Lithium BMS....explain for dummies!!
 

:help: Ok guys....I'm not an engineer. I'm a retired CPA. So....reading plume's of tax law and digesting it is easy for me. But....this electric stuff....it's gotta be really dummied down for me to grasp it. :shock::shock:

So....can we have some post that would 'splain exactly what BMS is and does? I know it stands for "Battery Management System" so from that....and stuff that I've read, a BMS is NOT the battery charger. Right? The BMS somehow monitors each "cell" of a lithium pack so that each cell will not overcharge and go KA-Boom?

Anyway.....if you could offer some "BMS Post for Dummies" it would help!! :thumbup::mrgreen:

Re: Lithium BMS....explain for dummies!!
 

We will if you do the same for the new tax laws :lhmo::lhmo::lhmo:

Re: Lithium BMS....explain for dummies!!
 

:shock::shock::roll: Sure.....the short explanation is "Your taxes will likely go down next year.....and then not long after.....back up." :lhmo::lhmo:

I haven't read the 150 page (as most who voted for it) of the law. And remember.....Congress pass's the law, then in the law they direct Treasury to issue the detailed rules and regulations that follow the law....and what is known as "Congress's intent" of the law.

The devil is in the details.....and we likely won't see all the details for another 6 to 8 months at the earliest. :cry::cry:

Re: Lithium BMS....explain for dummies!!
 

Battery management system monitors & protects each cell from being drawn too low (by disabling cart), and protects against overcharge (by disabling charger). That's the short story.

Re: Lithium BMS....explain for dummies!!
 

Ok.....So how is the BMS "wired" into a charging system? The charger must first "plug into" the BMS, and then the BMS manages each cell's individual charge? So, if one cell is at 100% and another at 98%, the charger keeps running until the 98% cell is charged....and the other cells that were at 100% no longer receive a charge?

(The discharge question will follow :shock: )

Re: Lithium BMS....explain for dummies!!
 

looking for the Sergio or JohnnieB answer

Re: Lithium BMS....explain for dummies!!
 

The thing to remember is that BMS represents a segment or category of products and not a specific implementation standard.

Some BMS systems will "shunt" a very small amount of current around cells that reach their full capacity first, but typically they just send a signal to shut down the entire charging system when any single cell reaches its maximum voltage.

If the BMS has a cell balancing feature, that typically works when the charger is OFF, it can be as simple as using a resistor load to discharge the higher cells or as complex as a parallel buss that connects high and low cells in order to simultaneously lower the high cell and raise the lower cell.

BMS systems also monitor individual cell voltages and will send a signal to shutdown the Controller if any gets too low.

Some BMS systems also provide a "Limp Mode" where low cells can be partially by-passed in order to allow for a reduced output to get the cart to a safer place.

Some systems use individual chargers for each cell which removes all of the complexity of cell balancing while allowing the easy introduction or replacement of cells regardless of their SOC.

There are lots of other possible features like WiFi interface, simplified CAN bus communication, etc that individual BMS devices may have.

Re: Lithium BMS....explain for dummies!!
 

Dave,
I don't think you are going to get one answer on this as it depends on the charger and controller capabilities as to how it is wired.

From what I've been able to discern, the charger will supply current, until the BMS tells the charger to stop. The stop signal will be determined by the charger.

The BMS will actively monitor each series cell until it can't keep the highest voltage cell under a configured voltage maximum(based on battery type, not all lithiums are the same). That seems to be done by different methods. The BMS can remove voltage through resistance or try to divert it to a cell with lower voltage. Diverting current would be preferred, since you aren't just wasting energy as heat.

I am watching with interests in the answers and hope mine is not totally off base. I want to take the plunge into lithiums before next spring. I think we need a sticky thread with BMS solutions that have been used.

Re: Lithium BMS....explain for dummies!!
 

As described, BMS = battery management system. It is as Sergio pointed out the interface between the charger and the battery cells. Lithium battery cells of 3.7 or 3.4v comprise the battery pack.

These cells can be soft bag cells or hard case. Either hard case or soft the chemistry is the same and it has very specific needs when it comes to charging and discharging. The capacity of the cell can vary by design and construction. This why you will see 60,80, 100, even 200 ah cells of the same voltage.

The charger must be compatible with the pack in terms of volts and amps output, The BMS will do the cell monitoring and protecting during charge and discharge (aka use). Protection is not limited to input/output amperage & voltage, temperature is also closely monitored. Newer LifePo4 battery composition is more stable than early Lithium-ion chemistry. It should be noted that Life batteries will cycle nearly @ times as many charge cycles as regular old lithium without the fire danger associated with the older technology.

P.S.
I would hate to be a CPA this year.

Re: Lithium BMS....explain for dummies!!
 

Yeah....Me-2!! At least, not a "practicing" tax guy!!! My disease "kicked" me out of my firm in my late 40's. I was mad for about 3 years because I loved what I did and it just wasn't a job. I was in practice when the 1986 Tax Reform Act was passed. The '86 act made the knowledge of information much more complex than it previously. Alternative Minimum Tax, Phase outs, Section 179 deductions, and piles of what and when a tax credit could be used. :shock::shock:

Now I can only imagine the phone calls that are coming in asking what could or should I do before the end of 2017? So....it's like tax season.....before the tax season!! Nothing like "going into" the 2018 tax season already tired!! :thumbdown:

Then of course.....there's the "segment" of clients that get surprised for a $300 bill from the CPA for spending an hour or better advising them how to save thousands of dollars before the EOY. :roll::roll:

BTW.....thanks for your responses to my question. It really gives me a better understanding of how this works, and more importantly, what to look for. Additional responses are welcome!!