Lithium System Upgrade (REC BMS, Victron, Other)

[wholybee]

Originally Posted by HankOnthewater

Now we learn, that really the useable SoC of LFP is between 20 and 80% (=60% of total capacity), that is if we want the LFP batteries to last. The target SoC of AGMs was 50 to 100%, = 50% useable capacity.

This is a myth that won't seem to die. You can use all of your LFP capacity without significant loss of life. There are examples of LFP batteries installed in boats 15 years ago, charged to 100% every cycle, that still have more than 80% of their capacity. They will wear out due to calendar aging faster than what using 100% of the capacity will do. I think this is propagated because people won't let old habits die, and they spent so much time worrying about caring for Lead-Acid, it just feels wrong to let LFP be. And because LFP is expensive, people want to do everything they can to do it right.

Don't overcharge LFP. Charge it to 99%.(99% can be achieved at 13.8V) Don't discharge to below 0%. The BMS will prevent that. But really, the bottom end shouldn't matter as much because you don't want your food to spoil, so you should be kicking in chargers at 10% or so so the freezer doesn't stop working. But if you get distracted and the BMS disconnects at the bottom end once in a while, aside from losing your food, that will not damage the battery.

Now, _storing_ at 100% is something else. They should be stored in a partially discharged state. But charging to 100% and then discharging it, has the battery at 100% for an insignificant amount of time.

[more]

best BMS on market for 12v is this
JK SMART BMS 4S

https://www.youtube.com/watch?v=LDalnC01MZE

200a 100€ +- https://www.aliexpress.com/item/1005004220673099.html

i dont have 12v version i have 48v version and eva bottom class 280a x 16 i pay this battery 1410€ with delivery and tax

3.2V 280AH LiFePO4 Lithium iron phospha Battery 280000mAh For 12V 24V RV Campers Golf Cart Off-Road Off-grid Solar Wind TAX FREE
16PCS 3.2V 280ah
Total:US $1,659.60 Order date: Mar 26, 2022

and i think i waste money but have lot time i put in 16S with JK 8S-24s 2A balancer. and battery still today in 48v house sistem working without problem.


what i like in jk bms. something wrong with 1 cell with charging,he simply block charging discharging still work or oposit battery empty he block discharging ,charging work. and software limiting current from 10 to 200A.winter leave boat. simpply Bluetooth limit current on 10-15A(depend your need) or have karen guest on boat and you dont want hair dryer,iron somebodies use limit current 100A

[Pizzazz]

Some useful info on LFP batteries from the industry:

- Biggest difference is grade A vs. grade B. The vast majority of cells that go to the retail market (i.e. not electric utilities or vehicle manufacturers) are grade B. So, it is highly unlikely that most of us will have access to grade A cells despite what vendors say or what fake QR codes they print. The utilities can get 10-yr warranty while most of us cannot. There are no subdivisions between grade A and grade B. Either a cell passes the tests or it does not. If a cell fails the tests, it could fail after 750 or 2,000 or 3,000 cycles, no one knows for sure. If it passes the tests, there is a very high chance it will last 6,000 cycles at 0.5C or 8,000 cycles at 0.25C. Momentary (minutes) loads at 1C/2C is OK, at least for grade A. It is as simple as this.

- The second biggest difference is the quality of the equalization or more so, how much time you allow the BMS to equalize the cells. This should not be a problem on a boat as long as you invest in a good quality BMS.

- Recommended usable range is 10-90%, most agree that 5-95% is OK with no notable acceleration in degradation.

- Battery capacity degrades at approx. 2-3% per year, faster in the first year, and faster if cycled heavily. On a boat, we do not cycle the batteries heavily.

- Round trip efficiency, dc-dc is around 94% (I think for LA it was 87%). AC-AC efficiency depends on your inverter efficiency and setup (24V preferred here).

Lastly, for a wet cell system, the useable capacity is 50-80%, even 40-80%. You cannot go higher than 80% because it takes too long to charge and the efficiency of charging is really bad above 80%. You can go down to 10-20% if your electrical devices can handle the voltage drop (most on a boat are designed to operate down to 9-10V).

