Planning My Lithium Power System - Looking for Feedback

[Fuss]

Ok Harry, here’s my advice…
do your research , learn everything as if you are going to write your dissertation for your doctor title, by this time you should have a balanced system.
and later when you know it’s balanced… put some tape over your battery monitor and 3 weeks later , guess the % and take off the tape… then report back here.

[Fuss]

and Harry, we don’t want to hear of any BMS high volt cutoffs or low volt cutoffs as part of the equation

[sailingharry]

Originally Posted by Fuss

and Harry, we don’t want to hear of any BMS high volt cutoffs or low volt cutoffs as part of the equation

?????

[Fuss]

Your name’s Harry isn’t it,
Your planning a lifepo4 install in the future.
Ok, it’s the wrong thread…but in the grand scheme of things..a minor point!

[sailingharry]

Just not entirely sure what your point even is. On another thread, I had a discussion with Captain rivet about balancing, and he had some interesting real world experience about active vs passive balancing. Is that your point?

[SV Confianza]

Originally Posted by CarlF

To cover a few issues.

1) Charging a big house bank from the alternator through a 30 amp DC-DC charger is just not enough amps to be worth the trouble. Better to just isolate the alternator to charging the start battery and charge the house bank with more solar or a genset. But, a conservative, properly designed LFP system with the alternator charging the house bank should never have a BMS disconnect. And if it somehow does, there are now easy, inexpensive ways to protect the alternator without using “communication”.

To make it worth the trouble the alternator should be big - something like the Balmar XT170. It should have a temperature sensor, alternator protection device, and avalanche diodes.

2) The alternator and inverter/charger should be set lower than the maximum voltage for the battery to leave “headroom” against a shutdown. I use 14.0v which charges to about 95%. Then I use the solar controller set to 14.2v to slowly charge the last little bit — with the alternator not charging..

3) Use a VictronDC-DC charger to charge the start battery from the house. This will safely route any BMS surges to the lead start battery.

4) If using more than 2 drop-in batteries, use equal length cables to a bus bar. Place a MBRF fuse on each battery positive terminal and then also a class T from the bus bar to the boat panel. Use large cables.

5) Have an ABYC electrician do partof the work.. Many insurance companies are suspicious of owner installed lithium batteries (you can’t blame them) and will ask for the installer’s name on an insurance application.

1. Best to charge the house bank of lithium with the alternator since the lithium accepts charge most efficiently, assuming a regulated alternator that can handle lithium.

2. I’ve never heard of this one before. We have been charging at 14.6 with no problems for 3 years (2 alternators, 3 solar controllers)

3. Pretty sure common thought is the dc dc charger does NOT prevent bms cutoff surges. We use a stay alive relay to keep the house paralleled with the start bats for this reason. See full description of the setup here.

4. I’d say this is much more on the “depends” side. With a bus bar you will charge most evenly (and efficiently) and best preserve battery life, yes. Does it matter in your setup? Depends. See will prowse video on his daisy chained LFP batteries he had been running for years.

5. I keep hearing this all over the net, but I haven’t seen an actual case where it’s mattered.

As with all my posts, happy to have feedback/disagreements on my points.

[Fuss]

Originally Posted by sailingharry

Just not entirely sure what your point even is. On another thread, I had a discussion with Captain rivet about balancing, and he had some interesting real world experience about active vs passive balancing. Is that your point?

Captainrivet and real world experience…oh dear oh dear!!….but anyway…my point was do your research and don’t have bms cutoffs as part of the equation.

Think of it like a fuse, it’s for protecting the cables against a completely unexpected event…. The fuse should never blow under normal circumstances.
The bms should never cutoff under normal circumstances … because the alternators, mppt chargers, multipluses are all programmed to not go there.

[sailingharry]

Originally Posted by Fuss

Captainrivet and real world experience…oh dear oh dear!!….but anyway…my point was do your research and don’t have bms cutoffs as part of the equation.



Think of it like a fuse, it’s for protecting the cables against a completely unexpected event…. The fuse should never blow under normal circumstances.

The bms should never cutoff under normal circumstances … because the alternators, mppt chargers, multipluses are all programmed to not go there.

Ummm yeah. No duh. I've said over and over, a BMS cut off is a major disaster and I don't expect to ever have one in the life of my battery. I mean, seriously!

A BMS that complies with abyc, along with most of the notes, virtually eliminates a BMS cut off.

All charge sources are programmed to stop charging before cut off levels.
At the BMS high voltage warning level, the charge bus is disconnected. That eliminates any potential further charge.
At 10% charge, the inverter is shut down, eliminating the heaviest load. It also sounds an alarm so I can take action.
That leaves the only possible BMS disconnect is an unattended boat with no charge sources leading to a completely flat battery. Not very likely!

So yeah, a battery disconnect is about as likely as a blown fuse.

And even if you use drop-ins with unsophisticated bms, it still shouldn't happen if you set it up right.