3.11 Button and Shutdown

The user button starts the BMS and can run a function while the BMS is ON. The BMS can also shut itself down, on a press or on an event you choose. This page helps you choose the button type, assign the press functions and set the shutdown so the system does not switch OFF when you need it.

Applies to

Boards: BMS1820, BMS3610, BCU2002, BMS1601, BMS1810. Each of these boards has a user button input and can shut itself down.

3.11.1 How It Works

User Button Functionality sets how the button input works. With a push button, the BMS keeps itself powered after the press that starts it, and it switches itself off in a shutdown. With Advanced Push Button, three press lengths each run their own function. The BMS asks for one more click before it acts, so an accidental press does nothing (Fig.3.11.1).

Fig.3.11.1: Press and Confirm with the Advanced Push Button

1 Hold and release hold the button for the time of the function you want Short press 1 to 5 s LED: 5 flashes Short Press Function Mid press 5 to 10 s LED: 4 flashes Mid Press Function Long press over 10 s LED: 3 flashes Long Press Function 2 BMS waits the LED keeps flashing while it waits for the click 3 Confirm one more click, shorter than 1 s, within 15 s? Function runs the function assigned to this press Request dropped nothing happens; start again yes no A press shorter than 1 s does nothing. Long press: the LED starts to flash at 10 s, while you still hold the button. Simple Push Button: press twice within one second to shut down. Two Way Switch: no press functions.

On a time axis, each press shows the LED pattern the BMS answers with, and the function runs when the click ends (Fig.3.11.2).

Fig.3.11.2: Advanced Push Button over Time

0 5 10 15 20 Time after the start of the hold (s) Short press: hold 1 to 5 s, LED 5 flashes Button ON OFF LED ON OFF click function runs Mid press: hold 5 to 10 s, LED 4 flashes Button ON OFF LED ON OFF click function runs Long press: hold over 10 s, LED 3 flashes from 10 s on Button ON OFF LED ON OFF click function runs No click within 15 s: the request is dropped no click for 15 s Button ON OFF LED ON OFF request dropped Button ON: pressed. Blue band: the hold time of this press. The click must come within 15 s after the release and be shorter than 1 s. With no request waiting, the LED shows its normal pattern of one flash. What follows the click depends on the assigned function.

3.11.2 Button Types

Table.3.11.1: User Button Functionality Options

Type What it does Use it with
Advanced Push Button Short, mid and long presses run the functions you assign, each after a confirm click (3.11.3). The BMS can shut itself down. A momentary button, when you want to restart, clear errors or shut down by hand.
Simple Push Button Press the button twice within one second: the BMS shuts down. The press functions are not used and the LED shows no pattern. The BMS can shut itself down. A momentary button that only switches the BMS ON and OFF.
Two Way Switch The BMS stays ON while the switch is ON. Setting the switch to OFF acts like a sudden power cut, so the values since the last save can be lost (4.4 Logs and Event History). There are no press functions, and the BMS cannot shut itself down, so Shutdown Trigger has no effect. A two-position switch that stays where you set it.

With Simple Push Button, one press starts the BMS, two presses within one second shut it down, and a single press while it runs does nothing (Fig.3.11.3 and Fig.3.11.4).

Fig.3.11.3: Simple Push Button

User Button Functionality = Simple Push Button 1 Press the BMS is OFF: press the button once BMS starts the BMS is ON and keeps itself powered 2 Press twice? while the BMS runs, two presses within 1 s? Shutdown the BMS saves its values, then switches itself off; a press starts it again Shutdown Trigger also applies Nothing happens the BMS stays ON yes no No press functions Short, Mid and Long Press Function are not used; the LED shows no press pattern The event chosen in Shutdown Trigger also shuts the BMS down (3.11.4). After any shutdown, a press on the button starts the BMS again.

Fig.3.11.4: Simple Push Button over Time

User Button Functionality = Simple Push Button Time press: BMS starts one press: nothing happens two presses within 1 s press: BMS starts Button ON OFF BMS ON OFF Shutdown Shutdown Trigger Shutdown The dashed line is the event chosen in Shutdown Trigger. The BMS saves its values before it goes OFF. Button ON: pressed. Time is not to scale. The LED shows no press pattern with this type.

