4.3 Storage and Shutdown

A pack that is not used still loses charge, and a pack that stands too long can end up too low to charge. This page shows what drains an unused pack and how long it can stand, how to prepare it for storage or transport, and how to bring it back into service.

Applies to

Boards: BMS1820, BMS3610, BCU2002, BMS1601, BMS1810.

4.3.1 How It Works

The BMS is either running or shut down; it has no separate sleep mode. What it draws from the pack differs by a factor of thousands between the two states, so the state decides how long the pack can stand.

  • While the BMS runs: the BMS, its slave modules and every constant load draw from the pack all the time, for example contactor coils held by the BMS outputs, a display or a gateway. Enter the measured sum as Self Discharge Power (3.6 Current Measurement). With Balancing Method set to Always, the BMS also balances at rest (3.4 Cell Balancing).
  • U.V. Protection does not stop this drain: it switches off the discharge path only. The BMS keeps running, and the cells keep falling. Only a shutdown stops the drain (3.11 Button and Shutdown).
  • After a shutdown: the board draws only a very small power, and the slave modules drop to their low draw by themselves when the master stops communicating. The own self-discharge of the cells remains; the cell datasheet gives its size.
  • The state of charge: while the BMS is shut down, nothing is counted. At the next start it goes on from the SoC it saved at the shutdown (3.2 Capacity and SoC).

Table.4.3.1: Typical Consumption per Board

Board BMS running BMS shut down
BMS1820 about 1345 mW about 0.05 mW
BMS3610 about 1615 mW about 0.05 mW
BCU2002 about 2400 mW about 1 mW
BMS1601 about 1015 mW about 0.05 mW
BMS1810 about 1015 mW about 0.05 mW
BMS1802, BMS1202 (each slave module) about 300 mW about 0.05 mW

These values are for the board alone. Measure your own system, because the loads add to them. A board on an external supply draws from that supply and not from the cells; slave modules always draw from the cells they monitor.

To estimate how long a pack can stand, divide its charge by the charge it loses per day (4.3.5). A falling cell reaches EMPTY SoC Min. Cell Voltage first and U.V. Protection after it, when you have set them as 3.2 Capacity and SoC advises.

Fig.4.3.1: Charge in a Stored Pack, BMS Running and BMS Shut Down

0 30 60 90 120 150 180 210 240 0 10 20 30 40 50 Storage time (days) Charge in the pack (% of Usable Pack Capacity) EMPTY SoC Min. Cell Voltage U.V. Protection BMS shut down: about 0.05 mW, too small to see at this scale BMS running: 950 mW, about 0.45 Ah per day about 112 days discharge path off, but the BMS keeps drawing its power Calculation example: 16S, 51.2 V, 100 Ah, 50 % at the start. The cells' own self-discharge is not drawn; it adds to both lines. The distance between the two red levels depends on your settings and your cells; it is not to scale.

This page has no settings of its own. Shutdown Trigger and the press functions are set in 3.11 Button and Shutdown, Self Discharge Power in 3.6 Current Measurement.

4.3.2 Preparing for Storage

Store the pack at the state of charge and the temperature that the cell datasheet gives. If it gives none, store the pack about half charged in a cool and dry place. A full pack ages faster, and an empty pack has little charge to lose before its cells are too low.

  1. Charge or discharge the pack to the storage level.
  2. Press Read All Settings, then Export Settings, and keep the file with the documents of the pack (2.1 Managing Settings).
  3. Note the date and, from Live View, the SOC and the cell voltages.
  4. Stop the load and the charger.
  5. Shut the BMS down: a press assigned to Shutdown Board, the double press of Simple Push Button, or Shipping Mode in Shutdown Trigger. No press has Shutdown Board by default, so assign it and save first. With Two Way Switch, set the switch to off. The mechanics are in 3.11 Button and Shutdown.
  6. Check that the LEDs are dark and that LiMon™ has lost the connection.
  7. Disconnect the load and the charger from the pack.

During a long storage, check the pack at the interval that the cell datasheet gives: press the button, note the cell voltages, recharge to the storage level if they have fallen, and shut the BMS down again.

