Battery Management System

[Lollandster]

The FETs are for the LVC. It has to be able to provide up to 100A through a circuit that can be disconnected and if you don't want to use a big mechanical relay then transistors are the weapon of choice.

The 16 shunts are used to discharge cells that are high. As I said earlier the charger can't charge single cells, only the whole pack. So if one cell is low it needs to bring the rest of the pack down to charge it. This is very slow indeed.

[Just]

16 shunts are used to discharge cells that are high

Do they just discharge the cells or also charge others with this discharge current?

What is LVC?

[Lollandster]

Just discharging. As I said in my long post, it would need to disconnect the discharging cell from the series to be able to charge another cell and that would require a big FET for every single cell. If you parallel connect two cells that are in series you'll have a short circuit.

[Just]

it would need to disconnect the discharging cell from the series to be able to charge another cell and that would require a big FET for every single cell

Do you know such BMS? Do you know where might it be purchased?

As for the shunts, do they just short between "+" and "-" poles of the cell while discharging it?

Here is another issue:
A couple of days ago I fully charged one of my 10Ah LiFePo4 cells with a single-cell charger. Today I tried to charge it again and was able to add an additional 1Ah. Does it say something? Should the cell be in a bad condition?

[Lollandster]

Try asking on the ES-Forum, they often answer questions like this in seconds.

[Morgen 3Eman]

Hi Folks,

Your conversation has one point in error.  The shunt resistor doesn't actually discharge the cells that reaches full voltage early, it merely bypasses   the charging current around the cell. ( Truthfully, there will probably be some small current drawn from the cell)   The charging voltage is still applied to the cell terminals.  That way, the fully charged cells stay fully charged without receiving excess charge, and those that have not reached full voltage continue to receive charging current.

TTFN,
Dennis

[Lollandster]

ok, thank you for clearifying that Dennis. I knew I couldn't have got it all right.

[Just]

Dennis, you describe a perfect BMS, which I'm looking for. Using such BMS the battery should get balanced on a single charge. Could you let me know where I can purchase such BMS? I need one, which support up to 100Amps in peaks.

Lollandster described the BMS, which are many in the market, but they not so good. In fact that many BMS sellers/producers recommend to perform up 10 times of the charge-discharge cycles in order to get the battery balanced. This recommendation meats the BMS, which Lollandster described in its posts.

So, where to purchase the BMS, which make the battery balanced on a single charge?

[Morgen 3Eman]

Hi Just,

I have no idea where you can buy a BMS, mine came with the battery I bought from GM.  I just know how they work.

Google is your friend, tho.  Gary from GM Canada may be able to supply such a thing.

TTFN,
Dennis

[Just]

Dennis, could you do the following:
1) fully discharge your battery
2) replace one of the discharged cells in the battery with another fully charged cell
3) try to charge the battery

If all the cells in your battery will be fully charged again on a single charge cycle, then your BMS works as you described it. But, if the charger stops just after a few minutes (since one of the cells is already fully charged), then your BMS works as Lollandster described.

So, just try and let as know! It will be a good experiment for you too!   

[Morgen 3Eman]

Hi Just,

I'm a lazy old geezer, and have better things to do.  Sorry, but no, I will not do your bidding.  Do your own homework.

TTFN,
Dennis

[GM Canada]

Hi Just,

I have no idea where you can buy a BMS, mine came with the battery I bought from GM.  I just know how they work.

Google is your friend, tho.  Gary from GM Canada may be able to supply such a thing.

TTFN,
Dennis

http://www.goldenmotor.ca/categories/Parts-and-Accessories/Battery-Parts/

Gary

[Just]

So, as for the BMS, when balancing of the cells is occurring - only when a charger is connected to it or all the time?