ken via EV wrote:
I'm looking for a bms leafs cells from about 50 - 70 volts .
looking for something way cheaper than lihton or orian . maybe just a
simple board with simple fucntions like beep as an alarm , for hvc or lvc,
don't mind doing a little baby siting or mamnaul interevontion .
Hi Ken,
How "simple" do you have in mind? Do you want a battery MONITORING system
(simply tells you their voltages), or a battery MANAGEMENT system (that actually
does something to correct imbalances)?
The simplest MONITORING system would probably be an optocoupler and LED in
series across each cell. Choose the LED so the voltage drop of the optocoupler
LED plus the indicator LED is your desired over-voltage. For example, if you
want it to be 4v, and the opto LED has a 1.1v drop, then pick a blue or white
LED with a 2.9v drop.
Wire the transistor output side of all the optocouplers in parallel, and connect
them to you "overvoltage" indicator or alarm. When any cell goes over-voltage,
it will activate. Then you have to look at the indicator for each cell to see
which one it was.
For low voltage, it's pretty much the same system, except the optocoupler
outputs are all in series. The dropping LED would be a lower voltage (yellow or
green), plus a series resistor to limit the maximum current. When a cell is
above the threshold, the green LED lights and the opto is on. If any cell drops
below the threshold, its optocoupler turns off, which breaks the series loop,
and activates your low-battery indicator or alarm. Again, you have to look at
the LEDs on each cell to know which one it was.
If you want a battery MANAGEMENT system, that will be more complex. The cheap
ones basically stick a resistive load across the cell when it goes over-voltage.
But this assumes that your charger is "smart" enough to go to a current lower
than the bypass current. And, that the BMS can shut down the charger or
controller to prevent over-and under-voltage events.
--
I look for what needs to be done. After all, that's how the universe
designs itself. -- R. Buckminster Fuller
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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