BMS24T lithium battery management system

jonr

This is about what I would expect to see in a lithium BMS for large cells.   1.2A of balancing.   Apparently about $400.  Any thoughts?

http://www.chargery.com/doc/Chargery_BMS24T_specification_V1.13.pdf

mike95490

Buy a fire extinguisher.

To charge your large cells, you are using solar PV ?  and a MPPT charge controller?  Vehicle Alternator ?  Whatever it is, lets assume it puts out 30A to the batteries.

When the BMS senses the very first cell cell is full, it can only do 2 things:

 a) Balance 1.2 A around the full cell and let the rest charge at 10A, still putting 8.8A into the full cell

 b)Disconnects the MPPT charger from the battery bank and slowly balance all the cells with 1.2A,  till it reconnects the MPPT to the battery. 

However, a MPPT controller receives it CPU power from the battery it is supposed to be charging and disconnecting the battery while solar is connected is a No-No.

But first you have to snake a bunch of wires around the batteries to connect each one to the BMS. 

Do you install a fuse on each wire ?  Why not ?

I want people to THINK about what is supposed to happen and get good answers before you purchase gear

jonr

If good balance is maintained, the voltage limited charger will stop charging before any cell reaches over-voltage.   So no need for a) or b).   But under failure conditions b) could happen (and a fuse on a lead acid charger link could blow too).  Perhaps the BMS24T's charger disconnect output should be wired to an alarm  (better than no BMS).  Or used to otherwise signal the charger to stop (best solution that is used if you use their charger).  Or it could power a relay or SSR to disconnect the MPPT solar charger *input* (simple and effective solution).

So not relevant to the BMS24T, but do good MPPT chargers actually die or start fires when batteries are disconnected while charging?  I have a bunch of non-solar chargers, power supplies and DC-DC converters that aren't bothered by such things.

Dave Angelini

At Shenzhen, 518054, China. Tel: 86 (0)755 26436165, fax: 86 (0) 755 26412865

Just never park the  electric car in the garage and the folks at the above will be there to help.

You are not talking about using this with a home solar battery based system right?

karrak

jonr said:

Or used to otherwise signal the charger to stop (best solution that is used if you use their charger). 

Lots of MPPT chargers and inverters on the market today can be stopped via an external signal.

Only issue I have with the Chargery unit is there doesn't seem to be any way to be able to monitor your battery remotely via computer/phone or the internet.

Simon

mike95490

karrak said:Lots of MPPT chargers and inverters on the market today can be stopped via an external signal.

Other than the Midnight Classic, what other chargers have a shutdown connection ?

 

Dave Angelini

My schneider mppt-80s and 60s all shut down if the Lion battery is overcharging. The new outback 100A will also. 
You can also manually shut down the charger from SCP, or Combox. It is a nice slow shut-down and start-up. Much better than banging the in/out breakers.

Dave Angelini

I do not use the Emergency Power Off on the XW for shutting down outside for fire people. It also shuts down the mppts & inverter.
Outback calls it something different but it does the same thing. A few clients have needed this to get a certificate of occupancy.

jonr

Based on another discussion, it looks like @mcgivor uses a similar model (perhaps BMS16). No fires?

Dave Angelini

It is all balance of requirements. Electronics and their failure modes need to be addressed. A fairly non-smart lead acid battery just does not have that extra layer of failure that a lithium battery and its electronics have. If that is not a problem then it is addressed.

For someone offgrid who does not want to lose power ever, they will need a second independant battery system or be able to get one in a reasonable amount of time. Like going to Costco for an emergency bank of golf cart batteries which I have done for a few clients near me.

My point is adding electronics to a battery is an extra source of failure that was not there before. Fire for any type of batteries can happen. It is pretty rare with a reasonable amount design skill and maintenance. You need to watch a lithium battery a bit more than once a month like a flooded😉

bevans

Who can comment on the LFP banks with integrated BMSs like the Discover and Simpliphi products? 

Would you say that kind of setup presents the same kind of “source of error” concerns we’d get by introducing a BMS to a lithium bank as an add on? 

The banks with integrated BMSs are advertised as a plug, play and forget storage solution, but would it really be that hands off?

Dave Angelini

It is hands off until there is a failure in the bms or battery. With multiple battery and bms you reduce the chance of losing power.

Some folks do not mind losing power but many like the peace of mind of a second system completely backed up to a second or third inverter/charger.

Your chevy volt battery could be made that way with multiple BMS controlling sections of the volt battery to get a second or 3rd battery system.

bevans

Thanks Dave. How are multiple battery systems typically set up? For instance, if I used the Discover battery and also the Volts. Sounds like this necessarily requires another inverter, or can I just have one of my Classics charging the Discover and the other charging the Volts? 

I’m still trying to gauge how safe and hands off I can make the Volt batteries I found these BMSs made specifically for the LG-produced Volt batteries for each of the 8 batteries I have: https://www.ebay.com/itm/BMS-for-48v-Chevy-VOLT-battery-w-LCD-display-capacity-voltage-w-cell-balancing/183400034288?hash=item2ab37e6ff0:g:9hYAAOSwBrBbgsJB  ). Practically, I need a energy storage system that I can walk away from for 2-3 weeks (or even months) while traveling for work. If my Volt batteries all have BMSs and my Classics are programmed for emergency shutdown, what other risks do I face with this setup? Are there additional system design considerations I can include to make these set it and forget it, or is that just not going to happen?


Ps - just checked 12 cells in each of the 8 Volt batteries today and they are all within one hundredth of a Volt of each other. All 96 cells are either 3.78 or 3.79v. 

mcgivor

There is no practical way to have two different chemistries, even within their sub group, in a single system because the voltages are different, they would have to be separated. Sharing the load on the AC side is possible with the use of an auto transfer switch which is what I do with LFP and LA, with a programed invert block to allow the LA to take over loads in the morning because they get sun first. There could be more sophisticated ways of doing such an integration, but I'm not sure it's the best choice not being on site, too much to potentially go wrong.

With lithium cells you need to measure in thousands of a volt, if you don't have an accurate meter with such resolution you will need one, there is a big difference in the thousands of a volt, for the most part my cell are < 20 mV apart, the accuracy of the meter has to be taken into consideration, even with two identical Fluke 179's there is a couple of milivolts difference. 

The BMS linked is not something I would recommend, it is an analog device, no control of charge or discharge current, is of unknown origin without a warranty at 3 times the cost of one which dose all the above and more,  is digital, from a company that  backs up their equipment with a warranty.

mike95490

Unless your BMS is a truly "Engineered" product, it's likely a hacked together bundle of parts and is more prone to failure than the battery.  And when the BMS fails, it takes out the battery.

bevans

Thank you both for the continued feedback. Mcgivor, I admire what you’re doing in the AC side to share the load, and respect that’s beyond what I’m capable of now. 

I’ll get a more accurate meter, and scrap the analog BMS.