With Two Way Switch, the switch alone powers the BMS, so the BMS goes OFF as soon as you set the switch to OFF (Fig.3.11.5 and Fig.3.11.6).

Fig.3.11.5: Two Way Switch

User Button Functionality = Two Way Switch 1 Switch ON set the switch to ON BMS ON stays ON while the switch is ON 2 Switch OFF set the switch to OFF BMS OFF the switch cuts the supply; nothing is saved at this moment No press functions the BMS cannot shut itself down, so Shutdown Trigger has no effect Setting the switch to OFF acts like a sudden power cut: the values since the last save can be lost (4.4). The BMS does not keep itself powered in this mode, so a momentary button switches it OFF as soon as you release it.

Fig.3.11.6: Two Way Switch over Time

User Button Functionality = Two Way Switch Time switch ON switch OFF switch ON Switch ON OFF BMS ON OFF the supply is cut Shutdown Trigger no effect, the BMS stays ON The BMS follows the switch. The dashed line is the event chosen in Shutdown Trigger. Time is not to scale. A switch OFF acts like a sudden power cut (4.4).

3.11.3 Press Functions

This section applies to Advanced Push Button only. To run a function:

  1. Hold the button for the time of the function (Table.3.11.2), then release it.
  2. Check the LED. The board LED and the external LED flash the pattern of the press the BMS has recognised.
  3. Click once more, shorter than 1 s, within 15 s. The function runs.

Table.3.11.2: Press Times and LED Patterns

Setting Hold the button LED while the BMS waits
Short Press Function 1 to 5 s 5 flashes, then a pause
Mid Press Function 5 to 10 s 4 flashes, then a pause
Long Press Function over 10 s 3 flashes, then a pause
  • A press shorter than 1 s does nothing when no request is waiting.
  • For a long press the LED starts to flash at 10 s, while you still hold the button.
  • Without a click within 15 s the BMS drops the request and the LED goes back to one flash, its normal pattern.
  • A second press that lasts 1 s or longer does not confirm the request.

Table.3.11.3: Functions You Can Assign to a Press

Function What it does When to use it
No Function Nothing. The LED still shows the pattern, but the click has no effect. For a press you do not use.
Restart System Restarts the BMS. For normal recovery after you have fixed a fault (4.1 Protection and Recovery).
Clear All Errors Clears the trip counts and User Attention Required, after it first forces the power outputs ON for 60 s; it does not clear a CRITICAL event. Only after you have found and fixed the cause, or for the low-cell recovery in 4.3 Storage and Shutdown; read the warning in 4.1 Protection and Recovery first.
Shutdown Board Shuts the BMS down right after the click, also while current flows. To switch the BMS OFF by hand, for example for service or storage. Stop the load first.

Sleep Board is also in the LiMon™ list. It has no function on the current firmware; leave it unassigned.

3.11.4 Shutdown

A shutdown is the BMS switching itself off completely. It comes from the button (Shutdown Board, or the double press of Simple Push Button) or from the event you choose in Shutdown Trigger.

  • What switches OFF: both paths and all outputs, then the BMS electronics. The LEDs go dark, communication stops and LiMon™ loses the connection.
  • What the BMS saves first: its energy values, run time and event log.
  • What stays: the cells stay connected to the board, which now draws only a very small power. The pack still discharges slowly, so do not leave it in this state for a long time (4.3 Storage and Shutdown).
  • How it starts again: only with a press of the user button. Connecting a charger or a supply does not start the BMS, so the button must stay within reach.

