Advice on BMS & Battery Questions

[rbanic]

Hi,

I have been tasked with research on building a battery and re-deploying a solar system utilized by an animal shelter in my country. They have no electricity nor water and they use a generator to power the water pump. They spend over 60 EUR per month on fuel. They already have 8 solar panels, 4 mono and 4 poly, I only know the specs of one type and it is Canada Solar CS6P-235P. They also have a Victron BlueSolar 12/24V 30A MPPT and a generic 3kW 24V inverter.

My colleague who volunteers there has asked me and another engineer from the company we work at to give stuff a look and try to come up with a list of what needs to be bought. We're also going to do the assembly. I feel fairly comfortable with electronics and know the safety rules (I finished 4 years of electronics in high-school) and the other colleague is an EE, but we never worked with solar nor LiFePO4 before.

We decided on a 8S pack of Grade B 102Ah cells from Luyuan (because of the cost, we have a spending limit of 650 EUR and even then 100 EUR comes out of donations from our colleagues, and the shelter will try to collect more donations. They are a no-kill shelter so they don't get as much money as the other shelters from the country (Croatia)). We are deciding on a BMS right now and this is where the first confusion comes in. I'm looking at both Daly Smart BMS (https://www.aliexpress.com/item/1005002897035148.html) and JBD (https://www.aliexpress.com/item/1005002684884280.html). Now Daly looks more "professional" but from what I understand is that JBD is actually also quite good? We also looked at the Daly + active balancing but from skimming the forum I found that doesn't seem that important?

Last question for now would be, how does it actually work if the 8S pack is detected as a 24V pack but the nominal is 25.6V, does that mean it won't charge over 24 or? I'm a bit confused here sorry ?.

Kindest regards,
Roberto Banić

 

[Rocketman]

I used a JDB - renamed here as “Overkill”. It has been working fine for me 12v system - I do like that I can adjust to settings to what I want on the app.

There is a high-end bms manufacturer in Croatia - Rec-Bms. Their bms usually costs as much as your budget - I would see if they will do a donation.

The bms will have settings around high cutoff 29v - cell 3.625. You should set the SCC (solar charge controller) to about 28.4v. That way you never overcharge the batteries.

You also need to have a low power disconnect- so if the battery gets too low the loads stop. Make sure the inverter’s low power disconnect is at a high enough level - it won’t damage the cells.

(In my opinion) - you do not want to rely on the bms cutoff’s - everything should be designed to run and stop before the bms has to enforce limits.

You should have a battery monitor (I like Victron BMV712 or Smartshunt) - but they are expensive- there are cheaper shunt based monitors. With this you know how full or empty your batteries are.

Also, you need a battery charger- so you can start the generator and recharge the batteries when the solar is poor. Be sure and design in a good transfer switch so the generator power and the inverter power don’t run at the same time. (If you had the budget - I would recommend a Victron Multiplus for the inverter/charger it has a built in transfer switch).

Good Luck

 

[rbanic]

Hi, thank you.

REC-BMS seems to be a Slovenian manufacturer so not Croatian so I don't think much luck there.

I didn't know I could set a different cutoff on the BlueSolar unit, I didn't even know it was configurable, that needs to be looked into then. This is the exact unit.


The low power disconnect do you have a recommendation for a cheaper one, because with the current total of 664 USD for Batteries+BMS+Some solar wires and connectors we are pushing the limit already. Is it that bad to rely on the BMS limits?

We were also going to go and use the Daly battery monitor that can be integrated into the BMS.

The battery charger is planned but won't be used for now as it is beyond the budget. We are going to use an appropriate DPDT switch to transfer the AC source between the inverter and the genny. We won't be charging the batteries with it because with the usage projection we have 2.4kWh and they might be using a 1000W kettle over the day for 2-3 coffees (5 min work time each time), so they won't be draining more than 250Wh every day during "work hours" and overnight they'll be relying on 4-5 lights at a time max at 9W each and they won't be on all the time either. So the simplest solution for now is if the batteries are fully down is to use the genny until the next sunny day and until we get more dontains for a charger.