If the BMS must stay ON during storage, for example for remote monitoring, set Shutdown Trigger to Critical Cell Voltage and read the shutdown loop warning in 3.11 Button and Shutdown. The BMS then shuts itself down before it empties the pack.

4.3.3 Transport

Use Shipping Mode for transport. The shutdown comes 10 minutes after you save the option, so you have time to disconnect LiMon™ and close the pack. Prepare the pack as in 4.3.2, then check these points:

  • Power path: both paths are OFF and the main contactor is open, so the output terminals are not connected to the cells. The cells and the wiring before the contactor stay live.
  • Button: place or cover it so that it cannot be pressed by accident during transport, and make sure that the receiver can reach it. A press is the only way to start the BMS.
  • Charger: a charger cannot start the BMS, so the receiver has to press the button first.
  • Two Way Switch: Shipping Mode has no effect with this button type. Set the switch to off and secure it.
  • Documents: send the settings file and your noted values with the pack, and point the receiver to 4.3.4.
  • Transport rules: the state of charge, the packaging and the labels for lithium batteries are set by the transport regulations. Ask your carrier; the BMS settings do not replace these rules.

4.3.4 Returning to Service

  1. Check that the load and the charger are OFF. The BMS takes the zero of the current sensor at every start (3.6 Current Measurement).
  2. Press the button. The paths can switch ON right after the start, so treat the output terminals as live.
  3. Connect LiMon™ and read Live View: the expected cell count and no new event.
  4. Compare the cell voltages with your notes. A small and even fall is normal. A cell that has fallen much more than the others points to a weak cell or a leak; find the cause before you charge.
  5. If you used Shipping Mode, set Shutdown Trigger to the option for normal use and save it.
  6. Connect the charger and charge to FULL. The storage time was not counted, so FULL is what corrects the SoC (3.2 Capacity and SoC).
  7. Connect the load.

A pack stored too long can show one or more of these:

  • The BMS does not start: a pack below the supply range of the board cannot start the BMS from its own cells. The ranges are 12 to 80 V on BMS1820 and BMS3610, 15 to 80 V on BMS1810, and 12 V to the battery voltage on BMS1601. BCU2002 has no cells of its own and needs an external supply of 18 to 80 V. A board that accepts an external supply can start from it; the supply pins are on the pinout pages of BCU2002, BMS1601 and BMS1810. On BMS1820 (hardware v2.3) and BMS3610 (hardware v1.1) with the 12 V option, the external 12 V goes to connector P5 of the schematic: pin 6 is the input and pin 3 is ground. This input and the battery supply are alternatives: use one of them, never both at the same time.
  • A charger does not start the BMS: press the button. With Critical Cell Voltage or Timeout or Critical, connect the charger first, as in the shutdown loop warning of 3.11 Button and Shutdown.
  • Cell Under Voltage Protection: the discharge path is OFF and the charge path stays ON. With one main contactor the contactor stays open, so the charger cannot reach the pack (3.8 Power Path).
  • User Attention Required: a protection has used up its Error Recovery Attempts, or a CRITICAL fault is present, for example Max. Cell Delta Voltage when the cells have drifted apart. Read the events first (4.1 Protection and Recovery); case 3 below covers the cell delta.
  • A CAN charger gives no current: with Stop Charger on Error on, the BMS asks for zero current while a protection is active. Turn the option off for the recovery and ON again afterwards.

To recover the pack: read the lowest cell voltage first. If it is below the minimum voltage in the cell datasheet, do not charge the pack; ask the cell manufacturer. Then disconnect the load and keep it disconnected, read the events, and follow the case that fits your pack.

Case 1: separate charge contactor, or BMS1601. The charge path stays ON under U.V. Protection, so Clear All Errors is not needed. Connect the charger and charge with a steady current, within what the cell datasheet allows for low cells. Do not run Clear All Errors here: it starts a precharge with the charger running, which can end in Pre-Charge Fault (3.9 Precharge).

Case 2: one main contactor. The main contactor needs both paths ON, so the charger cannot reach the pack. Before you start, check these points:

Then run the recovery:

  1. Connect the charger and set a steady charge current of several amperes, within what the cell datasheet allows for low cells.
  2. Run Clear All Errors from the button. The BMS forces its outputs ON for 60 s, so the main contactor closes and the charger can start.
  3. Check that the charge current flows within these 60 s. Once the BMS sees the charge, it does not open the path again. If no current has flowed, run Clear All Errors once more.

