Lithium reverse drain

[opfrei]

Hi all, diy newb here trying to clean up the electrical on my sailboat.

Current power storage consists of 8x 130Ah lithium batteries, which are charged by the alternator and/or an 815W PV solar array via Xantrex C40 charge controller.

In rewiring my house branch breaker panel, I accidentally bypassed the charge controller, which subsequently caused the batteries to reverse drain through the panels that night.

The batteries held a 14V charge prior to this incident, but they have now dropped to 11V. The health status indicator on each battery still blinks green, although I don’t know how much it tells.

In the meantime, I re-connected the charge controller, correctly this time, as well as an automotive battery charger @10A overnight to hopefully get my batteries back up to full.

Woke up this morning and batteries still only show 11.3V despite automotive charger saying it reached full charge. I’m worried I made a big mistake... Did I damage my panels? Or worse yet, fry my batteries? Please help!

 

[Megawatt]

Hi all, diy newb here trying to clean up the electrical on my sailboat.

Current power storage consists of 8x 130Ah lithium batteries, which are charged by the alternator and/or an 815W PV solar array via Xantrex C40 charge controller.

In rewiring my house branch breaker panel, I accidentally bypassed the charge controller, which subsequently caused the batteries to reverse drain through the panels that night.

The batteries held a 14V charge prior to this incident, but they have now dropped to 11V. The health status indicator on each battery still blinks green, although I don’t know how much it tells.

In the meantime, I re-connected the charge controller, correctly this time, as well as an automotive battery charger @10A overnight to hopefully get my batteries back up to full.

Woke up this morning and batteries still only show 11.3V despite automotive charger saying it reached full charge. I’m worried I made a big mistake... Did I damage my panels? Or worse yet, fry my batteries? Please help!

Oprefi it sounds like it’s your battery’s can you take your battery’s to your local parts automotive house and they will load test them for you and see if the cells aren’t damaged. If that’s not it we’ll look at the panels.

 

[James]

I presume that they are 4 cell batteries,
nominal cell voltage is 3.6v
therefore the nominal voltage of the battery will be around 14.4v
maximum charge voltage would be 16.8v

if you are trying to push charge into the batteries, a standard automotive charger is not going to do it, they typicaly put out 13.8 to 14v and this is barely going to charge the batteries before the charger cuts off as it sees around 14v as fully charged (for a lead acid battery)

also, 8 x 130Ah is a lot of battery power 1040Ah at 10A charge rate, it would take 100h to charge from empty to full.
be very carefull with such a large stored energy. carefull consideration should be taken to prevent
under / over charge
under / over temperature
short circuits could easily cause a lot of damage if not fused correctly.
most batteries of that type will easily give 10 to 15 times there capacity in amps under heavy use.
i.e, 1040Ah battery pack will provide 10 to 15 THOUSAND AMPS for a short duration
[automerge]1567017182[/automerge]
Also, I am concerned that you have the wrong charge controller,
if it is this one, it is suitable for lead acid or NiCd
NOT lith ion

https://www.solar-electric.com/lib/wind-sun/c-series-charge-controller-datasheet.pdf

 

[opfrei]

Thanks for your response, James.

The batteries are Valence U-Charge Model #U27-12XP. Datasheet shows the following: Group 27 / Nominal Voltage 12.8V / Nominal Capacity 138Ah / Peak Load 300A / Cut-off Voltage 10V / Max Charge Voltage 14.6V / Float Voltage 13.8V

It also mentions that they are compatible with lead-acid chargers, and the 40A Xantrex charge controller can be tuned to match the bulk/float voltages specified on the batteries. The PV system was installed by the previous owner and has been used to charge the batteries successfully for a few years now, so that shouldn’t be a problem..?

I wouldn’t be surprised if the automotive charger isn’t cutting though, and given that it would take days for the panels to charge the batteries back up to full (if everything still works properly), I am tempted to borrow a high capacity/voltage AC charger in the meantime... Thoughts?

Also, would removing the batteries and taking them to a specialist be the only way to test their health or can I do it from the boat somehow?

Also, can someone please explain reverse drain (when not connected to a charge controller)? How could such a huge battery bank have depleted itself through 800W of panels overnight? And how can I test for damage to the panels?

Many thanks!

 

[James]

Ok, that information changes things a bit,

In my Opinion you have nothing to worry about, the batteries according to there spec. sheet must have some form of charge monitoring / control built into them to allow them to be charged by normal lead acid charging solutions.

I further suspect that they may not have been fully charged when they "depleted themselves"
the panels are unlikely to be damaged, do you have any method of measuring the current? if the batteries are flat or near to, you should see about 80% of the alternators rated current (probably 80 to 100A) when the engine is running at above 2000 RPM
that would give you a clear indication that they are taking charge.
if they are near to flat, you can push that current into the batteries for 10 hours before they are near to fully charged.

also, remember that they are capable of providing 300A each battery for 30 sec, 300 x 8 is two and a half THOUSAND AMPS
that is what they will provide for a 30 second duration, if you had a short circuit then it would likely be more than that.
BE AWARE of the power involved with that much stored energy.

 

[opfrei]

Thanks again James. I am worried about starting the engine on such low batteries (11.1V now) and also putting potentially too much stress on the alternator. The automotive AC battery charger I have is capable of providing 50A of current and it also has a lead-acid OR deep cycle charge settings. So far I have only set it to 10A on deep cycle. Would it be safe to set it to 50A? (I heard it could be harmful to provide excessive current to highly discharged lithium batteries). Since the highest specified battery voltage is 14.6V could the charger not reach that?

 

[James]

According to the spec of the batteries, they can be charged at 2c.
That means 2 x 138A each
Total max charge current would be 2080A
Yes that really is over 2000Amps
50 Amps spread across all 8 batteries is still like filling a swimming pool with a garden hose.
It will do it but it will take some time.

The battery in my mobile phone charges at 3 Amps

 

[opfrei]

So, I was able to find an appropriate AC charger to get the batteries back up to charge but am still concerned there might be a current leak somewhere. How can I test for this?

Also given this is such a large bank, what kind of protections should I integrate into the system. For now, there are no fuses- scary I know but that’s how it came!