Costs. Wholesale, you can get grade A cells for around $220/kWh and grade B cells for about $120/kWh. Tesla probably pays $85/kWh for grade A but that is Tesla. You cannot get these prices retail. So, if you see prices less than $350/kWh from whoever, you know you are getting grade B cells. It could still serve your purpose well but you are taking a risk. I would happily buy grade B cells for the house bank but would not trash the vendor afterwards if I do not get lucky with the particular cells or blame the BMS if the cells fail. Some people just buy more grade B cells than they need and accept failure will happen.

Good luck.

[hjohnson]

Originally Posted by more

best BMS on market for 12v is this
JK SMART BMS 4S

200a 100€ +-

The problem with the jk BMS is that a) they don't integrate cleanly, especially with the advanced alternator regulators and b) they're MOSFET based, which have pretty nasty failure modes. There's a big reason to go with the dual bus contactor based BMSs in safety critical systems.

[geoffr]

Originally Posted by hjohnson

I get that you're trying to retain existing components (the Xantrex and the MPPTs) but I think you're adding a fair bit of complexity to keep those around, especially the solar controllers. The Victron MPPTs aren't stupid expensive, and well worth swapping in.

I would love to change my GVB-8 controllers to Victron, in fact when I bought them I wanted Victron! The problem is Victron doesn't make a boost MPPT controller (my flexible solar panels need boosting for my 12V bank)

[geoffr]

Originally Posted by HankOnthewater

As your diagram shows, it is not really KISS. The diagrams I have drawn for my setup are just as complicated, but not looking as professional as yours. What software did you use for that?

I started with my old LA diagrams as as you said it got more and more complicated
I use Microsoft Viso for the diagrams (I have it for work), I know others with the REC BMS have used diagrams.net (free online) - google REC BMS and diagrams for some instructions..

[HankOnthewater]

Originally Posted by geoffr

I started with my old LA diagrams as as you said it got more and more complicated
I use Microsoft Viso for the diagrams (I have it for work), I know others with the REC BMS have used diagrams.net (free online) - google REC BMS and diagrams for some instructions..

Thank you GeoffR

[HankOnthewater]

Indeed there are a lot of myths around Lithium setups. I recall another thread on CF recently where ?Sailorboy asserted that one must have peer reviewed research before we believe anything on the internet. Funny that, I did not see much proper research provided.

Thank you Barmecasa (post #15) and Wholeybee (post $ 16), and particularly highlighting the difference using the battery to ~99% charge and storing it at that SoC.

My battery documentation does not mention anything about preferable range of SoC, just recommends for storage 40-60% SOC. It mentions preferable cell voltages for charging, and absolute max charge voltages, and a dozen or so graphs, I guess for my interpretation.

In the end, batteries (any kind) remain a consumable, like fuel, pumps, sails, rigging and virtually everything on a boat. Just we like to stretch the time period between purchases, or to leave the next purchase to the next owner.

[Mal Reynolds]

Originally Posted by Pizzazz

Some useful info on LFP batteries from the industry:

- Biggest difference is grade A vs. grade B. The vast majority of cells that go to the retail market (i.e. not electric utilities or vehicle manufacturers) are grade B. So, it is highly unlikely that most of us will have access to grade A cells despite what vendors say or what fake QR codes they print. The utilities can get 10-yr warranty while most of us cannot. There are no subdivisions between grade A and grade B. Either a cell passes the tests or it does not. If a cell fails the tests, it could fail after 750 or 2,000 or 3,000 cycles, no one knows for sure. If it passes the tests, there is a very high chance it will last 6,000 cycles at 0.5C or 8,000 cycles at 0.25C. Momentary (minutes) loads at 1C/2C is OK, at least for grade A.

Can you be more specific about your source for this? Grade A & B test documentation? What are they testing? Is there a Grade C?

Most of us peon boaters are using prismatic cells, so I assume the above refers to prismatic?

My impression of the market is there doesn't seem to be much difference between cells at the retail level. A cheapo LiTime does just as well as a Victron or Lithionics.

[wholybee]

Originally Posted by Pizzazz

Some useful info on LFP batteries from the industry:


Good luck.

What does "from the industry" mean?

I think the assertion that most cell sold retail are grade B is simply because most people shop AliXXX, Ebay, and Amazon. If you avoid those retailers, it is not difficult to buy grade A cells.

I have not seen a recommended range anywhere except hearsay on Internet forums. Battery manufactures certainly list max charge voltage and min discharge voltage, but I have never seen a "recommended" range that is narrower than those. I have seen research and graphs showing the relationship between storing at specific SOC compared to temperature. Noting that temperature was a significant influence. If the cells were kept at temperatures comfortable for people (don't put them in your engine room) then the effect of SOC is greatly diminished. If kept cold, SOC has very little effect at all.