Thanks for all the info

 

[curiouscarbon]

Hello! Cool project.

I studied some computer science and now the past few years been studying solar mainly via leads on this forum ?

Based on a number of threads created by people operating a Daly BMS and odd problems they had, I decided against including it in any of the projects I am involved in.

The JBD BMS (some call it overkill BMS because a US based company "overkill solar" sells tested JBD BMS.

I have built a 12V (4cell) 100Ah pack with that BMS and it has operated reliably since mid-2020.

For solar charger, I too use victron bluesolar MPPT device. The "smartsolar" ones have bluetooth built in, but the "bluesolar" ones need a plug in bluetooth adapter (this convention still kind of confuses me)

Connecting a 300 watt or even two 300W solar panels to the bluesolar and to the JBD BMS 100Ah 12V DIY pack worked reliably like a charm. It was able to run a hair dryer for a few minutes easily with no errors, but normal use has been much less watts load.

Be sure to put a fuse on the positive battery terminal ??️

 

[curiouscarbon]

to change the settings on the bluesolar charger device, an adapter to enable bluetooth is needed. its called ve.direct plug to access data and settings. there is a phone application called "victronconnect" that allows easy changing of the charger voltage settings etc

this is the (overpriced) bluetooth adaptor https://www.amazon.com/Victron-Energy-ASS030536010-VE-Direct-Bluetooth/dp/B01CGFF8Q2/

another option is to connect the bluesolar to computer over usb with this other adapter : https://www.amazon.com/Victron-Energy-VE-Direct-USB-Cable/dp/B01LZ6WTLW/

the victronconnect software exists on desktop too.

hope this helps somewhat and good luck!

 

[curiouscarbon]

oh, one more fun fact. in the victronconnect software on phone, it is possible to play around with the settings of any victron device in a virtual playground environment. on the left side of the app, there's an option titled "demo library" and then can select "solar chargers" and mess around with the settings as if you were connected to a real device. handy for exploring at leisure with no worry of damaging anything

 

[rbanic]

Hm if it is so I might go for the JBD, it ends up being cheaper anyways. Fuse will be put of course .

Thank you for the links, this is stupid expensive what the hell?! For some FTDI chip with a proprietary pinout probably... The info definitely helps.

And regarding the virtual environment thanks, that will for sure prove to be useful.

 

[rbanic]

I was hoping there's be some chinese knockoff cables but no cigar.

 

[curiouscarbon]

this is stupid expensive what the hell?! For some FTDI chip with a proprietary pinout probably...

completely agree! really silly for a tiny chip and short cable.

thankfully there is some documentation about the interface. some have even made DIY adapter but i have no experience with that.

Victron VE.Direct Protocol (Serial Data)

Victron sells a number of devices that have a “VE.Direct” port that is actually a configurable port that is by default a UART serial data port. This document generally describes the electrical and data format to use to properly interpret the...

diysolarforum.com

Victron Bluesolar/Smartsolar MPPT VE.Direct Protocol

Victron Bluesolar and Smartsolar communication protocol documentation. How to communicate with microcontroller over UART serial data connection.

diysolarforum.com

basically it's UART

i have had success reading it over UART with a microcontroller, but never tried writing parameters.

 

[Goboatingnow]

completely agree! really silly for a tiny chip and short cable.

thankfully there is some documentation about the interface. some have even made DIY adapter but i have no experience with that.

View attachment 113265

Victron VE.Direct Protocol (Serial Data)

Victron sells a number of devices that have a “VE.Direct” port that is actually a configurable port that is by default a UART serial data port. This document generally describes the electrical and data format to use to properly interpret the...

diysolarforum.com

Victron Bluesolar/Smartsolar MPPT VE.Direct Protocol

Victron Bluesolar and Smartsolar communication protocol documentation. How to communicate with microcontroller over UART serial data connection.

diysolarforum.com

basically it's UART

i have had success reading it over UART with a microcontroller, but never tried writing parameters.