Table.3.11.4: Shutdown Trigger Options

Option The BMS shuts down when When to use it
Disable Never by itself. The button can still shut it down. Systems that must stay ON.
Shutdown Timeout No charge or discharge current has flowed for the Shutdown Timeout. Any current of 0.5 A or more restarts the time. Packs that stand unused for long periods, so the BMS does not slowly empty them.
Shipping Mode 10 minutes have passed after you save this option, even if current flows. After the next start the BMS runs as with Disable. Once, before storage or transport. After the first start, set and save the option you want for normal use.
Critical Cell Voltage Any cell stays at or below Shutdown Cell Voltage for a short time and the BMS is not charging. Discharging does not prevent it. To keep an empty pack from being drained further by the BMS itself.
Timeout or Critical Either of the two above, whichever happens first. Unused packs that also need the low-voltage shutdown.
  • Shutdown Timeout: choose it longer than the longest time the system stands idle in normal use. The time starts again at every start of the BMS. Currents below 0.5 A count as no current (3.6 Current Measurement).
  • Shutdown Cell Voltage: take the value from the cell datasheet and set it below U.V. Protection (3.3 Cell Voltage Limits). The discharge path then opens first, and the BMS shuts down only if a cell keeps falling. Do not rely on the default of 3300 mV: it is above the default U.V. Protection of 3050 mV, and a healthy pack of some cell types rests below it.
  • Shipping Mode after Shutdown Timeout: the time already counted carries over, so the BMS can shut down sooner than 10 minutes if the pack has been idle.

Shutdown loop

With Critical Cell Voltage or Timeout or Critical, a pack with a cell below Shutdown Cell Voltage and no charge current shuts down a short time after every start. A press on the button only repeats this, and a charger cannot start the BMS. Connect the charger first, then press the button, so that charge current of 0.5 A or more flows before the BMS shuts down again. Check that your charger starts quickly enough, and keep Shutdown Cell Voltage below U.V. Protection.

3.11.5 Settings

Table.3.11.5: Button and Shutdown Settings (LiMon™ Peripheral tab)

Setting What it does How to choose Unit Range Default
User Button Functionality How the button input works (3.11.2). Match it to the part you have fitted: momentary button or two-position switch. list — Advanced Push Button
Short Press Function Function of a press of 1 to 5 s (3.11.3). The function you use most, because it is the quickest. list — No Function
Mid Press Function Function of a press of 5 to 10 s. A function you use less often. list — No Function
Long Press Function Function of a press over 10 s. A function that should be hard to run. Change the default if the system must not force its outputs ON from the button. list — Clear All Errors
Shutdown Trigger The event that shuts the BMS down (3.11.4). Disable unless the system needs an automatic shutdown and the button stays within reach. list — Disable
Shutdown Timeout Time without current before the shutdown. Longer than the longest normal idle time. Never 0: the BMS would shut down as soon as no current flows. LiMon™ accepts other values, the BMS uses 1…255. hours 1…255 24
Shutdown Cell Voltage Cell voltage for the low-voltage shutdown. From the cell datasheet, below U.V. Protection. mV 0…10000 3300

The LiMon™ reference describes every field of the screen: 7.5 Peripheral Settings.

3.11.6 Checking the Result

  • Press functions: hold the button for each press you have assigned. The LED shows the pattern of Table.3.11.2, and the function runs after the click.
  • Clear All Errors: the LED flashes twice instead of once during the 60 s.
  • Simple Push Button: two presses within one second shut the BMS down; a press on the button starts it again.
  • Two Way Switch: the BMS stays ON after you take your hand away.
  • Shutdown Timeout: Live View shows no current while the time runs. For a test, set 1 hour on the bench and wait with no current flowing.
  • After Shipping Mode: start the BMS with the button, then set Shutdown Trigger to the option you want for normal use and save it.

3.11.7 Common Mistakes

  • Critical Cell Voltage on a pack with no charger at hand: the shutdown loop of 3.11.4. The BMS cannot stay on long enough for you to work on it.
  • Shutdown Cell Voltage left at the default: the BMS can shut down a healthy pack that rests below 3300 mV, as soon as it is not charging.
  • Two Way Switch with a momentary button: in this mode the BMS does not keep itself powered, so it switches OFF as soon as you release the button.
  • Simple Push Button expected to run press functions: this type only shuts down on the double press. Use Advanced Push Button for press functions.
  • No confirm click: the LED flashes and nothing happens. The hold only selects the function; the click runs it.
  • Long Press Function left at its default: a long press and a click force the outputs ON for 60 s. Set it to another function if your users have access to the button.
  • Shutdown Timeout 0: the BMS shuts down right after a start unless current flows.
  • A small load expected to keep the BMS ON: a load below 0.5 A counts as no current, so the time runs out and the load loses power.
  • Automatic shutdown with the button out of reach: a charger or a supply does not start the BMS again. Someone has to press the button.
  • Shipping Mode saved on a system in use: the BMS shuts down after 10 minutes, even under load.