Lithiumind™

Simple, 1-board Battery Management System (BMS) for standard Li-Ion, LifePO4 and LiPo cells

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Description

This Battery Management System provides basic BMS functionality for small batteries in cost sensitive consumer products, such as e-bikes and e-motorcycles.

Highlights

• For small battery packs: between 8 and 24 cells in series
• Standard cobalt, LiPo and LiFePO4
• Centralized topology: a single board has n+1 wires ("spaghetti") going to n cells.
• "Bullet proof": not damaged by:
  • Miswiring, in any combination
  • Break in power wires, even under load
  • Misplugging
  • Thermocouple short to cell
• Simple analog technology
• Significantly lower cost than a sophisticated BMS
• Significantly higher performance than other simple BMSs and Chinese protectors
• Self powered (from battery)
• Potted PCB assembly

Functions

• Battery protection:
  • Under and over cell voltage limit, field adjustable
  • Low voltage reserve, field adjustable
  • Under and over temperature limit
  • Over current limit
• Battery enhancement:
  • Dissipative balance (at the 100 % SOC end), field adjustable
• Battery monitor:
  • 50 A current sensor (expandable)
  • Fuel gauge (SOC)
• Control:
  • Charger shut-off
  • Motor driver shut-off, including interlock when still plugged in the wall
  • Throttle back-off when in reserve

Display

• LED display:
  • Power, status
  • Individual LEDs for each balance load available as special order
• Text display (optional):
  • Serial port for laptop or LCD display (not included)
  • Pack voltage, current, SOC; cell min and max voltages; status, etc.
  • On board supply for LCD display available as special order

Limitations

• This is not a sophisticated, digital BMS: it cannot report individual cell voltages and temperatures
• This is not a "protector": does not include a power switch to interrupt the battery current
• It is not possible to stack-up multiple BMS units to handle more cells in series

Adjustments

The BMS has 4 screwdriver adjustments:

• Maximum cell voltage, above which it shuts off the charger
• Balance cell voltage, above which it turns on a cell's balancing load
• Reserve cell voltage, below which it cuts back available throttle range
• Minimum cell voltage, below which it turns of the motor driver

The range of these adjustments is appropriate for various Lithium cell chemistries.

Wiring

Every application is different, so we can only provide one example here.

Example for an e-bike with a 12 V DC-DC converter and a motor controller that requires a contactor.

The BMS has a 2-piece terminal block for safe connection to the cells:

1. Remove the terminal block's plug from the BMS
2. Wire cells to plug
3. Measure the voltages on plug to confirm proper wiring
4. Reconnect the plug to the BMS

While it is possible to reduce the height of the product (to about 0.5") by clipping off the terminal block plug and soldering wires directly to the PCB, this is a dangerous practice and will void any warranty.

Specifications

These are simplified specifications.
Detailed specifications are in the manual

Cell voltages

Battery current

By building your own current divider, you can extend the current sensing range, such as to 100 A continuous, 250 A peak.

Temperature sensor

The user must provide a leaded thermistor, to sense the battery temperature.

Symbol	Item	Conditions	Min	Nom	Max	Units
Rtherm	Resistance			10		kΩ @ 25 °C
B25/50	Curve	NTC	3380K			-
Toltherm	Tolerance				3	%

While the BMS will operate if a 10 kΩ resistor is substituted for the thermistor, it will not protect the battery from over-temperature.

Monitor outputs

Current output is positive both while charging and discharging.

Serial port

Control outputs

Operating conditions

Mechanical

Programming

• The number of cells is programmed with a soldering iron, by making a solder bridge between adjacent pads corresponding to the number of cells in series
• The cell voltage thresholds are adjusted with a small screwdriver, while measuring the voltage of a test point with a voltmeter

Operation

Function of adjustments

BMS operation based on these settings:

• The charger is on until the voltage of the most charged cell reaches the MAX voltage; it remains off until all cells are below the BALANCE voltage, at which point it comes back on
• A cell's balance load is on whenever its voltage is above the BALANCE voltage
• The Reserve output is on as long as the voltage of the least charged cell is below the RESERVE voltage
• The motor is on until the voltage of the least charged cell drops below the MIN voltage; it remains off until all cells are above the RESERVE voltage, at which point it comes back on

Ordering

Not yet in production

Production quantities expected in July.
Please pre-order samples through a reseller.

Small orders through resellers

To order a small quantity of Lithiumind BMSs, 24 cells (can be used with any number of cells up to 24), please contact one of our resellers.

(These resellers have placed orders, but have no stock yet: Alliance)

Model	Number of cells	Manufacturer Suggested Retail Price [USD]
7SB0024B	8~24	-

For systems bought through a reseller, tech support is provided by the reseller, while Elithion offers paid tech support.

Large and direct orders

To order a large quantity of Lithiumind BMS directly from Elithion, for a specific number of cells in series (anywhere between 8 and 24 cells), please note the prices listed below and then please contact us

Price each: ($ 130 + $ 4 / cell) + $ 1000 / number of units
Price per order: ($ 130 + $ 4 / cell) * number of units + $ 1000

For example:

Model	Number of cells	Price each [USD]
		1 ea.	3 ea.	10 ea.	30 ea.	100 ea.	300 ea.	1000 ea.	3000 ea.
7SB0008B	8	1172	505	272	205	182	175	173	172
7SB0012B	12	1188	531	288	221	198	191	189	188
7SB0016B	16	1204	537	304	237	214	207	205	204
7SB0020B	20	1220	553	320	253	230	223	221	220
7SB0024B	24	1236	569	336	269	246	239	237	236

Once production starts, typical delivery times are expected to be 30 days from date of order for up to 100 units, 60 days for more than 100 units.

Elithion provides free tech support to direct clients.