Those few that installed LFP 15 years ago mostly report that they still have greater than 80% capacity. So I think 2% per year is too high of an estimate. Unless you are abusing them with heat.

My experience is that LFP is more efficient than 94%. Victron states 99%, and on my (CALB cells) battery, that is very close.

Without checking current prices, your estimates seem close. But keep in mind prices trend down over time. Not long ago I would have expected numbers 2x those.

[djdeakyne]

Hi, My setup is similar to yours.
I would recommend to not use the Tyco relays. They draw lots of power, even though they have economizers. They get hot, buzz, and fail. These will cost you more but I like the Blue Sea ML-RBS 7713 Latching Relay with auto-release. They draw minimal power and you can also manually switch them with the lever on top. They also have a remote override switch for your panel.


Good choice with the REC and Cerbos. The Wifi module is probably redundant since Cerbos already has wifi built in and you can program the REC with an RS-485 cable and if you don't like that, you can always buy Wifi later. I was fine with the RS-485 cable. Once you have the REC setup, you don't need RS-485 anymore and you'll just use CANbus to the Cerbos. Cheers, Dave

[geoffr]

Originally Posted by djdeakyne

Hi, My setup is similar to yours.
I would recommend to not use the Tyco relays. They draw lots of power, even though they have economizers. They get hot, buzz, and fail. These will cost you more but I like the Blue Sea ML-RBS 7713 Latching Relay with auto-release. They draw minimal power and you can also manually switch them with the lever on top. They also have a remote override switch for your panel.

Dave,
How did you implement the ML-RBS - I thought they didn't directly work with a simple signal and that they need a pulse to switch?

Good point on the WiFi not really needed...

[geoffr]

Dave,

I take that back - I was thinking of the older ML-RBS 7700 series, not the 7710 series.

Interesting the 7710 series take 13mA to hold the coil with 7A at charging vs the Tyco of 0.13A and 3.8A inrush for 130ms.

The REC Active says it has a 3.15A slow blow fuse which looks like it will just work for the Tyco, but not the 7710 - did you need to add an external relay?

[djdeakyne]

Hi Geoff,
You have been doing your homework, great questions.
You are correct, the Tyco holding current is 130mA which is 10 times higher than the 7710 Series. That's 3 Ah/day getting turned into heat.

The REC 3.15 Amp fuse rating if for the entire BMS. The relay outputs are not fused. There are 4 small internal fuses that protect the cell sense lines.


The Relay and Opto outputs have absolutely no fusing on them at all. That fusing has to be provided by you. SY Destiny, over on the Facebook group 'Lithium Batteries on a Boat', has a brilliant design to pulse and power the 7700 but best of all, he uses a 15 ohm resistor to protect the relay instead of a fuse. The 15 ohm resistor limits the current to .8 amps and will never blow and need replacing.


I was uneducated and bought the 7700's. I modified a Solid State Relay board to provide the pulse and release signals. If I used the 7710 Series, I would not have had to worry about making pulses and could have just used a simple SSR setup to bump up the inrush current.

As long as we're at it, the big contactors are used as the final fail-safe for the bank. You will want to use the REC Opto outputs, set lower than the Relay voltage (like .1 volt) to tell your Victron and Balmar gear to stop charging before you reach the Overvoltage setting. The Opto's have to be split and buffered to talk to the charging sources so you might as well do the Relay outputs also. I like buffering every output anyway, whether it needs it or not, when it comes to something as critical as the BMS.
Cheers.

[Caz]

Originally Posted by geoffr

Looking for the wisdom of the internet as I'm putting together our upgrade to Lithium. I thinks I've got it all sorted out, but wanted to see if the wisdom here catches any errors or mistakes or suggested improvements.

I still haven't decided on the size of the LiFePO4 bank. Old LA is 675Ah (Trojan T105s). There is thinking of adding a 40A DC A/C in the future which would obviously mean a larger battery (and probably a second AC charger in parallel)

(Drawing attached)

Thanks!

Looks like a comprehensive. I am in the middle of my LiFePO4 install so will compare to my design and provide feedback.

Does the Visio sw draw the hump over wires automatically?