Not tried on a board yet

That the path stays closed after the 60 s comes from the description of the firmware owner; it has not been tried on a board yet. Watch the current when the 60 s end.

Case 3: a CRITICAL fault, such as Max. Cell Delta Voltage. Clear All Errors does not clear it, and the fault comes back after a restart while the cells stay apart. Set Imbalanced Max. Cell Delta above the present Vcell Delta for the recovery, save it, and press Restart System with no load and no charger current. Then charge as in case 1 or case 2, and set the value back when the cells are together again. If you do not want to do this, send the pack for service.

While the pack charges:

  1. Stay with the pack and watch Live View. The cells should rise evenly and stay cool; stop if a cell stays behind. The protection clears when every cell that tripped is at or above U.V.P. Release.
  2. Stop the charger and press Restart System with no load and no charger current. Then charge to FULL with your normal current.

Clear All Errors on a low pack

Clear All Errors overrides the protections for 60 s. Both paths are ON, so a connected load would drain the low cells further. Case 2 is the one exception named in the warning of 4.1 Protection and Recovery; never use it on a temperature or a contactor fault.

4.3.5 Example

Calculation example: 16S pack, 100 Ah, left running

These are chosen values to show the calculation; use the consumption you have measured.

  • Pack: 16S, 51.2 V, 100 Ah, stored at 50 %, so 50 Ah.
  • Consumption: 950 mW ÷ 51.2 V ≈ 18.6 mA, and 18.6 mA × 24 h ≈ 0.445 Ah per day.
  • Time to the EMPTY voltage: 50 Ah ÷ 0.445 Ah per day ≈ 112 days (Fig.4.3.1).
  • With two slave modules: 950 mW + 2 × 300 mW = 1550 mW, about 0.73 Ah per day, so about 69 days.
  • Stored at 10 % instead of 50 %: 10 Ah ÷ 0.445 Ah per day ≈ 22 days.
  • BMS shut down: 0.05 mW is about 1 µA, or about 0.00002 Ah per day. The own self-discharge of the cells is far larger, so the cell datasheet sets the storage time.

4.3.6 Checking the Result

  • After the shutdown: the LEDs are dark and LiMon™ has no connection.
  • At each check during storage: the cell voltages have fallen slowly and evenly.
  • After the return: Live View shows the expected cell count and no new event, and Read All Settings shows the Shutdown Trigger you want for normal use.
  • After the first full charge: SOC 100 %, as in 3.2 Capacity and SoC.
  • After a recovery: Live View shows both paths ON, User Attention Required is gone, and Imbalanced Max. Cell Delta is back at your value.

4.3.7 Common Mistakes

  • Storing a full pack. Most cells age faster at full charge. Bring the pack to the storage level first.
  • Storing an empty pack. The little charge left is soon gone and the cells can fall below their minimum voltage. Charge to the storage level first.
  • Leaving the BMS running with a load behind it. The pack empties in months or less (4.3.5). A load below 0.5 A is also missing from the SoC, because it reads as no current. Shut the BMS down and disconnect the load.
  • Relying on U.V. Protection for a stored pack. It opens the discharge path, but the BMS keeps draining the cells. Use a shutdown.
  • Shipping Mode with the button out of reach. Nobody can start the BMS at the destination, and a charger does not start it either. Make sure that the receiver can reach the button.
  • Shutdown Trigger not set back after Shipping Mode. A later save can arm Shipping Mode again, and the BMS then shuts down 10 minutes later, even under load. Set and save the option for normal use.
  • No backup before storage. If the BMS is replaced or its settings are lost, the values and the calibration have to be set again. Export a file first.
  • No note of the SoC and the cell voltages. Without them you cannot tell whether one cell has fallen more than the others.
  • Trusting the SoC after storage. It shows the value from the shutdown, not the charge left today. Charge to FULL before you rely on it.
  • Charger current flowing at the start. After a recovery with the charger connected, the current reading is shifted until the next clean start (3.6 Current Measurement). Restart with no current.
  • Clear All Errors with the load connected. The forced outputs let the load pull the low cells further down. Disconnect the load first.