The write back is described in the Victron hex protocol. The read is in plain ascii

 

[Goboatingnow]

(In my opinion) - you do not want to rely on the bms cutoff’s - everything should be designed to run and stop before the bms has to enforce limits.

This is key safety takeaway. It’s something that’s seems lost on many people. A bms disconnect should be setup to be a critical safety event. Normal cut of points should not trigger bms intervention

 

[Goboatingnow]

Have you considered some Ardunio bms projects.

 

[rbanic]

This is key safety takeaway. It’s something that’s seems lost on many people. A bms disconnect should be setup to be a critical safety event. Normal cut of points should not trigger bms intervention

Ok so then we're going to for sure put a fuse to limit the max current to whatever the BMS is rated at -10A I guess? And the low voltage cut off will be at whatever it needs to be separate from the BMS, hope that thing doesn't cost too much.

Have you considered some Ardunio bms projects.

No since it's probably easier time wise and skill wise, and less of a screwup chance to just buy something prebuilt. The battery supplier (Luyuan) can sell us the JBD for around 80 EUR I think for a 150amp unit.

 

[Goboatingnow]

Ok so then we're going to for sure put a fuse to limit the max current to whatever the BMS is rated at -10A I guess? And the low voltage cut off will be at whatever it needs to be separate from the BMS, hope that thing doesn't cost too much.


No since it's probably easier time wise and skill wise, and less of a screwup chance to just buy something prebuilt. The battery supplier (Luyuan) can sell us the JBD for around 80 EUR I think for a 150amp unit.

I’d thread carefully Chinese BMS have an annoying habit of dying

Also fuses won’t protect BMSes. They protect wires

 

[rbanic]

What would we use to enforce the "upper limit" of current draw then, without relying on the BMS cutoff? The high voltage disconnect will be done by the BlueSolar as mentioned already.

 

[Goboatingnow]

What would we use to enforce the "upper limit" of current draw then, without relying on the BMS cutoff? The high voltage disconnect will be done by the BlueSolar as mentioned already.

I don’t understand what you mean by the blue Solar disconnect. This is not a battery protect feature.

Your bms dhoujd have overcurrent detection and protection.

 

[rbanic]

@Rocketman said "You should set the SCC (solar charge controller) to about 28.4v" won't that prevent overcharging? As well as the BSM protecting overcharging and overcurrent. I got a bit confused when you said "A bms disconnect should be setup to be a critical safety event" by that you mean just the low voltage disconnect or some other disconnect too?

 

[curiouscarbon]

High Voltage Disconnect (Any Cell)
Low Voltage Disconnect (Any Cell)
High Temperature Disconnect
Low Temperature Disconnect
High Current Disconnect

All five of these features are essential to safe operation imo, ideal to have at least these.

JBD battery management devices generally have all five. extra joy is being able to easily reprogram the numbers used for each protection.

some Battery Management Systems have all five protections, but cannot be programmed

for myself, i will only put BMS into service that have all five protections and can be reprogrammed, because it feels like the minimum level of safety tolerable in my case

some JBD BMS are not programmable from what i've read, so if getting one, maybe check with seller that it is "smart" ie able to be programmed

cheers!

 

[curiouscarbon]

BMS on this forum often refers to a specific dedicated safety device, often using either solid state MOSFET or physical relay as safety on/off switch. It's only job is to disconnect the battery cells if it senses danger in the form of too high or low voltage or temperature or too high amps.

However, to complicate things, it can also be used to refer to any and all devices that are configured for safe operation.

Typically on this forum, the charger is considered a separate device from the BMS, even though the charger's appropriate settings do contribute to safe operation.

 

[Goboatingnow]

A lithium battery must be monitored at cell level not battery level. Hence charge sources like mppt controllers can not be safety used without bms cell level monitoring nor can they be set to protect lithium batteries.

As was said every bms shoujd implement the 5 safety critical disconnects at a cell level monitoring . Anything after that are bonus features