Merged LiFeYPO4 1000Ah Winston prismatic cells and all electric galley...

[Catapault]

Originally Posted by s/v Jedi

I agree with CNB that a latching solenoid is much more robust and reliable. The RBS series from Blue Sea Systems is excellent. They have models that are driven by a pulse which is perfect for use with a microcontroller, or they have models that use a on/off constant level signal which is good to drive with a relay from any BMS. These are 500A rated.

If you can program, I recommend using an Arduino to build your own BMS. You can buy little cheap modules that measure cell voltages so it’s just coding the alarms and high and low voltage disconnect; temperature very easy as well.

Do you have any links to the mentioned ' little cheap modules that measure cell voltages' that are considered decent please ?

[Catapault]

Biggest Issue I've found with REC-BMS is getting one in Europe.

Global supply chain issues of electronics seem to have them way behind, best delivery found so far is 3 months, probably more.

[s/v Jedi]

Originally Posted by Catapault

Do you have any links to the mentioned ' little cheap modules that measure cell voltages' that are considered decent please ?

I use these INA226 modules. You need one for each cell you have (I have 8 cells, 24V) which is the max. voltage for this method. They cost around $4 each.

You connect them all to the common negative, so the first module reads 3.2V, the second 6.4V etc. You simply subtract the voltage measured at the previous cell to get the individual cell voltages.

This method allows to do this without the need for galvanic isolation and without specialized chips.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Edit: you only use the voltage measurement, not the shunt based current measurement.

[hzcruiser]

Originally Posted by CaptainRivet

A simple 500A high current switch that is 1) Lithium or 2) starter/emergency house.
I have a strict load and charge bus separation and the 2 big inverters are connected straight to the LFP. [...]

I'm very happy for you if that works for you!

[Catapault]

Originally Posted by s/v Jedi

I use these INA226 modules. You need one for each cell you have (I have 8 cells, 24V) which is the max. voltage for this method. They cost around $4 each.

You connect them all to the common negative, so the first module reads 3.2V, the second 6.4V etc. You simply subtract the voltage measured at the previous cell to get the individual cell voltages.

This method allows to do this without the need for galvanic isolation and without specialized chips.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Edit: you only use the voltage measurement, not the shunt based current measurement.

Thanks,
I may actually have some of those lying around, will have a play.

Can easily run those off an ESP32 such as https://hatlabs.github.io/sh-esp32/ (I'm biased on that board as I helped design it, and it is specifically designed for marine 12v environments ).

It would not surprise me if I home grow a BMS / overall managment system at some point, but for V1 I'll go off the shelf I think, as I need it running NOW.

[s/v Jedi]

Originally Posted by Catapault

Thanks,
I may actually have some of those lying around, will have a play.

Can easily run those off an ESP32 such as https://hatlabs.github.io/sh-esp32/ (I'm biased on that board as I helped design it, and it is specifically designed for marine 12v environments ).

It would not surprise me if I home grow a BMS / overall managment system at some point, but for V1 I'll go off the shelf I think, as I need it running NOW.

If you have good cells, a simple cell monitor is more than enough to start with. My max. delta V after two years of cruising is 8mV.

Also, if you have a Victron BMV battery monitor then you can use midpoint monitoring to keep an eye on balance. When you get an alarm there, check all cell voltages.

I used 10AWG cell wiring to a fuse box to connect monitors etc. to. This also allows you to charge/discharge individual cells at meaningful amperages.

[goboatingnow]

I’d agree. In circuit cell balancing is a nice to have but can be ignored especially in fractional C situations

You need cell level HVC LVC and temperature monitoring as a minimum. Then potentially add over current protection and charge stop voltage points etc.

[CatNewBee]

Originally Posted by hzcruiser

1.5A balancing current should be way more than ever required.



By the looks of it, RECBMS is likely to use FETs. Or what do you think?

For 1.5A, not for 500A., and easy to override if necessary.

[newhaul]

Originally Posted by CatNewBee

For 1.5A, not for 500A., and easy to override if necessary.

1.5a is what I have on my Daly 200 BMS and that's. 006C for my 250ah bank . So about the minimum for top balancing my bank and barely enough for a 500ah bank

[hzcruiser]

Originally Posted by CatNewBee

For 1.5A, not for 500A., and easy to override if necessary.

Not sure what you mean... "For 1.5A" ?

[hzcruiser]

Originally Posted by newhaul

1.5a is what I have on my Daly 200 BMS and that's. 006C for my 250ah bank . So about the minimum for top balancing my bank and barely enough for a 500ah bank

Did you measure the balancing currents or how do you come up with 1.5A being the minimum?
As Jedi has mentioned, balancing should rarely happen anyway and if a cell is a few mV away one would guess the balancing current to be less than 500 mA.

[hzcruiser]

Originally Posted by s/v Jedi

If you have good cells, a simple cell monitor is more than enough to start with. My max. delta V after two years of cruising is 8mV.

Also, if you have a Victron BMV battery monitor then you can use midpoint monitoring to keep an eye on balance. When you get an alarm there, check all cell voltages.

I used 10AWG cell wiring to a fuse box to connect monitors etc. to. This also allows you to charge/discharge individual cells at meaningful amperages.

That's some nice installation!

[newhaul]

Originally Posted by hzcruiser

Did you measure the balancing currents or how do you come up with 1.5A being the minimum?
As Jedi has mentioned, balancing should rarely happen anyway and if a cell is a few mV away one would guess the balancing current to be less than 500 mA.

It's a simple matter of percentages. I don't want to spend hours balancing on an annual basis when I do my capacity test. If I ever need to balance.

[wholybee]

Originally Posted by CatNewBee

...

- any BMS with cell modules
- any BMS with built in FET transistors that switch the power
- any BMS with preset values that cannot be programmed.

There are not many left after this.

I am not in the market for a new BMS, so maybe there are some good new ones around.

I think people dismiss FETs too quickly. One of the properties of FETs is that they are very fast. In a well designed circuit, a FET can be subjected to many times it's max ratings, and be switched off before any damage occurs. I have subjected my Overkill Solar BMS to a direct short (1000A?) and the FETs protected it and still work fine. In most applications, FETS have/are replacing relays, and are far more reliable. In my lifetime, I have replaced a whole lot more failed relays than FETs. A failed relay might involve some arcing, voltage spikes etc. that could damage sensitive equipment.

A FET BMS is also a much simpler install, and arguably easier to troubleshoot when something goes wrong. It's closer to a "drop in" install vs a significant system change with separate charge/load busses etc.

The most recent failed relay I replaced was a Lithium install using a BMS with cell modules. What a POS. I totally agree with that one.

Whether or not you use FETs or Relays, you need to have a plan for failure if you go far from modern society. Carrying a spare FET BMS isn't that expensive, and much cheaper initially than an expensive REC BMS with spare relays. And if you are really cautious you would have a spare REC BMS as well.

Just my humble opinion.

[hzcruiser]

Originally Posted by newhaul

It's a simple matter of percentages. I don't want to spend hours balancing on an annual basis when I do my capacity test. If I ever need to balance.

Ahhh, here we go, you want to balance once a year only.... well that's really apples and oranges.