighting during the day with Solar PV.

I am trying to understand what this means for the batteries and really trying to work out if I need to jump on a plane to Greece to resolve it. Opinions welcome.

Thanks.

 

[SeaGal]

With the weather we've been having recently, Greece sounds like a good idea.

If you're busy you could pay someone to pop over there for you and have a look - for a thorough investigation I suggest a week or two sailing around the islands would be advisable to make sure everything is working as it should ?

Seriously though, if the BMS is doing its job, the batteries should be fine - can you remotely monitor what voltage the cells are at?

 

[mikefitz]

Opinions welcome

Depends on any critical loads, like bilge pump, that may drain the battery to cut off. Some chargers , including solar controllers, will not operate unless they 'see' a resionable voltage from the battery.
Unless the typical daily loads exceed typical solar input, then the battery should stay charged without shore power.
What data are you receiving from the remote monitoring? If voltage readings, what is the lowest and highest readings?

 

[Lawrence_craig]

Thanks both. I can see the overall system voltage. (see photos, first image shows over a monthly period, you can see it used to charge fine, then I lost the stream for a while. 2nd photo shows cycle today)

As you can see, the Solar system is not making up for the overall daily discharge.

I suspect the BMS will be cutting out once the cell voltage gets too low. Will monitor over the coming days. But will this be doing any damage to the cells if it's continually (daily) dropping to cut off voltage?

I suspect there is a shore power/charging issue, so is good enough justification to go treat myself to some souvlaki. (if my friends in the boat yard can't spot an issue).

 

[SeaGal]

11V over 4 cells is still 2.75V per cell, assuming the cells are still balanced - I guess you don't have individual cell voltages?

So, it looks like the BMS is doing its job and protecting the cells. LFP should be safe to go down to 2.5V, so I don't see there is an issue with potential damage.

If you're not comfortable with that voltage can you remotely adjust the low voltage cut off (e.g. bump it up to 11.5 or 12V?)